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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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2021 No. 3, Publish Date: 2021-02-03
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2021, 38(3).  
[Abstract](52) [PDF 1519KB](27)
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OVERVIEWS
DAMAGE IDENTIFICATION OF CIVIL STRUCTURES BASED ON FINITE ELEMENT MODEL UPDATING
Shun WENG, Hong-ping ZHU
2021, 38(3): 1-16.   doi: 10.6052/j.issn.1000-4750.2020.06.ST02
[Abstract](142) [FullText HTML](26) [PDF 1642KB](90)
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The finite element model updating is advantageous in damage identification because it is physically meaningful and simultaneously identifies the damage location and extent. It provides a direct and important basis for structural safety assessment. We firstly present the background and basic process of model updating based damage identification, and summarize its development in the past thirty years. A finite element model of a civil structure is usually large in scale and contains many parameters to update. It makes the model updating process time consuming. Therefore, substructure-based model updating methods are developed to identify the damage of large-scale civil structures to improve the efficiency of the model updating process. The two methods are applied to the damage identification of a high-rise building model to illustrate their advantages in practical damage assessment. A civil structure is large in scale while the damage is localized. The substructuring method divides the global structure into several independent substructures for the analysis. The substructure-based damage identification is achieved by updating a few substructures, avoiding repeated analysis of the large whole structures, and therefore improving the accuracy and efficiency of the model updating process.
METHODOLOGIES
THE METHOD FOR HARDNESS PREDICTION OF METAL MATERIALS BASED ON ENERGY EQUIVALENCE PRINCIPLE
Zhi-jie ZHANG, Peng-fei ZHENG, Hui CHEN, Li-xun CAI
2021, 38(3): 17-26.   doi: 10.6052/j.issn.1000-4750.2020.04.0249
[Abstract](85) [FullText HTML](18) [PDF 2172KB](26)
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Hardness of materials is a mechanical property widely used in material science and engineering. Based on energy equivalent principle, a semi-analytical prediction model is proposed to obtain Brinell hardness and Rockwell hardness if materials are uniform, continuous, isotropic and their stress-strain relations conform to Hollomon-law. The hardness can be determined by Hollomon-law parameters of materials. Several parameters in the prediction model are determined through finite element analysis (FEA). For a wide range of assumed materials, a large number of FEA calculations are carried out to verify the prediction model. The results show that the model generates a good prediction. For six kinds of tested ductile metallic materials by hardness test, the Brinell hardness and Rockwell hardness predicted by the model are in good agreement with the hardness test results.
CIVIL ENGINEERING
DESIGN OF CRACK MONITORING SYSTEM FOR CHINESE ANCIENT WOODEN BUILDINGS BASED ON UAV AND CV
Na YANG, Chong ZHANG, Tian-hao LI
2021, 38(3): 27-39.   doi: 10.6052/j.issn.1000-4750.2020.04.0263
[Abstract](153) [FullText HTML](19) [PDF 1426KB](48)
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There are many cracks in Chinese ancient wooden buildings, and the formation and development of these cracks are complicated. These cracks can easily cause component brittleness, which seriously threaten the condition of Chinese ancient wooden buildings. Based on an unmanned aerial vehicle (UAV) and computer vision (CV), it designs a crack monitoring systems for Chinese ancient wooden structures, including an UAV system, a camera system, and an image processing system. In the UAV system, a UAV suitable for crack monitoring is designed, and the feasibility of hovering photography of the UAV is analyzed. In the camera system, the camera distortion correction and pixel resolution calibration are done, and an improved SIFT + RANSAC method is proposed to improve the accuracy of crack image mosaic. In the image processing system, a set of preprocessing methods is adopted, and Hessian matrix is combined with adaptive threshold segmentation algorithm, extracting crack features effectively. Then the size of members and cracks are accurately identified by CV measurement method. Finally, the feasibility of the proposed crack monitoring system is verified based on the wooden pavilion model of Chinese ancient buildings.
INVESTIGATION ON THE SEISMIC BEHAVIOR OF STEEL-PLATE AND HIGH DUCTILE CONCRETE COMPOSITE LOW-RISE SHEAR WALLS
Ming-ke DENG, Jun-chao LIU, Yang-xi ZHANG, Hai-bo LIU, Wu-bin JING
2021, 38(3): 40-49.   doi: 10.6052/j.issn.1000-4750.2019.07.0414
[Abstract](131) [FullText HTML](26) [PDF 1075KB](34)
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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 effect on the peak load and stiffness of the steel-plate and HDC composite low-rise shear walls. When the axial load ratio increases 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 predicting 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.
EFFECT OF SHEAR-SPAN RATIO ON SHEAR FAILURE AND SIZE EFFECT OF CONCRETE BEAMS WITHOUT WEB REINFORCEMENT STRENGTHENED BY CFRP
Liu JIN, Hai XIA, Xuan-ang JIANG, Xiu-li DU
2021, 38(3): 50-59, 85.   doi: 10.6052/j.issn.1000-4750.2020.01.0028
[Abstract](62) [FullText HTML](24) [PDF 1507KB](22)
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The shear-span ratio has an important influence on the crack development and on the failure mode of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP). However, there were few studies on the effects of its shear strength and size effect. A mechanical analysis model for shear failure of reinforced concrete beams strengthened with CFRP was established by using three-dimensional numerical meso-scale simulation method, considering the meso-heterogeneity of the concrete and the interaction between the CFRP and concrete. Based on the verification of the rationality of the meso-scale method, the influence mechanism and law of the shear-span ratio on the shear failure and size effect of CFRP-strengthened RC beams were simulated and analyzed. The results show that: the shear-span ratio has a great influence on the shear failure mode of the strengthened beam, and the larger the shear-span ratio, the closer the beam is to the cable-stayed failure with better ductility. The shear-span ratio had better shear capacity for CFRP-strengthened beams and the influence on the size effect of shear strength was small. The shear-span ratio has a greater influence on the CFRP shear contribution in the strengthened beam. The larger the shear-span ratio, the better the shear effect of CFRP on strengthened beams. The beam reinforcement effect of the shear-span ratio (λ = 2.5) is most effective.
THE MECHANICAL MODEL OF ROCKING COLUMNS IN PALACE-STYLE TIMBER FRAMES IN TANG DYNASTY
Juan WANG, Zhi-han CUI, Xi-ming ZHANG
2021, 38(3): 60-72.   doi: 10.6052/j.issn.1000-4750.2020.04.0255
[Abstract](100) [FullText HTML](25) [PDF 2739KB](32)
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With a long history, palace-style timber structure buildings in Tang Dynasty, which are represented by the East Hall of Foguang Temple in Shanxi province, have significant historical and cultural values. The horizontally layered structure, including the column frame layer, Tou-Kung layer and roof frame layer, has good seismic performance, in which the rocking resistance of the columns plays an important role. Taking a single column of the palace-style timber frames in Tang Dynasty as the research object, the resistance mechanism of the rocking column under horizontal loading was analyzed. The process of the column rocking was divided into six states. The geometric conditions, equilibrium conditions and stress distribution of the contact surface for each state were obtained considering the stress-strain states of the compression surface of the column ends during rocking and that the timber in compression may induce elastic-plastic strain. The change of the shape of the compression surface of the column ends and the translation of the action points of Ludou and stone base were analyzed in detail. A mechanical model of the lateral force resistance and horizontal displacement of the rocking column was established and verified by a comparison with the results from numerical simulation and existing models. The differences of the lateral resistance of the column frames of different structural configurations in Tang and Song Dynasties were also analyzed. The results provide a theoretical basis for the study of the seismic performance and reinforcement of ancient structures in early historical period.
ANALYSIS ON THE FIRE RESISTANCE OF SQUARE CONCRETE-FILLED STEEL TUBULAR COLUMN TO COMPOSITE BEAM WITH OUTER RING PLATE CONNECTIONS AFTER EARTHQUAKE DAMAGE
Wen-da WANG, Run-ting CHEN
2021, 38(3): 73-85.   doi: 10.6052/j.issn.1000-4750.2020.04.0259
[Abstract](111) [FullText HTML](15) [PDF 1551KB](17)
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To study the fire resistance of the square concrete-filled steel tubular column to composite beam with outer ring plate connections after earthquake damage, finite element numerical models were established and verified by experimental data of other researchers. The finite element models for the fire resistance of composite beam joints under three fire conditions after earthquakes were established. The impact of the shedding position and degree of the fire protection layer of the column in hysteretic loading and three fire conditions on the fire resistance and failure modes was analyzed. The results indicate that the stress value and deformation degree of the steel tube increased obviously with the increase of the damage degree of the joint under the hysteretic loading at the column end. When the joint was exposed to fire in the area below the RC slab, the temperature gradient of the stud from the bottom to the top was obvious with the increase of the fire time. The temperature field distribution of the RC slab was wavy due to the influence of the stud. Different damage degrees and different fire conditions had significant effects on the failure modes. However, there was no significant difference on the failure modes with or without the fire protection layer falling off under the three fire conditions. Under the two fire conditions in the area below the RC slab and the area above the RC slab, the shedding fire layer had a significant influence on the fire resistance of severely damaged joints. Under the condition that both the upper and lower areas of the RC slab were under fire, the shedding fire layer had no significant influence on the fire resistance of the joints.
EXPERIMENTAL STUDY ON PULLOUT BEHAVIOR OF LAP SPLICE CONNECTIONS BETWEEN DOUBLE-STEEL-PLATE COMPOSITE WALLS AND RC RAFT FOUNDATION IN NUCLEAR ENGINEERING
Yun-lun SUN, Si-yu KONG, Yan CHEN, Jian-sheng FAN, Ran DING
2021, 38(3): 86-97, 147.   doi: 10.6052/j.issn.1000-4750.2020.04.0261
[Abstract](47) [FullText HTML](10) [PDF 1471KB](17)
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Combining the advantages of steel and concrete, the double–steel-plate composite (DSC) structures exhibit the advantages of high bearing capacity, good seismic performance and durability, and convenient construction, and they have been increasingly used in nuclear engineering projects. The connection between DSC walls and reinforced concrete raft foundation is the key to make full use of the aforementioned advantages. Compared with the traditional embedding connection and anchoring connection, the lap splice connection can greatly improve the construction efficiency, which gains more and more attention. However, there is few research on such connection. Therefore, in this paper, four 1∶2 scaled lap splice connections between double-steel-plate composite wall and RC foundation are designed, and the static monotonic loading tests are carried out. Through the observation of bearing capacity, stiffness, crack pattern and strains of steel plate and rebar, the influences of the arrangement of lapped bars and tie bars on the mechanical performance of the connections are explored. The test results show that this kind of connection can achieve equal strength and shows satisfactory ductility. Transverse bars can control the crack development effectively and improve the integrity of the connection greatly; in addition, the tie bar strain along the lap length is not linearly distributed. The higher eccentricity of the lapped bars, which means larger unbalanced moment between the reinforcement and the steel plate, will result in lager strains of the transverse bars and lower slip of lapped bars. This paper provides experimental basis for the design of lap splice connections.
EXPERIMENTAL INVESTIGATION AND FINITE ELEMENT MODELING OF INTERFACE BOND-SLIP BEHAVIOR BETWEEN SHAPE STEEL AND ECC
Liang BAI, Miao ZHANG, Lei YANG, Shuai HU, Zheng-fu BAO
2021, 38(3): 98-111.   doi: 10.6052/j.issn.1000-4750.2020.04.0265
[Abstract](114) [FullText HTML](17) [PDF 13036KB](49)
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In order to study the interface bond-slip behavior between shape steel and Engineered Cementitious Composites (ECC), the shape steel-ECC specimens were designed to conduct push-out testing. The influences of the volume fraction of PVA fiber, stirrup reinforcement ratio, ECC cover thickness and shape steel embedment length on the failure modes, on the load-slip curves and on the bond stress of shape steel-ECC specimens were analyzed, also the bond stress distribution along steel embedded length was proposed. The result shows that the volume fraction of PVA fiber and ECC cover thickness have great influences on bond stress. The maximum bond stress occurred near the loading end, and the equivalent bond stress increased with the increase of the load. According to the test results, the expression of bond stress in different states were established, and the bond-slip constitutive laws were proposed. On this basis, the finite element model of shape steel-ECC specimens was established by using a nonlinear spring to simulate the interface bond-slip behavior between shape steel and ECC. The finite element analysis results were compared with the test results, which indicated that the finite element simulation method proposed could accurately analyze the interface bond-slip behavior of shape steel-ECC.
AXIAL PERFORMANCES OF A GFRP CONNECTOR FOR SANDWICH INSULATION WALL PANELS
Zhi-zhou HE, Peng PAN, Hai-shen WANG
2021, 38(3): 112-121.   doi: 10.6052/j.issn.1000-4750.2020.05.0279
[Abstract](59) [FullText HTML](20) [PDF 1408KB](16)
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Sandwich insulation wall panel (SIWP) is a type of precast components with load-bearing, enclosure and insulation functions. The SIWP is composed of inner and the outer reinforced concrete slabs and middle insulation layer. The connectors penetrate the insulation layer and transfer loads from the outer layer to the inner layer. The performance of the connectors is crucial to maintain the safety of the panels. However, the conventional connectors may not have adequate stiffness if the insulation layer is too thick, and the quality control is difficult for the installation. In this study, a GFRP I-shaped connector was developed, the associated anchorage method featured with the anchorage rebar penetrating the holes at connector ends was proposed, and tests and finite element analyses were carried out. The experimental results find that the failure modes of the connector are concrete punching and splitting failure. The pull-out and compression strength of the connector are 25.6 kN and 36.8 kN, respectively. The finite element analyses suggest that the anchorage rebar is important for the failure mode. Based on the test and analysis results, methods to determine the punching failure surface and estimate the load bearing capacity are proposed, which are expected to provide references for engineering design practices.
A STUDY ON THE DESIGN METHOD FOR AXIAL COMPRESSIVE RESISTANCE OF GLASS COLUMNS LATERALLY AND TORSIONALLY CONSTRAINED BY STRUCTURAL ADHESIVE
Xiao-kun HUANG, Shu-kun DUAN, Qiang LIU, Ming-zhe CUI, Jian-guo NIE
2021, 38(3): 122-131.   doi: 10.6052/j.issn.1000-4750.2020.04.0280
[Abstract](66) [FullText HTML](23) [PDF 1278KB](7)
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One form of glass columns in engineering application is that the columns are connected with glass panels through structural adhesive, where the stability of the columns can be improved by the constraint effects from the structural adhesive. Considering the lateral and torsional spring constraints of structural adhesive on the glass column, the critical load formula of the glass column under axial compression is derived based on equilibrium equations. The influences of the elastic modulus of structural adhesive, the height, section depth and section thickness of the glass column on the critical load are discussed. It is found that the elastic modulus of structural adhesive and the section thickness of the glass column influence the critical load most significantly. The critical load formula is then extended to laminated glass columns based on the equivalent stiffness method. For the structural silicone adhesive commonly used in engineering practice, the design criteria for the load resistance of the glass columns are derived with the consideration of glass cracking and adhesive failure. The rationality of the theoretical research is verified by FEM analysis.
MULTI PARAMETER EVALUATION INDEX OF PROGRESSIVE FAILURE OF LANDSLIDE
Ying-fa LU, Ling-chen ZHANG, Yu-fang ZHANG, Jian LI, Min-wei LIU, Lei ZHU
2021, 38(3): 132-147.   doi: 10.6052/j.issn.1000-4750.2020.05.0286
[Abstract](46) [FullText HTML](15) [PDF 3216KB](17)
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The traditional strength reduction method (SRM) uses strength reduction to characterize the softening mechanical behavior of rock and soil after failure. The reduction coefficient is essentially a description of the overall stability coefficient of the slope, but its physical significance is not obvious. The stability of slope is a complex scientific subject related to many factors. When the local part of slope is in the state of failure stress, its whole failure may not happen, and the entire system composed of failure zone and non-failure zone is essentially in the state of an unstable mechanical state. It is difficult to obtain the real solution by the method of continuum mechanics. A multi- parameter evaluation index is put forward to describe the stability of the point, the surface (sliding surface) and body (sliding body) of slope. The definitions for point failure and surface failure (failure area ratio, failure stress rate, failure strain rate, etc.) are also presented. The different coefficients are developed, such as coefficient of frictional resistance, coefficient of normal force, coefficient of sliding force, coefficient of displacement along sliding surface, etc., for describing the law of force and displacement change. The safety factors of the entire slope are also clarified, such as surplus frictional resistance method, main thrust method, surplus frictional force method, comprehensive displacement method, surplus displacement method, and so on. It is possible to describe the all-round evolution process of slope by using the multi- parameter evaluation index. Under the condition of making full use of the partial strength reduction method (PSRM), or the perfect elasto-plastic model (PEPM), and the complete process constitutive model (CPCM), the multi parameters of point, surface and body of slope can be obtained with the change of displacement and force. Taking the traditional and extended unbalanced thrust method as an example, the progressive failure process of slope can be described by using the multi- parameters and can reveal the characteristics of the critical stress state movement step by step. The calculation results of Taohuashan slope in Huangshi City of Hubei Province show that: the multi parameter evaluation index can describe the evolution law of progressive failure of the slope, the values of the point and surface multi- parameters obtained by PSRM with the PEPM are smaller than that obtained with the CPCM; and the overall safety factors of the main thrust method, comprehensive displacement method and surplus displacement method using the PEPM are larger than that of the CPCM, but the stability coefficient of surplus frictional force method is opposite, etc. The focus of this study is to establish the slope multi-parameter stability evaluation index, and to make the traditional stability coefficient can be compared with the method proposed in this paper, which provides a theoretical support for slope monitoring and early warning.
STUDY ON EARTHQUAKE RESILIENCE ANALYSIS AND OPTIMIZATION FOR URBAN BRIDGE NETWORK SYSTEM BASED ON NSGA-II ALGORITHM
Zheng KOU, Ning LI
2021, 38(3): 148-158, 180.   doi: 10.6052/j.issn.1000-4750.2020.05.0290
[Abstract](199) [FullText HTML](28) [PDF 1638KB](42)
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Urban bridges are important infrastructure that affects regional economy and social community. When subjected to strong earthquakes and other disasters, the seismic performance of urban bridge structures, especially the resilience of the transportation system composed with key bridges, are very important to social stability and regional economy development. In recent years, the seismic resilience had attracted the attention of researchers. To incorporate the recoverable performance and the resiliency measurement into the evaluation and optimization of the seismic performance of a bridge system, there are still many issues to be studied. This paper further quantitatively analyzes the post-earthquake recovery process, residual function, idle time and repair time, and their influence on the resilience index. And the performance assessment process of urban bridge system was developed. According to the different damage states of the bridge, the resiliency indexes, the repair time, the economic loss after the earthquake and the recoverability of different recovery strategies are calculated. The model of the post-earthquake recovery process is proposed for quantitatively evaluating the recovery stratigies. The resilience is included in the evaluation framework of the seismic performance of the urban bridge system, and the post-earthquake recoverability evaluation framework of the urban bridge system is proposed so that decision makers with different risk-bearing capabilities can make decisions on different recovery processes. The post-earthquake economic loss, resiliency and pre-earthquake repair/reconstruction cost are used in conjunction with the multi-objective optimization algorithm, NSGA-II, to seek a pre-earthquake resilience improvement strategy for the help of selecting maintenance or resilience improvement measures. The calculation of the proposed method is given as an example, which provides new ideas for improving the seismic resiliency of urban bridge system.
A METHOD TO SIMULATE GROUND MOTION BASED ON PCA AND PSO INTELLIGENT ALGORITHMS—A CASE STUDY OF MODERATE MAGNITUDE EARTHQUAKES IN WESTERN CHINA
Jin-jun HU, Hui ZHANG, Chao-yue JIN, Zhong-wei WANG, Lei HU
2021, 38(3): 159-168.   doi: 10.6052/j.issn.1000-4750.2020.05.0293
[Abstract](50) [FullText HTML](24) [PDF 10846KB](20)
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The numerical simulation method of ground motion can provide ground motion input for seismic hazard analysis and seismic design of structures. Due to the uncertainties associated with ground motion simulation parameters and the limitations of simulation technology, the simulated ground motions may be quite different from the actual ground motions of the target area. With the increased number of observed regional strong ground motions, it is meaningful to integrate the measured ground motion characteristics into the simulated ground motions to reflect the local characteristics of ground motion. But at present, there is no synthetic ground motion method considering the characteristics of ground motion in the target area. To solve this problem, the ground motion time history is synthesized by machine learning method combined with the actual observed ground motion in the target region. The principal component analysis algorithm is applied to extract the mother waves which represent the characteristics of the ground motion from the huge target ground motion database; the reasonable prediction equation is selected to predict the response spectrum; then the improved particle swarm optimization algorithm is applied to quickly solve the combination coefficient of the mother waves of the ground motion. Thus, the weighted new response spectrum matches that from the prediction equation, and the synthetic time history of ground motion not only meets the results of seismic hazard analysis, but also conforms to the characteristics of the local ground motion. Based on the method proposed in this paper, the feasibility and effectiveness of the method are verified by using the strong motions in Sichuan of China, which provides a new idea and method for the synthesis of ground motions considering the characteristics of regional ground motions.
EXPERIMENTAL STUDY ON FRACTAL CHARACTERISTICS OF STEAM FREE REACTIVE POWDER CONCRETE UNDER IMPACT LOAD
Lei XIE, Qing-hua LI, Shi-lang XU
2021, 38(3): 169-180.   doi: 10.6052/j.issn.1000-4750.2020.05.0298
[Abstract](66) [FullText HTML](15) [PDF 1421KB](41)
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The peak strength and energy absorption of steam free reactive powder concrete (RPC) under 6 air pressures (0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 1.0 MPa, 1.1 MPa) are obtained by 80 mm split Hopkinson pressure bar (SHPB) test system. The mass distribution characteristics of fragments corresponding to strain rates ranging from nearly 90 \begin{document}${{\rm{s}}^{ - 1}}$\end{document}-290 \begin{document}${{\rm{s}}^{ - 1}}$\end{document}are analyzed by sieving test. The fractal dimension is used to characterize the fragmentation degree of specimens, and then the variation rule of peak strength and the energy absorption value with the fractal dimension are also explored and compared with other existing cementitious materials. The experimental results indicate that the average particle size of fragments decreases linearly with the increase of strain rate, the coarse particles gradually change into the fine particles while the mass of the medium particles do not change significantly. There exists an exponential relationship between the fractal dimension and the impact speed as well as strain rates. The peak stress and energy absorption value increase with the fractal dimension. The comparison shows that the crushing resistance capacity of steam free RPC is better than that of ordinary concrete and steel fiber reinforced concrete. The quantitative analysis of the relationship between fractal characteristics and mechanical properties, helps to gain more comprehensive evaluation of the investigated material.
DYNAMIC COUPLING MODEL OF BALLASTLESS TRACK-VEHICLE CONSIDERING THE BASE STRUCTURAL DAMAGE AND ITS SOLUTION
Yao SHU, Zhong-cheng JIANG, Jun ZHANG, Bo ZHANG, Guo-yun LIU, Xin-wen YANG
2021, 38(3): 181-191, 213.   doi: 10.6052/j.issn.1000-4750.2020.05.0305
[Abstract](84) [FullText HTML](14) [PDF 1468KB](28)
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To explore the interaction mechanism between the damage to the ballastless track structure and the dynamic interaction of the vehicle and track, a dynamic coupling model of ballastless track-vehicle involving structural damage was established based on the classical theory of vehicle-track coupling dynamics. The damage effect of the ballastless track structure was considered by using the elastic damage constitutive model of concrete. The vehicle was simplified as a multi-body system. The random track irregularity was assumed to recur in a period of the length of a single car. Hertz nonlinear contact was used to transfer the vertical coupling force between the vehicle system and the damaged ballastless track system. To accelerate the solving convergence rate of the dynamic model including material nonlinearity and contact nonlinearity, the implicit dynamic prediction-correction algorithm and the cross iteration of the track-vehicle system were used. The solving method realized a fast and implicit solution of the dynamic vertical coupling model of vehicle and damaged ballastless track.
WIND TUNNEL TEST ON TRI-COMPONENT FORCE COEFFICIENTS OF THE TRAIN-BRIDGE SYSTEM FOR A LONG-SPAN RAIL-CUM-ROAD CABLE-STAYED TRUSS BRIDGE
Wei-wei GUO, Bao-shuo CAI, Ya-feng LOU, Hui-bin ZHANG
2021, 38(3): 192-201.   doi: 10.6052/j.issn.1000-4750.2020.05.0306
[Abstract](186) [FullText HTML](28) [PDF 1416KB](23)
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To investigate the aerodynamic characteristics of train-bridge systems in a complex traffic condition, a section model wind tunnel test was carried out for a long-span rail-cum-road cable-stayed truss bridge. The tri-component forces on the train-bridge system were measured under different angles of attack when a single train, two trains or three trains passed. The effects of the track positions, bridge towers, road traffic flows, meeting of the trains on the tri-component coefficients of the vehicle and the truss were studied. The results show that when a train moves from the windward track to the leeward, the drag coefficients of the vehicle and the truss gradually decrease, while the lift coefficient of the vehicle and the moment coefficient of the truss reach the maximum on the leeward track. As a train passes through the tower, the average surface wind pressure of the shielded vehicle is significantly reduced, and the shielding effect is most obvious when it is on the windward track. However, the surface wind pressure near the tower edges remarkably fluctuates. When two trains meet on the bridge, the drag and lift coefficients of the vehicle increase with the meeting spacing. When three trains meet on the bridge, the drag and lift coefficients of the vehicles behind the windward train significantly decrease. The middle train has the smallest lift coefficient and a negative drag coefficient. As the number of trains on the bridge increases, the drag and lift coefficients of the truss gradually increase, while the moment coefficient remains almost the same.
RESEARCH ON DYNAMIC SPLITTING-TENSILE PROPERTIES OF CONCRETES WITH DIFFERENT STRENGTH AT HIGH TEMPERATURE
Long MENG, Rui-yuan HUANG, Dong JIANG, Kai-tao XIAO, Ping LI
2021, 38(3): 202-213.   doi: 10.6052/j.issn.1000-4750.2020.05.0310
[Abstract](62) [FullText HTML](23) [PDF 1753KB](12)
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The large-diameter split Hopkinson pressure bar (SHPB) device and heating device were used to perform dynamic splitting-tensile experiments on three concrete materials with different strengths (C20, C45 and C70) at different temperatures (20 ℃, 200 ℃ and 400 ℃). The dynamic splitting strengths and corresponding failure patterns of concrete materials under the coupling effect of temperature and stress rate are obtained. The results show that the dynamic splitting strength of concrete material increases with the stress rate, but when the stress rates are similar, the dynamic splitting strength decreases significantly as the temperature increases. On this basis, the equations describing the relationship between the dynamic splitting strength and the stress rate of concrete materials at different temperatures are given, and the related material parameters are determined. Comparing the dynamic splitting strength of concrete materials under the coupling effect of stress rate and temperature, it is found that the temperature sensitivity of dynamic splitting strength decreases as the stress rate increases, and gradually decreases with the concrete material strength, but the stress rate sensitivity of dynamic splitting strength increases with the temperature.
EXPERIMENTAL STUDY ON SEISMIC BEHAVIOR OF STEEL PLATE SHEAR WALLS WITH DIAGONAL CHANNEL STIFFENERS
Zai-gen MU, Yu-qing YANG
2021, 38(3): 214-227, 238.   doi: 10.6052/j.issn.1000-4750.2020.05.0312
[Abstract](42) [FullText HTML](11) [PDF 2792KB](18)
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In order to study the diagonal channel stiffened steel plate shear wall (SPSW) with a large span-to-height ratio, three 1/3-scaled SPSW specimens were tested under cyclic quasi-static loading. One of the specimens was spliced SPSW without diagonal channel stiffeners and the other two were spliced SPSWs with diagonal channel stiffeners. The experimental results show that SPSWs have good energy dissipation capacities, and the hysteretic curves of the diagonally stiffened SPSWs are plump spindle-shaped. The closed section formed by the channel stiffener and the plate avoids the torsion of the stiffener during the loading process. Channel stiffeners can increase the elastic buckling load and limit the out-of-plane deformation of the infill plate in the elastic stage. Moreover, diagonal stiffeners improve the bearing capacity of the specimen in elastoplastic stage. The formulas for calculating the shear force, axial force and bending moment of the frame column are derived. The results show that the axial force and shear force of the columns are greatly affected by the diagonal channel stiffeners, thus the supporting effect of the stiffener should be considered in the design.
WIND-INDUCED FAILURE PROCESS OF RC HYPERBOLIC COOLING TOWERS CONSIDERING THE MATERIAL NONLINEARITY
Jun-feng ZHANG, Hao PEI, Bing ZHU, Qing-shuai LIU
2021, 38(3): 228-238.   doi: 10.6052/j.issn.1000-4750.2020.05.0324
[Abstract](32) [FullText HTML](9) [PDF 1684KB](14)
Abstract:
To investigate the ultimate wind load and wind-induced failure process of cooling towers, a hyperbolic cooling tower was taken as an example in ABAQUS. The tower shell was modelled by layered shell elements, including the concrete and reinforcement. Based on linear and nonlinear verification calculation, the smeared crack model and bilinear model were used to represent the nonlinear behavior of the concrete and reinforcement, respectively. The failure process under the load combination of gravity and wind loads (Load Case Ⅰ) and the load combination of gravity, winter temperature and wind loads (Load Case Ⅱ) were analyzed. It was shown that when the wind load factor λ was 1.384 for Load Case Ⅰ, the circumferential cracks caused by meridian forces were initiated at hs/Hs=0.37 of the windward meridian and went through the shell. Then they continuously expanded along the circumferential direction and the meridian cracks inside the windward and outside the sideward were also caused by circumferential moment. In this process, the stress of steel at the cracks increased quickly, the load displacement curves exhibited nonlinearity, and the displacement at the windward and sideward quickly increased. There was also significant redistribution of the internal forces at these areas. The cooling tower failed as the successive concrete cracking and the yielding of the double reinforcement in the throat region when the ultimate wind load λ was 2.007. For Load Case Ⅱ, the meridian cracks first appeared at the upper area of the sideward at λ=1.0 because of the temperature effect, with a slightly greater degree than that of Load Case Ⅰ. However, the load displacement curves were almost the same for the two load cases because the effect of temperature was limited. The most significant cracking was still circumferential cracking in the windward. The failure of the structure was also controlled by the wind load, with an ultimate load factor λ of 1.842.
MECHANICAL ENGINEERING
THE DUCTILE FRACTURE CRITERION OF STAINLESS-STEEL TUBES IN THE SHEARING PROCESS BASED ON MODIFIED GTN MODEL
Jian-peng DONG, Shi-long WANG, Jie ZHOU, Bo YANG, Chi MA
2021, 38(3): 239-247.   doi: 10.6052/j.issn.1000-4750.2020.05.0303
[Abstract](54) [FullText HTML](10) [PDF 1585KB](8)
Abstract:
To improve the defect that the modified Gurson-Tvergaard-Needleman model (modified GTN model) cannot accurately simulate the shearing process of stainless-steel tubes, a displacement-related damage function is constructed as a new fracture criterion based on the original model. A VUMAT user subroutine of the modified model is developed in ABAQUS using the implicit backward Euler stress updating algorithm. A shear experiment of SUS304 stainless-steel tubes was carried out, and the accuracy and validity of the proposed method was verified by comparing the experimental and simulated results.
OTHER ENGINEERING DISCIPLINES
RESEARCH ON SIMPLY SUPPORTED BEAM -TRACK INTERACTION AND REASONABLE GAP POSITION OF RACK RAILWAY
Qian ZHANG, Xiao-pei CAI, Xiang-hui CAI, Min ZHANG
2021, 38(3): 248-256.   doi: 10.6052/j.issn.1000-4750.2020.04.0269
[Abstract](96) [FullText HTML](17) [PDF 3150KB](15)
Abstract:
The beam-track interaction of rack railway on a simply supported beam bridge has an important impact on vehicle safety and structural stability. Based on the finite element theory, a space-coupling calculation model for the rack (rail) -sleeper-beam-pier is established. The beam-rail interaction of rack railway on a simply supported beam bridge under different loads is analyzed. The results show that the beam-track interaction of rack railway on a simply supported beam bridge is stronger than that of a continuous welded rail (CWR) on bridge. Under the longitudinal train load, the rail force, beam rail relative displacement, longitudinal force and displacement of pier top are 40% larger than those of the CWR on bridge. It is recommended to strengthen the restraint between track foundation and beam to increase the longitudinal resistance and prevent the crawling of the track under longitudinal force. The maximum stress of rack is less than its allowable stress so that the rack strength is not used as a control factor for structural design. It is recommended that the position of rack gap be staggered from the beam gap to effectively prevent the rack gap from changing too much.

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