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Engineering Mechanics

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Chief Editor: Xinzheng LU

Editor & Publisher: 《工程力学》杂志社

ISSN 1000-4750CN 11-2595/O3

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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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2021 No. 9, Publish Date: 2021-09-13
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2021, 38(9): 1-1.
[Abstract](19) [FullText HTML](5) [PDF 1422KB](15)
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2021, 38(9): 1-14.   doi: 10.6052/j.issn.1000-4750.2020.09.0655
[Abstract](96) [FullText HTML](17) [PDF 16143KB](33)
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The post-earthquake damage of a ceiling system has an important effect on the buildings in normal usage and on the rapid recovery of functions, resulting in the severe economic loss. The research conducted on a seismic behavior study on the ceiling system is summarized from the aspects of experimental study, of numerical simulation and of vulnerability analysis. For the experimental study, a thorough review of the failure mode and of the dynamic response about the ceiling system under earthquake. Based on this, the studies on the effects of installation of compression posts, of the use of retainer clips, of the physical condition of grid components, of the tiles density and of the ceiling area on the ceiling system behavior under earthquake are summarized, and the reinforcement measures for the weak part of the ceiling system are introduced. For the numerical simulation, the different numerical models of the ceiling system and their parameter calibration methods are developed. For the vulnerability analysis, some issues are introduced involving the studies of vulnerability research methods and the selection of relevant indicators. The future imperative research for the improvement of the ceiling system seismic behavior are identified and presented. The results indicate that various problems about seismic behavior study of the ceiling system are needed to investigate as the parameter calibration of a numerical model, the study on key affecting factors and the establishment of a universal seismic grade. In addition, the study on the interaction between the ceiling with other non-structural components is also of a great significance to improve the theoretical system of seismic performance research of the ceiling system.
2021, 38(9): 15-25.   doi: 10.6052/j.issn.1000-4750.2020.08.0618
[Abstract](123) [FullText HTML](19) [PDF 5894KB](23)
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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.
2021, 38(9): 26-35.   doi: 10.6052/j.issn.1000-4750.2020.08.0581
[Abstract](94) [FullText HTML](21) [PDF 5320KB](23)
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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.
2021, 38(9): 36-44, 63.   doi: 10.6052/j.issn.1000-4750.2020.06.0381
[Abstract](111) [FullText HTML](17) [PDF 4958KB](36)
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In order to study the shear response of reinforced concrete (RC) beams strengthened with high ductile concrete (HDC) jacketing layer, 7 HDC jacketed RC beams and 4 non-strengthened RC beams were designed. The failure modes, load-deflection curves, shear capacities and cracks of the beams with different shear span ratios, stirrup ratios, thickness of HDC jacket and stirrups in HDC jacket were studied by static tests. The test results show that the HDC jacket can significantly improve the shear capacity of the beams. The HDC jacket can share partially shear loads which were taken by stirrups, and improve the shear failure pattern. After the ultimate displacements were reached, beams strengthened with HDC jacket exhibit good integrity and high residual bearing capacity. A formula based on the truss-arch model for calculating the shear capacity of beams strengthened with HDC jacket is proposed, and the calculated results are in good agreement with the test results.
2021, 38(9): 45-63.   doi: 10.6052/j.issn.1000-4750.2020.08.0573
[Abstract](101) [FullText HTML](10) [PDF 6149KB](19)
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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 (Wa0) 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.
2021, 38(9): 64-74.   doi: 10.6052/j.issn.1000-4750.2020.08.0595
[Abstract](170) [FullText HTML](27) [PDF 6293KB](30)
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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.
2021, 38(9): 75-88.   doi: 10.6052/j.issn.1000-4750.2020.08.0603
[Abstract](83) [FullText HTML](22) [PDF 6330KB](18)
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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, etc. 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.
2021, 38(9): 89-99, 109.   doi: 10.6052/j.issn.1000-4750.2020.08.0604
[Abstract](106) [FullText HTML](23) [PDF 5168KB](35)
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It is a key step to determine the structural capacity at different limit states for a seismic fragility assessment. However, limit state definition is highly dependent on engineering practices, which includes strong fuzziness. Therefore, it is necessary to conduct a comprehensive study on the influence of fuzziness at limit states in a seismic fragility assessment. This study performs a seismic fragility assessment by considering fuzziness at limit states, where ten types of membership functions are considered with varying fuzziness levels. Four reinforced concrete frame structures with varying heights and fortification levels are taken as the study cases. The fuzziness-probability integration is adopted to derive seismic fragility functions corresponding to different types of membership functions. The seismic fragility results with and without considering fuzziness at limit states are compared to extract the effect of limit state fuzziness with considering varying membership functions and different fuzziness levels. Moreover, the modified seismic fragility function considering limit state fuzziness is derived. The analysis results show that different membership functions show a significant effect on seismic fragility results considering limit state fuzziness. As the promotion of fuzziness level, the difference in seismic fragility results considering limit state fuzziness is growing accordingly. The proposed modified fragility function considering limit state fuzziness can well represent the effect of fuzziness at limit states on the seismic fragility analysis.
2021, 38(9): 100-109.   doi: 10.6052/j.issn.1000-4750.2020.08.0607
[Abstract](114) [FullText HTML](36) [PDF 8479KB](30)
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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.
2021, 38(9): 110-123.   doi: 10.6052/j.issn.1000-4750.2020.09.0629
[Abstract](90) [FullText HTML](24) [PDF 6288KB](12)
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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.
2021, 38(9): 124-132, 181.   doi: 10.6052/j.issn.1000-4750.2020.09.0635
[Abstract](109) [FullText HTML](22) [PDF 6057KB](31)
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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.
2021, 38(9): 133-145.   doi: 10.6052/j.issn.1000-4750.2020.09.0645
[Abstract](122) [FullText HTML](54) [PDF 5321KB](50)
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A new method based on the long short-term memory (LSTM) neural network model is proposed for calculating seismic responses of nonlinear structures. It adopts a unidirectional multilayer stacked LSTM architecture and recursively calculates structural responses using a sliding time window. Updated accuracy evaluation indexes are suggested to take into account the sensitivity difference in different response amplitude ranges and avoid the phase sensitivity issue of traditional ones. The new method is validated by multi-layer frame structures subjected to measured ground motions, the principles for selecting network hyperparameters are given, and the generalization ability of the method for different conditions is discussed. The results indicate that the LSTM model achieves good computational accuracy and is robust to various type of ground motions. Due to the cloud deployment feature of the neural network model, the new method is expected to contribute to application scenarios where traditional numerical methods are limited, such as rapid simulation of seismic response in urban areas.
2021, 38(9): 146-160.   doi: 10.6052/j.issn.1000-4750.2020.09.0649
[Abstract](91) [FullText HTML](23) [PDF 6488KB](20)
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This paper proposes two types of box-column steel frames with double flanged rigid connections, namely, the plane core-tube frame and the damped core-tube frame. Correspondingly, two prototypes of 5-story structures were designed. Quasi-static testing on 0.7-scale subsystems was conducted following a pseudo-dynamic test of the subsystems. Structural properties including the hysteretic performance, strain variations of typical members, degradation of structural stiffness, energy dissipation are analyzed and compared. The results indicate that both frames remain elastic while the intermediate columns with friction dampers consume 71.3% of the dissipated energy in the building at the stage of 0.005 rad. (1/200) interfloor drift. As the drift reaches the threshold of 0.02 rad. (1/50) of the elastoplastic angles of steel structures, the hysteretic curves of the two substructures are bilinear. The panel zones of the connections remain elastic. Plasticity of a column base of the damped frame develops more slowly than that of the plane frame. As the drift ratio goes to 0.04 rad. (1/25), the areas of the hysteretic curves are enlarged without plastic deformation in the panel zones. The base buckling of the plane frame is severer than that of the damped frame. The connections of the two frames are reliable. The intermediate column with friction dampers effectively restrains the plasticity development in the damped frame through frictional energy dissipation in the quasi-static test. The stiffness, energy-dissipation capacity and seismic performance of the damped frame are much better than those of the plane frame.
2021, 38(9): 161-170.   doi: 10.6052/j.issn.1000-4750.2020.09.0656
[Abstract](66) [FullText HTML](11) [PDF 5186KB](16)
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The logical problem in Terzaghi's one-dimensional consolidation theory between boundary conditions and initial conditions and the phenomenon that the velocity of water in soft clay can be negligible under low hydraulic gradient have been gradually recognized. However, under a continuous drainage boundary condition, the one-dimensional consolidation theory considering both the continuous drainage boundary condition and the threshold hydraulic gradient, especially the analytical solution for this model of consolidation, is rarely reported in the literature. It introduces a continuous drainage boundary and develops a single-sided drainage consolidation model of homogeneous soil layers considering the threshold hydraulic gradient in clay soil. The finite Fourier transform method was adopted to obtain solutions for excessive pore pressure, average degree of consolidation and settlement. Furthermore, the influence of continuous drainage boundary condition and initial hydraulic gradient on the consolidation behavior is analyzed when a constant load is applied to a soil layer. The results show that the effect of the continuous drainage interface parameter b on the consolidation behavior of soil with initial hydraulic gradient is the same as that with Darcy's law. The larger the b, the better the permeability of the drainage surface, and the faster the dissipation rate of the pore pressure, and the shorter the consolidation time. On the contrary, the smaller the b, the worse the permeability of the drainage surface, the less the dissipation rate of the excess pore pressure, and the longer the consolidation completion time. When the continuous drainage condition is considered, the influences of the dimensionless variable R (the product of initial hydraulic gradient, specific weight of water and the thickness of the soil layer divided by external load) on the consolidation behavior considering the continuous drainage boundary are not significantly different from that with a fully permeable boundary. The larger the R, the longer the time for the seepage front to reach the bottom of the soil layer. The larger the R, the greater the residual value of the excess pore water pressure in the soil layer when the consolidation is completed. The larger the R, the smaller the average consolidation degree defined by the pore pressure, and the smaller the final settlement.
2021, 38(9): 171-181.   doi: 10.6052/j.issn.1000-4750.2020.09.0659
[Abstract](41) [FullText HTML](15) [PDF 9429KB](13)
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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.
2021, 38(9): 182-191, 202.   doi: 10.6052/j.issn.1000-4750.2020.09.0665
[Abstract](105) [FullText HTML](20) [PDF 4829KB](14)
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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: 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; When the ratio of office live load to dead load is 1.0, the higher the concrete strength, the larger the reliability index.
2021, 38(9): 192-202.   doi: 10.6052/j.issn.1000-4750.2020.09.0703
[Abstract](80) [FullText HTML](18) [PDF 4912KB](15)
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The hybrid reinforced concrete (Hybrid-RC) beam consisting steel bars and fiber-reinforced polymer bars can provide better bearing capacity, durability and ductility. However, literature review showed that the design methods for the normal section of Hybrid-RC beams under bending failed to predict the failure mode of these structures accurately. Therefore, it revises the existing design method, and verifies its effectiveness through database comparison. On this basis, a new design idea of Hybrid-RC beam is proposed to reduce the service cost and achieve higher service load.
2021, 38(9): 203-211.   doi: 10.6052/j.issn.1000-4750.2020.10.0722
[Abstract](140) [FullText HTML](73) [PDF 5155KB](40)
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On October 10, 2019, a three-span concrete continuous box girder on National Highway 312 in Xishan District, Wuxi City, overturned under the action of two vehicles. Investigated the accident site first, then established a geometrically nonlinear finite element model based on wreckage photos and construction drawings, and studied the overturning mechanism. An overload determination method based on the strength and overturning stability effects is proposed. The results include: the overturning test results based on the standard lane load demonstrate that the bridge does not meet the overturning test requirements specified in the Specification for Design of Highway Reinforced Concrete and Prestressed Concrete Bridge and Culvert (2018 edition); the superstructure under the action of the overloaded vehicle first rotated, then slid, and finally exhibited a combination of substantial rotation and sliding overturning mode; the superstructure has a certain safety margin between bearing separation and overturning; the calculation based on the strength and overturning stability effect proves that the overturning effect generated by the overloaded vehicle is greater than the overturning capacity of the structure, indicating that the overturning is mainly attributed to the overload. However, the structural bending capacity turns out to be sufficient through further calculation, indicating that the overturning damage occurred earlier than the occurrence of strength damage, and that the overturning resistance and bending resistance do not match.
2021, 38(9): 212-227.   doi: 10.6052/j.issn.1000-4750.2020.11.0795
[Abstract](49) [FullText HTML](13) [PDF 6675KB](22)
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The cyclic tests were conducted on three 1/3 scaled three-story coupled steel plate shear wall specimens. Unstiffened, vertical channel stiffened, and grid stiffened steel plates were employed as web plates of specimens, respectively. Vertical boundary elements of the coupled steel plate shear walls were concrete-filled square steel tubes. Force-displacement hysteresis curves and failure modes of the specimens were obtained. Envelop curves, stress development, ductility, and energy dissipation were investigated. The finite element analysis software ABAQUS was used to simulate the behavior of specimens. The results show that unstiffened and vertical channel stiffened web plates buckle before yielding, and grid stiffened web plates yield before buckling. Coupling beams and horizontal boundary elements yield after the yielding of web plates. Concrete-filled square steel tubes yield early and have good strength and inelastic deformation. The specimen with unstiffened web plates has the least strength and energy dissipation. The specimen with vertical channel stiffened web plates is the next. The specimen with grid stiffened web plates has stable hysteretic characteristics. The strength of specimens with grid stiffeners and vertical channel stiffeners is increased by 11.7% and 6.9%, respectively compared with that of the unstiffened specimen. The equivalent viscous damping coefficient of specimens with grid stiffeners and vertical channel stiffeners is increased by 65.9% and 19.9% compared with that of the unstiffened specimen. The ductility factors of three specimens are greater than 4.5. It indicates that the coupled steel plate shear walls with different stiffeners have excellent ductility. The analysis results are in good agreement with the experimental results. The stiffener has little influence on the internal force of the coupling beams and boundary elements but increases the strength of the web plates. Compared with two single pier steel plate shear walls, the strength and energy dissipation of the coupled steel plate shear wall have an increase greater than 20%.
2021, 38(9): 228-238.   doi: 10.6052/j.issn.1000-4750.2021.02.0116
[Abstract](72) [FullText HTML](21) [PDF 6579KB](23)
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In view of the difficulty of monitoring the states of bolt connections of large-scale structures, proposed a method for bolt looseness recognition by sound signals, which takes the advantages of the wavelet time-frequency analysis and the powerful image classification ability of the lightweight convolution neural network MobileNetv2. Continuous wavelet transform was carried out for the preprocessed sound signals to obtain the wavelet time-frequency diagrams. The lightweight convolutional neural network MobileNetv2 was trained using the wavelet time-frequency diagrams as samples. The trained model was used to identify the sound signals generated by loosen bolts. An outdoor test of a steel truss model showed that the proposed method could accurately recognize the sound signals of loosen bolts at different positions, with different numbers and different degrees of looseness, and with various environmental noise signals. This novel method has high identification accuracy and good stability, and requires low calculation cost and storage space. It can be carried out easily by mobile devices and embedded devices, providing a new idea for online damage recognition of large and complex structures under environmental excitation.
2021, 38(9): 239-245, 256.   doi: 10.6052/j.issn.1000-4750.2020.09.0624
[Abstract](61) [FullText HTML](19) [PDF 5048KB](10)
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Static ice pressure due to thermal expansion is a key parameter for the design of hydraulic structures in cold regions. Thermal ice stress is affected by various factors, including thermal conditions of ice sheet (ice temperature, temperature rise rate, etc.), ice sheet constraint conditions, ice sheet thickness, etc., which leads to uncertainties in the estimation of thermal ice stress. To investigate the spatial and temporal distribution of thermal ice stress, a prototype observation was conducted to No.6 pond of Qinghuahu lake in Daqing City, Heilongjiang Province, and the ice temperature and thermal stress were fully analyzed. The analysis results indicate that ice temperature mainly depends on the fluctuation of air temperature, and that the ice temperature of each layer fluctuates more gently with time than air temperature. With the increase of ice depth, the fluctuation range of ice temperature decreases, and ice temperature increases. The surface ice temperature is well linearly related with air temperature by the change rate between 0.38 and 0.56, and the influence of air temperature on ice temperature is quite obvious within 30 cm, and ice temperature below 30 cm presents a linear distribution along depth. Based on Bergdahl's rheological constitutive relation of static ice, a mathematical model of thermal ice stress is proposed. The undetermined parameter in the model is determined by regression combining with measured data, and its values obviously depend on measuring positions. The calculated values of ice stress agree well with the measured ones. From station 1 to station 4, the overall thermal ice stresses increase. The stress is non-monotonically distributed along ice depth, i.e., thermal stress in surface ice is slightly smaller, reaches a maximum at the depth of 10~30 cm, and then gradually declines with depth. Moreover, thermal ice stresses only appear on the upper part of the ice within 0.7 m.
2021, 38(9): 246-256.   doi: 10.6052/j.issn.1000-4750.2020.09.0638
[Abstract](69) [FullText HTML](19) [PDF 6531KB](14)
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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. 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. 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. 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.