## Online First

Articles online first have been peer-reviewed and accepted, which are not yet assigned to volumes/issues, but are citable by Digital Object Identifier (DOI).
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, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0659
Abstract:
To study the mechanical properties and constitutive relation of DSS (duplex stainless steel) S22053 under cyclic loading, specimens machined from S22053 hot-rolled steel plate were tested under monotonic and cyclic loading patterns. Based on the monotonic curves, the material mechanical properties under monotonic load were analyzed. The material parameters of the Chaboche model were obtained using the results of the specimens with constant strain amplitude, and the test curves were simulated by the finite element software Abaqus. The results reveal that DSS S22053 has good ductility and low proportional limit. No obvious yield platform or yield point was observed. The cyclic backbone curve can be well fitted with the Ramberg-Osgood model. The three types of combined parameters calibrated by different component models can simulate the hysteresis curve of materials well, and the three-back stress component model (N2L1) has the best fitting effect. The results can be used to analyze and calculate the mechanical performance of DSS structures under seismic load.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.10.0753
Abstract:
In the limit equilibrium method for slope stability analysis, it is difficult to consider the stress state of the soil and the calculation of slope sliding surface stress has relied on the finite element numerical method for a long time. To solve this problem, the idea of slope surface unloading and equivalent stress is proposed. After considering the slope surface as a semi-infinite boundary, the slope stress is solved by the elastic theory. Then the stability safety factor is calculated according to the slip surface stress. Finally, the position of the potential sliding surface, the stress distribution of the sliding surface and the safety factor are compared with the existing theories based on the several example. The research results show that the concept of slope surface unloading and equivalent stress is clear and conforms to the slope force characteristics. The sliding surface stress obtained by this method is basically consistent with the finite element calculation results. The searched potential sliding surface position and the corresponding stability safety factor are very close to the finite element strength reduction method and the limit equilibrium method calculation results. In addition, the calculation method can be effectively combined with prestressed support structures, reflecting the reinforcing effect of prestressing.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0376
Abstract:
To investigate the effect of corrosion on the compressive bearing capacity of cold-formed thin-walled steel short columns, six specimens under axial compression and six specimens under eccentric compression around strong axes were designed and processed. First, the relationship between the mechanical properties of materials and the degree of corrosion was analyzed through tensile tests. Then, the bearing capacity tests of specimens were carried out, and the failure modes and ultimate load-bearing capacity were analyzed. The results show that the yield, tensile strength, modulus of elasticity and the elongation of corroded steel decrease linearly with the increase of corrosion degree. The corrosion of steel does not change the final failure mode of the short column specimens, but with the increase of eccentricity, the local buckling of the web becomes a coupling failure mode dominated by distortion buckling. Under the same corrosion rate, the ultimate bearing capacity of axially compressed specimens degrades more obviously than that of eccentrically compressed specimens. The ABAQUS finite element software was used to simulate the specimens. The results show that the ABAQUS software can better predict the bearing capacity and buckling behavior of the specimens.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.S007
Abstract:
To explore the force mechanism and failure mode of short-edge roof joints, three small scale roof joint specimens with different edges and shapes of slotted holes were subjected to cycle loading. The failure mode, hysteresis curve and upper stirrup strain of the concrete column are summarized. The test results show that the use of the recommended concrete edge distance by the code for shear anchors cannot avoid the damage to the concrete edge of the roof joint. However, the upper layer stirrup of the concrete column has an obvious restraining effect on the concrete edge. The long-hole steel plate with a reasonable length can effectively delay or even prevent the occurrence of the concrete edge damage.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0691
Abstract:
In order to reveal the interfacial bond behavior between circle steel tube and recycled aggregate concrete (RAC) after exposure to high temperatures, a push-out test of 20 specimens after exposure to high temperatures was designed and completed by considering two parameters, the maximum temperature (T) and the replacement percentage (γ). The failure process and morphology of the specimens were observed, the load-slip curves of the loading end and the free end were obtained, and the influences of test parameters on interfacial bond behavior and bond damage process were analyzed. The regression bond strength formulas and bond-slip constitutive equations of RAC-filled circle steel tube (RACFCST) subjected to high temperatures were proposed. The results show that the shape of load-slip curves can be divided into two types according to the maximum temperature (i.e., T≤400 ℃ and T=600 ℃). The curves shape at the loading end and the free end are similar and the initial slip at the loading end develops earlier. The interfacial bond behavior of RACFCST is similar to that of CFCST (the average performance difference of them under different replacement percentages is within 11%). The bond strength decreases at first and then increases with the increase of T and γ. With the increase of T, the bond shear stiffness first decreases, and then increases and finally decreases, and the energy dissipation capacity of interface increases gradually. Moreover, the bond shear stiffness and the energy dissipation capacity show the law of first increasing followed by decreasing and finally increasing with the increase of γ. Raising the temperature will induce the early occurrence of bond damage and then postpone it, but the effect of γ is not obvious. The growth of bond damage increases first and then decreases with the increase of T and γ.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0665
Abstract:
In this paper, a new point estimate method and a simplified fourth-moment method are used to analyze the reliability of bearing capacity formula (proposed by Ding Faxing) of concrete-filled steel tubular stub columns (CFST) under axial compression considering the shape constraint coefficient of different steel tube cross sections. The influences of different section shapes, different strengths of concrete and steel, two load combinations and different load ratios on the reliability index are considered. The results show that: (1) the reliability indexes of the bearing capacity formulas of CFST with different cross sections are higher than 3.7, which meets the requirements of target reliability index of 3.2; (2) When the ratio of office live load to dead load is 1.0, the higher the concrete strength, the larger the reliability index.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0582
Abstract:
The pulse-like properties of near-fault ground motions are of great importance in earthquake engineering in the recent twenty years. They are closely related to the rupture process and structural damage. The causes of these pulses are briefly summarized, and the baseline correction methods and identification procedures of near-fault pulse-like ground motions are systematically reviewed. Furthermore, a comparison is conducted on the statistical relationship between the earthquake parameters and pulse properties, such as the number of inherent pulses, pulse period and pulse amplitude. The results show that the traditional baseline correction methods cannot effectively recover the earthquake information in the frequency domain, that the existing identification and extraction procedures of inherent pulses mainly focus on the pulses induced by the directivity effect, and that the influence of tectonic conditions and fault types on the statistical analyses of pulse parameters has not been adequately considered. We suggested that more attention should be paid to the time-frequency based baseline correction methods, that the pulses induced by fling-step effect and the impulsive characteristic of vertical components of ground motions should not be overlooked, and that the influence of tectonic conditions and fault types on the near-fault pulse characteristics need further studies.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.S002
Abstract:
The nodal displacements gain higher convergence rate compared with displacements elsewhere in Finite Element Method (FEM). When the problem is smooth enough, the errors of displacements at element corner nodes can gain convergence order of at most \begin{document}$2m$\end{document} using elements of degree \begin{document}$m$\end{document} in 2D FEM. In this paper, taking the 2D Poisson equation as the model problem and based on an obtained FEM solution, residual nodal load vectors are derived by using super-convergent solutions calculated by Element Energy Projection (EEP) technique. Without changing global stiffness matrices, simple back-substitutions alone would yield nodal displacements of higher convergence rate. Numerical examples show that the nodal displacements can gain super-convergence order of \begin{document}$2m + 2$\end{document} at most when EEP simplified form is used to calculate the residual load vectors. In particular, for linear elements, the accuracy is doubled, and the benefit is very significant.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0635
Abstract:
An all-steel assembled buckling-restrained brace is proposed, in which both the core and the restraining members are made of section-steel. The brace has the advantages of assembly, replaceable core, easy fabrication, low cost and can be used for strengthening existing members. The steel core is composed of two angle steels and stiffening plates to form a T-shaped section. The restraining members are formed by bolting plates and angle steels through mat strips. Quasi-static cyclic tests for six specimens were carried out to investigate the hysteretic performance, seismic performance and failure modes. The effects of adding filler plates in the core, the gap between the core and the restraining members, the spacing between the two angle steels of the core, and the stopper configuration on the hysteretic performance were analyzed. The results show that the actual performance of the brace was basically consistent with the design performance. The brace specimens exhibited stable hysteretic performance. Adding filler plates in the middle of the core shows little influence on the hysteresis performance. An excessive gap between the core and the restraining member and excessive spacing between the two steel angles of the core reduced the hysteresis performance. The hysteretic performance of the braces with middle stoppers were better than the brace with end stoppers. The analysis of the seismic performance of the specimens shows that the braces have satisfactory ductility and cumulative plastic deformation capacity, which can be used as dampers in structures. By analyzing the failure modes, the stress concentration of the welding at the end of the stiffening plates will make the failure position move from the yielding segment to the stop of the weld. The middle stopper of the core can reduce the adverse effects of friction.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.S025
Abstract:
The finite element software ANSYS was used to establish the finite element model for the radial steel gate with compression bars. The static and dynamic characteristics of the gate with compression bars were compared with the traditional gate, and the effectiveness of the arrangement of compression bars was verified. According to the operation characteristics of the gate, compression bars were evenly arranged at the branch point of the arm and the lower flange of the longitudinal beam. The influence of the compression bar arrangement on the static and dynamic characteristics of the radial gate was analyzed by the finite element model. The static analysis, modal analysis and harmonic response analysis were carried out for the two types of gates. The results indicate that: the stress and displacement of the proposed gate with compression bars are greatly reduced under the hydrostatic load, and the overall ultimate bearing capacity of the gate is greatly increased with the minimum increase of steel consumption; in the case of no water closure, the natural frequency of the gate increases with the arrangement of the pressure bar; the amplitude response frequency of the pressure bar arrangement gate increases, and the response amplitude of each key node decreases, which achieves the purpose of improving the overall stability and anti-vibration performance of the structure.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.S021
Abstract:
Plastic-hinge-supported walls can replace the bottom strengthening area of traditional RC shear walls and form a stable plastic energy dissipation zone at the bottom of the wall. By setting shear components that only bear horizontal shear and vertical load and bending components that only bear bending moment, a bending-shear-decoupling design is realized for shear walls. Based on the separation of bending and shear, the experimental study on the seismic performance of prefabricated plastic-hinge-supported walls considering the out-of-plane deformation is carried out. We introduce the quasi-static test of two 1/3 scale wall specimens, which used a concrete shear wall and a steel plate shear wall. The test results show that the connection mode of the prefabricated plastic-hinge-supported wall proposed in this paper is reasonable and effective, and that the wall specimen has good seismic performance even with the presence of out of plane deformation.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0640
Abstract:
A set of safety evaluation methods of high-speed trains under the action of downburst are established by using physical simulator. The results show that under the combined effects of wind speed field and pressure field of downburst, the wind load acting mechanism is significantly different for each relative positions of the train distance from the downburst center. Under the action of downburst, the side force contributes the most to the wheel rail lateral force, and the overturning moment contributes the most to the wheel rail vertical force. The evaluation index for the safe operation of trains such as transverse force, derailment coefficient, wheel unloading rate first increase and then decrease as the radial distance increases. The relative radial distance of r/Djet= 0.83(Djet denotes nozzle diameter) is the most unfavorable radial position for the safe operation of trains. The train safety operation indicators increase with the increase of wind speed and vehicle speed, and the critical wind speed of downburst for safe train operation decreases sharply with the increases of vehicle speed.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0678
Abstract:
Bolted shear connector is one of the basic elements to realize the demountable function of prefabricated steel-concrete composite members. To solve the problem of inadequate deformability of the bolted shear connector, a high-deformability plug-type bolted shear connector (PTBSC) was proposed. The experimental studies and finite element analyses show that the shear-slip relation curve of a PTBSC is bilinear, with significant yield strength and ultimate strength. The development of evaluation methods for yield strength and ultimate strength of a PTBSC is required. A theoretical formula for the PTBSC yield strength was derived and verified by comparing to the corresponding finite element analyses results. The effect of parameters included in the theoretical formula was analyzed. The PTBSC yield strength increases by increasing bolt diameter and bolt strength grade. The yield strength reduces by increasing the slenderness ratio of bolt shank. Increasing the compressive strength of the infilled-plug material can also improve the PTBSC yield strength. When the strength is greater than 100 MPa, the yield strength basically remains unchanged. The PTBSC ultimate strength is proposed by employing a calibrated empirical equation, using the PTBSC finite element analyses results. When the ultimate strength is 0.7 times of the ultimate tensile strength for a PTBSC bolt, the error is within 20%. Therefore, the PTBSC ultimate strength can be well predicted with certain margin of safety.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0603
Abstract:
An experimental study was conducted on seven precast steel-concrete composite tube (SRCT) shear walls to evaluate their axial compressive behaviors. Performance of the test specimens was evaluated in terms of failure modes, load-bearing capacity, ductility and initial stiffness, et al. The test results show that SRCT shear walls have high bearing capacity, stiffness and ductility. They show good axial compression performance. The ratio of distance to thickness is inversely proportional to the load-bearing capacity and initial stiffness of the wall, and proportional to the ductility of the wall; The layout of the stud has some effect on the bearing capacity of the wall, but it has little effect on the initial stiffness of the wall. The bearing capacity of SRCT shear wall with the stud of quincunx arrangement is better; The arrangement of bolts has great influence on the bearing capacity of SRCT shear wall. With the strengthening of the bolts, the bearing capacity of the wall are enhanced. The calculation methods of vertical bearing capacity and initial stiffness of SRCT shear wall considering the local buckling of steel plate and the restraint effect of steel tube on the inner concrete are put forward. The proposed calculation values are in good agreement with the test values.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.S022
Abstract:
A near-field finite element model of a storage tank that considers soil-structure dynamic interaction and fluid-solid coupling effect is established in this study. Artificial boundaries are adopted to simulate the wave radiation effect of the semi-infinite foundation. The seismic wave input method based on the substructure of the artificial boundary is used to input the seismic waves into the numerical model. Then, the influence of soil-structure dynamic interaction on the seismic response of the liquid storage tank is investigated. The results show that the natural frequencies of the storage tank-liquid coupled system become lower when the soil-structure interaction is considered. Compared with the model without considering soil-structure interaction, there are additional vibration modes in which the soil participates. Affected by the different spectral components of the incident seismic waves and the change of the natural frequencies of the liquid storage tank, soil-structure interaction has different influences on the peak seismic response under different incident seismic waves and liquid storage volumes. For the subsequent responses after the peak seismic response, the scattered waves generated by the interaction between the foundation and the storage tank propagate outward and are eventually absorbed by the artificial boundaries when considering soil-structure interaction. It results in a rapid attenuation of the subsequent vibration amplitudes of the storage tank and the internal liquid.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0644
Abstract:
Effective vibration recognition can improve the performance of vibration control and structural damage detection and is in high demand for signal processing and advanced classification. Signal-processing methods can extract the potent time–frequency-domain characteristics of signals; however, the performance of conventional characteristics-based classification needs to be improved. Widely used deep learning algorithms (e.g., convolutional neural networks (CNNs)) can conduct classification by extracting high-dimensional data features, with outstanding performance. Hence, combining the advantages of signal processing and deep-learning algorithms can significantly enhance vibration recognition performance. A novel vibration recognition method based on signal processing and deep neural networks is proposed herein. First, environmental vibration signals are collected; then, signal processing is conducted to obtain the coefficient matrices of the time–frequency-domain characteristics using three typical algorithms: the wavelet transform, Hilbert–Huang transform, and Mel frequency cepstral coefficient extraction method. Subsequently, CNNs, long short-term memory (LSTM) networks, and combined deep CNN-LSTM networks are trained for vibration recognition, according to the time–frequency-domain characteristics. Finally, the performance of the trained deep neural networks is evaluated and validated. The results confirm the effectiveness of the proposed vibration recognition method combining signal preprocessing and deep learning.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.S038
Abstract:
The one-gravitational (1-g) shaking table model test is a frequently-used method to study the seismic responses of underground structures. However, past studies show that the test results were distinct. In some tests, no damage of the underground structures was observed under extremely strong earthquake motions. There were problems when one tried to observe the damage pattern of model structures. The seismic responses of underground structures can be influenced by many factors including the buried depth of structures. In the study, we investigate how the buried depths of a structure influences the test results using the 1-g shaking table tests of free-field sand and the Integral Response Displacement Method. The seismic responses of the free-field soil in the depth direction were acquired through the tests, including the distributions of the soil deformation, shear strain, shear stress and acceleration. The seismic responses of a structure at different buried depths were obtained using the Integral Response Displacement Method. The results show that the variation of the buried depth would change the soil deformation, shear force and inertia force loaded on the structure. The change was not dependent on the scaling ratio of the buried depth, but was mainly determined by the soil properties and seismic motions. Therefore, when conducting the experimental design, the buried depth of the model structure should be carefully determined with respect to the seismic responses of the site. In the 1-g shaking table test, the deformation of the soil played the most critical role for the seismic responses of the model structure. The effect of the deformation of the soil accounted for 70% to 80% of the overall seismic responses of the structure. The model structure would have the greatest seismic responses when it was buried at the depth with the largest relative soil deformation.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0569
Abstract:
The statistical moments of response are one of the main ways to describe the response of a random structural system. Compared with the probability density function (PDF) of the response, the statistical moments of the structural response can be easily obtained, and therefore it is quite concerned by researchers. Among them, the efficient calculation method for statistical moments of structural response has always been a hot research topic. The conjugate unscented transformation method (CUT), which keeps the tradeoff of accuracy and efficiency, is used as the basis in this paper. First of all, by introducing the normal-nonnormal transformation (NNT), the first type of extended conjugate unscented transformation method (ECUTI) is proposed, which is appropriate for the statistical moment estimation of random systems involving arbitrary random variables. Secondly, based on the high dimensional reduction model (HDRM) and the ECUTI, the second type of extended conjugate unscented transform method (ECUTⅡ) which is suitable for the statistical moment estimation of random system of arbitrary dimensions is proposed. Finally, the proposed methods are verified through three numerical examples. The results of examples show that: 1) The two types of proposed methods can satisfy the accuracy and efficiency on the basis of expanding the scope of application of the CUT; 2) The ECUTI and the ECUTⅡ are recommended for statistical moment estimation of the response for low-dimensional and high-dimensional problems, respectively.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.S018
Abstract:
Numerical tests of concrete subjected to cyclic loading were preformed using particle flow code software, and the simulation results show that: (1) the distribution of local friction energy reflects the potential area of damage; (2) the cumulative friction energy has a linear relationship with the number of loading cycles; (3) the cumulative rate of friction energy is sensitive to the load level. Based on the correlation between friction energy and fatigue damage, a bond-degradation model based on cumulative friction energy is proposed, and the relationship between model parameters and fatigue life is analyzed. The simulation results of the fatigue test show that: the proposed model can simulate the fatigue life of concrete under cyclic loading, as well as the fatigue damage behavior such as deformation evolution, stiffness degradation and crack evolution. The model can be used to analyze the cumulative characteristics of concrete fatigue damage under complex load conditions.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.S036
Abstract:
Wireless intelligent sensors combined with cloud storage technology can realize long-term health monitoring for structures. Modal identification is an important part for structural health monitoring. The Hilbert-Huang transform (HHT) is widely used for structural modal identification because it is suitable for nonlinear and non-stationary signals and is self-adaptable. The algorithm of modal identification in the long-term monitoring cannot rely on subjective parameter selection, while the first step of the traditional HHT may produce false intrinsic mode function (IMF) components. The identification and elimination of false IMF components often rely on subjective judgment. In this paper, a new algorithm based on deep neural networks (DNN) and Kullback-Leibler (K-L) divergence is proposed, which can automatically identify and eliminate the false components generated by empirical mode decomposition (EMD).
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0679
Abstract:
Geometric nonlinearity is one of the main nonlinear influence factors of long-span bridge structures. Its influence on the bridges and the running safety of trains cannot be ignored. In this paper, the Hu-Su-Tong Yangtze River Bridge, the world's first super kilometer cable-stayed rail-cum-road bridge, is adopted as engineering background. Based on the in-situ wind field measurement, the actual wind field characteristics is extracted, and the spectral representation method is used to simulate the three-dimensional wind speed field of the bridge. The wind load model considering the complex nonlinear spatial characteristics is established. The bridge model is built up considering the geometrically nonlinear factors such as the sag effect, beam column effect and large displacement effect. The whole-process iterative method is used to calculate the wind-train-bridge coupling vibration responses. The traffic safety analysis is given. The results show that considering the nonlinear factors increases the dynamic responses of the bridge and train to a certain extent and significantly increases the low-frequency component of the dynamic responses of the train. The large displacement effect has a greater impact on the structural response and the beam column effect has a less influence. Ignoring the influence of the nonlinear factors lead to an inaccurate response analysis and an unsafe evaluation. The wheel off-load index of the train exceeds the safety threshold when the train speed is 200 km/h and the wind velocity is more than 35 m/s, or when the wind velocity is 30 m/s and the train speed is more than 210 km/h. It means that the running safety of the train is threatened. The nonlinear wind-train-bridge coupling vibration analysis of the Hu-Su-Tong bridge has important scientific research significance and plays an important role in providing engineering guidance to ensure the safety of bridge structure and train operation.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0474
Abstract:
It proposed a form-finding method for railway catenary based on the dynamic theory, which is described by absolute nodal coordinate formulation (ANCF) in the flexible multibody dynamics theory. In the context of nonlinear problems, the catenary is modeled using ANCF cable element based on the flexible multibody system formulation and variable-length element theory. According to the static equilibrium conditions, the dynamic model is degraded and the form-finding model of tensioning structure is built. Meanwhile, considering the pre-sag design requirement of the contact wire, the models of contact wire and steady arm are separated out and solved using the form-finding model of tensioning structure. The force of droppers is updated for computing the equilibrium of droppers and messenger wire system according to the form-finding model. The equilibrium of railway catenary is determined. Three examples are adopted for verifying the proposed method, the results show that the proposed method can compute the equilibrium configuration of railway catenary exactly and the maximum relative error is less than 2%, which satisfies the engineering requirement.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S031
Abstract:
Road snowdrift disaster is an important disaster type in snow disaster areas, which poses a great threat to transportation. This paper takes the two-dimensional embankment as the research object, and uses Fluent software to simulate the flow field of embankments under different slopes, so that to obtain the wind speed and wall shear velocity around embankment under different slopes. And then the influence of slope on snow distribution around embankment is analyzed according to the mechanism of snow particle motion. The results show that the flow field around the embankment is closely related with the shear velocity of the embankment surface; the gentle upwind slope can reduce the snow around the embankment. It is recommended to build roads on the embankment with a small slope in areas with frequent snowdrift disaster. The research results can provide a reference for the construction of embankment.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0638
Abstract:
A reliable finite element model (FEM) is crucial for the health monitoring and performance evaluation of sluices on soft foundations. Due to the parameter uncertainty, FEM is difficult to accurately reflect the true dynamic characteristics of the sluice. In this paper, we propose an FEM parameter updating method for sluices on soft foundations, which combines modal parameters and is based on the beetle antennae search particle swarm optimization (BAS-PSO) algorithm. First, the elastic modulus and density that have a great impact on the modal parameters of the sluice are selected as the parameters to be updated. A genetic algorithm support vector regression (GA-SVR) proxy model, which can reflect the nonlinear relationship between the updated parameters and the modal parameters of the sluice on the soft foundation, is established. Second, an objective function based on the minimum relative deviation between the modal parameters identified by the measured response and the modal parameters calculated by the GA-SVR proxy model is proposed. The optimized mathematical model to update the FEM parameter of the sluice on the soft foundation is constructed. Finally, a BAS-PSO optimization algorithm is proposed to solve the optimization mathematical model, which overcomes the drawbacks of local optimization and slow convergence. The physical model of the sluice on the soft foundation shows that the modal parameters calculated by the modified FEM are numerically consistent with the vibration modal parameters of the sluice, and that the proposed method is reliable and feasible, providing a new idea for the FEM parameter updating of sluices on soft foundations.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0618
Abstract:
With advantages such as simplicity of testing, low cost and practical feasibility, etc., operational modal analysis has been widely used in engineering practice. In state-space model-based modal analysis, determination of the model order is one of the key problems to obtain accurate and stable modal parameters. A method for auto model order reduction and modal identification is proposed using expectation-maximization (EM) algorithm and modal-form state-space model. By transforming the general state-space model into a special modal-form, not only the parameter space is simplified, but the modal responses can be estimated. Modal contribution ratio which represents the importance of each mode to the total response is used as a criterion for auto order reduction in EM algorithm. Meanwhile, combined with spectrum analysis and damping ratio threshold, spurious modes are eliminated for the selection of practical structural modes. Through validation analysis of synthetic and field data, it is shown that the method is practically feasible and effective.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.S043
Abstract:
To study the influence of different welding processes on the residual deformation of flexural steel beams under load, we carried out welding strengthening test of four Q345B I-shaped bending steel members under load. The welding processes of the four steel beams are designed considering engineering applications. The changes of the mid-span deflection of the steel beams and the lateral deflection of the upper and lower mid-span flanges during the whole welding process were measured. This paper explains some special problems and test phenomena in the test, analyzes the influence of the welding processes on the mid-span residual deflection and mid-span rotation angle, and compares the calculated and experimental values of the welding residual deflection. The aims are to provide experience in conducting welding reinforcement test, to better understand the influence of welding process on the development of welding residual deformation, and to provide experimental basis and suggestions for the test design and design methods of welded steel beams under load.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0531
Abstract:
An earthquake-resilient prefabricated joint was proposed, which is composed of replaceable energy-dissipating hinges, core area of constrained joint, precast concrete beams and precast columns. The replaceable energy-dissipating hinge is an artificial plastic hinge, and its hysteretic performance is the key factor influencing the seismic performance of prefabricated joints. The replaceable energy-dissipating hinges were set between the precast beams and the extended beam in the core area of the prefabricated joint, and the hysteretic performance test under low-cycle reciprocating load was carried out. Following this test, only the metal dampers damaged in the energy-dissipating hinges were replaced, and a second test was conducted. The two tests were to investigate the seismic performance of the replaceable energy-dissipating hinges such as the failure mode, M-φ hysteresis curve, skeleton curve, bearing capacity, ductility and energy dissipation capacity. Through the comparative analysis of the two tests, the recoverability of the seismic performance of the replaceable energy-dissipating hinge was revealed. The results show that the replaceable energy-dissipating hinge has a full hysteresis curve, strong rotation capacity, strong energy-dissipating capacity, good ductility and no obvious strength degradation. Replaceable energy-dissipating hinges achieve that the damage and destruction of the prefabricated joint are concentrated on the replaceable energy-dissipating hinges, and the energy consumed by the energy-dissipating hinges accounts for more than 70% of the total dissipated energy in the prefabricated joint. The seismic performances of the replaceable energy-dissipating hinges in the two tests were similar, indicating that the seismic performance of the energy-dissipating hinges can be restored by replacing the damaged metal damper.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0549
Abstract:
The dynamic reliability evaluation of urban building cluster is of great significance for regional disaster prevention and mitigation. The spatial variability of ground motion and the soil-structure interaction caused by site effect have important impacts on nonlinear seismic response of building cluster. Yet existing regional earthquake disaster simulation methods based on deterministic analysis cannot reasonably reflect the overall behavior of the stochastic dynamic system of building cluster. The measured earthquake field excitations and the soil-structure interaction effect are introduced, and the time-domain solution method of the building cluster system considering the structural nonlinearity is developed in it. Further, based on the idea of probability conservation, the framework of dynamic reliability evaluation of stochastic building cluster based on the probability density evolution method is established. Taking a building cluster of high-rise frame structures as an example, the deterministic nonlinear seismic response analysis considering site effect is carried out. Next, the dynamic reliability evaluation of a stochastic building cluster is completed, and the impact of site effect on dynamic reliability of building cluster is evaluated. Finally, some useful conclusions are obtained.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0424
Abstract:
Behaviors such as interface failure and contact widely exist in refined simulations of structural failure, progressive collapse and foundation-soil interaction. As a novel numerical method, the finite particle method (FPM) is well adapted to structural analyses of strong nonlinear behaviors, with the advantage of improving computational efficiency through parallel computing. These merits make it possible for FPM to conduct fine interface simulations at a lower cost. A universal triangular interface element is proposed in the parallelized FPM framework for simulating interface behaviors such as bonding, cracking and contact. The parallel strategy for the interaction-pair search is introduced first. Then, the state criterion and mechanical models of three types of interface behaviors, namely the acceleration-based interface bonding, the cohesive-zone-based interface cracking and the penalty-based interface contact, are discussed. Using a self-developed universal computational platform of FPM, numerical tests of interface behaviors of this interface element are conducted to validate its accuracy and effectiveness.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0469
Abstract:
Based on the unified strength theory, considering the effect of intermediate principal stress and lateral free boundary of target to analyze the elastic-plastic stage and plastic stage of the linear strain-hardening target material, analytical solutions of radial pressure on the cavity wall are obtained and the unified penetration model of the linear strain-hardening target material is built. On this basis, resistance formulas and penetration depth formulas of the rigid projectiles with medium-low speed (v0≤1000 m/s) penetrating into metallic thick target finite in radial extent are deduced, then their solutions are obtained by utilizing the Simpson method. Meanwhile, influencing factors for ballistic terminal effects including strength criterion difference are analyzed. The results indicate that the proposed computing method can precisely describe the dynamic responses of projectiles and targets during the whole penetration process. Through this method, a series of different criteria-based analytical solutions are obtained and the ranges of penetration depth of targets under different striking velocities are predicted effectively. Moreover, various parameters have influences on the anti-penetration performance of the target, such as the strength parameter, the striking velocity, the target radius and the shape of the projectile nose; among them the penetration depth has increased by 22.45% as the strength parameter value changes from 1 to 0. In addition, as the ratio of target radius to projectile becomes smaller, the penetration depth becomes bigger, and it has increased significantly when this ratio is less than or equal to 16. It is indicated that the penetration depth is obviously affected by the target boundary size at this time, and it cannot be calculated as an unlimited-size target any more.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0629
Abstract:
As a high-order statically indeterminate structure, long-span cable-stayed bridges usually consist of many components such as main towers, stay cables, main beams, auxiliary piers, and connecting piers. Due to the mutual influence between components under earthquakes, the accurate simulations of the correlations among component seismic responses are critical to the vulnerability assessment of the overall system of a cable-stayed bridge. Pair Copula can simulate the correlation between two components. It is theoretically feasible to use Pair Copula in a hierarchically iterated way to simulate the whole system of a cable-stayed bridge. Therefore, a new seismic vulnerability assessment method of a cable-stayed bridge system is proposed based on Pair Copula iterative model. Based on structural uncertainty parameters and ground motion uncertainty, Latin hypercube sampling technique is used to establish bridge-ground motion probabilistic seismic response analysis samples. The correlations among the seismic responses of components are quantified through nonlinear dynamic time history and correlation analysis. Pair Copula models are fitted with maximum likelihood estimation and optimized based on AIC and BIC criteria. Through the hierarchical iteration of Pair Copulas, the overall model of a cable-stayed bridge is established, and its seismic vulnerability is evaluated. The engineering example shows that the correlation among multiple components can be accurately simulated based on the technology of hierarchical iteration of Pair Copula. With the assumption that the seismic responses of components are completely unrelated, the seismic vulnerability of a whole cable-stayed bridge system will be significantly overestimated.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S020
Abstract:
A numerical analysis model of shear walls with mortise-tenon joints was established on the platform of finite element software ABAQUS. The influence of longitudinal reinforcement ratio of boundary element on mechanical behaviors of shear walls with mortise-tenon joints and low shear span ratio was studied. The results show that friction model can be used to simulate the new and old concrete interfaces of mortise-tenon joints. The calculation results of numerical analysis model are in good agreement with the test results, which can reflect the failure characteristics of shear walls with mortise-tenon joints. The bearing capacity of shear wall can be improved by increasing the longitudinal reinforcement ratio of boundary element, and the increase is more obvious when the reinforcement ratio is low. Vertical cracks occur along the lateral convex roots of shear walls with mortise-tenon joints, showing good deformation capacity. When the longitudinal reinforcement ratio of boundary element increases to 4.62%, brittle shear failure does not occur to the wall. When the horizontal reinforcement is 8@200, the longitudinal reinforcement ratio of boundary element exceeds 2.36%, the longitudinal reinforcement does not yield under the peak load, and flexural failure no longer occurs to the wall.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S016
Abstract:
The aerodynamic force on circular cylinders changes because of the formation of asymmetric flow when the cylinder rotates. The effect of the rotation on aerodynamic force has wide application in wind power generation or navigation, and the characteristics of the aerodynamic force on a rotating circular cylinder significantly influence the development of these applications. In this study, the features of the aerodynamic force on a circular cylinder are illustrated to reveal the effect of the rotation ratio. The results show that an average lift coefficient increases with the increase of the rotation ratio. Meanwhile, the mean drag coefficient decrease when the rotation ratio increases. The variation of the lift coefficient with the rotation ratio differs from the drag coefficient. The lift coefficient changes more considerably than the drag coefficient.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0505
Abstract:
Air-gap eccentricity and mass eccentricity are two common eccentric faults in the traction motor of electric multiple units (EMU), and the resulting unbalanced magnetic pull (UMP) and mechanical unbalance force often induce more complex rotor dynamic vibrations, which may endanger the safe and reliable operation of train traction drive device. To this end, the Jeffcott model for a traction motor rotor system under a static-dynamic air-gap eccentricity and a rotor mass eccentricity is established. Then the air-gap flux density distribution and the Maxwell stress distribution on the rotor core surface are derived when the traction motor with load is running under the static-dynamic air-gap eccentricity, and the unified analytical expressions of UMP are subsequently presented, which are applicable to motors with a static-dynamic air-gap eccentricity, with no-load or load operations, and with any pole-pair number. The fourth-order fixed-step Runge-Kutta algorithm is used to calculate the dynamic response of a certain traction motor rotor under UMP and the mechanical unbalance force, and the effects of an initial static eccentricity, of a mass eccentricity, of radial stiffness and of rotational speed on the vibration characteristics of the system are discussed in detail. Results show that the rotor orbit of the traction motor is elliptical but nearly circular under the eccentric faults. The mass eccentricity, radial stiffness, and rotor speed affect the magnitude of rotor orbit, while the initial static eccentricity and radial stiffness can move the center of orbit along the direction of the static eccentricity. In addition, the existence of the air-gap eccentricity makes the displacement spectrum of motor rotor with a mass eccentricity more obviously contain the components of zero frequency, of natural frequency, of rotation frequency, of double rotation frequency, of double power frequency and its combinations with rotation frequency, and so on.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.0337
Abstract:
Flanged RC squat walls are widely used in conventional buildings and nuclear facilities owing to the significant lateral strength and stiffness in both principle directions. The building codes are found to have some problems in predicting the peak shear strength of flanged RC squat walls, such as insufficient parameters and the exclusion of the influence of the flanges. Moreover, calculated values are more discrete than experimental values. In this paper, we established a database of the comprehensive information of 152 flanged RC squat walls. The performance of popular building codes in predicting the peak shear strength of this kind of walls was compared and analyzed. Based on the crack patterns on the web, a model of flanged RC squat walls considering the influence of the flanges was built, based on which the equation for the peak shear strength was deduced. The results reveal that the proposed equation can calculate the peak shear strength of the shear walls in the database with a mean value of 1 and a small variation coefficient. These results can provide guidance for the design of structural walls and the revision of building codes.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0536
Abstract:
The thermal expansion at 15 different temperatures and the high temperature creep at multiple stress levels of 1670 MPa parallel steel wires, which are widely used in practical engineering, were experimentally investigated by a charge-coupled device camera (CCDC) system. The tensile strength of the specimens which experienced 2-hour’s high temperature creep investigation was measured at the ambient temperature. The curves of thermal expansion strain and high temperature creep strain of the parallel steel wires were obtained. The test results show that the thermal expansion strain of the parallel steel wires increased nonlinearly with the increase of the temperature and the microstructure changed at 750 ℃. Both the heating temperature and the stress level significantly affected the high temperature creep strain. At a higher temperature, the effect of the stress level on the residual tensile strength of the parallel steel wires was more significant. Compared with the 1860 MPa pre-stressed twisted steel wires, the 1670 MPa parallel steel wires had a lower creep strain at a high temperature. Based on the test data, the function of the thermal expansion coefficient of parallel steel wires with respect to the temperature and the high temperature creep model are proposed. The thermal expansion coefficient and the high temperature creep model proposed in this paper can benefit the mechanical response analysis of pre-stressed steel structures at elevated temperatures.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0595
Abstract:
Self-drilling screw connections between thin steel sheets were tested under shearing forces, and the impacts of the sheet thickness and the screw diameter on the shear behavior of the connections were investigated. It has been indicated that: the obtained three typical failure modes including bearing failure of steel sheets, pull-out failure and shear failure of screw, depend on the ratio between the screw diameter and the thickness of the sheet adjacent to the screw head. The shear resistance of each connection is positively correlated with the sheet thickness and the screw diameter, and the initial stiffness and the ductility of the connections are also related to these two parameters. Elaborated finite element (FE) models for the self-drilling screw connections were developed by introducing the Johnson-Cook damage constitutive model and the linear damage accumulation rule, and by considering the geometric characteristics of screw threads. The developed FE models were validated against the obtained test results, which provide accurate simulations of shear behavior of self-drilling screw connections. By using the calculation formulas for the shear resistance of self-drilling screw connections in the Chinese code GB 50018−2002, a new three-stage simplified mechanical model was proposed herein by considering the impacts of the compressive stiffness of steel sheets and of the shear stiffness of screw, as well as of the multi-screws effect, which has been further verified for accurately predicting the shear force versus deformation relationships of self-drilling screw connections.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0437
Abstract:
Probabilistic safety performance of nuclear containment structure subjected to severe accident conditions is the focus of probabilistic safety assessment (PSA) of nuclear power plant structures. Based on detailed three-dimensional finite element model of the nuclear containment structure, probabilistic safety performance of nuclear containment structure under severe accident conditions is evaluated. To realize the automatic running of nonlinear finite element analysis, Python and Matlab scripts are developed. To quantitatively evaluate the effect of statistical uncertainty on the fragility parameters, statistical inference and bootstrap method are used to estimate the confidence interval of the fragility parameters. Moreover, statistical characteristics of reliability index and total failure probability of the nuclear containment structure are quantitatively analyzed by bootstrap method. Finally, median value and confidence interval method are used to evaluate the safety margin of the nuclear containment structure. Results indicate that confidence interval of fragility parameter,\begin{document}${p_{\rm{m}}}$\end{document}, estimated by statistical inference and bootstrap method are almost the same. As for confidence interval of fragility parameter \begin{document}${\beta _{\rm{S}}}$\end{document}, statistical inference method tends to overestimate the confidence interval of fragility parameter \begin{document}${\beta _{\rm{S}}}$\end{document}. Statistical uncertainty of fragility parameters has negligible influence on reliability index and total failure probability, and the influence of the statistical uncertainty of the fragility parameters the on total failure probability is greater than that of reliability index. There is small difference between the safety margin calculated by median value method and the safety margin with 95% confidence level calculated by confidence interval method. In general, nuclear containment structure used in this study meets the requirements of probabilistic performance under severe accident condition, and it also meets the requirements of safety margin of no less than 2.5.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0366
Abstract:
In order to study the anti-continuous collapse mechanism of an unbonded post-tensioning precast structure with prestressed spliced connections under the condition of side column failure, four one-half scaled precast beam-column substructures were tested in the laboratory. The performance of three types of precast beam-column connections are investigated by using a pushdown loading approach. The test results demonstrated that different connection types exhibit different failure modes. The installation of unbonded post-tensioning connections is an effective way to resist the progressive collapse of precast concrete frames. The hybrid connection achieved greater load resistance than the summation of the load resistance of the unbonded post-tensioning connection and steel angle connection individually. Higher effective prestress in unbonded post-tensioning tendons could increase the load resistance in a relatively small deformation stage. However, the higher effective prestress may decrease the ultimate load capacity of the frame at a large deformation stage. Finally, high-fidelity finite element models, which were relied on commercial software ANSYS/LSDYNA, were developed. After validation, the results, which could not be measured during tests, were presented and discussed. Then, parametric studies were carried out based on the validated models. The numerical results showed that bonded post-tensioning tendons could increase the resistance of the specimen with unbounded post-tensioning tendons. Increasing the concrete strength could also increase the load resistance significantly. However, higher axial compressive forces at side columns will aggregate the P-Δ effects, which leads to lower deformation capacity and ultimate load resistance capacity.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0378
Abstract:
In the finite element numerical simulation, it is an urgent challenge to determine the ground motion input for the layered foundation under SV wave of oblique incidence over critical angle. Exact dynamic stiffness matrix in the frequency domain (i.e., frequency domain stiffness matrix method) of layered foundation is used to derive the formula for calculating the equivalent node force of ground motion input under arbitrary angular oblique incidence of SV wave, and the validity and accuracy of the ground motion input applied to ABAQUS numerical simulation are demonstrated by simulating seismic wave field of homogeneous half-space and layered foundation under oblique incidence of SV wave through ABAQUS software. It is shown that the inclined SV wave incidence with an arbitrary angle can be realized through ABAQUS simulation by means of stiffness matrix method, and the method is of high accuracy, especially in the case of SV wave incidence with an inclined angle greater than the critical one. The oval like motion trails of surface particles in uniform half space and the wave motion characteristics of layered half space are simulated commendably by finite element numerical modelling. On the above basis, the frequency domain stiffness matrix method is further combined with equivalent linearization method, which solves the ground motion input problem of two-dimensional layered half space considering soil nonlinearity for the inclined incidence with arbitrary angle.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0559
Abstract:
According to statistical analyses and shaking table tests of seismic damage of RC frames, the performance levels and corresponding damage degrees based on inter-story drift subjected to earthquakes were proposed. Seismic vulnerability analysis was adopted to analyze existing RC frame structures built in different historic periods to obtain the vulnerability curves and their matrixes. In order to evaluate the damage degree subjected to the expected earthquake in future, the seismic damage index method was also put forward. Finally, taking an exhibition hall as an example, the seismic performances of the structure before and after seismic strengthening were evaluated, and the effect of seismic reinforcement was verified.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S042
Abstract:
The prestressed reinforcement technology of raw-soil structure is a new aseismic reinforcement technology for the defects of arch kiln structure. The prestressed reinforcement technology is mainly divided into three types: prestressing wall piercing bolt, prestressing steel arch ring and prestressing steel strand. In situ blasting test of reinforced arch kiln structure shows that the seismic performance of the arch kiln in y direction is improved more significantly. The prestressed wall piercing bolt plays an obvious role in drawing the kiln face under the blasting excitation. The stress concentration in the side doors of arch kiln should be paid more attention in reinforcement design. The reinforcement technology can be promoted and applied in the reinforcement and reconstruction project of dilapidated houses. The technology has important scientific theoretical value, practical significance and application prospects.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0671
Abstract:
Fatigue failure is one of the main failure modes of metal components. In order to describe the uncertainty associated with metal fatigue crack growth, a stochastic description based on the “time t(a) to first reach a predefined crack length a” allows for the process mean in each specimen to equal to a proportional Paris law. Then, a simple model and a random effect model based on the inverse Gaussian process (IGP) are established, which are used to describe the variability across a single specimen and specimens, respectively. Then the model parameters for the simple model and the random effect model are estimated by using the maximum likelihood estimate (MLE) method and the expectation maximization algorithm (EM), respectively. Finally, the proposed models are used to fit the 68 Virkler fatigue datasets and the good-of-fit test is analyzed. The results show that the proposed models are effective candidates for description and interpretation of the uncertainty of metal fatigue crack growth.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0479
Abstract:
The formulas for the shear capacity of steel-concrete composite beams either in current specifications or proposed by researchers do not consider the contribution of the shear resistance of the flanges of steel beams. Therefore, the calculation results are relatively high. Based on the reasonable material constitutive relations and ABAQUS, a full-scale finite element model of composite beams considering the stress characteristics of the bolts was established to study the shear properties. The accuracy of the model was verified by a comparison with existing test results in the literature. Through a parametric analysis, the boundary shear span ratio of composite beams was determined, and the redistribution rule of the internal force of the studs of composite beams under shear loads was revealed. The combination rule of the steel beam and the concrete wing plate and the sharing proportion of the shear load were also revealed. Based on the superposition principle, a formula for calculating the shear capacity of I steel-concrete composite beams considering the shear contribution of the concrete slabs, steel girder webs and flanges was presented. The comparison results show that the accuracy of the proposed formula is higher than those suggested by GB 50017−2017 and other researchers.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0573
Abstract:
Geometrically similar specimens and non-geometrically similar specimens are respectively recommended for the size effect model (SEM) and the boundary effect model (BEM). Considering the individual characteristics and advantages of the SEM and BEM, it proposed an improved discrete particle fracture model for concrete. The fracture tests of two types of specimens with geometrical and non-geometrical similarity are used to determine the material parameters of concrete, that is, the fracture toughness and tensile strength. The determined strengths are compared with the experimental strengths. The determined fracture toughness is compared with the values determined by the SEM. The results show that when the ratio of the ligament length (W-a0) to the representative size of aggregate di is approximately 10, the correlation coefficient of the determination curves for the fracture toughness and tensile strength is the best. The determined fracture toughness and tensile strength are in good agreement with the experimental strengths and the fracture toughness from the SEM. Based on the determined concrete material parameters using the geometrically similar, the non-geometrically similar, and the geometrically and non-geometrically similar specimens, the corresponding design curves of concrete under different conditions are established. The design curves can cover all test data by ±20%. Based on a statistical analysis, the fictitious crack growth length Δafic=ndi and the characteristic crack length \begin{document}$a_\infty ^ *$\end{document}=0.5di can be taken. Then the analytical relations between the peak load and fracture toughness and between the peak load and tensile strength are established. The purpose of directly determining the fracture toughness and tensile strength of concrete using the experimental peak loads is achieved. ±15% of the predicted curves can cover all the experimental data. Based on the analytical formulas, the peak loads of large-scale real concrete structures that exhibit linear elastic fracture can be predicted.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S034
Abstract:
Snowdrift disasters are one of the important factors considered in road planning in cold areas. Numerical simulation, as one of the main means of snowdrift research, has developed rapidly in recent years. However, the parameters of numerical simulation need to be further improved due to the complexity of the snowdrift. Based on the Euler-Euler model, this paper uses the empirical formula of snow phase concentration to simulate snowdrift according to the two-equation model, and verifies the simulation method by using snowdrift results on flat ground. The influence of the turbulent Schmidt number on the simulation results of snowdrift on the embankment is analyzed, and the snowdrift on a typical embankment is simulated under different wind speeds. The results show that the simulation of snowdrift on flat ground is consistent with the measured results, and the turbulent Schmidt number has large influence on the calculation results of snow concentration. The distribution of snow concentrations under different wind speeds is consistent. These results provide a reference for further research on the redistribution and prevention of snowdrift on the road.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0423
Abstract:
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0575
Abstract:
To develop the self-centering two-column bents and achieve the seismic damage control, lead-extrusion dampers (LEDs) were selected as the external energy dissipaters, and a rocking self-centering bridge bent system equipped with LEDs was proposed. The seismic performance of this system was studied, and a corresponding design method which was based on the equivalent energy-based design procedure (EEDP) was developed. Initially, the numerical analysis model of RSC-LEDs bridge bent was established, and the simulation method was validated by an existing cyclic test of a RSC bridge bent specimen. Then the effect of LED output force, gravity load of superstructure, prestressing force, areas of unbonded tendon and cap beam-to-column stiffness ratio on the seismic performance of RSC-LEDs bridge bents was studied. 32 RSC bridge bents with different parameters were designed to conduct regressive analysis, and semi-empirical formulas were given to calculate the effective stiffness and yield strength of RSC-LEDs bridge bents. Combining the Chinese seismic code and EEDP, a two-stage seismic design method was proposed for RSC-LEDs bridge bents, and the results show that the obtained semi-empirical formulas can estimate the effective stiffness and yield strength accurately. The RSC-LEDs bridge bents designed by the proposed method can achieve the target capacity curve, and is able to remain elastic under E1 level earthquake. The LEDs start to dissipate energy under E2 level earthquake and the seismic displacement demand can be controlled within a design range.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0270
Abstract:
At present, due to the limitations of test size and test equipment, it is hard to obtain wind environment with high-accuracy and detailed wind field distribution by wind tunnel tests. Besides, the research on urban wind environment is relatively lagging behind in China, which impedes the rapid social development. The present paper performs a case study of Tongyong Shidai international community. A 10 m (width)×3 m (height)×21.0 m (long) wind tunnel is employed to obtain the detailed wind field distribution. And the impact factors, such as the inflow boundary, wind speed, wind direction angle, adjacent high-rise buildings and vegetation, are considered. The research results show that the uniform inflow and C-type geomorphic inflow can generate the same average wind profile, but turbulence intensity profiles are different. The flow field inside the community has some disturbance under low inflow velocity. As the inflow velocity is greater than 7 m/s, the flow field distribution tends to be stable. The shape of the adjacent high-rise buildings will change the residential area's wind field; Vegetation can reduce the average wind speed of pedestrian height. For the considered community, the large, medium and small size trees can reduce the average wind speed by 12.8%, 10.6% and 7.2%, respectively.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.S008
Abstract:
To solve the adaptability of conventional bored piles and driven piles under coral reef geological conditions, we propose a new type of prefabricated ultra-high-performance concrete (UHPC)-perfusion RC composite pile. Taking the approach of a cross-sea bridge as an example, the combined pile scheme was compared with the original scheme to illustrate the economic and technical advantages of the former. To grasp the force characteristics and the calculation method of the bearing capacity of the connecting section, five groups of push-out tests and finite element analyses were carried out to investigate the influence of the height ratio, number of shear keys and the interfacial adhesion on the bearing capacity and failure mode of the combined key. The reasonable height ratio of composite key teeth, the design process of connecting section and the calculation method of bearing capacity were determined.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0477
Abstract:
In this study, the complex rough surface is simplified as the superposition of a series of trigonometric curves based on the least square method. In order to calculate the interface contact stiffness, the optimal substrate modeling thickness is determined by the elastic-plastic finite element method. The relationship between normal contact pressure and normal contact deformation and normal contact stiffness is quantitatively investigated. The mechanism of fractal dimension and characteristic scale parameters of rough surface on normal contact stiffness is revealed. The results show that there is an optimal thickness of the substrate, which can effectively improve the calculation efficiency of the contact stiffness of the rough surface. The normal contact stiffness increases nonlinearly with the increase of normal contact deformation and normal contact pressure. The surface fractal dimension and characteristic scale parameters have significant effects on the normal contact stiffness, and the normal contact stiffness increases with the increase of the fractal dimension. However, the normal contact stiffness decreases with the increase of characteristic scale parameters.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0377
Abstract:
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0359
Abstract:
Multi-particle dampers have a good application prospect in the field of civil engineering structures because of their good damping efficiency and wide frequency band. However, the highly complex nonlinear mechanical properties and the lack of a reasonable mechanical model limit its application and development in practical engineering. In view of this, an equivalent single-particle mechanical model with inerter was established without considering the accumulation of particles. The introduction of inerter further considered the influence of particle rolling on the damping mechanism and effect. Then, the theoretical analysis of a single-degree-of-freedom structure with a multi-particle damper was carried out. The influence of inertance on the frequency response curve of displacement in the non-collision stage and the steady-state analytical solution of periodic collision after collision were analyzed emphatically. Numerical simulation and experimental research were also carried out to verify the correctness of the theoretical analysis. The results show that the equivalent model proposed can further clarify the nonlinear characteristics of the multi-particle damper after considering the inerter. The inertia coefficient has a significant influence on the frequency response curve of the controlled structure in the non-collision stage and the analytical solution (boundary and stability) of the periodic motion after collision. The steady-state analytical solution of periodic motion provides a theoretical basis for further parameter influence analysis and for damping mechanism analysis of particle dampers.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0532
Abstract:
It proposes a novel approach to improve the seismic behavior of hybrid FRP-steel reinforced concrete columns through the employment of high ductile engineered cementitious composites (ECC) in the plastic hinge region. A number of hybrid FRP-steel reinforced ECC-concrete columns were tested under reversed cyclic loading. The influence of matrix type, reinforcement type and axial force ratio on the seismic behaviors of columns in terms of failure mode, crack pattern, load carrying capacity, residual deformation, ductility and energy dissipation capacity were systematically investigated. It is found that the substitution of concrete with ECC in plastic hinge region can efficiently avoid the local buckling of FRP bars and thus significantly improve the seismic performance of the columns. Compared with the steel reinforced ECC-concrete composite column, the hybrid reinforced composite column exhibits evidently lower residual deformation and obviously higher post-yielding stiffness. With the increase of axial force ratio, the ultimate strength increases while the deformation capacity decreases. Through finite element parametric analysis, it is found that the ultimate strength and deformation capacity of the composite columns increase with the increase of the ECC compressive strength as well as the total reinforcement ratio; with the total reinforcement ratio remaining unchanged, the higher the area of FRP reinforcement, the better the ductility of the column.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S028
Abstract:
A new form of steel wood composite column is proposed. The composite column is wrapped around the cross steel bone, and the steel and wood are connected by bolting or welding flanges. 12 composite columns are tested under axial compression loads, and working mechanism and failure mode of steel wood composite column are studied. Meanwhile, the influences of steel thickness, slenderness ratio and bolt spacing on the axial bearing capacity are discussed. The test results show that the steel bone is mainly subjected to axial pressure, and the timber can provide certain buckling restraint to avoid steel buckling; the thickness of steel is the main factor for bearing capacity; the slenderness ratio of steel is greater than 5.5, and the effect of timber restraint is obvious; the bolt spacing has little effect on bearing capacity. Through the comparative analysis of finite element simulation and experiment data, the agreement is good. It can provide reference for the subsequent research on steel timber composite structures.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.ST01
Abstract:
The stainless-clad (SC) bimetallic steel combines the excellent corrosion resistance of stainless steel with the high strength and low cost of conventional mild (CM) steel. It possesses better comprehensive mechanical properties and may lead to a shorter construction period, longer design service life, lower full-life cycle cost and higher social benefits, and therefore great potential is expected for the utilization in engineering structures with high requirements on corrosion resistance. At present, the SC bimetallic steel has been successfully used in high-rise building curtain walls and railway steel bridge decks. In order to further promote its application and development in the field of structural engineering, more research and discussions are urgently needed from the perspective of fundamental mechanical properties and engineering techniques. This article provides a comprehensive review of studies on manufacturing, engineering practice as well as mechanical properties of the SC bimetallic steel at material and component levels, including the tensile properties, bending properties, high temperature properties, fracture and fatigue properties, cyclic loading properties, high-strain rate properties, corrosion resistance, bonding interface performance, structural stability, residual stress, welded joint, defect repair as well as finite element modeling. It is expected to provide a reference for further research, design and application of the SC bimetallic steel in the field of structural engineering.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0517
Abstract:
In the process of blank manufacturing, the non-uniformity of mechanical properties of materials leads to residual stress in an aluminum alloy thick plate, so that in the subsequent high-speed cutting process, with the removal of a large number of materials, the release of residual stress causes deformation of the whole structure, which seriously affects the dimensional stability of the whole structure. Therefore, it is very important to study the relationship between part deformation and part structure to realize the high efficiency and precision of machining process. Firstly, the release of residual stress in an aluminum plate is reasonably equivalent to the application of external loads, and the deflection equation of machining deformation in the thickness direction of the aluminum plate is established by using the bending deformation formula of material mechanics. According to the actual measurement, the formula analytic value and the finite element simulation value of the machining deformation are in a good agreement with the actual measured value. In order to further analyze the relationship between part structure and its fatigue life, the nominal stress method is used to simplify the analysis by equating the minimum fatigue life of the part with the maximum stress of the part under fatigue loading. After static analysis of some typical structures, the neural network model with three web positions as input, and the maximum stress of the part and the maximum machining deformation as output is obtained. Finally, the neural network model is used to construct a multi-objective optimization problem that minimizes the maximum machining deformation and maximum fatigue stress, and the optimal solution obtained by solving the multi-objective problem with genetic algorithm is that the distance between the bottom of the three webs and the bottom of the part is 8.868 mm, 27.992 mm, 28.000 mm, respectively. At this moment, the maximum machining deformation of the part is 0.088 mm, the minimum random fatigue load life is 4.432×107.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.10.0758
Abstract:
To achieve a balanced distribution of component redundancy in the single-layer reticulated shell structure and to enhance its ultimate bearing capacity, we used the component redundancy evaluation method proposed in reference [12] based on sensitivity analysis to measure the importance of components in the structure. The structural components were divided into three types, important components, general components and secondary components according to the redundancy. The cross-section size of components was taken as the optimization variable, and the minimization of the sum of the standard deviations of the redundancy of all structural components and the components of different types was taken as the objective function. In the optimization the particle swarm optimization method was used to search for the optimal solution of the cross-section size of structural components. The results show that the redundancy coefficient of structural component can accurately reflect its importance in structure and its influence on structural performance after it is damaged, a reasonable distribution of the cross-section size of components can be realized by reducing the difference of the redundancy of structural components, and the overall performance and ultimate bearing capacity of the structure can be improved effectively.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S023
Abstract:
Snow accumulation around buildings is one of the most common natural disasters in snowy and windy areas in winter. Although numerical simulation has achieved fruitful results in recent years, the parameter setting is still insufficient due to the limited measurement data of the snow around a single cube model in the wind and snow flow. Therefore, the simulation method has not been widely verified due to the lack of field measurements, which limits the further improvement and promotion of the prediction method. To reveal the influence of aspect ratio on the snow distribution around buildings, the snow distribution around cuboid models at various conditions was measured on-site. Meanwhile, the numerical method was used to simulate the wind field around the models. The wind field and snow distribution around the model were compared to show the correlation. The results show that the wind speed around the model can well predict the snow erosion and accumulation range. For buildings with different aspect ratios, the snow distribution on the windward side is only related to the height of the building. The aspect ratio has slight influence on it. The cross-wind erosion range is proportional to the length of the building, and the leeward side erosion range is greatly affected by the length of the building. The width of the building insignificantly influences the distribution of surrounding snow.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0503
Abstract:
The bolted joint plate structure is one of the most widely used detachable fixed joints in aircraft structures. In this paper, we study the dynamic modeling of bolted-joint plates and establish the dynamic equivalent model of bolted-joint plates based on the thin-layer element theory. The weighted sum of the natural frequency error and the modal confidence criterion residual are used as the objective functions. We propose to use the water cycle algorithm to globally modify the material parameters of the thin-layer elements. By an example of a clamped-clamped five-bolt lap plate, we verify the feasibility and robustness of the proposed dynamic modeling method. The results show that the established dynamic prediction model of the bolted joint plate structure can accurately characterize its dynamic characteristics and reduces the effect of the measurement noise compared to the current dynamic modeling methods.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.10.0708
Abstract:
The scheme for the cross-section damage defects in a circularly curved beam is established to simulate the depth, the location and the number of multiple cracks, through implementing cross-section reduction induced by microcrack damage. The h-version adaptive finite element method of a variable cross-section Timoshenko beam is introduced to solve the free vibration of a circularly curved beam with cracks damage. Using the proposed method, the final optimized meshes and high-precision solution of natural frequency and mode shape satisfying the preset error tolerance can be obtained, and the disturbance behavior of multi crack damage on the vibration mode of a circularly curved beam is studied. Numerical examples show that the non-uniform mesh refinement can adapt to the change of mode of vibration induced by crack damage, which is applied to the free vibration research of various circularly curved beams with included angles and crack damage distribution conditions. Furthermore, the influences of crack damage depth, of crack damage number, and of crack damage distribution on the natural frequency and mode of vibration of a circularly curved beam are quantitatively analyzed, and the accuracy and practicability of the proposed algorithm are verified.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0108
Abstract:
Due to the constraints of manufacturability, current topology optimization technologies are mostly used only in the conceptual design of structures. Therefore, it is necessary to research the method of topology optimization that is directly facing manufacturing. Based on the heuristic BESO (Bi-directional Evolutionary Structural Optimization) algorithm, this paper proposes an efficient topology optimization method that can precisely control the minimum structural size. First, through sensitivity interpolations and refinement of boundary elements, current BESO algorithm is improved and the problem of non-smooth boundary is solved. Then, the skeleton configuration of the structural topology is extracted by using the topology refinement method. On this basis, the structural members whose size violate the minimum size constraint can be determined, and thusly the minimum length scale of the topology structure is precisely controlled based on the improved BESO algorithm. Additionally, to avoid the premature problem, a relaxed constraint method is adopted, in which the minimum size constraint is gradually strengthened during the optimization process. Numerical examples demonstrate the effectiveness of the proposed topology optimization method.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0361
Abstract:
The durability models for concrete structures in a carbonation environment have been proposed based on diffusion theory, on accelerated tests and on engineering experience. Due to the inherent uncertainty of structures and to the complexity of actual service environment, the calculation results of these models often have a big deviation from the actual test results. In the light of the point, a durability model updating method in a carbonation environment is proposed based on Bayesian theory by utilizing the durability inspection data with carbonation depth, with corrosion ratio of steel reinforcement and with cracking ratio of concrete. With the actual test results, the updated durability prediction model which consistent with the actual durability condition of the structure, is more consistent with the actual durability state of the evaluation structure. According to the model, the probability prediction of the residual durability life and durability rating are carried out, so as to provide a reference for the durability evaluation of existing structures.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0407
Abstract:
Partially encased composite (PEC) column flanges can be classified as a flat plate fixed on three sides, free on the other side, and restrained by concrete on one side outside the plane. The local buckling of this kind of plates can be avoided by limiting the width-to-thickness ratio. To obtain the width-to-thickness ratio limit of such high-strength steel plate, the elastic-plastic buckling stress of plate under uniform compressive stress is derived by using Bleich approximate calculation method, and the approximate solution of width-to-thickness ratio limits are obtained, based on the inelastic local buckling theory of a thin plate, combined with Ramberg-Osgood constitutive model of high-strength steel. Furthermore, the numerical tests of axial compression of PEC columns with high-strength steel are carried out by the finite element method. The accuracy of the approximate solution of the width-to-thickness ratio limits proposed is verified by the finite element results and by the existing experimental results. The comparison with the relevant codes shows that: the unilateral restraint action of concrete can increase the width-to-thickness ratio limits of the high-strength steel plate supported on three sides by 39%; the width-to-thickness ratio limits of high-strength steel plate with unilateral restraint fixed on three sides free on one side calculated by the approximate formula proposed is 19% smaller than that of the Australian code AS/NZS2327: 2017 and only 5% less than that of the European code EN 1994-1-1. It is suggested that the width-to-thickness ratio limits of a high-strength steel plate with unilateral restraint fixed on three sides free on one side can be conservatively taken as the smaller value of the calculation results of the approximate formula proposed and the calculation result of EN 1994-1-1.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0255
Abstract:
With a long history, palace-style timber structure buildings in Tang Dynasty, which are represented by the East Hall of Foguang Temple in Shanxi province, have significant historical and cultural values. The horizontally layered structure, including the column frame layer, Tou-Kung layer and roof frame layer, has good seismic performance, in which the rocking resistance of the columns plays an important role. Taking a single column of the palace-style timber frames in Tang Dynasty as the research object, the resistance mechanism of the rocking column under horizontal loading was analyzed. The process of the column rocking was divided into six states. The geometric conditions, equilibrium conditions and stress distribution of the contact surface for each state were obtained considering the stress-strain states of the compression surface of the column ends during rocking and that the timber in compression may induce elastic-plastic strain. The change of the shape of the compression surface of the column ends and the translation of the action points of Ludou and stone base were analyzed in detail. A mechanical model of the lateral force resistance and horizontal displacement of the rocking column was established and verified by a comparison with the results from numerical simulation and existing models. The differences of the lateral resistance of the column frames of different structural configurations in Tang and Song Dynasties were also analyzed. The results provide a theoretical basis for the study of the seismic performance and reinforcement of ancient structures in early historical period.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0028
Abstract:
The shear-span ratio has an important influence on the crack development and on the failure mode of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP). However, there were few studies on the effects of its shear strength and size effect. A mechanical analysis model for shear failure of reinforced concrete beams strengthened with CFRP was established by using three-dimensional numerical meso-scale simulation method, considering the meso-heterogeneity of the concrete and the interaction between the CFRP and concrete. Based on the verification of the rationality of the meso-scale method, the influence mechanism and law of the shear-span ratio on the shear failure and size effect of CFRP-strengthened RC beams were simulated and analyzed. The results show that: the shear-span ratio has a great influence on the shear failure mode of the strengthened beam, and the larger the shear-span ratio, the closer the beam is to the cable-stayed failure with better ductility. The shear-span ratio had better shear capacity for CFRP-strengthened beams and the influence on the size effect of shear strength was small. The shear-span ratio has a greater influence on the CFRP shear contribution in the strengthened beam. The larger the shear-span ratio, the better the shear effect of CFRP on strengthened beams. The beam reinforcement effect of the shear-span ratio (λ = 2.5) is most effective.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.ST02
Abstract:
The finite element model updating is advantageous in damage identification because it is physically meaningful and simultaneously identifies the damage location and extent. It provides a direct and important basis for structural safety assessment. We firstly present the background and basic process of model updating based damage identification, and summarize its development in the past thirty years. A finite element model of a civil structure is usually large in scale and contains many parameters to update. It makes the model updating process time consuming. Therefore, substructure-based model updating methods are developed to identify the damage of large-scale civil structures to improve the efficiency of the model updating process. The two methods are applied to the damage identification of a high-rise building model to illustrate their advantages in practical damage assessment. A civil structure is large in scale while the damage is localized. The substructuring method divides the global structure into several independent substructures for the analysis. The substructure-based damage identification is achieved by updating a few substructures, avoiding repeated analysis of the large whole structures, and therefore improving the accuracy and efficiency of the model updating process.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0411
Abstract:
Shaking table tests were carried out to study the influences of shear beams on the seismic response of double-column piers that were designed to support the girder of a full cable-stayed bridge model. The double-column pier with shear beams included two columns and five shear beams equally installed between the two columns. A full cable-stayed bridge model of 1/70-scale that included the pier (a double-column pier and a double-column pier with shear beams), tower, girder, pile group, and artificial soil was designed and tested on a shaking table array. The seismic response characteristics were compared between the double-column piers with and without shear beams when they were subjected to various earthquake waves of various frequency contents, such as the artificial, El Centro, and Mexico City waves. The experimental results show that the maximum strains at the bottom of the double-column pier with shear beams were less than those of the double-column pier under the artificial, El Centro wave, and Mexico City waves of various shaking amplitudes. The additional shear beams significantly mitigated the strain responses at the bottom of the double-column pier, and decentralized the inner force of the columns. The maximum accelerations at the bottom of the double-column pier with shear beams are 1.4-1.8 times those of the shaking table when the bridge model was subjected to the artificial, El Centro, and Mexico City waves with 0.1 g, 0.15 g, and 0.2 g. The pile-soil-structure interaction significantly affected the seismic response of the double-column pier with shear beams and increased its longitudinal acceleration responses. The seismic responses, such as the acceleration, displacement, and strain responses of the double-column pier with and without shear beams were significantly affected by the frequency spectral characteristics of the various earthquake waves. The extent of the influence was dependent on the relationship between the frequency contents of the earthquake waves and the frequency spectral characteristics of the piers.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0394
Abstract:
Ductile fracture is the most common form of steel damage. It is of a great theoretical significance and practical value to study the toughness fracture mechanism of steel and to accurately predict the ductile fracture behavior of steel. The fracture prediction method based on microscopic mechanism has good applicability for studying the toughness fracture behavior of steel. The existing ductile fracture model is improved based on the void evolution mechanism of the somatic cell model, and the parameters of the Q345 steel fracture model are verified. In addition, the damage factor is introduced into the ductile fracture model to consider the change of stress state during loading, thusly the fracture model can accurately describe the cumulative damage value at each loading moment. At the end of the article, Fortran language is used to compile the fracture model into USDFLD subroutine, and it is inserted into the finite element program ABAQUS to numerically simulate the uniaxial tensile test of a group of cross-type rigid joint specimens. The results show that the fracture model has good prediction accuracy under the tensile-shear composite stress state, and can accurately capture the steel fracture start position and crack propagation path. The improved ductile fracture model can also be used for the fracture prediction analysis of other ductile metal materials.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0442
Abstract:
The time delay effect in a real-time hybrid simulation (RTHS) is basically compensated through the compensation of the displacement command calculated by the numerical substructure, then the compensated command is sent to the actuator to vanish the delay. In RTHS, the loading is generally small related to the capacity of the actuator to keep the performance of actuator in a relatively ideal range. This also limits the conduction of large-scale RTHS. Due to the large loading, higher requirements are put on the control system and actuator of RTHS. Moreover, the state-of-art time-delay compensation method cannot eliminate the effects of time delay completely. For the problems mentioned above, this study proposed a method that can reduce the influence of the time delay after an RTHS. This method is based on the error propagation of the dual explicit numerical integration algorithm. To illustrate the method proposed in this study; it analyzed the effect of time delay on the RTHS results and in some cases with a large time delay, the time delay may cause results to be almost completely "wrong"; it gave the theoretical derivation process of the method proposed; it performed simulation verification in four cases when the physical substructures are linear stiffness, linear damping, nonlinear stiffness and nonlinear damping, respectively. The results show that: the method proposed can restore test results according to the error propagation of the dual numerical integration algorithm, reduce the errors caused by the time delay. In the case that the effort of delay compensation is not satisfactory due to the limitation of the test equipment, the method can simultaneously correct the displacement, velocity and acceleration results after the test.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0439
Abstract:
In the existing fatigue analysis methods, structural material parameters and geometric dimensions are usually considered to be deterministic variables. For real structures, however, the structural parameters are bounded but uncertain. It is unsafe to estimate the fatigue life of a structure according to the nominal values. In this paper, we apply the interval analysis method based on non-probabilistic set theory to estimating the roof fatigue life under fluctuation wind load. Considering the thickness and elastic modulus of large-span roofs under bounded-but-uncertain circumstances, we calculate the dynamic response range of long-span roof structures under fluctuating wind load by the interval finite element method and interval dynamic response analysis method. The time history curve of the interval stress of large-span roofs is obtained through the constitutive equation and stress. The amplitudes of the interval stress are calculated by the rain-flow counting method. Considering the S-N curve of the roof material, we estimate the fatigue life interval of large-span roofs by Miner's law.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.0324
Abstract:
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.0312
Abstract:
In order to study the diagonal channel stiffened steel plate shear wall (SPSW) with a large span-to-height ratio, three 1/3-scaled SPSW specimens were tested under cyclic quasi-static loading. One of the specimens was spliced SPSW without diagonal channel stiffeners and the other two were spliced SPSWs with diagonal channel stiffeners. The experimental results show that SPSWs have good energy dissipation capacities, and the hysteretic curves of the diagonally stiffened SPSWs are plump spindle-shaped. The closed section formed by the channel stiffener and the plate avoids the torsion of the stiffener during the loading process. Channel stiffeners can increase the elastic buckling load and limit the out-of-plane deformation of the infill plate in the elastic stage. Moreover, diagonal stiffeners improve the bearing capacity of the specimen in elastoplastic stage. The formulas for calculating the shear force, axial force and bending moment of the frame column are derived. The results show that the axial force and shear force of the columns are greatly affected by the diagonal channel stiffeners, thus the supporting effect of the stiffener should be considered in the design.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0265
Abstract:
In order to study the interface bond-slip behavior between shape steel and Engineered Cementitious Composites (ECC), the shape steel-ECC specimens were designed to conduct push-out testing. The influences of the volume fraction of PVA fiber, stirrup reinforcement ratio, ECC cover thickness and shape steel embedment length on the failure modes, on the load-slip curves and on the bond stress of shape steel-ECC specimens were analyzed, also the bond stress distribution along steel embedded length was proposed. The result shows that the volume fraction of PVA fiber and ECC cover thickness have great influences on bond stress. The maximum bond stress occurred near the loading end, and the equivalent bond stress increased with the increase of the load. According to the test results, the expression of bond stress in different states were established, and the bond-slip constitutive laws were proposed. On this basis, the finite element model of shape steel-ECC specimens was established by using a nonlinear spring to simulate the interface bond-slip behavior between shape steel and ECC. The finite element analysis results were compared with the test results, which indicated that the finite element simulation method proposed could accurately analyze the interface bond-slip behavior of shape steel-ECC.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0545
Abstract:
A spatial structure based on the Kresling origami has multiple stability states under external compression. To realize an intelligent structure with a programmable failure mode, the finite particle method (FPM) is used to study the instability of spatial structures based on the Kresling origami. We propose a method of controlling the structural stiffness by adjusting the material, prestress, and structure arrangement. First, the calculation of the cable, rod, and membrane structures using the FPM is introduced. The method is verified by a bi-stability analysis of the Kresling pattern. Then, the instability modes of the cable-rod model, the cable-rod-membrane model and the nested model based on the Kresling origami are analyzed. The influences of the elastic modulus, prestress level and structural arrangement on the structural instability mode and strain energy conversion are investigated. At last, the programmable failure of a double-layer Kresling structure is realized by adjusting the Young’s modulus of the structure, providing a new method for the design of intelligent structures in the future.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0500
Abstract:
High-strength steel framed-tube structures with end plate-connected shear links (SFTSs) is an innovative high-rise earthquake-resilient structural system. It improves the seismic performance of conventional steel framed-tube structures and achieves rapid post-earthquake repairability. Since the traditional seismic design method based on the current code cannot accurately predict and control the inelastic performance of the structure, the damage of the structure may be concentrated on individual floors, thus forming a weak layer. To design a structure with an ideal failure mode, we propose a specific four-level seismic fortification objective for SFTSs, which requires no damage under frequent earthquakes, replaceable under the design and rare earthquakes, and collapse prevention under very rare earthquakes. A trilinear capacity curve considering multiple performance objectives under different seismic levels was adopted in the proposed performance-based plastic design method of SFTSs. The effects of higher mode shapes and post-yield stiffness were also considered. A 30-story SFTS model was designed according to the proposed method. Nonlinear time history analyses of the model were performed under 20 selected ground motions using OpenSees. The results demonstrate that the model designed with the proposed design method exhibited the intended failure mode and achieved the performance objectives under the different seismic levels, indicating excellent seismic performance of the model. The effectiveness of the proposed performance-based plastic design method of SFTSs was verified, which can be applied to the practical engineering design of SFTSs.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.09.0686
Abstract:
To study the dynamic characteristics of discretely connected precast RC diaphragms (DCPCDs) and the response to human-induced excitation, two DCPCD specimens and one cast-in-situ slab specimen were tested. All specimens were simply supported at four sides. The vibration response of the specimens under pedestrian load was analyzed considering the step frequency, walk path, load distribution form, number of pedestrians and distribution of loads. The results show that the plate seam reduces the vertical stiffness of the floor and increases the damping ratio. The second and the third mode shapes are anti-symmetric in the orthogonal slab laying direction (OSLD) and the slab laying direction (SLD), respectively. Increasing the number of connectors can effectively increase the natural frequency and reduce the vibration response of the DCPCDs. The mid-span connectors have the most significant impact. The peak acceleration increases with the increase of the step frequency and number of people. The peak acceleration when walking in the OSLD is greater than that when walking in the SLD and diagonal direction. The greater the load distribution density and the closer the load distribution is to the center of the floor, the greater the peak acceleration will be. The natural frequency of the DCPCD specimens meets the serviceability requirement, but the acceleration varies significantly under different support conditions. The numerical calculation methods of the natural frequency and peak acceleration of the DCPCDs were proposed based on the vibration theory of orthotropic two-way plates. The calculated values are well correlated with the test values. For serviceability, it is recommended that the stiffness ratio between the OSLD and SLD is between 0.3-0.75.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0426
Abstract:
The harmonic synthesis method is used to simulate the time history of turbulent wind in a land wind field with Davenport and Kaimal wind speed spectrum. According to the average wind velocity at the corresponding height and combined with Bernoulli theory, the wind load time history is obtained. The finite element model of a 3 MW wind turbine steel tower is established by considering the aerodynamic thrust, wind load time history and second-order effects of gravity. The dynamic response of the steel tower is also solved. Taking the variations of both load effect history and material density into account, the Monte Carlo method is used to analyze the failure probability of foundation slab void according to the criterion in the code, and the corresponding variation laws of reliability index with different radii of foundation slab are discussed. The results show that: the total bending moment and total shear force at the bottom of the wind turbine tower are approximately perfect dependent of each other and have a large coefficient of variation, regardless of normal operating conditions or extreme load conditions; for the selected Davenport wind speed spectrum, the failure probability of the foundation slab void of the wind turbine is about 0.00820 and 0.0188 under normal operation and extreme load conditions, respectively, and for the selected Kaimal wind speed spectrum, the corresponding failure probability is about 0.0107和0.0281, respectively; the reliability index increases with the increase of the radius of foundation slab, by no less than 39.90% for both two working conditions when the radius increases to 1.2 times.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0435
Abstract:
In order to study the failure mechanism of RC columns strengthened by CFRP subjected to axial and cyclic lateral loads, a three-dimensional meso numerical model of reinforced concrete square columns strengthened with CFRP is established, considering the heterogeneity of concrete materials and the bond slip between reinforcement and concrete. On the grounds of the good agreement between the meso-scale simulation results with the available experimental results, the section size of the specimens is enlarged. Furthermore, the effects of axial compression ratio, volume allocation rate of CFRP on the aseismic performance and size effect on shear strength of reinforced concrete short columns strengthened with CFRP are explored. The results show that: the bearing capacity of specimens increases as the increase of axial compression ratio, but the ductility decreases; increasing the volume allocation ratio of CFRP has a limited effect on the increase of bearing capacity, which will enhance the ductility of columns; with the increase of specimen size, the nominal shear strength of columns tends to decrease, and there exists size effect behavior.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0478
Abstract:
Based on the assumption proposed by Deng et al that the permeability coefficient of drains decreases with time in the form of an exponential function, and on that the radial-vertical flow of soil is considered, the governing equation for consolidation of sand-drained ground is derived and the analytical solution is obtained by using separated variable method. The correctness of the solution is verified by comparing the degenerate solution of the study with the existing analytical solution and the analytical solution with the finite difference solution. According to the solution, the influence of consolidation behavior of sand-drained ground is analyzed. The analysis shows that the consolidation rate of sand-drained ground decreases with the increase of well resistance factor \begin{document}$\alpha$\end{document} whether the vertical flow is considered or not, and that the variation of well resistance has an important influence on the consolidation behavior of sand-drained ground in the later stage of consolidation. When the radial-vertical flow is considered, the final average consolidation degree can reach 100% with different \begin{document}$\alpha$\end{document}. The consolidation rate of sand-drained ground is accelerated by the vertical flow, and the consolidation rate increases with the increase of the vertical permeability coefficient kv. When the ground thickness H is thin, the vertical permeability coefficient kv has a great influence on the consolidation behavior of sand-drained ground in the initial stage. When the ground thickness H is thick, the vertical permeability coefficient kv has a great influence on the consolidation behavior of sand-drained ground in the later stage.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0461
Abstract:
In order to study the flexural performance of a novel prestressed steel-encased concrete composite beam with corrugated steel webs, four bending tests were carried out taking prestressed tendons, the number of shear connectors and the width of concrete slab as parameters. Results show that corrugated steel can work well with concrete, effectively strengthen the steel-concrete interface to avoid the occurrence of longitudinal slip failure. However, its axial stiffness is small and contributes little to bending capacity. Prestress and the concrete flange plate have a greater contribution to the bending capacity of the composite beam, and the longitudinal horizontal shear failure occurs when the number of shear connectors is insufficient. On the basis of experimental study, the finite element model is established. Results show that the new composite beam can take full advantage of the combined functions of each component and improve the flexural capacity and ductility of the specimen. Compared with the straight steel composite beam, the corrugated steel composite beam has better rigidity and higher bearing capacity. With the increase of concrete strength, the bearing capacity increases slightly. With the increase of the thickness of the lower flange plate, the bearing capacity of the steel plate is significantly increased, which has little influence on the stiffness. Stiffness and bearing capacity increase with the increase of prestressing degree, but ductility decreases. Finally, a calculation formula of flexural capacity is derived.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0557
Abstract:
This paper develops a non-contact recognition system of the influence line of human-induced deflection combined with the portable camera and wireless sensor, which avoids the shortcomings of traditional identification methods. It concludes of long-time blocking off traffic and of consuming a lot of human resources and material resources. The engineers can use this system to identify the influence line of bridges in operation. A portable camera obtains the pedestrian behaviour on the bridge. The occlusion model is introduced to improve the Yolo algorithm to identify the pedestrian on the bridge. Tracking the changes of the coordinates of the target pedestrian can obtain the pedestrian position information and the pedestrian load acquired by the wireless sensor is taken as the structural input data. Visual recognition technology is used to track the structural behaviour and the displacement response under pedestrian loading as the output data of the structure. According to the input and output data of the structure, the deflection influence line of bridge under pedestrian loading is calculated reversely. The initial influence line is processed by high-order filtering to eliminate the interference of environment and other factors. Then, the measured bridge influence line with characteristics of quasi-static characteristics is fitted using the polynomial segmentally, which can provide an accurate and efficient basis to detect the bridge damage for structural engineers.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S037
Abstract:
Based on the concept of energy concentration and dissipation, it was proposed to set the damping story on one tower of the connected structure to form a connected structure control system with energy-dissipation story. By means of the D'Alembert principle, vibration differential equation of the system was derived and the optimal parameter characteristics and damping effects of three different connected control systems were studied. The results show that the optimal damping coefficients and stiffness of these three connected structure control systems show a downward trend with the rise of the damping story. Among them, the optimal damping coefficients are relatively stable, while the optimal stiffness changes greatly; When the damping story is set on the lower floors, the connected structure can get a relatively good damping effect, and the damping effect of the damping story located in the higher stiffness tower is better, while the value of the optimal parameter is larger; There is a certain difference in the damping effect of the left and right towers. The floor response of the left tower shows a more obvious trend that the lower the position of the damping layer, the better the effect is; while the right tower has a better damping effect on the floor near the damping story; The top response of the connected structure with damping story is significantly suppressed.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0462
Abstract:
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S041
Abstract:
Accurate and reliable prediction of structural performance under earthquake requires appropriate ground motion selection. The most important steps are to specify the target spectrum and to select the matching and scaling methods correspondingly. The inherit problem of the commonly utilized Uniform Hazard Spectrum (UHS) is too conservative, while Conditional Mean Spectrum (CMS) based on synthesis and de-aggregation of seismic hazard overcomes this drawback, which has been widely concerned round the world. However, some issues on the application of CMS on soil zones and super high-rise structures remain unaddressed. This paper focuses on the typically super high-rise building in Shanghai site, Shanghai Tower. Based on the Probabilistic Seismic Hazard Analysis, the spectral acceleration at the first fundamental period with 10% of exceedance in 50 years was determined. Then, de-aggregation of probability seismic hazard was carried out to determine the mostly contributed ground motion and spectral parameters at the first fundamental period of SHT in accordance with the attenuation of Shanghai site. CMS can be created and compared with Shanghai Standard Spectrum when utilized as the target spectrum to select ground motions by matching target mean and variance, and inter-storey drift ratios are compared. Results show that ground motion suite targeted on CMS has larger dispersion, and Shanghai Standard Spectrum is conservative to long-period structures.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0581
Abstract:
Shear failure is one of the main failure modes of shear walls. The failure behavior of reinforced concrete (RC) shear wall with aspect ratio of 1.0 is analyzed by means of meso-scale numerical analysis. The influences of axial compression ratio on failure mode, shear bearing capacity, ductility and energy dissipation capacity of shear walls with different sizes are studied. The size effect in shear failure of shear wall is analyzed, and the influence of axial compression ratio on the size effect of nominal shear strength is also revealed. The results indicate that all the simulated RC shear walls with different axial compression ratios exhibit obvious shear failure; When the axial compression ratio increases, the shear bearing capacity of shear wall increases, but the ductility and the deformation capacity decreases; With the increasing size of shear wall, its nominal shear strength decreases, that is, there is an obvious size effect; The greater the axial compression ratio is, the more brittle the shear failure is and the more obvious the size effect is; And when the length of shear wall is greater than 1600 mm, its nominal shear strength tends to be constant, and the size effect gradually disappears.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0607
Abstract:
The working principle and mechanics behavior of disc spring device are analyzed to accurately simulate the mechanics performance of disc spring device and the self-centering RC shear wall. Furthermore, the restoring force model of disc spring device is proposed and developed. The accuracy of the restoring force model is verified through experiments. The hysteretic performance of the self-centering RC shear wall with disc spring device is numerically simulated and compared with the experimental results due to cyclic reversed loading. Results indicate that the numerical model using a restoring force model of disc spring device can effectively simulate the hysteretic behavior, self-centering performance and energy dissipation capability of the self-centering RC shear wall. The bearing capacity of the self-centering RC shear wall increases with the increase of the pre-pressed force of disc springs, the additional friction force and the stiffness of disc spring device. The energy dissipation capacity increases with the increase of the additional friction force. The residual displacement increases with the increase of additional friction and decreases with the increase of the pre-pressed force of disc springs and the stiffness of disc spring device.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0451
Abstract:
Through pressure measurement in a wind tunnel, the wind pressure distribution, total forces and Strouhal numbers of rectangular tall buildings with different corner radius under various wind angles were investigated. The near wake characteristics of the rectangular tall buildings with and without rounded corners were observed by PIV experiment, through which the influence mechanism of rounded corners on the wind load characteristics of the buildings was revealed from the perspective of flow field. Results indicated that under critical wind angle, the separated shear layer reattaches on one side face to form a separation bubble. Therefore, the drag force attains a valley value, and the lift forces and Strouhal number reach peak values. Compared with the building without rounded corner, the critical wind angles of those with rounded corners are smaller. The parameters which control the Strouhal number are the transverse projected width and the distance between vortex pairs in the wake. For the rounded-corner buildings of specific rounded radius, the Strouhal number is increased within some wind angles. The drag force is closely related with vortex pairs in the wake. After adopting the rounded corner, the dimensions of the vortex pairs decrease, while the transverse velocity in the wake increases which implies the intense mixing motion of the fluid and weakened vortex pairs. It gives rise to the decreasing of drag forces. In addition, the irregularity and randomness of vortex shedding are enhanced, while its strength is attenuated by the rounded corner. Then the lift forces are caused to be decreased. However, this decrease tendency is not found for all wind angles.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0507
Abstract:
The ice load is an extreme environmental load received by the polar ship during its ice navigation. The field monitoring of hull structures is an important approach to study ice loads. Generally, the strain responses caused by ice loads are directly measured by installing strain sensors on hull structures at first, then ice loads are reversely identified according to those responses by Influence Coefficient Matrix Method. However, when strain sensors cannot work normally, the accuracy of identification results will be difficult to be guaranteed. Firstly, the influence of measuring point failure on identification results is studied by the finite element analysis of a typical polar ship's side grillage structure. Then, according to the in-depth analysis on measured strain data of multi-purpose ice-class ship Tian'en and the finite element strain data of a typical polar ship's side grillage structure, the spatial distribution of measuring point strains is determined. Furthermore, a method for identifying ice loads based on least square fitting under the influence of failure points is proposed. Finally, the ice loads under seven typical cases are identified accurately, which greatly reduces the identification error. As a result, the effectiveness of this method is verified.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.S044
Abstract:
In order to further investigate the seismic vulnerability of a subway station structure embedded in saturated sand layers, a numerical model of one-story subway station with double spans in saturated sand layers is established based on the u-p effective stress formulations of two-phase media, considering the influence of both site type and ground motion uncertainty. On this basis, the corresponding exceedance probability and vulnerability curves are obtained by using incremental dynamic analysis method, with respect to the damage index of the maximum drift angle for inter-story displacement. The results show that: when PGA<0.7 g, the seismic loads will result in slight or moderate damage in subway station structure; when PGA≥0.7 g, severe damage will occur with the tendency to collapse. This proposed approach of seismic vulnerability for subway station structure in saturated sand layers can provide guide for seismic design of subway station structure as well as prediction for disaster prevention.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0472
Abstract:
The welded hollow spherical joint (WHSJ) has been widely utilized in reticulated shell structures for 55 years since it was put forward in 1966. The corrosion of WHSJs can always be observed in actual conditions due to the invasion of surrounding environment and the unqualified maintenance. We investigate the axial compression capacity of randomly corroded WHSJs. Numerous numerical analysis was performed based on the stochastic finite element analysis. The influence of the probabilistic distribution model of corroded thickness on the reduction factor of the compression capacity of WHSJs was investigated. Analytical formula for predicting the reduction factor were proposed by curve fitting. The influence of the probabilistic distribution model of the corroded thickness on the changing rule of the reduction factor was revealed based on the numerous results derived from the stochastic numerical analysis. The fitting formula which can be used to predict the probabilistic distribution model of the reduction factor was proposed. The applicability of the conclusions on WHSJs with different geometrical sizes was validated through the results derived from WHSJs with different geometrical parameters. The results indicate that the proposed method can accurately determine the probabilistic distribution model of the reduction factor and the conclusions provide an analytical foundation for estimating the compression capacity of randomly corroded WHSJs.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.08.0554
Abstract:
Since the consideration on the saddles and clamps is not comprehensive enough in existing methods, a high-precision shape-finding method of the completed suspension bridges is proposed. This method takes the frictional effect and contact conditions between the main cable and saddles into account. According to the segmental catenary equation, the closure condition and the mechanical equilibrium relationship of the main cable at the saddle, the objective functions of mid-span and side-span systems of the main cable and saddles are derived respectively. The target configuration of a suspension bridge can be calculated by solving these objective functions using the Nelder-Mead algorithm, and then the fabrication lengths of hanger steel wires and the unstressed lengths of main cables can be credibly obtained because the influence of pin-connected cable clamps is considered into the shape-finding calculation adaptively. Finally, taking the Sunxi River Bridge as an example, the validity of this method is verified by the comparison between the calculation results and corresponding design ones of this bridge.
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.06.0431
Abstract:
Currently, the research on bearing mechanism and capacity calculation of horizontal anchor plate has the problem of artificially distinguishing shallow and deep bury conditions without consistent standard. In this article, a logarithmic spiral shape function was proposed to describe the continuous evolution of the sliding surface of the soil around the anchor plate, and the unified mechanical model of ultimate bearing capacity was established with no need to consider the bury condition. According to the relationship among the buried depth of anchor plate, the distance from the sliding surface intersection to the anchor plate and the distance from the tangent point of vertical line of the sliding surface to the anchor plate, the limit equilibrium analysis method was used in three different situations to deduce the unified theoretical solution of vertical pullout ultimate bearing capacity of horizontal strip anchor plate. The results show that, the new mechanical model can well reflect the continuous variation of the sliding surface with the buried depth ratio, and no need to artificially distinguish the bury condition. In the comparative calculation and analysis of five test cases in loose and dense sand, the unified theoretical solution ranks the second among nine methods, and has good adaptability.