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工程力学

Engineering Mechanics

Since 1984  Monthly

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Chief Editor: Xinzheng LU

Editor & Publisher: 《工程力学》杂志社

ISSN 1000-4750CN 11-2595/O3

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Articles online first have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
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2022 No. 2, Publish Date: 2022-02-01
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2022, 39(2): .  
[Abstract](29) [FullText HTML](17) [PDF 1419KB](9)
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OVERVIEWS
STUDY ON GEOMETRICAL IRREGULARITY OF RAIL INDUCED BY TRANSVERSE EARTHQUAKE
JIANG Li-zhong, YU Jian, ZHOU Wang-bao, FENG Yu-lin, PENG Kang, ZUO Yong-jian
2022, 39(2): 1-13.   doi: 10.6052/j.issn.1000-4750.2021.05.ST01
[Abstract](33) [FullText HTML](15) [PDF 7248KB](20)
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As an important lifeline for earthquake relief, railway transportation has undertaken extremely important transportation tasks during the earthquake relief period and post-disaster reconstruction period. Research on the rail irregularities caused by earthquake is the basis for ensuring the safety of train after earthquakes. A finite element model of China Railway Track System (CRTS) Ⅱ high-speed railway beam bridge was established and experimental verification was carried out. 40 seismic waves were selected from the PEER database, which had the highest matching degree with the design response spectrum. The distribution law of rail irregularity after transverse earthquake was studied. Based on random vibration theory and hypothesis testing principle, a method to determine the power spectral density curve of seismic induced rail geometric irregularity was proposed, and sampling of seismic induced rail geometric irregularity was constructed. The results show small amplitudes in residual gauge, vertical and cross-level irregularity and large amplitude in residual alignment irregularity; the residual alignment deformation is mainly concentrated in the area about 200 meters away from the subgrade; the track irregularity characteristics in the rest space are relatively stable, which can be predicted by a small space sample; the residual rail irregularity within 200 m near the subgrade should be processed as non-stationary signal, and the track irregularity in the rest space can be processed as stationary signal approximately; the power spectral density of stationary rail residual irregularity at each frequency obeys logarithmic normal distribution, and the power spectral density of non-stationary rail irregularity at each time frequency node obeys logarithmic normal distribution.
METHODOLOGIES
STRUCTURAL HEALTH MONITORING BASED ON INNER PRODUCT MATRIX AND DEEP LEARNING
WANG Hui, GUO Chen-lin, WANG Le, ZHANG Min-zhao
2022, 39(2): 14-22.   doi: 10.6052/j.issn.1000-4750.2020.12.0935
[Abstract](457) [FullText HTML](114) [PDF 4744KB](63)
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Structural health monitoring methods using vibration responses only under ambient excitation are appealing as its convenience to realize on-line monitoring. The basic concepts and characteristics of structural characteristic parameter (i.e. inner product vector) based on the correlation analysis of time domain vibration response are reviewed. In order to extract more structural characteristic parameters from the existing test data, the inner product vector is extended to the inner product matrix by using several inner product vectors which are constructed by setting each measurement point as the reference measurement point. Furthermore, taking the inner product matrix as the structural characteristic parameter and combining the feature extraction ability of deep convolution neural network, a structural health monitoring method based on deep learning and inner product matrix is proposed. The experimental results of monitoring the bolt loosening of a typical aeronautical stiffened panel show that the bolt loosening position can be correctly located using the time domain vibration response only under ambient excitation.
A p-TYPE SUPERCONVERGENT RECOVERY METHOD FOR FE ANALYSIS WITH LAGRANGE ELEMENTS ON TWO-DIMENSIONAL POISSON EQUATIONS
YE Kang-sheng, MENG Ling-ning
2022, 39(2): 23-36.   doi: 10.6052/j.issn.1000-4750.2020.12.0934
[Abstract](247) [FullText HTML](139) [PDF 9075KB](37)
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A p-type superconvergent recovery method for the finite element analysis with Lagrange elements on two-dimensional Poisson equations is proposed. Based on the superconvergent properties of mesh nodal displacements in finite element solutions, the method is inspired by the idea of dimensionality reduction of two-dimensional problems by the finite element method of lines. A row of adjacent elements with common opposite edges is taken out as a sub-domain. A local boundary value problem of the original partial differential equations on it which the true solution approximately satisfies is established by setting finite element solutions on each element's other opposite edges as Dirichlet boundary conditions. By increasing the element order along the elements' opposite edges direction unidirectionally, the local boundary value problem is solved by the finite element method to obtain the superconvergent displacement solution on the opposite edges of each element in this sub-domain. The superconvergent solution on the other opposite edges of elements can be obtained similarly with another sub-domain with respect to the edges to be recovered. Based on the recovered edge solutions, each element domain is taken out. The original Poisson equation on it is solved using a higher order Lagrange element with the superconvergent solution on its edges set as Dirichlet boundary conditions. Thus, the superconvergent solution of the whole domain can be obtained. Numerical examples show that the method can significantly improve the accuracy and convergence order of solutions with a small amount of computation.
CALCULATION OF SECOND-ORDER IN-PLANE BENDING MOMENT OF ELASTIC COMPRESSION-BENDING MEMBERS BASED ON BUCKLING MODES
FAN Hao, WANG Xin, DONG Wei-guo, WEN Si-qing
2022, 39(2): 37-50.   doi: 10.6052/j.issn.1000-4750.2020.12.0900
[Abstract](80) [FullText HTML](10) [PDF 5621KB](22)
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For a more common situation, in order to estimate the in-plane second-order effect of the elastic members under compressing, there seems no convenient and accountable method other than the complicated direct analysis method is available. Based on the differential equation of the in-plane second-order effect of a constant-section column under a uniform axial compression, the orthogonality relation of its buckling modes is proved, and the stability of all possible equilibrium states is discussed. Furthermore, the in-plane second-order effect is adopted by buckling modal series method for the first time, and its accuracy is demonstrated by several typical situations. For the computational complexity and awful accuracy of some specific situation, a simplified method is proposed in which only the first order in-plane result and the axial force and the deform shape of its first buckling mode are required. And the efficiency and accuracy of this new method are evaluated by several typical situations.
CIVIL ENGINEERING
STUDY ON THE EFFECT OF EMBEDDED CONDITIONS FOR HIGH-RISE BUILDINGS
FAN Zhong, WANG Jing, LIU Tao, YANG Su, YANG Kai, WANG Yi-hua, ZENG De-min
2022, 39(2): 51-66.   doi: 10.6052/j.issn.1000-4750.2021.07.ST04
[Abstract](71) [FullText HTML](15) [PDF 5269KB](41)
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The research progress of the seismic effect analysis of basement surrounding soil on high-rise buildings home and abroad was reviewed. Based on the interaction between the tower and, basement and, surrounding soil, a high-rise building analytical model that could consider the influence of foundations was established. The calculation parameters of the soil spring around basement and corresponding damping were determined according to the site conditions. The rationality of the calculation results of four kinds of embedded conditions including basement roof embedded, basement surrounding embedded, foundation embedded and soil-structure interaction under earthquake was investigated, and the influence of the length of one side opening of the tower on the mechanical performance of the overall structure and of the structural members was studied. The analysis results show that the lateral stiffness of the basement roof embedded model is relatively large, and the interaction between basement and tower cannot be considered. The basement surrounding embedded model cannot reflect the structural deformation and the inertial force caused by the basement mass, and the horizontal shear force decreases too fast along the vertical direction of the basement under earthquakes. Therefore, the calculation results are unsafe. The foundation embedded model ignores the effect of the soil around the basement, resulting in an excessive horizontal shear force of basement under earthquakes, and the calculation results are too conservative. The soil-structure interaction model can realistically simulate the stiffness and damping of the soil around the basement, compared with the other calculation models, although the situation of the tower changes little, the internal force of the basement components changes greatly. The single side opening has little influence on the overall mechanical performance of the tower, but the influence on the frame column and slab should be paid attention to.
DYNAMIC RESPONSE RECONSTRUCTION METHOD BASED ON EMPIRICAL MODE DECOMPOSITION AND MODEL CONDENSATION
ZOU Yun-feng, FU Zheng-yi, HE Xu-hui, LU Xuan-dong, YANG Jin-song, ZHOU Shuai
2022, 39(2): 67-75.   doi: 10.6052/j.issn.1000-4750.2020.12.0915
[Abstract](111) [FullText HTML](66) [PDF 9389KB](19)
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In terms of performing the dynamic response reconstruction of large civil engineering structures, the efficiency and accuracy of the current time-domain method based on finite elements are low and poor. A dynamic response reconstruction method combining empirical modal decomposition and modal condensation is proposed. Based on the modal synthesis method, the whole finite element model is divided into several sub-structures, and a super-element model with less DOFs is obtained by coordinate transformations. The reconstruction is carried out by combining the empirical modal decomposition method with intermittent criterion. Without considering the boundary conditions of each substructure, this method effectively reduces the dimension of the mathematical matrix of the relevant physical parameters of the finite element model, greatly improves the computational efficiency of response reconstruction, and is suitable for the dynamic response reconstruction of civil engineering structures. The effectiveness of the reconstruction method is verified by a numerical example of a cantilever beam, and the influence of noise and the number of main modes on the reconstruction effect are studied. The results show that the noise level has some influence on the precision of reconstruction, and that the number of main modes has trivial influence on the precision of reconstruction.
METHOD OF CALCULATING THE FLEXURAL STRENGTH OF FRP REINFORCED CONCRETE T-SHAPED AND RECTANGULAR BEAMS
PENG Fei, XUE Wei-chen
2022, 39(2): 76-84.   doi: 10.6052/j.issn.1000-4750.2020.12.0002
[Abstract](121) [FullText HTML](48) [PDF 4791KB](29)
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To establish a simplified method of calculating the flexural strength of concrete T-shaped and rectangular beams reinforced by fiber-reinforced polymer (FRP) bars, the effective FRP reinforcement ratio ρef and the corresponding balanced reinforcement ratio ρef, b were firstly derived from cross-section analyses under balanced failure. In conjunction with a statistical analysis of the experimental results of 257 FRP reinforced concrete (RC) beams, the transition region, where tensile failure and compressive failure were possible, was revised (ρef, b <ρef ≤1.5ρef, b). A numerical sectional analysis of tension-controlled sections was used for a detailed parametric study of a total of 25 344 sections. Based on a multiple regression analysis of the numerical results, simplified equations were developed for the flexural strength of tension-controlled sections. Besides, design equations were presented for the flexural strength of compression-controlled sections based on the fundamentals of the equilibrium of forces and the compatibility of strains. An experimental database of 257 beams was established and used to verify the accuracy of the proposed approach.
SHAKING TABLE TEST OF OFFSHORE WIND TURBINE SUPPORTING TOWER
SHEN Min-yu, ZHU Lei, JIA Jun-bo, LI Ai-qun
2022, 39(2): 85-95.   doi: 10.6052/j.issn.1000-4750.2021.01.0015
[Abstract](187) [FullText HTML](94) [PDF 5695KB](27)
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At present, the wind power generation technology develops rapidly. As the main supporting structure of the wind turbine, the safety of the tower structure is very important under the action of earthquake. Since the behavior of this kind of tripod structure has not yet been investigated through shaking table test, a 1∶20 scaled model of offshore tripod supporting structure was tested through seismic shaking table. Subjected to a series of seismic ground motions with three peak acceleration levels of 0.3 g, 0.6 g and 0.9 g, the dynamic characteristics of the model structure and the seismic response were studied. Two support condition sceneries of the foundation for the test model were considered: with supports at 1.3 m high of each pile foundation, and removal of the supports (simulated pile foundation failure). Compared with the case with the foundation support, the dynamic acceleration response of the structure after the removal of the support was slightly reduced, and the decrease in the amplitude of peak acceleration in X and Y directions was 9.87% and 5.40%, respectively. In addition, finite element analysis by ABAQUS was performed to analyze the elastoplastic response of the structure, and the simulation results were compared with the test results. Good agreement was observed between the two results, which validates the results of both the finite element analysis and the shaking table test, and provides a reference for the elastoplastic time history analysis of the prototype structure.
EXPERIMENTAL STUDY AND THEORETICAL ANALYSIS ON THE RESIDUAL CAPACITIES OF FIRE-DAMAGED CONCRETE CONTINUOUS SLABS
WANG Yong, WANG Gong-chen, WANG Ben-miao, ZHONG Bo, BU Yi-xiang, REN Zhao-qing
2022, 39(2): 96-109.   doi: 10.6052/j.issn.1000-4750.2020.12.0914
[Abstract](55) [FullText HTML](16) [PDF 6164KB](14)
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To investigate the effect of traveling fire on the residual capacity of fire-damaged slabs, residual capacity tests of four fire-damaged concrete continuous slabs were conducted. The effects of the parameters, including the traveling fire scenario, reinforcement ratios and reinforcement layout, on the deflection, concrete and steel strains and failure mode of the continuous slabs were studied. In addition, the vertical shear force was considered. The tensile and compressive membrane action regions were proposed to determine the residual capacity of the fire-damaged slabs. For the limit residual capacity of each span in the fire-damaged continuous slabs, a comparative analysis was conducted based on different theories. The results show that several kinds of failure modes often appeared in the fire-damaged slabs, including the mid-span flexural failure, local punching shear failure, punching shear failure near the internal supports and flexural failure near the internal supports. Compared to the traveling fire scenario, the heating time, spalling, reinforcement ratio and reinforcement layout have more important influence on the residual capacities of the fire-damaged slabs. According to the deflection failure criterion, the present method can be used to determine the upper limit loads of fire-damaged slabs.
EXPERIMENTAL STUDY ON THE PERFORMANCE OF ASSEMBLED STEEL-STRUCTURE BOX-SHAPED COLUMN FLANGE CONNECTION ACHIEVED BY PLUG WELDING-CORE SLEEVE
ZHANG Yan-xia, JIN Bo-wen, HUANG Zhe-wen, LIU Zi-yang, JIANG Kun
2022, 39(2): 110-122.   doi: 10.6052/j.issn.1000-4750.2020.12.0930
[Abstract](170) [FullText HTML](53) [PDF 6111KB](27)
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In order to solve the problems of a complicated construction procedure, low construction efficiency and high labor costs of the box-shaped columns with full penetration welded connection in assembled steel-structure, an assembled box-shaped column flange connection achieved by plug welding-core sleeve and its design method were proposed. It is designed to conduct the pseudo-static tests for three different forms of flange connections achieved by plug welding-core sleeve (PWCS), a connection with flange (FC), and a box-shaped column without connection (BCWC). The tests results indicated that: the initial rigidity of PWCS was increased by 16.6% and the maximum bearing capacity was increased by 9.97% compared to FC. The mechanical properties of the connection can be significantly improved by the setting of the core sleeve. Compared with 10.9s high strength bolts, the employment of bolts with larger pretension of 12.9s high strength can increase the extrusion force between flange plates, restrict the opening between flange plates, and improve the overall rigidity of the connection. The stiffeners can effectively prevent weld from cracking between the flange and column and, slightly improve the mechanical properties. It can be concluded that PWCS possesses similar mechanical properties compared with that of BCWC, and it can be designed as a rigid connection when applied in actual engineering. Besides, PWCS can be assembled efficiently on site, and the engineering costs can be controlled appropriately.
EXPERIMENTAL STUDY OF A MASONRY BUILDING RETROFITTED INTEGRALLY BY PRE-FABRICATED RC PANELS
WANG Xiao-ting, CHEN Xi, WANG Tao, PAN Peng, LI Wen-feng, MIAO Qi-song
2022, 39(2): 123-135.   doi: 10.6052/j.issn.1000-4750.2020.12.0931
[Abstract](207) [FullText HTML](62) [PDF 6631KB](21)
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The technological process was summarized by applying jacket retrofitting technology on a full-scaled substructure model of a five-story masonry residence. In order to evaluate the seismic performance of the retrofitted structure in longitudinal direction, series of lateral loads, whether quasi-statistic or pseudo-dynamic, were applied on the model. The seismic performance of the longitudinal lateral resistant system before and after earthquakes were assessed based on the experimental results. It demonstrates that the lateral stiffness of the strengthened reinforced concrete shear wall & masonry wall composite structure has an obvious improvement, the composite structure behaves more like RC shear wall structure; the failure mode is controlled by masonry structure after a decrease of the integrity of the jacket-retrofitting units; the strengthened composite structure has adequate redundancy when encountering an overfortification level earthquake; the damaged structure can still overcome another extremely rare earthquake without any collapse. It can be proved that the seismic performance of masonry dwellings retrofitted with PC panel jacket units will improve dramatically.
STUDY ON DAMAGE-BASED RESTORING FORCE MODEL OF STEEL REINFORCED CONCRETE SPECIAL-SHAPED COLUMNS
LIU Zu-qiang, DU Zhen-yu, XUE Jian-yang, ZHOU Chao-feng
2022, 39(2): 136-147.   doi: 10.6052/j.issn.1000-4750.2020.12.0936
[Abstract](99) [FullText HTML](41) [PDF 5254KB](14)
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Based on the experimental results of 16 solid-web steel reinforced concrete (SRC) special-shaped columns under low cyclic reversed loading, the hysteretic performance and damage-based restoring force model of the column were investigated. A composite skeleton model, including the ascent stage consisting of two straight lines and the decent stage in the form of exponential function, was put forward. The calculating method for the characteristic value of skeleton curve with different section forms, axial compression ratios and steel ratios was proposed by using theoretical derivation and regression fitting. Considering the influence of second-order moment effect, lateral stiffness due to axial compression, strength degradation, Bauschinger effect and loading history, the unloading stiffness degradation law of the hysteresis hoops of special-shaped column was proposed quantitatively by means of introducing the damage model based on experimental results fitting; and then the corresponding restoring force model was established. The results show good seismic performance of specimens with shuttle-shaped hysteresis curves. All hysteretic hoops under different loading cycles roughly pass two common points. According to the theoretical derivation and considering the influences of various parameters, the damage-based restoring force model of SRC special-shaped column was established, of which the calculated results agree well with the experimental results. It can provide basis for the nonlinear seismic response analysis of SRC special-shaped column structures.
TWO-STAGE SUPPORT VECTOR MACHINE METHOD FOR FAILURE MODE CLASSIFICATION OF REINFORCEDCONCRETE COLUMNS
LI Qi-ming, YU Ze-cheng, YU Bo, NING Chao-lie
2022, 39(2): 148-158.   doi: 10.6052/j.issn.1000-4750.2020.12.0937
[Abstract](158) [FullText HTML](61) [PDF 4840KB](32)
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A two-stage support vector machine (SVM) method for the failure mode classification of reinforced concrete (RC) columns is proposed. A two-stage SVM model is established to classify the seismic failure modes of RC columns according to three failure modes, namely, flexure failure, flexure-shear failure and shear failure. The optimal values of model parameters (i.e., penalty parameters and kernel function parameter) of the two-stage SVM model are determined by using ten-fold cross-validation and grid-search based on 270 experimental data. Subsequently, the characteristic parameters including the axial load ratio, shear span ratio, hoop spacing to depth ratio (s/h0), longitudinal reinforcement index and transverse reinforcement index on the seismic failure modes of RC columns are analyzed by the support vector machine-recursive feature elimination (SVM-RFE). The classification accuracy of the proposed classification method is validated by comparing with two classical machine learning methods and five traditional classification methods. The results indicate that the accuracy of the proposed method is generally higher than 90% for three failure modes, which is 10% higher than the classical machine learning methods and 20% higher than the traditional classification methods. The shear-span ratio and longitudinal reinforcement index have significant influences on whether the RC column fails in flexure. They are followed by the transverse reinforcement index and s/h0, while the axial load ratio has negligible influence. The longitudinal reinforcement index has significant influence on whether the RC column fails in flexure-shear. It is followed by the shear-span ratio and s/h0, while the transverse reinforcement index and axial load ratio have negligible influence.
THE DYNAMIC RESPONSE OF NPP CONTAINMENT CONSIDERING THE FLUID-STRUCTURE INTERACTION EFFECTS
ZENG Bin, WANG Yu-wei, PAN Zuan-feng, XU Qing, XUE Wei
2022, 39(2): 159-167.   doi: 10.6052/j.issn.1000-4750.2020.12.0939
[Abstract](57) [FullText HTML](10) [PDF 5155KB](28)
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The water in the containment tank of a nuclear power plant (NPP) sloshes when the structure is subjected to earthquake action. The dynamic response of the containment is affected by the fluid-structure interaction effect. The simplified additional mass method which does not consider the water sloshing and the smoothed particle hydrodynamics (SPH) method which considers the water sloshing are used to study the dynamic response of the containment of NPPs. The dynamic response including the base shear, displacement and acceleration under seven cases of various water levels is obtained when the structure is subjected to the commonly used Northridge earthquake wave and the Shanghai synthetic seismic wave. The comparison of the simulation results of the two methods shows that the dynamic response obtained by the SPH method is smaller than that by the simplified additional mass method. It indicates that the water sloshing in the tank has a damping effect on the overall dynamic response of the structure. The dynamic response at various water levels is analyzed by the SPH method. The results show that when the water level is 4.0 m, the dynamic response of the containment is relatively smaller. Therefore, 0.4 m is a reasonable water storage level of the water tank.
A PREDICTION MODEL OF THE COMPRESSIVE STRENGTH OF THREE-LEAF WALLS BASED ON LIMIT ANALYSIS
JIANG Yu-hong, YANG Na
2022, 39(2): 168-177.   doi: 10.6052/j.issn.1000-4750.2020.12.0941
[Abstract](55) [FullText HTML](21) [PDF 5263KB](7)
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Based on the method of limit analysis, the finite element method with the plastic limit upper bound is applied to predict the compressive strength of three-leaf masonry structures. Combined with the common failure modes of three-leaf walls under compression, the constitutive model parameters are obtained from the tests of material specimens and small masonry specimens. Based on the parameters, a prediction model for the compressive strength of three-leaf walls is proposed under the boundary condition of non-uniform compressive stress. According to the experimental data in literature, the compressive strengths of several three-leaf walls are predicted by this model. The predicted strengths are compared with the experimental results and the results of the compressive strength formulas to illustrate the accuracy of the model.
STABILITY OF SINGLE-LAYER THREE-WAY RETICULATED BARREL VAULTS CONSIDERING GLOBAL GEOMETRIC IMPERFECTION, MEMBER IMPERFECTION AND ECCENTRICITY
JIANG Shou-fang, LI Hui-jun, LONG Ting-ting
2022, 39(2): 178-188.   doi: 10.6052/j.issn.1000-4750.2021.01.0005
[Abstract](75) [FullText HTML](31) [PDF 5751KB](12)
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Single-layer reticulated barrel vaults are sensitive to imperfections. To figure out the impact of global geometric imperfection, member imperfection and eccentricity on the load-bearing capacity of reticulated barrel vaults, a model integrated with the three imperfections and the corresponding modelling procedures were clarified. The effect of the imperfections and their couplings on the stability of barrel vaults were studied. The method was developed to determine the most unfavorable combination of the three imperfections. The numerical results show that the load-bearing capacity of barrel vaults is most sensitive to the global geometric imperfection, and is obviously influenced by the member imperfection. The effect of the member imperfection is related to the magnitude of the global geometric imperfection, and becomes weaker with the increase of the global geometric imperfection. The limit load of barrel vaults is also affected by the member bowed direction. The limit load roughly linearly decreases with the increase in the member eccentricity. The effect of the member imperfection and eccentricity on the limit load is also apparent compared with global geometric imperfection, and should not be neglected whether the magnitude of the global geometric imperfection is large or small. The developed MCIMM is highly efficient to determine the most unfavorable combination of the three imperfections. The initial stiffness and limit load of barrel vaults decrease with the increase in the member imperfection and/or eccentricity.
STRUCTURAL NONLINEAR DAMAGE IDENTIFICATION BASED ON THE GNAR MODEL AND ITAKURA DISTANCE
ZUO Heng, GUO Hui-yong
2022, 39(2): 189-199.   doi: 10.6052/j.issn.1000-4750.2021.01.0007
[Abstract](143) [FullText HTML](70) [PDF 5263KB](21)
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To solve the problem of time-domain nonlinear damage identification, a damage identification method based on the general expression of the linear and nonlinear auto-regressive model (GNAR model) and the Itakura distance is proposed. Describe the basic theory and give the basic model order determination and parameter estimation methods. The optimized structure of the GNAR model is selected by the pruning algorithm. The Itakura distance is used as the damage indicator for nonlinear damage identification. The nonlinear damage experiment of a three-story frame was used to verify the effectiveness of the proposed method. The method is applied to the nonlinear damage identification experiment of a transmission tower steel frame model. The results show that the proposed nonlinear damage identification method can easily identify the nonlinear damage of the frame and transmission tower steel frame structure. The environmental change has little effect on the damage identification results. The damage probability of the damaged floor calculated by the proposed method is higher than the undamaged floors. The proposed method is helpful to find the location of the nonlinear damage source efficiently.
RESEARCH ON THE CREEP OF CONCRETE FILLED STEEL TUBULAR COLUMNS BASED ON THE GENERALIZED KELVIN CHAIN
YANG Chao, CHEN Meng-cheng, ZHANG Ming-yang, LI Qi, FANG Wei, WEN Qing-qing
2022, 39(2): 200-207.   doi: 10.6052/j.issn.1000-4750.2021.01.0042
[Abstract](190) [FullText HTML](70) [PDF 4648KB](23)
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Concrete creep is an inherent time-dependent behavior of concrete and an important composition of structural responses. Its calculating method is usually established on the basis of uniaxial test and theory. To explore the creep behavior of concrete-filled steel tubular columns, the creep of circular concrete columns and concrete filled circular steel tubular (CFST) columns were measured by a self-made and self-balanced loading device. The results show that the creep deformation of CFST columns is smaller than that of concrete columns. In the present concrete creep tests, the maximum difference between the two aforementioned creep deformations was close to 50%. It is attributed to the fact that the core concrete cannot exchange moisture with its external atmosphere environment so that no dry shrinkage and creep of the core concrete occurred. It is also attributed to the confining pressure of the steel tube. According to the theory of viscoelasticity, a Volterra integral equation for solving the concrete creep under uniaxial stress condition was established by introducing a model consisting of a multi-parameter Kelvin element chain. The model parameters were approximately expressed as a successive retardation spectrum. Therefore, the constitutive relationship of concrete creep stress and strain increments under uniaxial stress condition was derived by discretizing the time variable t and integration by parts. Based on the principle of creep superposition and the Poisson effects, the constitutive model of the concrete creep stress and strain increments under uniaxial stress condition state was extended to a multiaxial stress state to analyze the CFST creep. The commercial finite element analysis software Ansys was secondarily-developed. The constitutive equation under multiaxial stress state for concrete creep performance was compiled with the Fortran language and introduced into the user subroutine Usermat of Ansys. Finally, the finite element numerical analysis for the long-term creep performance of CFST columns was carried out. Comparing the numerical solutions with the test results, it is found that the proposed method provides another effective approach to the analysis of concrete creep.
STUDY ON SEISMIC EFFECTIVENESS OF TIE UP METHOD FOR FIXING CULTURAL RELICS BASED ON SHAKING TABLE TESTS
WANG Meng, YAN Yi, FU Meng, ZHANG Xiao-peng, CHAO Zhen
2022, 39(2): 208-221.   doi: 10.6052/j.issn.1000-4750.2021.01.0047
[Abstract](171) [FullText HTML](94) [PDF 6348KB](13)
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To study the seismic effectiveness of the commonly used tie up method for fixing cultural relics, two typical cultural relics specimens were selected, and the shaking table tests of cultural relics specimens-fixed measure seismic system were carried out to obtain the seismic responses of cultural relics specimens and the interaction responses between cultural relics and fishing lines under different working conditions, and then the seismic effectiveness of typical tie up method was verified. The corresponding finite element models were established, and parameter analyses were carried out, which provided a necessary technical method for supplying test data and quantifying evaluation method. The results show that : the finite element results agree well with the test results. In the case of larger peak acceleration of earthquake wave, the motion states of different types of cultural relics are different. The lower the centre of gravity is, the smaller the rocking responses are, but the overall sliding responses slightly increase. Compared with the floating cultural relics, the rocking responses and sliding responses of cultural relics are effectively reduced by using tie up method. The seismic responses of cultural relics and the variation range of the internal force of the fishing lines are significantly reduced by appropriately increasing the initial pretension of fishing lines. However, when the initial pretension is too large, the reaction force on cultural relics is large. For the fragile cultural relics, some cushions between fishing lines and cultural relics can be used to reduce the local damage to cultural relics. With the increase of the initial pretension of fishing lines, the influence of the number of fishing lines on the responses of cultural relics is weakened. In the case of identical conditions, the larger the height-width ratio of cultural relics, the larger the seismic responses, and the larger the variation range of internal force of fishing lines, it was suggested to increase the initial pretension of the fishing lines to achieve better fixed effect.
STUDY ON MECHANICAL PROPERTIES OF STUD SHEAR CONNECTORS IN STEEL-UHPC COMPOSITE STRUCTURES
WU Fang-wen, FENG Yan-peng, DAI Jun, WANG Guang-qian, ZHANG Jing-feng
2022, 39(2): 222-234.   doi: 10.6052/j.issn.1000-4750.2021.05.0389
[Abstract](60) [FullText HTML](19) [PDF 5832KB](22)
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In order to further study the mechanical properties and failure modes of studs embedded in ultra-high performance concrete (UHPC) and normal concrete (NC), a total of eight stud push-out specimens were tested and the influences of concrete type, diameter and length of stud on ultimate shear capacity were discussed. Based on the finite element model, the effects of ultimate tensile strength, diameter and length diameter ratio of stud and concrete strength on shear performance were further analyzed. The effects of diameter and length of stud and concrete strength on the effective distribution length of shear stress of stud were studied. The results show that the shear fracture near stud roots is the leading dominant failure mode. The shear capacity and shear stiffness of studs embedded in UHPC are higher than that of ordinary concrete, but the ductility is lower. The shear stress of stud peaks at the root and decreases rapidly along the direction of the nail cap. The diameter of stud has a significant effect on the effective distribution length of shear stress. Finally, according to the test results, the load-slip curve and a formula for the calculation of shear capacity under the stud shear failure mode are put forward, and the calculated results are in a good agreement with the test results, which can provide a reference for pertinent engineering design.
MECHANICAL ENGINEERING
RESEARCH ON THE VIBRATION OF COLD ROLLING MILL F5 UNDER MULTI-SOURCE EXCITATION
ZHANG Yi-fang, XIAO Biao, YAN Xiao-qiang
2022, 39(2): 235-243.   doi: 10.6052/j.issn.1000-4750.2021.01.0006
[Abstract](225) [FullText HTML](108) [PDF 5721KB](14)
Abstract:
Serious vibration occurred on the F5 stand when producing thin strips on a 1550 cold tandem mill. The field test showed that the dominant frequency of the vibration is 144 Hz, which was close to the natural frequency of the F5 stand. Moreover, there were many excitation frequencies in the strip excitation spectrum and the servovalve pressure spectrum of the screwdown system. To explore the vibration source and suppress the vibration, the industrial field experiment was conducted to concluded that the vibration was affected by the joint excitation of strip steel and the hydraulic screwdown system. The characteristics of different frequency combination acting on the mill were obtained by solving the model of the strip-screwdown excitation. A method was proposed to suppress the vibration. It used the desired excitation combination by adding the vibration suppressor in the control system to eliminate a specific frequency. The satisfactory suppression effect was obtained after the implementation. The research provides a reference for analyzing vibration mechanism of cold tandem mill and expands the method of vibration suppression.
COLLISION MODELING AND PARAMETER OPTIMIZATION OF CARBODY BASED ON EQUIVALENT STIFFNESS METHOD
ZHANG Jing-ke, ZHU Tao, LEI Cheng, WANG Xiao-rui, YANG Bing, XIAO Shou-ne, YANG Guang-wu
2022, 39(2): 244-256.   doi: 10.6052/j.issn.1000-4750.2021.01.0012
[Abstract](64) [FullText HTML](25) [PDF 6177KB](11)
Abstract:
In order to solve the problems of low efficiency of numerical simulation of rail vehicle collision dynamic behavior and, the lack of crashworthiness analysis methods, a collision modeling and parameter optimization method is proposed for a carbody structure based on an equivalent stiffness method. According to the equivalent stiffness method and the equality principle of bending strain energy of a simply supported beam, the conditions for the equivalent bending stiffness of the hollow profile to a solid-core beam are put forward, the substitution formula of the equivalent parameters of the above two structures are deduced, and the equivalent parameters are optimized by the multi-island genetic optimization algorithm. The main vibration modal frequencies of the equivalent and the original model of the carbody structure are compared in detail, which proves the superiority of equivalent model reflecting the dynamic characteristics of original model, and the effectiveness of equivalent model of carbody structures. The change trend and error of numerical simulation results of the original and equivalent structures of an urban rail vehicle body are compared and analyzed, including the first-order vertical-bending and, the first-order torsional frequencies and, the main collision responses such as the speed, the acceleration, the energy and, the interface force of the carbody at a collision speed of 15 km/h. The research indicates that: the equivalent model of the hollow profiles can better reflect dynamic characteristics of the original model, in which the relative errors of the first-order vertical-bending and the first-order torsional frequencies of the carbody structure are 2.19% and 4.21%, respectively; the main occupant safety assessment index errors of the two models of carbodies are both less than 10%; and comparing with the original model, the element number is reduced by 38.91% and, the CPU calculating time is reduced by 27.63% in numerical simulation, which shows that the application of the carbody equivalent model in collision simulation can be feasible and effective.

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