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Engineering Mechanics

Since 1984  Monthly

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Chief Editor: Xinzheng LU

Editor & Publisher: 《工程力学》编辑部

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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[Abstract](36) [FullText HTML](21) [PDF 8965KB](1)
Abstract:
In order to study the seismic performance of frame joints with concrete-filled steel tubular column and double-sided composite beam, three cross-shaped frame joints of a double composite steel-concrete beam and one cross-shaped frame joint of a normal single composite steel-concrete beam were designed, and low-cycle reciprocating loading tests were carried out to compare and analyze their failure modes and ultimate bearing capacity, initial stiffness, energy dissipation capacity, ductility, stiffness degradation, and other seismic performance indicators. By changing the thickness and load transfer mode of the bottom concrete slab, the influence of different thickness and different load transfer mode of the bottom concrete slab on the mechanical properties of the double-sided composite beam is studied. The results show that: compared with normal single composite steel-concrete beam-frame joints, double composite steel-concrete beam-frame joints have higher bearing capacity and stiffness, and are suitable for structures with larger loads, but have no obvious advantages in ductility, stiffness degradation and energy dissipation capacity. There is no obvious difference in the effect of concentrated and uniform load transfer on the seismic performance of double composite beams, and prefabricated concrete slabs and bolted connections are more convenient and reliable.
[Abstract](67) [FullText HTML](50) [PDF 1122KB](0)
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In order to improve the cooperative deformation capability of the concrete and the steel plate, the high ductile concrete (HDC) was proposed to replace the concrete. Two steel plate–HDC composite coupling beams and two steel plate-concrete composite coupling beams were tested under reversed cyclic lateral loading. The specimens’ failure process, failure modes, hysteretic behavior, energy dissipation and stiffness degradation were studied. The results shows that the failure mode of specimens with span-to-depth ratio of 1.5 is the shear failure while the shear-bond failure occurs on the specimens with span-to-depth ratio of 2.5. Compared with steel plate-concrete composite coupling beams, the proposed steel plate–HDC composite coupling beams exhibit high ductility and damage resistant capability under reversed cyclic lateral loading. Ultimate rotational capacity and energy dissipation of steel plate–HDC composite coupling beams are 44.4% and 83.5% higher, respectively than those of steel plate–concrete composite coupling beams when the specimens failed in shear. Steel plate–HDC composite coupling beam with span-to-depth ratio of 2.5 exhibits significantly improved energy-dissipation capacity. According to the test results, the specimens’ design value of shear-compression ratio is 0.48~0.57, which is significantly higher than the limited shear-compression ratio of the coupling beams with small span-to-depth ratio. Based on the test results and analysis, a formula for the shear capacity of the coupling beam with small span-to-depth ratio is presented, and the calculation values are in good agreement with experimental results.
[Abstract](4) [FullText HTML](4) [PDF 327KB](0)
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Peak ground-motion acceleration (PGA) is a fundamental parameter in seismic design codes and in earthquake early warning systems. We collected the seismic data recorded by 40 strong-motion stations of the KiK-net seismic station array in Japan, and studied the statistic distribution of PGA amplification factor fPGA. It was demonstrated that the fPGA under a given seismic intensity input was basically log-normally distributed with its mean and standard deviation depending on the site conditions. Any individual site characteristic parameter, such as VS30, VS20 or soil thickness D, was poorly correlated with the statistic parameters, i.e., the mean and standard deviation, while a satisfactory correlation was obtained with respect to linear combinations of VS30, VS20 and D. By the regression of the data, the statistic parameters of fPGA were calculated according to a linear combination of site characteristic parameters to build the probability density function of the log-normal distribution model of fPGA. Following the fPGA probability model, the ground surface PGA corrected by specific site characteristic parameters could be predicted under different probability levels, and testified by seismic data. The probabilistic predictions of PGA meet the demands of risk analysis in engineering practice, paving the way for site-corrected surface PGA prediction in earthquake early warning and fast seismic intensity estimation.
[Abstract](3) [FullText HTML](1) [PDF 403KB](1)
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In the analysis of soil-structure seismic response or of near-field seismic wave propagations, the visco-elastic artificial boundary elements are often applied to transfer the infinite-domain problem into a finite-domain problem. Since the material parameters and the size of the visco-elastic artificial boundary elements are different from those of the internal medium elements, there are differences in the numerical stability conditions between the artificial boundary domain and the internal domain when the explicit time domain step-by-step integration algorithm is used. At present, however, there are no appropriate analysis methods and research results to determine the explicit numerical stability conditions and the stable integration time steps. In this study, we propose a stability analysis method for explicit time-domain stepwise integration algorithm when using the two-dimensional visco-elastic artificial boundary elements. Firstly, several typical local subsystems of the artificial boundaries are established. The transfer matrix of each subsystem is analyzed, and the analytical solutions of the stability conditions for each subsystem are obtained. By comparing the stability conditions of the subsystems and the internal medium system, a uniform stability condition of explicit time domain stepwise integration algorithm is obtained when using the visco-elastic artificial boundary elements. When the internal medium areas also satisfy this stability condition, this condition becomes a sufficient condition for the stability calculation of the overall system and can be used to deciding the stable discrete time step in the numerical analysis.
[Abstract](38) [FullText HTML](29) [PDF 2543KB](0)
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The seismic failure mode of uniform damage refers to that the structure has a uniform damage and story drift along the height and develops a global energy dissipation mechanism, and it is an ideal and expected failure mode. In this paper, a uniform damage-based seismic optimization design approach for RC frame structures considering the soil-structure interaction is proposed. By taking the uniformity of maximum inter-story drift ratio (IDR) as the design objective, the seismic optimization design approach was developed. Moreover, the optimization procedure accounted for the IDR distribution and component rotation demands. The component’s sectional reinforcements were selected as the design variables, and the material cost and the reinforcement ratio were considered as the design constraints. Based on the Beam on Nonlinear Winkler Foundation (BNWF) model, the numerical model of the RC frame structure considering soil-structure interaction was established. Two RC frame structures with 5 and 12 stories were employed as the prototype structures. The effects of convergence parameters on the convergence speed and stability were investigated. The transfer of story reinforcements in the optimization was studied. The change of component rotation and IDR distribution after the optimization was analyzed. The analytical results indicate that the developed approach can achieve a uniform IDR distribution and a smaller maximum IDR, thus improving the seismic performance.
[Abstract](87) [FullText HTML](35) [PDF 1209KB](0)
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Chloride ion ingressing into concrete will cause durability problems and eventually lead to the degradation of structural seismic performance within time. At material level, this paper simulates the influence of chloride ion erosion on the properties of RC frame structure materials by considering the weakening of area of reinforcement, the softening of the cover concrete, and the ultimate strain reduction of confined concrete, etc., which was verified by relevant experiment data. At structure level, based on the mechanical properties degradation model of above materials and fiber, the pushover analysis of RC frames of three, six and eight layers (0, 30, 50 and 70 years) and the dynamic time history analysis of the six-layer multi-age frame were carried out, and then the degradation of bearing and deformation capacity and the variation of interstory drift ratio are studied. The results show that: after structural corrosion, with the increasing of service age, the yield displacement, ultimate displacement, failure displacement, ductility and softening stiffness are gradually reduced, and the yield PGA and collapsed PGA of the structure are also decreasing, while the maximum interstory drift ratio of the structure is increasing. Moreover, the interstory drift ratio of the structure under strong earthquakes is more sensitive to the service age than moderate earthquake.
[Abstract](36) [FullText HTML](25) [PDF 2176KB](1)
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Structural damage detection techniques using time domain vibration responses are of interests in structural health monitoring. Two structural characteristic vectors (SCVs) defined by cross correlation functions of time domain vibration responses, i.e. inner product vector (IPV) and cross correlation function amplitude vector (CorV), as well as the corresponding damage detection technique are reviewed. In order to utilize more information in the correlation functions, the two SCVs are then generalized to several derived SCVs, and the damage detection procedure using data fusion technique with these SCVs is also proposed to enhance the accuracy of the damage detection results. The damage detection results of an experimental 8-storey shear frame structure show that the small damage in the frame structure can be located by the proposed method.
[Abstract](36) [FullText HTML](22) [PDF 1764KB](4)
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Ten push-out experimental specimens were cast and tested to study the interfacial bond-slip behavior of section steel and high-performance fiber concrete (HPFC). The main parameters investigated were strength grade, concrete cover thickness and embedded length. The failure process and load-slip(P-S) curves were obtained. The influence regularities of design parameters on the characteristic bond strength were studied, and the formulae of characteristic bond strength were established. The effective bond stress was introduced and deduced. Through the analysis of the whole process of the effective bond stress slip curve, the development of bond stress was obtained. The results show that : the characteristics bond strength were increased by the increase of the concrete cover thickness and the concrete strength; the calculated value of the characteristics bond strength appeared were similar to that of the test values; the effective bond stress reflected the development and transformation of bond stress at the interface between section steel and high-performance-fiber-concrete; the proportional relationship among the components of the bonding force was derived by process analysis. The research provides an experimental support for analyzing the mechanical behaviors of steel reinforced high-performance-fiber-concrete.
[Abstract](35) [FullText HTML](26) [PDF 1201KB](0)
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A four-node co-rotational quadrilateral shell element for smooth and non-smooth shell structures is presented. Each node of the element has three translational degrees of freedom and two or three vectorial rotational degrees of freedom. For the nodes of smooth shells or nodes away from the intersection of non-smooth shells, the two smallest components of the mid-surface normal vector are defined as the nodal rotational variables. For the nodes at intersections of non-smooth shells, two smallest components of one orientation vector, together with one smaller or the smallest component of another nodal orientation vector, are employed as rotational variables. In a nonlinear incremental solution procedure, the vectorial rotational variables are additive and the symmetric tangent stiffness matrices are obtained in both global and local coordinate systems, thus, one-dimensional linear storage scheme can be adopted, saving computer storage and computing time effectively. To alleviate membrane and shear locking phenomena, one-point quadrature is adopted in calculating the element tangent stiffness matrices and the internal force vector, and the physically stabilized method is employed to avoid the occurrence of spurious zero energy modes. The reliability and computational accuracy are verified through two smooth shell problems and two non-smooth shell problems undergoing large displacements and large rotations.
[Abstract](32) [FullText HTML](20) [PDF 822KB](0)
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With the increase of service time, prestressed concrete beams under corrosive environment attacking will gradually exhibit the deterioration of ductility and load bearing capacity due to the corrosion of stressed tendons in erosion environment, which seriously affects the safety of building structures. In order to study the load bearing capacity of prestressed concrete beams under a corrosive environment, the corroded prestressed concrete beams under concentrated loads was taken as the research object, and the deteriorated property of corroded materials and the effect of prestressing for load bearing capacity were analyzed. Based on the truss-arch model, the distribution coefficients of truss role and arch role were calculated, and the calculation formula for load bearing capacity along with the assessment method of failure mode of the prestressed concrete beams were proposed. The experimental data of 76 prestressed concrete beams were used to validate the suggested model. The results show that: for the load bearing capacity of prestressed concrete beams, the calculated values are in a good agreement with the test values, and the mean value and the variance of the ratio between them are 1.116 and 0.033, respectively. Using the proposed model, the prediction of the failure mode agrees well with the observed failure mode of experimental concrete beams, and the suggested method can reflect the fact that the failure mode of the concrete beams changed by time as the corrosion degree increases. Thus, the proposed model can be applied to calculate the load bearing capacity and assess the failure mode of corroded prestressed concrete beams.
[Abstract](162) [FullText HTML](29) [PDF 1021KB](0)
Abstract:
To investigate the seismic behavior of reinforced concrete (RC) beams with high ductility concrete (HDC), eight RC beams were designed and strengthened with HDC jackets and carbon fiber strips. The failure modes, deformation capacity and energy dissipation capacity of the specimens were studied under low cyclic loading tests. The experimental results show that: The tensile strain hardening and multiple cracking of HDC can effectively control the development of shear cracks of the beams strengthened with HDC during the failure process and the HDC-strengthening system is effective to improve the brittle failure characteristics; HDC can provide obvious constraint for the core concrete. The shear strength, ductility and energy dissipation capacity of the strengthened beams are significantly improved. The HDC jacket could be more effective than the carbon fiber strips in enhancing the behavior of the beams; When the shear span is relatively large, using mesh reinforcements in the HDC jacket improves the ductility and energy dissipation capacity. However, it contributes little to the shear capacity. A calculation method for the shear capacity of strengthened beams is proposed based on a truss-arch model. The calculated results have good agreement with the test results.
[Abstract](35) [FullText HTML](33) [PDF 1322KB](0)
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A new prefabricated self-centering steel frame with slit steel plate shear walls was proposed in this paper. A low-cycle reciprocated static loading test of the new structure was designed and conducted to study the stiffness, energy dissipation performance, failure mode and self-centering capacity. The results show that the prefabricated self-centering steel frame had favorable gap opening and closing mechanism and could automatically re-center after the earthquake. The function of the main structure could be efficiently restored by replacing the slit steel plate shear walls. The structure possessed high initial stiffness and good energy dissipation capacity. Under horizontal loads, the slit steel plate shear wall was able to dissipate energy through the development of buckling and thus effectively protected the prefabricated self-centering steel frame. At the elastoplastic interstory drift limit of 0.02 rad (1/50) stipulated in the code, the prefabricated self-centering steel frame was essentially in the elastic state with small residual opening. During the test, the maximum cable force was far less than the yield force, which provided a good foundation for the structure to withstand a greater earthquake action.
[Abstract](32) [FullText HTML](24) [PDF 1317KB](0)
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Based on the recursive decomposition algorithm (RDA) of network connectivity reliability analysis, a unified RDA is developed by integrating the three parts of the original RDA for different network weighting forms. To estimate the seismic reliability of dependent failure lifeline engineering systems, the sequential compounding method (SCM) and Gumbel Copula function are used to calculate the joint failure probability of a disjoint minimum path and a disjoint minimum cut event in RDA, respectively. The unified RDA for the seismic reliability estimation of dependent failure lifeline engineering systems is developed. The calculation results of the reliability of a 36-node grid network show that the method can be used for dynamic seismic reliability estimation of dependent failure network systems with high accuracy.
[Abstract](28) [FullText HTML](26) [PDF 1766KB](0)
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A new type of double-skin steel-concrete composite shear wall with vertical seams between shear wall and boundary elements were proposed, and the wall plates are connected using bolts and plate connectors. Quasi-static tests on four specimens were carried out to study the seismic behavior of the composite shear wall. The results of tests were compared with the same types of composite shear walls without vertical seams, in which the upper and lower steel faceplates were weld together. The test results showed that the new type of double-skin steel-concrete shear wall had good seismic performance. The average values of the yield drift angle and ultimate drift angle of the four specimens were 1/169 and 1/37, respectively. The seams weakened the bearing capacity of the test specimen, but improved the ductility and the performance of energy consumption. The failure mode of specimens was bending failure at the bottom of the wall, indicating that the stress between walls could be effectively transmitted through bolts and plate connectors. A finite element model was developed using ABAQUS to analyze the performance of this type of double-skin composite shear wall. The force mechanism of bolt group in the plate connectors, the effects of vertical seams on the failure mode of boundary columns, and other factors including strength of material, shear-span ratio and axial compression ratio which may affect the performance of the composite shear wall, were also analyzed based on the FEM model.
[Abstract](25) [FullText HTML](14) [PDF 345KB](0)
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The steel orthotropic deck was used in the steel box girder of a suspension bridge. Four types of fatigue cracks were discovered at some connections of the orthotropic deck during service. Subsequently the pavement on the deck was replaced with epoxy asphalt concrete. To analyze the effect of the new pavement on the fatigue sensitive regions, a finite element model was established and field bridge tests were conducted at three states, namely, original pavement, surfacing, and new pavement. The test lasted for 6 years under the new pavement state. The stress and deformation of the fatigue sensitive regions were measured. The fatigue life improvement was analyzed considering the temperature based on the measured data. The results show that the epoxy asphalt concrete pavement was in a stable working state during the test period, that the stress improvement effects in the fatigue sensitive regions 1 to 4 were 80%, 14%, 32%, 46% in a low temperature environment, respectively. The stresses of the four fatigue sensitive regions were linearly correlated with the temperature, and the linear ratios are -4.00, 0.64, 1.89, 1.91, respectively. After normalizing the measured stress by the average annual temperature, the fatigue life was improved by 2.95 times in Region 1, and by 1.64 times in Region 4. The fatigue lives in Regions 2 and 3 were not improved obviously, and the cracking probabilities of Regions 2 and 3 were still high in a high temperature environment.
[Abstract](29) [FullText HTML](18) [PDF 1556KB](0)
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The discrete linear spatial truss structure composed of many bar members is taken as a continuous beam by using an equivalent method. The transient vibration suppression of the truss structure is studied by adding nonlinear energy sinks (NES) to the equivalent beam. The lattice structure of the beam is modeled as an equivalent linear continuous system (finite length beam) by an equivalent method, which is verified by a finite element model. The vibration control equations of an equivalent cantilever beam with a NES attachment are established. The Galerkin method is adopted for discretization. The displacement responses of beams with and without a NES attachment under external excitation are analyzed. The vibration suppression effect of NES on the structure is studied by calculating the external excitation response of NES attachments at different positions in the structure. In addition, the external excitation response of NES attachments with different masses at different positions are also investigated. The effect of NES additional mass on the vibration reduction is obtained. The results show that the NES attachments can reduce the response efficiency of the x-truss under transient excitation When the mass of the NES attachments increases, the vibration amplitude of the system declines more rapidly and the energy consumption efficiency of the NES attachments becomes higher. The NES passive vibration reduction effect is compared with the linear stiffness damping damper (TMD). The results show that, in the structure with additional NES, the attenuation of the structure amplitude is appreciable at about 5 seconds after the excitation occurred, and the decline in the amplitude is steeper. This means that the NES passive reduction effect is much better than that of the linear stiffness damping damper (TMD). Additionally, the attenuation effect of the NES attachments with different qualities is verified through experiments, in which the same displacement excitation amplitude (15 mm) is applied to the free end of a beam. The results show that the greater the mass of the NES attachment is, the higher is the attenuation efficiency of the transient response of the cantilever structure. The experimental results are in good agreement with the theoretical calculation results.
[Abstract](33) [FullText HTML](22) [PDF 3201KB](1)
Abstract:
The characteristics of the lateral and torsional seismic responses of steel braced concrete frame structures are studied. It is revealed that the dynamic buckling of steel brace will have an impact on the resistance torque during the repeated loading process, and the plastic hinge state of the structure will change imbalanced, resulting in inelastic torsion. By using D'alembert principle, the mechanism of the steel braced structure causing inertial force, inertial torque and inelastic torsional surge induced by the brace buckling is studied, and the similar performance is verified by shaking table test and finite element nonlinear analysis. The anti-torsion effect of buckling-restrained braces on structures and the working mechanism of preventing inelastic torsional burst of structures are studied. Finally, suggestions are proposed to use the ordinary steel braces as the first seismic defense line of CBF concrete frame structures, and the technical measures of using buckling-restrained braces to reduce of inelastic torsion are given.
[Abstract](27) [FullText HTML](16) [PDF 892KB](1)
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The local cracking problem of steel-UHPC (ultra-high-performance concrete) composite structures under negative bending moments is the basis of the application and development. Based on the UHPC tensile bilinear constitutive model and plane cross-section assumption, a section stress method is set up to describe the stress distribution of the steel-UHPC composite slabs and calculate the cracking load under a pure bending condition. The proposed method is verified by 4 specimens of 2 groups and the test results in the literature. The results indicate that the section-stress method can accurately describe the cracking behavior of steel-UHPC composite plates under pure bending and the average ratio of calculated to measured values is 0.95. The UHPC cracking strength is an intrinsic property dependent on the nature of the material itself and is not influenced by the steel-UHPC composite slab. The height of the UHPC strain hardening zone represents the combination effect and reinforcement constraint when visible cracks appear. By reducing the cover thickness or increasing the reinforcement ratio, the UHPC strain hardening height can be increased and the flexural behavior of the steel-UHPC composite slab can be improved.
[Abstract](28) [FullText HTML](18) [PDF 1276KB](1)
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With the fast development of nuclear power industry in China, it is inevitable to encounter non-rock site during site selection. Focusing on the seismic response of the nuclear island in non-bedrock site under oblique incidence, a three-dimensional finite element model for the soil-structure system including the CAP1400 nuclear island structure and near-field rock site is established. Based on the viscous-spring artificial boundary and oblique incident ground motion input method, the influence of oblique incident angle of P-wave and non-rock layered site on the seismic response of the nuclear island is studied. Research shows that non-bedrock site will increase the acceleration response of the nuclear island structure and its floor response spectrum, and in most conditions will also increase the relative floor displacement; As the incident angle of P wave increases, the nuclear island structural vertical response decreases, the horizontal response increases, and the spectral characteristics of the floor response spectrum will change.
[Abstract](11) [FullText HTML](8) [PDF 0KB](0)
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Based on the reinforced concrete (RC) column test data in the Pacific Earthquake Engineering Research Center (PEER) database and the existing seismic damage index models, the damage characteristics of the RC columns at different damage levels were summarized. Damage evaluation criteria for damaged columns were proposed. The evolutionary damage to the sectional materials, including the cover concrete, confined concrete and longitudinal reinforcement, during the earthquake damage process was investigated. Evolutionary damage models for the sectional materials were proposed, where the uneven damage to the materials at different positions of the plastic hinge zone of the RC column was considered. Based on the OpenSEES platform and the fiber model, a numerical model of the seismic damaged RC frame columns was established, which was directly based on the constitutive relationship of materials. The model considered the damage difference of materials in different positions of the damage area and the damage difference of materials in different positions of the same section. The test data of 13 existing RC frame columns were randomly selected to verify the numerical model calculation results of seismic damaged RC frame columns. The results show that the model accurately predicted the post-earthquake behavior of the RC columns. These results provide an analytical model for the performance evaluation of and retrofitting decisions for RC structures after an earthquake.
[Abstract](34) [FullText HTML](3) [PDF 433KB](0)
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This paper presents a superconvergent patch recovery method for the superconvergent solutions of modes in the finite element (FE) post-processing stage of non-uniform and variable curvature curved beams. An adaptive method for the in-plane and out-of-plane free vibration of curved beams with variable cross-section is also proposed. In the post-processing stage of the displacement-based finite element method, the superconvergent patch recovery method and the high-order shape function interpolation technique are introduced to obtain the superconvergent solution of modes (displacement). Using the superconvergence solution of modes to estimate the errors of the FE solution of modes in the energy form under the current mesh, an adaptive mesh refinement is proposed by mesh subdivision to derive the optimized mesh and accurate FE solutions to meet the preset error tolerance. Numerical examples show that the proposed algorithm is suitable for solving the continuous orders for frequencies and modes in the in-plane and out-of-plane free vibration of different kinds of curve shapes, boundary conditions, non-uniform cross-section, and variable curvature forms of the non-uniform curved beams. The computation procedure can provide accurate solutions. The analysis process is efficient and reliable.
[Abstract](2) [FullText HTML](2) [PDF 307KB](0)
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Surface damage and deformation are important indicators for testing, appraisal and monitoring of structural safety. The adoption of digital image method can effectively overcome the shortcomings of current manual inspection methods. However in engineering practice, challenges are encountered such as the difficulty in correcting the geometric deformation of the image during quantitative detection, the difficulty of damage localization of images in the overall structure, and the inability to measure the spatial deformation of the steel structure. By combining the research and application of multi-view geometric 3D reconstruction method, the above problems can be effectively solved. First, this paper discusses the principle and algorithm for the implementation of multi-view geometric 3D reconstruction, and introduces the classic and efficient algorithms for practice. Second, aiming at the problem of the digital image detection method in engineering practice, a surface projection method for the correction of imaging geometric deformation and damage localization, and a reverse engineering modeling and feature extraction method for the geometric deformation damage detection are proposed. Finally, through three application studies including structural surface crack identification, large structure surface damage localization and steel structure component deformation identification, the specific operation methods and comparative advantages of multi-view geometric 3D reconstruction method for structural surface damage and deformation identification are discussed. The multi-view geometry three-dimensional reconstruction method has the benefits of low equipment requirements, convenient operation, rich model color and relatively high point cloud precision, After combined with the digital image method, it shows great research and application potential in the field of engineering structure inspection and monitoring.
[Abstract](10) [FullText HTML](4) [PDF 311KB](0)
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In order to explore the reasons of fatigue failure of vena cava filters, it is necessary to study the fatigue strength of the filter under cyclic variable loads. SolidWorks software was used to build models of 8 filters, ABAQUS software was used to analyze the fatigue strength of 8 filters under circumferential pulsating cyclic load and radial compression cyclic load, and the safety of one filter was verified by experiments. In the circumferential fatigue analysis, all the alternating strain points of 8 filters are below the fatigue limit curve, and the safety factors are greater than 1, which meet the fatigue life requirements. In the radial fatigue analysis, some alternating strain points of the new filter and the TrapEase filter are above the fatigue limit curve, and the safety factors are less than 1. The other 6 filters meet the fatigue life requirements. The recyclable filter may not meet the requirement of fatigue life of 10 years and can be used as a temporary filter. Through 14 days, 21 days and 28 days of animal experiments, three small sweetgum pigs were implanted with Aegisy filter. The safety of Aegisy filter is comprehensively evaluated. The results show a good reference for the design, development and clinical application of vena cava filters.
[Abstract](0) [FullText HTML](3) [PDF 469KB](0)
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Based on the results of an experimental study on the seismic performance of 4 full-scale concrete columns reinforced with high performance ferrocement laminates (HPFL) under constant axial forces and cyclic horizontal loads, the numerical simulation analysis of the specimens is carried out. The performance characteristics of the seismic capacity, ductility, stiffness and energy dissipation capacity of the reinforced columns are further studied. At the same time, a method for strengthening RC columns with seismic damage under loading and a simplified calculation method for flexural bearing capacity of such structures are also proposed. Based on this, using reinforcement method and finite element analysis methods proposed, the main factors affecting the seismic performance of RC columns with seismic damage under loading are studied, including axial compression ratio, shear span ratio, transverse mesh reinforcement ratio and reinforcement form. The research shows that: the finite element simulation values, theoretical values and experimental values are in a good agreement. After the HPFL reinforcement, the bearing capacity, ductility and energy consumption capacity of the components are significantly improved, and the degradation rate of stiffness is significantly reduced. After the longitudinal reinforcement of the reinforcement layer is anchored into the base, the improvement of the seismic performance is more superior. With the increase of the axial compression ratio, the bearing capacity is greatly increased, and the ductility is insufficient. As the shear-span ratio increases, the bearing capacity and ductility of the specimens decrease. With the increase of load level difference, the later deformation capacity is obviously weaker. Compared with the ring reinforcement, the spiral reinforcement has the same initial stiffness, the former has better ductility and the latter has higher bearing capacity.
[Abstract](2) [FullText HTML](3) [PDF 334KB](0)
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An oblique three-dimensional (3D) isolation bearing was introduced based on the properties of lead rubber bearings (LRB) to meet the vertical strength and damping demands. A mechanical model considering the influence of the pressure and nonlinear stiffness degradation of LRB was established. The horizontal and vertical performance test was carried out on the 3D isolation bearings with inclination angles of 12 degrees and 15 degrees. The hysteretic behavior had non-parallel characteristics during the loading and unloading process. The vertical stiffness showed a nonlinear variation with the deformation. The variation of the vertical performance with the inclination angle and the vertical displacement was obtained. The proposed nonlinear theory and experimental results matched well. A numerical simulation of the 3D isolation bearings with different inclination angles was accomplished using the finite element method. The variations of the vertical nonlinear stiffness with the friction coefficient, shear strain, and inclination angle were discussed based on the simulation results.
[Abstract](68) [FullText HTML](7) [PDF 333KB](0)
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Both thirty-three concrete stub columns reinforced by prestressed steel hoops (PSHC) and nine unreinforced columns were tested under axial compression. The studied parameters were the hoop ratio (the spacing of hoops and the concrete diameter), the prestressing level and the initial axial compression ratio. The influences of these parameters on the carrying capacity and deformation capacity of PSHC were obtained and discussed. The results show that the bearing capacity and deformation capacity of the PSHC can be improved by 107% and 540%, respectively, compared with the comparison column. The reinforcement effect will become better with the increase of the hoop ratio. When the prestress ratio increases gradually, the carrying capacity of PSHC increases gradually and the peak strain decreases gradually. The initial axial compression ratio has no obvious influence on the reinforcement effect, the PSHC can be used as a non-unloading reinforcement method. Based on the experiment results, a prediction equation was proposed and verified by the comparison of prediction values and test data in this investigation and other references.
[Abstract](2) [FullText HTML](0) [PDF 376KB](0)
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For the construction of steel structures of Beijing Daxing International Airport Terminal, and based on the completed full-scale multi-planar DKT-joint tests, 192 groups of finite element models with different parameters are simulated and analyzed to further study the mechanical mechanism of the DKT-joint. The influences of opening size, thickness and quantity of stiffeners on mechanical properties of the multi-planar DKT-joint are investigated. Multiple nonlinear regression towards the design and ultimate bearing capacity of the multi-planar DKT-joint containing various stiffener arrangements under axial compression is conducted, and the magnification coefficient η for design value and ultimate capacity of the DKT-joint is obtained. The formulas of design value and ultimate capacity of the multi-planar DKT-joint containing internal stiffeners are derived based on current Standard for design of steel structures. Experiments and finite element analysis (FEA) results indicate that the formulas of design value and ultimate capacity of the multi-planar DKT joint containing internal stiffeners meet the precision requirements well, and can provide reliable reference for the design of similar joints in practical engineering.
[Abstract](5) [FullText HTML](2) [PDF 352KB](0)
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In order to study the effects of fastener clamping force failure on dynamic performance of vehicle-track system, a detailed fastener model was established in the paper, and the vertical nonlinear stiffness behavior of the WJ-8 fastener in different stages was analyzed. An improved bilinear tension stiffness spring model and a no-tensioned spring model were proposed to represent the invalid fastener. The influence of different failure types of fasteners on dynamic response of vehicle-track system was also analyzed. The results show that, the vertical stiffness of the fastener can be divided into two parts: uplift stiffness and compressive stiffness. When the uplift force exceeded the clamping force, the vertical uplift stiffness of the fastener would decrease rapidly and the fastener would lose its constraints on the rail uplift deformation. Both clamping force failure and complete failure of fastener would weaken rail constraints and increase vibration. Clamping force failure mainly increases the vibration of rail in 8~50 Hz central frequency band, while the complete failure brings an increase in the whole frequency band.
[Abstract](4) [FullText HTML](2) [PDF 387KB](0)
Abstract:
To investigate the effect of the amount and position of the heated compartments on fire behaviour of continuous slabs, this paper conducted fire tests on three continuous slabs. One has fire exerted at the side span only, one has fire exerted at both the side and the mid spans, and the other has fire exerted at all the three spans. The furnace temperatures of each span, the temperature of concrete and steel, the slab deflection, the restraint forces at slab corners and failure modes were obtained. Adopting the plastic damage model on the ABAQUS platform, the numerical analyses were conducted to predict the temperature, the deflection and the mechanical mechanism of tested slabs. The comparison between the test results and numerical results were also conducted, showing that the amount and position of the heated spans have significant effects on the cracking pattern, the deflection and the failure mode of continuous slabs. The short vertical slab cracks appear on the bottom surface of the heated spans, the cracks paralleled to the short-span appear on the top surface of the heated spans and the cracks are adjacent to interior supports. The mid-span vertical deflection gradually increases with the increase of temperature, and the increase of the deflection of mid span mainly depends on the heated effect of its adjacent spans. In addition, numerical results show that the moment mechanisms of the heated span during the heating stage is different with that during cooling stage. The moments near the internal supports are larger than those at other places. The axial forces in the continuous slab are compressive, and the maximum equivalent plastic tensile strains mainly concentrate near the internal supports (top surface) and the outer sides (bottom surface).
[Abstract](4) [FullText HTML](0) [PDF 389KB](0)
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The multi-loop cable-string dome (MLSD) is a complex suspended-dome structure. Sudden failure of any cables will cause a very significant dynamic impact on MLSD. Based on the AP method, this study proposes a dynamic analysis method to analyze the dynamic response of MLSD due to sudden cable broken. The sensitive analysis of different parameters was conducted, such as failure paths, failure time, damping ratio and initial loadings. The ideal parameters suitable for MLSD are recommended. The dynamic analysis results show that: the displacement and internal force response of the remaining MLSD due to cable sudden broken will be greater than the cable slowly failure. The dynamic amplification factor should be seriously considered when suffered from cable sudden broken. Moreover, the dynamic amplification factor (DAF) of some responses will be larger than 2.0 recommended by current design codes. Finally, the discussion on displacement DAFs due to different cables sudden broken shows that the DAFs due to the sudden failure of any cables of the same loop are the same. The DAFs caused by sudden failure of cables on the outer loop will be significantly greater than that of other loops. Both DAFs due to cable failure of the outer loop and the string are significant, but the DAFs value distribution are quite different. The dynamic response caused by multiple cable breakages is not always greater than that of a single cable.
[Abstract](5) [FullText HTML](2) [PDF 0KB](0)
Abstract:
An artificial climate simulation laboratory was used to perform an accelerated freeze-thaw cycle test on six reinforced concrete (RC) beam specimens with a shear-span ratio of 2.6, which were then subjected to quasi-static loading. According to the test results, the effects of the freeze-thaw cycles and concrete strength grades on the seismic performance indicators of RC beam specimens such as the failure mode, hysteretic curve, strength, deformation capacity and energy dissipation were analyzed. The results show that after the freeze-thaw cycles, the compressive strength of the concrete decreased, the internal porosity of the concrete became larger, the micro-cracks were increased, and cracks appeared on the surface of the beam specimens. Six beam specimens exhibited a flexure-shear failure mode after the quasi-static test. With the increase in the number of freeze-thaw cycles, the strength and energy dissipation capacity degraded, and ductility first increased slightly and then decreased greatly. With the increase in the concrete strength grade, the degree of damage caused by the freeze-thaw cycle of the beam specimens was reduced, the yield, peak and ultimate strengths of specimens were increased, the energy dissipation capacity was enhanced, and the ductility was not significantly changed.
Abstract:
The reinforcement slip in the beam-column joints or column footings can make a significant contribution to the total lateral displacement of reinforced concrete members. In order to accurately evaluate the seismic performance of reinforced concrete (RC) with freeze-thaw damage, the reinforcement slip effect is taken into consideration in this study based on the framework of the fiber model accounting for the uneven distribution of freeze-thaw damage. Firstly, the bond strength degradation model with the consideration of the distribution of freeze-thaw damage is built according to the bar pull-out test data. An analytical procedure is proposed for the prediction of reinforcement slip in the frozen-thawed anchorage area based on the assumption of simplified bond stress distribution along the bar and on the governing equations. The model is validated by comparing the data come from frozen-thawed bar pullout experiments. Then the proposed model is implemented to the zero-length section using the finite element software OpenSEES for formulating the modelling method for RC columns considering the uneven distribution of freeze-thaw damage and reinforcement slip effects. Pseudo-static test data from column specimens subjected to freeze-thaw cycles are used to validate the proposed column model and previous fiber model. The research results show that comparing with the fiber modelling results, the calculated hysteretic curves through using the proposed column model are closer to that of the test results, and that the strength errors, the ultimate displacement errors, and accumulated energy errors indicated that the proposed column model can accurately simulate the seismic response of RC column with freeze-thaw damage.
Abstract:
Aiming at the cushioning and protection performance of the composite sandwich structure of paper corrugated and paper honeycomb under the condition of drop impact dynamic compression, the effects of paper honeycomb thickness on the impact acceleration response, on deformation characteristics and cushioning energy absorption characteristics of single-sided and double-sided composite forms were studied. The studying results show that, the corrugation layer gets crushed first, then the honeycomb layer, moreover larger honeycomb thickness will cause the secondary collapse of the paper honeycomb core layer. Under the same impact energy or mass, the cushioning energy absorbing characteristics of single-sided composite layered structures with the same honeycomb thickness are better than those the double-sided composite layered structures, and the impact resistance of double-sided composite layered structures is better than that of the single-sided structures. For the composite layered structures with the honeycomb thicknesses of 10 mm, 15 mm, 20 mm, and 25 mm, the increase of honeycomb thickness decreases the cushioning energy absorption of the structure under low energy of drop impact, while the increase of honeycomb thickness reinforces the energy absorption capacity under the high energy of drop impact. The specific energy absorption, unit volume energy absorption and stroke utilization of the composite sandwich structure with paper honeycomb thickness of 10 mm, 15 mm, 20 mm and 25 mm are 1~3 times higher than that of the composite sandwich structure with honeycomb thickness of 70 mm. The paper honeycomb with lower thickness is more beneficial to the cushioning energy absorption of the composite sandwich structure.
[Abstract](40) [FullText HTML](30) [PDF 1487KB](0)
Abstract:
To investigate the characteristics of transverse force in the top slabs of a single-box triple-cell composite box girder with corrugated steel webs(CBGCSW) and the effective distribution width under wheel loads, a finite element model of a single-box CBGCSW with single-cell, double-cell and triple-cell was established. The regulation of transverse stress and effective distribution width of three different box girders were compared. The results of finite element analysis, which had been verified by scaled-models tests, show that the transverse force in a single-box multi-cell CBGCSW can be approximately simplified as that of a single-box single-cell box girder. However, there is a big error in calculating the effective distribution width of CBGCSW according to the current code. Using finite element models, the influences of the transverse location of wheel load, the distance between webs, the length of flange slabs, the thickness of top slabs, the size and type of corrugated steel webs on the effective distribution width of a single-box single-cell CBGCSW were analyzed. It is shown that the transverse location of wheel load and the distance between webs of loading chambers are the most important factors. The practical calculation formulas of the effective distribution width of a single-box single-cell CBGCSW were obtained by the surface fitting according to results of parametric analysis. The formulas of the effective distribution width of a single-box multi-cell CBGCSW were proposed to be 0.9 times of that of a single-cell CBGCSW. Finally, the transverse stress in the top slab of a single-box triple-cell CBGCSW were analyzed as an illustration under transverse single and multiple wheel loads, separately. The transverse stress was calculated by the elastic frame method, using the effective distribution width calculated by formulas proposed and the current code method. The results, compared with the finite element analysis, finding that when transverse multiple wheel loads were imposed the calculated transverse stress may be unsafe, on the condition that the effective distribution width of different chambers were adopted as the same value. Consequently, the stress reduction factor of transverse stress in adjacent chamber which is presented in this paper are proposed to improve accuracy. the formulas presented are more accurate than those of current code, and the errors can be reduced by 20-40%, comparing with current code method.
[Abstract](27) [FullText HTML](16) [PDF 1092KB](0)
Abstract:
A new semi-analytical model of torque and rotational angle relationship for multi-bundled conductors is proposed. It is suitable for the calculation of large-span large-rotational angles and twisting scenarios. The model considers the vertical and horizontal displacement of the spacer and the tension variation of the sub-wire during the torsion process. It also considers the nonlinear distribution of the rotational angle along the span length. The calculation results are compared with the finite element method and experimental results which show that the geometric nonlinearity of multi-bundled conductors has a significant effect on the recovery torque. The semi-analytical model has a high calculation accuracy in both small and large rotational angle scenarios and can provide a basis for determining whether the conductors are twisted. The relationship between T-θ curves and the number of spacers is analyzed in detail to investigate the effectiveness of increasing the number of spacers in suppressing the twisting. It is found that only a small increase in the number of spacers can ensure the safety by the fact that the stiffness remains positive and the conductor can be restored by itself even if it is twisted by 180°. For the case of extremely large torque, more spacers are needed to maintain a positive torsional stiffness when it is twisted by 360°, which means that the conductor still has the ability to restore after twisting occurs.
[Abstract](41) [FullText HTML](41) [PDF 979KB](0)
Abstract:
The warping torsion of thin-walled members with open and closed cross sections was well addressed by the classical theories presented by Timoshenko and Benscoter, respectively. However, the restrained torsional behavior of thin-walled members with open-closed profile cannot be correctly accounted for without considering the distinctive warping properties between open and closed parts of the cross section. The development of warping shear flows within the mid-plane of the cross section needs further elaborations. This work assumes that the torsional warping of open and closed segments correspondingly adheres to the classical assumptions of Vlasov and Umanskii. The warping displacements are required to coincide at the common points of the open and closed segments, leading to a compatible warping field which contains undetermined warping parameter. The warping parameter is explicitly obtained based on the equilibrium requirements. A one-dimensional finite element model is naturally developed for warping torsion analysis of a thin-walled member with open-closed cross section. It is shown by numerical investigations and parametric studies that the type I method based on the Second Umanskii theory can artificially introduce the additional shear flows that reduce the accuracy of shear stresses. As an alternative, the type II method based on the Second Umanskii theory can only obtain the average shear stress of each segment of thin-walled section which fails to provide the correct distribution of shear flows. The Beam-189 element model based on the Vlasov assumption unfortunately neglects the induced warping displacements and shear flows by the constrained effects of the closed contour. Hence, the use of Beam-189 element will reduce the accuracies of both normal and shear stresses. Close agreement can be observed between the Shell-63 element model and the present method for calculating the torsional deformation and stresses, which demonstrates the capability of the one-dimensional finite element model to describe the torsional and warping stiffness of the thin-walled members with open-closed cross section.
[Abstract](40) [FullText HTML](34) [PDF 2133KB](1)
Abstract:
Ultra-high toughness cementitious composites (UHTCC) have excellent performance in toughness and energy absorption. The damage law of UHTCC functionally graded slabs under contact explosion is numerically investigated using LS-DYNA software to design a protective structure with excellent performance. The anti-explosion property of the structure is discussed considering the effects of the target material, explosive content, reinforcement arrangement and energy absorption layer thickness. The results show that the UHTCC functionally graded slabs exhibit excellent blast resistance under blast loading as a consequence of the reduction of craters, scabbing and target damage, and the increase in blast waves absorption. Especially, the target damage can be effectively reduced by arranging the tie ribs and rationally setting the thickness of the energy absorption layer.
[Abstract](40) [FullText HTML](28) [PDF 1104KB](2)
Abstract:
The numerical analysis of static and dynamic problems of functionally graded material beams is usually conducted with the finite element method and suffers from the inherent deficiencies of the method. The governing equations for static analysis of functionally graded material beams are transformed to the forms for static analysis of isotropic material beams, and the Green’s functions corresponding to isotropic material beams are used for static analysis of functionally graded material beams. On this basis, the compliance matrix of a functionally graded material beam is further derived, and the equation of motion is established and solved for the dynamic problem of the functionally graded material beam. Numerical examples show that the proposed method can analyze the static and dynamic problems of functionally graded material beams with high efficiency and accuracy, indicating the feasibility of the present approach.
[Abstract](42) [FullText HTML](28) [PDF 1244KB](0)
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The concentrically braced frame (CBF), which shows good seismic performance with a low cost, is a popular seismic resistant structural system. Generally, CBFs are designed to meet the ductility requirement to ensure that the braces buckle in compression or yield in tension. As observed in previous major earthquakes, the ultimate failure mode of CBFs is the fracture of the braces. However, CBFs are often idealized as trusses in a frame analysis or design, considering the boundary of braces as pinned or fixed connections and ignoring the fracture behavior of the braces. In this paper, a numerical model using OpenSees considering the brace fracture and gusset plate effect was proposed. A single-brace model, a one-story frame model and a three-story frame model were simulated to verify the reliability of the numerical model. The simulated results showed good agreements with the corresponding experimental results. The calibrated three-story frame model was then adopted for an incremental dynamic analysis. The results indicated that the collapse margin ratio of the frame was overestimated if the brace fracture was not considered. It is strongly recommended that the brace fracture and gusset plate effect should be considered for the design and detailing of CBFs to reasonably evaluate the seismic performance.
[Abstract](3) [FullText HTML](0) [PDF 0KB](0)
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Wrinkling deformation is a common instability mode for flexible membrane structures. The numerical simulation on this problem is challenging. Based on the continuum and tension field theory (TFT), a complementarity co-rotational finite element method (FEM) for the wrinkling analysis of pneumatic membrane structures is proposed. By using the co-rotational approach, the finite deformation is decomposed into a rigid body motion in the global coordinate system and small strain deformation in the local coordinate system of the element. The tangent stiffness matrix of a spatial 3-node triangular membrane element is derived. It includes three parts: material stiffness, rotational stiffness and balanced projection stiffness matrices, and covers the influence of a follower load on the elemental stiffness. In the elemental local coordinate system, a wrinkling model is constructed based on the constitutive relation of bi-modulus material, which can judge the status of one element, i.e., ‘taut’, ‘wrinkled’ or ‘slack’. Furthermore, the oscillation of internal force during the iterative solution is eliminated by establishing an equivalent linear complementarity problem. The stability of the algorithm is improved. Numerical examples show that the proposed method can accurately predict the displacement, stress and wrinkling region of pneumatic membrane structures. Compared with the existing methods such as ‘quasi-dynamic’ and ‘penalty’ ways, the proposed method does not require additional solving techniques to ensure convergence. It is convenient for engineering applications.
[Abstract](4) [FullText HTML](3) [PDF 420KB](0)
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To improve the seismic behavior of low-rise shear walls, the double steel plates and high ductile concrete (HDC) composite low-rise shear wall (DHW) was proposed. One HDC low-rise shear wall (HW), two single steel plate reinforced HDC low-rise shear walls (SHW) and two DHWs were designed. The influence of the axial load ratios and steel distribution form on the failure modes, hysteretic performance, shear capacity, deformation capacity, energy dissipation capacity and stiffness degradation of the specimens were studied by quasi-static tests. The experimental results indicate that the failure modes of the HW, SHW and DHW are the shear failure, the flexural-shear failure and the flexural failure, respectively. The deformability and strength capacity of the steel-plate and HDC composite low-rise shear walls are significantly improved compared with those of the HWs. The axial load ratio has little impact on the peak load and stiffness of the steel-plate and HDC composite low-rise shear walls. With an axial load ratio ranging from 0.5 to 0.7, the deformation capability of the SHW decreases, whereas the deformation capability of the DHW does not decrease. Formulas for the bending capacity of the steel-plate and HDC composite low-rise shear walls are suggested, and the calculation results agree well with the test results.
[Abstract](77) [FullText HTML](65) [PDF 3723KB](0)
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Specimen tests were conducted to study the cyclic web buckling behavior of energy dissipation shear links. Numerical models for the links were established and the influence of different parameters was analyzed and summarized. The results indicate that the axial displacement constraint had little influence on the cyclic web buckling. The axial forces also had little influence if the tension or compression was not significant. By a parametric analysis, it was confirmed that the web height-thickness ratio had most significant influence on the web buckling displacement angle. The web aspect ratio and the ratio of transverse stiffener spacing to web height also had significant influence, but the influence became slight after the ratio exceeded two. The equivalent link length coefficient and the steel hardening characteristic had little influence. A theoretical prediction approach for the cyclic web buckling displacement angle was proposed. The experimental and numerical validation confirmed that the approach is reliable.
[Abstract](35) [FullText HTML](21) [PDF 1421KB](0)
Abstract:
Presents a Spatial-Truss-Confined Buckling-Restrained-Brace (STC-BRB) with shuttle- shape longitudinally, composed of a single steel tube core and the several shuttle-shaped trusses sharing a common external restraining tube. The strength and seismic design of an innovation research in the external restraining system of BRB has being focused on for over a few decades. The STC-BRB could significantly improve the material utilization and particularly enhance the architectural aesthetics when it is exposed externally. The elastic buckling, load resistance, and hysteretic responses of the STC-BRB are investigated numerically by adopting the finite element model (FEM) that has been validated previously by using the test results of Truss-Confined Buckling-Restrained Brace (TC-BRB). And the design method regarding the lower limit of the restraining ratios of the STC-BRBs is recommended. The elastic buckling performance of the STC-BRB is comprehensively investigated by using a beam element FE model, leading to an explicit expression of the elastic buckling load of the STC-BRB that is adopted to define the restraining ratio of the STC-BRB for its structural design. Consequently, the load resistance of STC-BRB under monotonic axial compression is numerically analyzed. Accordingly a lower limit of the restraining ratio of the STC-BRB in their monotonic axial load resistance design is recommended where the core reaches fully sectional yielding with a plasticity strain amplitude reaching 2% without global instability of the STC-BRB. The hysteretic responses of STC-BRB subjected to axially compressive-tensile cyclic loads are studied numerically, and the corresponding lower limit of the restraining ratio of STC-BRB is proposed in their energy-dissipating design. These two lower limits of the restraining ratios of the STC-BRB obtained in this study provide fundamentals for the preliminary static and seismic design of STC-BRB.
[Abstract](4) [FullText HTML](1) [PDF 961KB](0)
Abstract:
The steel-ultrahigh performance concrete (UHPC) composite box deck system has a good application prospect in the construction of long-span bridges. Based on an actual bridge, two large-scale steel-UHPC composite box girder tests were conducted mainly to studied the overall bending performance of the steel-UHPC composite box girders in the elastic stage. We focused on the deflection and strain distribution of the specimens. An analytical model of the composite box girder considering the shear lag, slip effect and shear deformation of the steel web was established and the analytical solution was derived. The results show that the shear lag effect was significant under concentrated loads. The ratio of the maximum to minimum values of the UHPC slab mid-span compressive strain was 5~7. With the increase in the UHPC slab depth, the stiffness of the steel-UHPC composite box girder increased and the strains on both the UHPC slab and steel girder decreased. Compared with the model without considering the shear deformation of the steel web, the analytical solution in this paper was generally in good agreement with the test results.
[Abstract](32) [FullText HTML](26) [PDF 4851KB](1)
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The morphology, product and degradation of corroded high strength steel wire were tested, which was essential for inspection and mechanical evaluation. The corrosion products were analyzed by high resolution X-ray diffractometer and environmental scanning electron microscope. Three-dimensional scanning was applied to determine the change of the cross section of corroded wire along the axial direction. Static tensile and fatigue loading tests were also carried out. The corrosion morphology of high strength steel wire is determined by the analysis of 3D scanning data. The degradation of the constitutive model parameters of corroded high strength wires are derived by the regression analysis of the test mechanical parameters and corresponding corrosion ratios. The test results show that: the variability of sectional area along wire axis increases with the increase of corrosion degree, the ultimate strength of corroded wire is less than the standard strength of 1770 MPa when corrosion ratio is more than 1.25%; the elongation is less than the specification limit of 4% when the corrosion ratio is greater than 5.05%; the fatigue life is less than 2 million cycles when the corrosion ratio is more than 4.16%; while corrosion has little effects on the elastic modulus. The index for evaluation of corroded wire is refined for the specification based on the above results.
Abstract:
In view of the decreasing trend of column widths in steel residential buildings, a new type of concrete filled rectangular steel tubular column-H-section steel beam connections with external stiffeners is proposed. The diaphragm is removed in this connection. Pseudo-static tests of seven new joint specimens were carried out. The test parameters were the section of the steel beam and the thickness and the height of the long side of the external stiffeners. The failure modes, hysteretic curves, skeleton curves, strength, stiffness degradation, strength degradation, ductility and energy dissipation capacity of the joints were studied. The test results show that there were three failure modes of this new joint, namely, tensile failure of beam flange, weld failure between beam flange and external stiffener, and column wall failure near the external stiffener. The ductility coefficient was 2.17 to 3.67, the equivalent viscous damping coefficient was 0.2 to 0.3, and the average drift ratio was 1/49. The seismic performance of the joint met the requirements of "strong joints and weak members". Increasing the thickness or the height of the long side of the external stiffeners can increase the strengths of the joints. The premature cracking of the beam flange, the welding seam between beam flange and external stiffener, or the column wall will reduce the ductility and energy dissipation capacity of the joints. It is proposed that the connection coefficient should be 1.4 when checking the ultimate strength of the column wall and joint weld. The strengthening or weakening measures on the flange at the beam ends can be taken to ensure that the new joints have a sufficient plastic deformation capacity.
Abstract:
In order to reduce the impact of pressure fluctuation caused by the high-speed train passing through a tunnel on the train operation, the pressure wave characteristics of a high-speed train passing through a tunnel with a communication channel are studied based on train aerodynamics. A numerical simulation model for a high-speed train composed of three cars was established. Based on a three-dimensional, unsteady, compressible Navier-Stokes equation and k-ε two-equation turbulence model and slip grid technology, the aerodynamic characteristics of a high-speed train passing through a tunnel with a connected aisle were numerically simulated. The results shown that: the aerodynamic characteristics of the train passing through a tunnel with a connected aisle were much better than that passing through a tunnel without a connected aisle; the connected aisle had more obvious effect on the initial pressure rise and fall, and the suppression of the expansion wave was more prominent; the higher the train speed is, the larger the channel area is, and the more obvious the pressure wave falls back; the setting of the contact channel makes the pressure wave waveform show a local jagged shape. A fast formula for calculating the pressure peak of a train passing through a tunnel is also proposed.
Abstract:
A lot of micro-fractures exist in rock. The wall wettability has a significant impact on the fluid flow due to their small width. Based on the Shan-Chen pseudopotential model, the lattice Boltzmann method is applied to establish the numerical model for studying the seepage properties of a smooth rock micro-fracture. The validity of the proposed model is proved by the simulation of a suspended liquid droplet in vapor and the wall contact angles. The seepage properties of a rock micro-fracture is studied considering the effects of the wall wettability, fracture width, pressure gradient and fluid viscosity. The results show that the hydrophobic wall has an accelerating effect due to the repulsion on the nearby fluid, while the hydrophilic wall has an obstructive effect. In general, the influence of the hydrophobic wall on the micro-fracture seepage is more significant than that of the hydrophilic wall. The effect of wall wettability on the seepage velocity increases with the decrease of the micro-fracture width. The stronger the hydrophilicity/hydrophobicity of wall is, the more significant the influence of fracture width will be. The average seepage velocity increases linearly with the increase of pressure gradient. The stronger the wall hydrophobicity is, the greater the linear slope will be. In addition, the larger kinematic viscosity of fluid is, the greater the flow resistance will be, which results in the decrease of the average flow velocity. In addition, there is an inverse relationship between the average flow velocity and the kinematic viscosity.
Abstract:
Rubber seals are widely used in the structure of aircraft doors, which play important roles on sealing, sound insulation and heat preservation. Aircraft door rubber seals are critical to the normal flight of the aircraft and the safety of the passengers. The dynamic friction performances of rubber seals for aircraft doors with different cross-section shapes under different conditions are studied. The rubber seals with different shapes applied to the aircraft door and the corresponding loading device are introduced. The dynamic friction performances of rubber seals with different shapes under different temperatures, different compression displacements and different surface treatment conditions are measured by means of a dynamic friction performance testing machine. The effect of environmental factors on dynamic friction performances of rubber seals are obtained, which is of a great significance for the design and optimization of dynamic friction performance of rubber seals.
[Abstract](2) [FullText HTML](0) [PDF 679KB](0)
Abstract:
In order to solve linear elastic fracture problems more effectively, an extended natural element method is proposed in this paper. Based on the ideas of partition of unity, enriched functions are added to the displacement mode of the natural element method in order to characterize the discontinuous displacement field along crack face and stress singularity around the crack tip. The level set method is employed to determine the crack surface and the crack tip region. The discrete linear equation of the equilibrium equation is derived by the virtual displacement principle. The shape function of the natural element method satisfies the Kronecker delta property and thus it is very convenient to impose the essential boundary conditions. The interaction integral method is then utilized to calculate the mixed-mode stress intensity factors. Several numerical examples are presented to demonstrate that the proposed method can deal with linear elastic fracture problems conveniently.
Abstract:
Defects such as inclusions are inevitably presented in the wires of integrated circuit. Under the effect of various internal mechanisms and external environment, the morphology evolution of the inclusions will affect the performance of the interconnects. Based on the weak statement of microstructure evolution for the interface migration, the governing equations of stress-induced solid-solid interface migration are derived, and the effects of the Young's modulus ratio of the inclusion and the matrix on the morphology evolution of inclusion are numerically simulated. The results show that: there are two kinds of bifurcation trends in the morphology evolution of the inclusions, and exist the critical stress \begin{document}${\widetilde \sigma _{\rm{c}}}$\end{document}, the critical aspect ratio \begin{document}${\beta _{\rm{c}}}$\end{document} and the critical line width \begin{document}${\widetilde h_{\rm{c}}}$\end{document}. When \begin{document}$\widetilde \sigma > {\widetilde \sigma _{\rm{c}}}$\end{document}, \begin{document}$\beta > {\beta _{\rm{c}}}$\end{document} or \begin{document}$h < {\widetilde h_{\rm{c}}}$\end{document}, the inclusion grows. Otherwise, the inclusion will shrink. As the modulus ratio increases, the critical stress or the critical aspect ratio increases, and the critical linewidth decreases. Also, when the Young's modulus ratio of the inclusion to the matrix \begin{document}$\alpha > 0.6$\end{document}, the effect of the modulus ratio on the critical stress and the critical aspect ratio can be ignored.
Abstract:
The research on homogenization of ordinary masonry has been relatively developed, but the research on historical masonry with random geometry and material is lacking. Based on the method of finite-scale test windows, a method for selecting a representative volume element (RVE) of masonry structures is proposed and is proved to be correct by comparisons with the results of published experiments and conventional finite element models (FEM). An appropriate RVE for Tibetan ancient stone masonry structures is selected. The influence of the size of RVEs and the distribution of components on the effective modulus are investigated. Based on the selected RVE, a homogenization model and a macro model of the Tibetan stone masonry structure are established. The results indicate that the selecting method, which is suitable for periodic and quasi-periodic masonry structures, can select an RVE with the mechanical properties close to the complete structure. As the size of the RVE becomes larger, its Voigt and Reuss effective modulus gradually converge to the modulus of the complete structure and present a trend of rapid and slow progresses. The difference in the component distribution will change the convergence amplitude of the effective modulus, but on a larger RVE, the influence of the component distribution will be offset by that of the size of the RVE. The homogeneous model can replace the conventional FEM to analyze local structures and give the rule of the stress distribution of Tibetan ancient stone masonry structures. The macro model can replace the conventional FEM to simulate the macro deformation of an overall structure.
[Abstract](32) [FullText HTML](20) [PDF 1804KB](0)
Abstract:
Lightweight aggregate concrete (LWAC) is more and more utilized in engineering structures because of the advantages of light weight and good thermal insulation performance. Both lightweight aggregate concrete and ordinary concrete were regarded as three-phase composites consisting of the aggregate particles, mortar matrix and interface transition zones (ITZs) between them. A 3D meso-scale mechanical model was established to simulate the shear failure behavior of concrete beams without web reinforcement. The shear failure modes and failure mechanism of ordinary and light aggregate concrete cantilever beams with different structural sizes under monotonic loading were modelled and studied. The size effect on the nominal shear strength was examined. In addition, the accuracy and safety of the formula for calculating the shear capacity of the relevant design codes are preliminarily discussed based on the simulation results. The results show that different from the ordinary concrete beam, the LWAC specimens sustained serious damage due to the lower strength of the aggregates. The shear failure modes of concrete beams with different sizes were basically the same. An obvious size effect on the nominal shear strength of both LWAC and ordinary concrete specimens was observed. Compared with the ordinary concrete beams, lightweight aggregate concrete beams showed a stronger size effect in shear failure behavior.
[Abstract](4) [FullText HTML](0) [PDF 856KB](0)
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The generation of inflow turbulence with prescribed atmospheric boundary layer (ABL) flow characteristics is one of the key issues for the accurate evaluation of wind effects on structures using large-eddy simulation (LES). The main objective of this paper is to validate and discuss the rationality and feasibility of different inflow turbulence generation methods for ABL flows with LES. The CDRFG (Consistent Discretizing Random Flow Generation) method and passive simulation method are used to generate the ABL flows, and the comparative analysis is carried out from the aspects of statistical characteristics, flow field structures and computational efficiency. Based on the numerical simulation results under different mesh systems, the meshing scheme of LES for wind effects on engineering structures is proposed. The results show that the flow field structures generated by the passive simulation method is more reasonable than that of CDRFG method, but the spatial coherency of turbulent flow field cannot be taken into consideration in advance. It also requires large computational costs and prior knowledge of flow field. The grid resolution of computational domain is of great importance for the accurate simulation of statistical characteristics and ABL flows structures. However, the grid resolution in the neighboring region around target buildings should be chosen according to the dominant frequency band for the wind-induced responses of engineering structures.
Abstract:
Based on the seismic resilience design concept, a rectangular-hollow double-column tall pier specimen and a rectangular hollow-double-column tall pier specimen with energy dissipation beams were designed and fabricated with the scale of 1/20. The pseudo-static tests were conducted on both specimens under low cycle loads. The failure patterns and process were discussed. The seismic behaviors of specimens, such as strength, cumulative hysteretic energy, curvature and displacement ductility, were compared. The experimental results show that compared with the rectangular-hollow double-column tall pier, the rectangular-hollow double-column tall pier with energy dissipation beams has better energy dissipation capacity, bearing capacity and displacement ductility capacity. Moreover, the energy dissipation beams can significantly mitigate the curvature of column so that the column can be effectively protected from the seismic damage. Consequently, the rectangular-hollow double-column tall pier with energy dissipation beams has a better seismic performance than the rectangular-hollow double-column tall pier.
Abstract:
Due to the characteristics of efficient energy absorption, constant-resistance-large-deformation (NPR) cables have been applied in many rock slopes and mining engineering for monitoring and reinforcement. The NPR cable-rock interaction differs from that of traditional cables owing to the pipe-shaped expansion during the working process, and it affects the performance of a NPR cable reinforcement system. Therefore, a coupled numerical method is used to study the characteristics of the NPR cable-rock interaction under static pull-out loading. The structure of the NPR cable is considered as a continuous zone via the finite-difference method (FDM), and the surrounding rock and grouting material was modelled by the discrete element spherical particles via the discrete-element method (DEM). The micro parameters of the grouting material and surrounding rock were carefully calibrated, and the comparisons of corresponding experimental tests in the laboratory to verified the macro parameters of the NPR cable. The numerical results were carefully discussed and analyzed. The constant-resistance forces between a onefold NPR cable and the NPR cable reinforcement system were compared. The spatial arrangement of the normal and shearing stresses on the cable-rock interface was obtained. Furthermore, the failure mode of grouting material and surrounding rock was researched at the micro scale. The results describe the interaction between the NPR cable and the surrounding rock and reveal its special anchorage mechanism, and help improve and predict the performance of the NPR cable reinforcement system.
[Abstract](33) [FullText HTML](28) [PDF 866KB](0)
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Creep test is performed on Chengdu clay to study the nonlinear property of clay creep. It is found that instantaneous elastic deformation, attenuated creep deformation, steady creep deformation, and accelerated creep deformation are included in clay deformation. The long-term elastic modulus of clay is nonlinear softening with the increase of time and stress. The viscosity coefficient is nonlinear softening with the increase of stress and nonlinear hardening with the increase of time. Based on the rheology theory, fractional calculus theory and Harris attenuation function, fractional derivative components, nonlinear elastic components and nonlinear viscous components are established, respectively. A nonlinear fractional derivative creep model with simple form, few parameters and clear concept is established. Then, the nonlinear fractional derivative creep model and Burgers creep model are compared. It is found that the fitting effect of nonlinear fractional derivative creep model is better in each stage, and can give more reasonable description of the nonlinear creep of clay, and can accurately reflect the whole process of clay creep. The scientific rationality of the nonlinear fractional derivative creep model is proved.
[Abstract](39) [FullText HTML](37) [PDF 4105KB](2)
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In order to satisfy the requirements on seismic behavior and spatial flexibility of high-rise buildings, based on the combination of high-performance materials and high-performance structures, the low yield point (LYP) steel plate shear wall structure with coupling beams was proposed. The finite element models of steel plate shear wall structures were established by ABAQUS, which were proved accurate through a comparison with the published tests. Using the verified numerical method, five coupled and uncoupled LYP steel plate shear wall structure models with different degrees of coupling were established. These models were subjected to static pushover loads and cyclic loads to compare their failure modes, lateral load carrying-capacities, hysteretic behaviors and energy dissipation performances. The influence of the interaction between infill plates and boundary frame on the mechanical properties of the structures and their members was discussed, and some suggestions were proposed for the design of coupled steel plate shear wall structures. The analysis results show that the interaction between infill plates and boundary frame can effectively improve the bearing capacity, bearing efficiency and energy dissipation capacity of the whole structure. Considering the material efficiency, bearing capacity and energy dissipation capacity, it is suggested that the coupling degree of the connecting beam should be controlled within 0.45. With the increase of coupling degree, the shear force shared by the boundary frame increases to 60%, the axial forces of the internal frame columns significantly decreases, and the rotation of coupling beams keeps decreasing. Therefore, the interaction between infill plates and boundary frame should be fully considered in the design of coupled shear wall structures, which is able to effectively reduce the design thickness of infill plates and the section size of boundary frame, and improves the material efficiency and design economy. At the same time, compared with the pure frame, the interaction between infill plates and boundary frame effectively improves the initial lateral stiffness and bearing capacity of the boundary frame.
[Abstract](79) [FullText HTML](39) [PDF 1220KB](0)
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In order to improve the deformability of reinforced concrete beams, high ductile concrete (HDC) was applied in the potential plastic region of a beam instead of ordinary concrete. Six reinforced concrete beam specimens with shear span ratio of 3.6 were designed, including five specimens made of HDC in the plastic region, and one conventional concrete beam designed for comparison. The hysteretic behavior, deformability and energy dissipation capacity were analyzed under a low cyclic loading test for the various length of HDC region, the reinforcement ratio of the longitudinal reinforcement, the reinforcement mode, and the stirrup ratio of beam ends. The experimental results show that compared with ordinary reinforced concrete beams, the failure mode of the beam with HDC in its potential plastic region is changed from bending-shear failure to bending failure with better ductile characteristics and better energy dissipation capacity. In the case of longitudinal reinforcement ratio and reinforcement mode, when HDC applied in the plastic region of a beam, the displacement ductility ratio and drift ratio are increased by 30% and 53%, respectively, while both the HDC and stirrup applied in the plastic region of a beam, the displacement ductility ratio and drift ratio are increased by 33% and 76%, respectively. The local use of HDC at the beam end can reduce the amount of stirrups, and the HDC length of the plastic hinge area at the beam end has little effect on the ductility of the specimen. In the plastic hinge zone, the displacements of HDC concrete beams under cracking load, yield load, peak load and ultimate load are calculated respectively, and the calculated values are in a good agreement with the experimental values.
[Abstract](68) [FullText HTML](28) [PDF 1528KB](0)
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Accurately simulating inflow turbulence for large eddy simulation (LES) is a hot topic in the field of computational wind engineering. Defining appropriate inflow boundary conditions in accordance with the turbulence characteristics of various atmospheric boundary layers (ABLs) is a prerequisite and indeed a great challenge in numerical research of wind effects on building structures at current stage. Based on the newly proposed LES inflow turbulence generation technology-NSRFG method, which belongs to the category of the turbulence synthesis method, the appropriate values of several parameters in the mathematical model were systematically studied. Detailed parameter sensitivity analyses were conducted to investigate several key parameters, including the sampling frequency intervals Δƒ, the introduced time scale factor \begin{document}${\tau }_{0}$\end{document}, the spatial scale factor θ, the decay coefficient \begin{document}${c}_{j}$\end{document} and the tuning factor \begin{document}${\gamma }_{j}$\end{document}, on the simulated turbulent fluctuating wind spectra, the RMS values as well as the spatial correlations. Based on it, a serials of model parameters corresponding to four typical standard wind terrains defined in Chinese building code were then proposed in order to build a ‘standard numerical wind terrain model’. Numerical simulations and equilibrium state verifications for those standard wind fields were subsequently performed. The results showed that key parameters had significant impacts on the numerical reconstructions of the turbulent wind fields by employing NSRFG method, and the proposed standard numerical wind terrain models would be referential for similar LES research of building structures.
[Abstract](43) [FullText HTML](58) [PDF 1275KB](0)
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To evaluate the damage degree of Composite Frame with Reinforced Concrete Column and Steel Beam after the earthquake, the seismic damage model of RCS composite frame structure was established by modifying the relevant parameters of the Park-Ang double parameter seismic damage model. By analyzing the influence of the slab on the key parameters of the model, the formula to calculate the ultimate deformation capacity of the composite beam members under the influence of the slab space combination effect was given. The formula was verified. Based on the test results, the parameter β under the influence of cyclic loading of the composite beam member was obtained by inverting the component at a damage index equal to 1 at the point of failure. The range of damage index corresponding to the degree of damage of the structure was given, and a seismic damage assessment method for this structure was proposed. The seismic damage assessment of a 4-layer RCS composite frame structure under the action of El-Centro wave shows that the seismic damage model proposed in this paper can better reflect the damage evolution process and degree of RCS composite frame structure. The research results provide a theoretical basis for seismic damage assessment and performance-based seismic design of RCS composite frame structures.
[Abstract](54) [FullText HTML](34) [PDF 501KB](0)
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This paper derives analytical solutions for the forced vibrations of Timoshenko curved beams and establishes the vibration equation of Timoshenko curved beams by analyzing the equilibrium equation for the intersection of curved beams. Green’s functions of Timoshenko curved beams are solved for different boundary conditions using the separation of variables and Laplace transform. Two characteristic parameters are introduced to measure damping effects on beam vibrations. Numerical calculations are conducted to validate analytical solutions, and the effects of various related physical parameters are investigated. The results show that by setting the radius R to infinity, it can be simplified to the Timoshenko straight beam vibration model, and on this basis, if the shear correction factor κ is set to infinity, it can be reduced to the Prescott straight beam vibration model. Finally, the moment of inertia γ is set to 0, which can be reduced to the Bernoulli-Euler straight beam vibration model. Numerical calculations are performed to validate the solutions.
[Abstract](34) [FullText HTML](27) [PDF 1809KB](0)
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Based on the classical shell theory and von Karman geometric nonlinear theory, the displacement-type geometric nonlinear governing equations and simply supported boundary conditions for functionally graded shallow circular spherical shells were derived. The uniform temperature field and the external uniform pressure were considered in the derivation. The two-point boundary value problem posed by this set of governing equations and the boundary conditions was solved with the shooting method. The numerical results of axisymmetric deformation of the shells were obtained. The effects of the geometric parameters of the shell, the transverse gradient properties of the shell’s materials, the volume fraction index and elasticity modulus of the constituent materials, and uniform temperature field on the buckling equilibrium paths, upper/lower critical loads and equilibrium configurations of the shell were investigated. The numerical results show that the upper critical load of the shells decreases significantly with the increase of the volume fraction index and the decrease of the elasticity modulus of the constituent materials. The effects of the volume fraction index on the lower critical load of the shells is complicated. The rise of the uniform temperature brings obvious increase/decrease of the upper/lower critical loads of the shells. The transverse gradient properties of the shell’s materials on the effects of the buckling equilibrium paths and post buckling stable configurations of functionally graded shallow circular spherical shells with simply supported edges are very significant. Two numerical tables and some numerical curves are given for the convenience of designers.
Abstract:
Accidental overload, prolonged environmental erosion and the deformation caused by temperature change, etc., easily lead to strength reduction and cracking of deep flexural members, eventually affecting their serviceability. A total of 15 high-strength lightweight aggregate concrete (HSLWAC) deep flexural members are tested to systematically study their damage evolution laws under shear load. The influencing factors for the shear service ability including shear span-depth ratio (a/h0), bearing plate width (lb) and beam sectional height are considered. The relationship between diagonal crack width and load level is established based on the trend of crack propagation, and the application of diagonal crack width limiting value in current codes to such members is discussed. Test results show that the maximum diagonal crack widths of specimens exhibit an increasing trend with the increase of a/h0 and lb, and a sufficient amount of horizontal and vertical web reinforcement can effectively inhibit the diagonal cracking of such members. Both the normalized diagonal cracking strength and the maximum diagonal crack width are less affected by the size effect. During the entire shear failure process, the diagonal crack width shows a significant correlation with the applied load, and the serviceability performance index on the basis of normal weight concrete specimens is able to predict the serviceability behavior of HSLWAC specimens. However, it is difficult to satisfy the diagonal crack width limiting value for HSLWAC members designed according to the minimum stirrup ratio in Chinese code, so the minimum stirrup ratio should be appropriately increased.
[Abstract](45) [FullText HTML](39) [PDF 1446KB](2)
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A modified generalized differential quadrature (MGDQ) method is utilized to investigate the coupling vibration and buckling characteristics of functionally graded material (FGM) beams with even porosity distribution in thermal environment and under the action of an initial axial mechanical force. Various types of temperature distributions are considered through the thickness direction, and the material properties are temperature-dependent according to modified Voigt mixture power-law model with porosity. Using an n-th order generalized beam theory (GBT), the free vibration and buckling governing equations for this system are derived by Hamiltonian principle as a unity. The control parameters for three different boundary conditions are proposed, and the MGDQ method can be utilized to solve the coupling vibration response with MATLAB computational procedure. Based on the duality between the static and dynamic behaviors of the structure, the buckling responses are obtained by writing loop subprogram, which can greatly simplify decoupling process and improve calculation efficiency. The effects of various beam theories, boundary conditions, different types of temperature rise, initial axial force, thermal-mechanical loads, porosity, material graded index and slenderness ratios on the vibration and buckling behaviors of FGM beams are discussed, and the significant duality for the two different mechanical behaviors of the structure are also revealed by several numerical examples.
[Abstract](63) [FullText HTML](37) [PDF 1005KB](0)
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Evaluating the shape and size of the fracture process zone near mode II and mode III dynamic crack tip is still a problem unsolved at present. An approximate method for evaluating the shape and size of FPZ is proposed and the feasibility of the method is demonstrated through a comparison with the results calculated based on the known stress fields. The shape and size of the FPZ near the dynamic crack tip are determined based on the new method, which depend on the crack propagation velocity. The results show that the FPZ at mode II and mode III dynamic crack tip distributes symmetrically with respect to the crack plane and increases with the crack propagation velocity. FPZ changes more rapidly when the Rayleigh wave velocity is approached. The size of FPZ calculated by Tresca criterion is larger than that calculated by Von Mises criterion.
Abstract:
The explicit numerical algorithm for the near-field wave motion of fluid-saturated porous media in time domain is investigated based on u -p dynamic formulation. The wave motion equations are decoupled, and dynamic coupling is eliminated by the diagonalization of the mass matrix and pore fluid compression matrix. Based on the decoupled wave motion equations, the central difference method and Newmark constant average acceleration method are adopted for the solution of solid-phase displacement and velocity, respectively. The formulation of pore fluid pressure is derived based on the backward difference method. Then the explicit staggered calculating formulas for the dynamic response of fluid-saturated porous media are derived, and a new full explicit numerical algorithm for the near-field wave motion of fluid-saturated porous media in time domain is developed. The rationality of matrix diagonalization in the algorithm is validated. The numerical results gained by the proposed algorithm accord well with the corresponding analytical results. This indicates the accuracy of the proposed algorithm. Combining the time domain numerical calculation method proposed with the transmission artificial boundary method, it is applied to the near field wave motion problem of fluid-saturated porous media, and the seismic response of saturated soil site is calculated and studied. The numerical results of the seismic response of saturated soil field accord with the elastic wave motion theory. This indicates the applicability of the developed algorithm to the near-field wave motion problem of fluid-saturated porous media. The stability characteristic of the developed algorithm is investigated based on the transfer matrix of the iterative calculating formulas of the algorithm. In the developed algorithm, all the variables of dynamic response are calculated in an iterative pattern. Thusly, this algorithm has the basic characteristic of the full explicit numerical algorithm in time domain. In the developed algorithm, all the components of the dynamic response are solved by recursive and iterative modes, which avoids solving the coupled dynamic equations. This developed algorithm has high computational efficiency and is an effective algorithm for solving near-field wave motion problems in fluid-saturated porous media in time domain.
[Abstract](44) [FullText HTML](27) [PDF 1157KB](1)
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To investigate the damage distribution and evolution of the tunnel lining by train loads, the incremental damage constitutive relation under complex stress state was derived based on the uniaxial tension and compression constitutive relation in the Code for design of concrete structures and embedded into the standard calculation program of ANSYS. Its reliability was verified through a comparison with the uniaxial tension and compression experiment results. The coupled circular tunnel-soil dynamic FE model was then established. Based on the improved Miner’s cumulative damage theory, the damage distribution, dynamic response and the evolution of damage increment and cumulative damage of tunnel lining due to long-term train loads were studied. It is found that the long-term train-induced damage is symmetrical about the tunnel centerline, and mainly distributes in the inverted arch with an angle of 120 degree. There are two damage concentration areas right beneath the train load applying points, where the damage amplitude is larger than any other areas. With the increase in train operation time, the amplitude of single train-induced dynamic stress in concentration area decreases by about 83% whereas that of dynamic strain increases by about 150%. The damage increment and cumulative damage both increase nonlinearly with the increase in train operation time. Accordingly, the improved Miner’s cumulative damage theory could improve the accuracy for fatigue life prediction of tunnel lining.
[Abstract](56) [FullText HTML](24) [PDF 1270KB](0)
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Due to the tectonic action, the interface of layered rock may be partially folded. The investigation of the influence of irregular interface on the scattering of cavities is of great significance for the seismic safety evaluation of the surface structure. Based on a substructure method, a complex scattering problem is transformed into a radiation problem and the evaluation of wave response of a layered half-space with regular boundary conditions (free field). The Fourier transform and dual variables are used to obtain the first-order ordinary differential wave equation. Besides, soil layers are merged by using the precise integration algorithm and load boundary conditions are applied to obtain the Green's function, and the dynamic stiffness is obtained. Based on a precise integration algorithm, the coefficient matrix of an improved transfer matrix method is proposed, and the wave motion of the layered half-space is calculated. The improved transfer matrix method has no restrictions on soil layer thickness and the number of layers. The accuracy and effectiveness of the proposed method are validated by comparing them with those of the results of the previous study. The scattering effects of horseshoe holes embedded in a complex layered half-space are investigated. The results show that the effect of local folds on the magnitude of surface displacement is related to factors such as incident wave type, incident wave frequency, and local fold geometry. The peak surface displacement is affected by the combined action of horseshoe-shaped cavity and local folds, and its characteristics are not obviously related to the type of incident wave.
[Abstract](29) [FullText HTML](19) [PDF 4781KB](0)
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The bending static properties and fatigue properties of rollable laminates made of glass fiber braided composites under large deformation are studied. The relationship between strain and displacement under large deformation is obtained by bending static tests. The load of fatigue tests is determined by finite element simulation of static tests and comparing the results of finite element simulation with static tests. The bending fatigue life and failure mode of different laminates, together with fatigue life curve of the same ply composite laminates under large deformation are studied. The results show that the composite laminates have obvious non-linear behavior in large deformation bending, and the bending fatigue performance of (±45°) laminates is better than that of (0°/90°) laminates. Besides, holding the ratio of minimum strain to maximum strain constant, there is a linear relationship between maximum strain and logarithmic fatigue life.
[Abstract](106) [FullText HTML](37) [PDF 1508KB](1)
Abstract:
To suppress the vortex-induced vibration (VIV) of a cylindrical structure, an optimal design simulation model of a nonlinear energy sink (NES) vibration-absorber is established based on Van der Pol wake oscillator model, structural dynamics and optimization algorithm. The Van der Pol wake oscillator model and the structural dynamic equation of a two-dimensional elastically supported cylinder are used to establish the model, which predicts one-degree-of-freedom VIV of a two-dimensional elastically supported cylinder. And the accuracy of the model is verified by comparing it with the reference’s experimental data. The nonlinear governing equations of motion with NES are embedded in the above model to modify the VIV model under the action of NES. Combining with an optimization algorithm which changes the parameters of the initial NES, nonlinear energy sink meeting design requirements are achieved. The effect and mechanism of the optimized NES parameters on suppression of the VIV are analyzed by a mount of simulations. The results of optimization case show that the amplitude of the cylinder under NES decreases by 66.39%, when \begin{document}$U_{\rm{r}} = 5.5$\end{document}. The effect of vibration reduction is obvious. At the same time, the structure parameters of NES obtained by this optimization method meet requirements of actual production and ensure the possibility of physical production design.
Abstract:
The dynamic response of aviation dummy under vertical impact is studied by combing experimental study and numerical simulation. Firstly, 14g and 19g dynamic impact tests were carried out to compare the lumbar response of aviation dummy under different impact loads. Secondly, the numerical analysis model for aviation dummy/seat restraint system was developed and validated. Then, parametric studies were conducted to investigate the effects of seatback angle and seat pitch angle on occupant injury and seat responses. Results show that the ratios of peak lumbar force, peak longitudinal friction and seat pan pressure are greater than the ratio of peak load pulse under both 14g and 19g impacts, so the lumbar force, longitudinal friction force and seat pan pressure all have amplification effect on the peak load pulse. The 14g pulse has a longer duration, and it causes greater Y-axis peak moment of lumbar and Y-axis peak moment of seat pan than 19g pulse. The peak compression load of the lumbar and the peak pressure of the seat pan both have a quadratic function relationship with the seat back angle. When the seat back angle is about 110°, the risk of lumbar injury of occupant is the largest. The peak compression load of lumbar and the peak pressure of seat pan increase with the increase of the pitch angle of seat, showing a quadratic function relationship, and the growth gradually becomes gentle.
[Abstract](102) [FullText HTML](36) [PDF 1729KB](1)
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The meso-finite element model of concrete with random three-dimensional polyhedral aggregate is firstly established by developing MATLAB and ABAQUS Python script programs. A highly efficient C++ program is then developed to insert 3D cohesive elements with zero-thickness into the aggregate-mortar interfaces and within the mortar matrix, to realistically simulate their complicated crack initiation and propagation. Parametric studies are carried out to investigate the influence of cohesive fracture properties on the load-carrying capacity and cracking process. The simulation results show that: the macroscopic stress-displacement curve is mainly affected by the tensile strength and fracture energy of mortar and interface viscous crack unit, and the position and shape of crack surface are determined by the relative ratio of tensile strength and fracture energy of mortar and interface bonded crack unit. The mechanical response of concrete reflects the characteristics of crack development, which are not only determined by fracture material parameters, but also affected by meso-structural factors such as aggregate size and shape. The meso-structural features of aggregates also have significant effects on the complicated 3D cracking process.
Abstract:
Based on ABAQUS platform, a refined numerical finite element model of joints in prestressed steel reinforced concrete beam-concrete filled steel tubular composite column frame was established, and the lateral hysteretic and monotonic load-displacement curves at the column top were calculated. On the basis of the comparison of the calculated monotonic and the measured hysteresis curves, the failure process of the joints under lateral loading at the column top was studied, and the stress for concrete, steel skeleton, steel bars and prestressing tendons were carefully investigated, in which the failure mechanism was discussed. Otherwise, the influences of axial compression ratio, prestressing level, steel tube ratio and stirrup ratio in the panel zone on the lateral load-displacement curve at column top and shear-shear deformation in the panel zone were studied according to the results of parameter analysis. Finally, the formulas for calculating the shear capacity in the panel zone of the joint were proposed. The results showed that the steel-tube, stirrups and prestressed tendons reached the yield and the concrete crushed in the panel zone when the lateral load reached the peak value, which could be deemed as the sign for calculating the shear capacity. The presented formula for calculating the shear capacity could be used for a reference in engineering design.
Abstract:
In order to reasonably determine the fatigue strength of an orthotropic steel bridge deck, the fatigue test achievements at home and abroad are analyzed, and the effective fatigue test data is selected. Combined with fatigue cracking mechanism of typical details, fatigue strength categories (fatigue strength corresponding to 2 million cycles) for orthotropic steel bridge deck are proposed, which adapts to the anti-fatigue design and construction level of China. Research results show that: the fatigue strength of deck-to-rib detail is greatly influenced by the weld type, which belongs to Category 50 for fillet weld and Category 60 for partial penetration weld; details of the connection between the longitudinal rib and the diaphragm the fatigue strength of the welded toe of the diaphragm is Category 70, and that of the longitudinal rib web is Category 55; the fatigue strength of diaphragm cutout detail belongs to Category 70; the fatigue strength of rib-to-rib detail is closely relevant to the splice gap, which indicates that Category 40 is suitable for the splice gap less than 3 mm, Category 70 is suitable for the splice gap between 4 mm and 6 mm, and Category 100 is suitable for the splice gap between 8 mm and 12 mm. The fatigue strength of diaphragm weld toe in rib-to-diaphragm detail, of diaphragm cutout detail and of rib-to-rib detail is consistent with the categories in current JTG D64 specification of China. The fatigue strength of deck-to-rib detail and of rib wall weld toe in rib-to-diaphragm detail is lower than that of the categories in JTG D64 specification. When performing the anti-fatigue design or the fatigue assessment for orthotropic steel bridge decks, reasonable fatigue strength categories should be determined by the comprehensive factors of a detail structure, manufacture quality, an actual service state and others.
Abstract:
It introduces the basic method and process of seismic performance assessment of RC frame structures with energy dissipation and isolated devices based on the FEMA P-58 theory. A typical multi-story RC frame structure is designed, based on which buckling restrained braces and isolation bearings are added to form a BRB-frame structure and an isolated frame structure. The finite element models of the three structures are established in OpenSees software. Appropriate seismic records are selected and scaled to analyze the structural responses of the three structures. The intensity-based assessment method in FEMA P-58 is used. The structural response and seismic loss results of the ordinary frame structure, BRB-frame structure and isolated frame structure under four seismic intensities levels (i.e., frequently occurred earthquake, design level earthquake, maximum considered earthquake, very rare level earthquake) are compared. The results of seismic performance assessment show that the use of either an isolated frame structure or an BRB-frame structure can effectively reduce the repair cost and repair time of the building under earthquakes. Compared with the ordinary frame, the repair cost and repair time of the isolated structure under rare earthquakes can be reduced by 65% and 58%, respectively, and those of the BRB-braced frame structure can be reduced by 47% and 34%, respectively.
[Abstract](52) [FullText HTML](30) [PDF 1035KB](0)
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The mechanical behavior of a plastic material ABS-121H for air conditioner in drop conditions was studied. Based on quasi-static tensile tests, dynamic tensile tests and failure tests, the elastoplastic model of material under different strain rates and the GISSMO failure model of LS-DYNA software were established. In addition, the accuracy of elastoplastic model and failure model were verified by air conditioner components tests and simulations. The results indicate that the elastoplastic constitutive model of the material which considers the strain rate effect can accurately reflect the acceleration and stiffness of the structure. The GISSMO failure model can precisely predict the failure behavior of the material under complex stress state. This study provides a promising approach for the establishment of material models for air conditioner drop simulation.
Abstract:
A boundary forced response displacement method is proposed for the seismic analysis of symmetrical underground structures based on the requirement of quasi-static pushover test of soil-underground structure systems. The implementation procedure and special features of the method are introduced in detail. We took the Daikai subway station which was damaged during the Kobe earthquake in Japan as an example for the analysis, and compared the results of boundary forced response displacement method, the FEM seismic deformation method and the dynamic time-history analysis method. The results show that the accuracy of the new method was much higher than the FEM seismic deformation method when the width of the model was reasonable. The errors of the internal forces and the story drift were less than 15%. The new method is an effective simplified method for seismic response analysis of symmetrical underground structures. The attenuation law of lateral boundary forced displacement was analyzed. It provides references for the quasi-static pushover test of soil-underground structure system.
Abstract:
Because it is difficult for the flow, vibration and gas exhaust of concrete, gaps may exist near the welded regions of angle shear connectors. Based on the engineering practice and standard provisions, a test on nine groups of full-scale push-out specimens of three different gap depths (0, 10 mm and 20 mm) was conducted. To reduce the discreteness, there were three duplicate specimens in each group. All specimens failed in concrete crushing in the test. Compared with the specimens without a gap, the crushing area was smaller and the deformation of the angle steel was larger in the specimens with a gap. The concrete gap had a significant influence on the strength and stiffness of the angle shear connectors. Compared with that of the specimens without a gap, the strength was decreased by 16.5% and 37.5% and the stiffness was decreased by 48.4% and 70.6% for the specimens with a gap of 10 mm and 20 mm, respectively. Different formulas in the literature were verified based on 62 groups of specimens in other papers and 3 groups of specimens in the current test. The formula proposed by Kiyomiya and Kimura was found to have good accuracy and small discreteness, while the formula proposed by JSCE was conservative. A new shear strength empirical formula was proposed based on the existing experimental data, which showed better accuracy and applicability. Based on the new shear strength formula and a mechanical model considering the concrete gap, a shear strength formula for angle shear connectors with concrete gaps was proposed. The proposed formula was verified based on 3 groups of specimens in other papers and 6 groups of specimens in the current test and was found to have good accuracy and small discreteness.
[Abstract](29) [FullText HTML](22) [PDF 1227KB](0)
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The dynamic stall in the flight of the aircraft with a large angle of attack will lead to the self-excited torsion or pitch motion of the structure, causing nonlinear stall flutter, which will directly affect the flight safety and structural safety of the aircraft. In current study, the standard Leishman-Beddoes nonlinear unsteady aerodynamic model is modified by Mach number to make it suitable for the calculation of dynamic stall aerodynamic in the case of low speed incompressibility. Then, based on the two-element segment aeroelastic model, Newmark time-domain propulsion method is adopted for the calculation of engineering stall flutter. The stall flutter wind tunnel test is designed and completed based on the calculation results. The experimental results show that the stall flutter calculation results based on L-B model are in a good agreement with the experimental results in most experimental cases. The research results also verified that: the modified L-B model can be used for stall flutter engineering analysis and for the limit cycle oscillation evaluation of low-speed aircraft with high aspect ratio, and the stall flutter speed and limit cycle amplitude are considerably affected by the initial angle of attack at the same time.
[Abstract](49) [FullText HTML](34) [PDF 998KB](0)
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Among researches about meso-mechanical behavior of coarse-grained soil material, the numerical simulation methods such as the discrete element method have gained many attentions in recent years. It proposed a new numerical simulation approach based on computational contact mechanics. This approach is an implicit numerical solution method with a solid theoretical basis, which divides soil particles into elements and simulates the particle contact behavior through computational contact mechanics. Compared with the discrete element method, this method enjoys an advantage in describing the internal mechanical properties of the particles. The stress distribution inside the particles can be calculated, which provides a basis for the calculation of the mesoscopic behavior such as particle breakage. With the multi-body contact finite element method program, several conventional triaxial numerical tests with different confining pressures were carried out, and the outcomes are in accordance with the general law of a geomaterial triaxial test. The experimental results preliminarily verify the applicability of the proposed calculation method.
[Abstract](18) [FullText HTML](12) [PDF 920KB](0)
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Transmitting boundary is a common method for boundary treatment in dynamic finite element analyses. In view of the transmission boundary of finite element analysis of cylindrical shear wave in semi-infinite domain caused by torsional vibration, two kinds of viscoelastic transmission boundary are proposed through two kinds of approximate derivation, and their calculation accuracy is calculated and analyzed. The numerical analysis results show that the two kinds of viscoelastic boundaries can well simulate the infinity of foundation in torsional vibration analysis. At the same time, for the torsional vibration considered here, the accuracy of the transmission boundary is higher when the spring stiffness in the viscoelastic boundary condition is equal to the actual static stiffness.
[Abstract](19) [FullText HTML](10) [PDF 1092KB](0)
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To provide a quick and easy calculation for the seismic design loads of tunnel lining, the simplified analytical solutions are widely employed in preliminary tunnel design. So it is very important to assess the accuracy and applicability of these analytical solutions. In this study, the time-domain finite element method is adopted to verify the accuracy of four simplified analytical solutions for different types of surrounding soil or rock and different tunnel depths. Through the numerical validation, it can be concluded that: the analytical solutions by Wang, Bobet and Park generate the same thrusts; with the increasing of flexibility ratio, the error deceases for shadow tunnels, and decreases first and then increases for deep tunnels; the Bobet’s and Park’s solutions generate the same bending moments, more accurate than Wang’s solution; the error of Bobet’s and Park’s solutions decreases with the increasing of flexibility ratio; the errors of Bobet’s and Park’s solutions are lower than 15% for tunnel’s internal forces when the tunnel depth is over 10 m, 5 m, 5 m, 1 m and 1 m, respectively for soft soil, medium soft soil, medium hard soil, hard soil or soft rock and hard rock.
[Abstract](65) [FullText HTML](20) [PDF 1126KB](2)
Abstract:
Floor response spectrum plays an important role in the seismic design and in the seismic margin analysis for the facilities and pipes inside a nuclear power plant (NPP). This study presents the results of a set of shaking table tests on a scaled nuclear power plant structure of 1:25, with the underlying soil simulated by a multi-functional laminated shear container where the viscous-elastic boundary has been well reproduced. A group of 10 ground motion records are selected as the input. The peak ground accelerations (PGA) of these motions are scaled to the operational basis earthquake (OBE 0.15 g), the safely shutdown earthquake (SSE 0.30 g), and the ultimate earthquake beyond the design basis standard (ULE 0.75 g), respectively. Considering the soil-structure interaction, the change of floor response spectra caused by the input intensity has been studied. The standard input earthquake for floor response analysis suggested by the "Code for seismic design of nuclear power plants" is also discussed accordingly. According to the analysis of equipment response, it is revealed that the evaluation method of seismic margin of existing nuclear power plant equipment is conservative. Especially the equipment response ratio of 1/1.5 ~ 1.5, the existing seismic margin assessment method to obtain the equipment seismic margin may be less than the qualified ground motion. In order to obtain the true seismic margin of the equipment, it is suggested that these kinds of equipment should be analyzed in a more detail.
[Abstract](50) [FullText HTML](19) [PDF 1403KB](0)
Abstract:
In this paper, we investigate the effect of crosswinds on the unsteady aerodynamic forces of moving trains. Two methods are introduced to simulate the fluctuating wind velocity at the position of a moving vehicle. Using the quasi-steady theory and aerodynamic weighting function approach, a calculation formula of the unsteady forces on moving trains is established by considering the nature of different turbulent components and various wind directions. A numerical example is given to explore the effect of different parameters on the simulated results. The results show that the filtering and time-lag effects are observed in the weighting function approach. As additional wind turbulences from different directions are considered, there are greater fluctuations in the force. The mean value and coefficient of variance of the unsteady forces are affected by the various wind directions and lateral turbulences, respectively.
[Abstract](56) [FullText HTML](28) [PDF 1569KB](0)
Abstract:
A central difference virtual initial condition method is proposed to address the instability of the solution of hysteretic damping system. The proposed method develops virtual initial conditions associated with the real initial conditions, which generates the direct integration solution eliminating the divergence term of complementary solution and converges to the exact solution. Then, the procedure of central difference virtual initial condition method is established based on central difference method which is of conditional stability. Numerical examples of three different natural frequency systems under three different seismic excitations are analyzed by the central difference virtual initial condition method, the analytical solution and the frequency domain method, respectively. The results show that the frequency domain analysis results only contain the steady state solutions, which will lead to significant errors in the initial stage of vibration of low natural frequency system; the central differential virtual initial condition method is stable for different conditions, and it will converge to theoretical solution including transient response.
[Abstract](95) [FullText HTML](26) [PDF 2633KB](0)
Abstract:
Considering the operational and parked states, a generalized single degree of freedom model was established to explore the influence mechanism of wind-wave loadings on the seismic response of offshore wind turbines (OWTs). The statistical relationship between the wind and wave was employed to determine the parameters of the power spectra of the wave. Subsequently, the seismic response of the NREL 5MW OWT was analyzed using FAST to validate the conclusions of the preliminary analysis and evaluate the effects of wind-wave loadings on the seismic response of OWTs. The results reveal that the aerodynamic damping and dynamic loading effects of the wind and wave had a significant influence on the seismic response of OWTs. For wind turbines in the operational state, the support structure is the most dangerous when the mean wind speed of hub-height equals to the rated speed. In addition, the wind-wave loadings reduce the internal force of the mudline and tower-top displacement under the excitation of strong earthquakes. However, they increase the internal forces and displacement amplitudes at these locations while the OWT is excited by a weak earthquake.