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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. 7, Publish Date: 2022-07-01
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2022, 39(7): .  
[Abstract](31) [FullText HTML](6) [PDF 1550KB](14)
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METHODOLOGIES
FINITE ELEMENT MODEL UPDATING METHOD BASED ON IMPROVED FIREFLY ALGORITHM
LIU Gang, CHEN Qi, LEI Zhen-bo, XIONG Jun
2022, 39(7): 1-9.   doi: 10.6052/j.issn.1000-4750.2021.04.0271
[Abstract](151) [FullText HTML](56) [PDF 5437KB](58)
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To solve the problems of slow convergence, of the low accuracy and of easily falling into local optimal solution of the standard firefly algorithm, an improved firefly algorithm with parameter adaptive strategy is proposed, and a finite element model updating method based on this improved firefly algorithm is established. An alternate generation random attraction factor is introduced to expand a search path, thus the ergodicity of the standard algorithm is improved, and result will no longer trapped in the local optimum. Furthermore, the adaptive step size factor is developed to reduce the random search range gradually with iteration in the updating process, so as to speed the convergence. The calculation results of single peak and multi peak test functions show that the improved algorithm significantly improves the convergence rate and accuracy. The numerical example of simply supported beam and the finite element model modification results of a real continuous rigid frame bridge show that: the maximum error of parameters of simply supported beam is reduced from 66.7% to 1.08% after modification, and the maximum frequency error of the continuous rigid frame bridge is reduced from 14.47% to 3.25%. The proposed method has good updating accuracy and is suitable for finite element model modification of large and complex structures.
A NUMERICAL EQUIVALENT INCLUSION METHOD FOR DETERMINING THE INTERACTION ENERGY BETWEEN INHOMOGENEITIES AND DISLOCATIONS
LI Pu, ZHU Kai, HOU Jia-hui, XIE Dong-dong, QIAN Hou-peng, JIN Xiao-qing
2022, 39(7): 10-18.   doi: 10.6052/j.issn.1000-4750.2021.03.0229
[Abstract](111) [FullText HTML](39) [PDF 5262KB](44)
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The mechanical properties and service life of materials may be significantly influenced by the interaction between inhomogeneities and dislocations in engineering structures. Previous analytical studies on inhomogeneity-dislocation interactions have been concerned primarily on some special inhomogeneity shapes (e.g. circle and ellipse). On the other hand, the involved singularity issue in dislocation studies is challenging, even intractable for commercial finite element software. Using the numerical equivalent inclusion method (NEIM) in conjunction with the Fast Fourier Transforms technique, this work presents an effective computational scheme for evaluating the interaction energy between an edge dislocation and inhomogeneities. The proposed computational method may successfully circumvent the numerical singularity. The results of norm analyses on relative errors demonstrate that the stress disturbance field caused by the impurity has a great influence on the final solutions, especially when the dislocation is located in the neighborhood of the inhomogeneity. The proposed method in this work shows excellent numerical convergence and stability, and appears to be convenient and efficient for handling arbitrarily shaped inhomogeneities interacting with an edge dislocation.
CIVIL ENGINEERING
EXPERIMENTAL AND NUMERICAL INVESTIGATIONS ON THE FLEXURAL BEHAVIOR OF STEEL-UHPC COMPOSITE SLABS WITH PERFOBOND RIB SHEAR CONNECTORS
ZHOU Min, XIAO Jing-lin, YANG Teng-yu, NIE Jian-guo, FAN Jian-sheng
2022, 39(7): 19-29.   doi: 10.6052/j.issn.1000-4750.2021.03.0239
[Abstract](292) [FullText HTML](124) [PDF 6059KB](68)
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A new type of steel-ultra-high performance concrete (UHPC) composite slab with perfobond rib shear connectors (PBL shear connectors) is studied, which can be used as large-span bridge decks and floors in buildings. According to the deck system of an ultra-long-span composite cable-stayed bridge, full-scale tests on three steel-UHPC composite slabs (SUCS) and a steel-C60 composite slab (SCCS) were conducted. The influence of the number and type of shear connectors were investigated. The experimental results demonstrate that, subjected to concentrated load, typical flexural failure of SUCS occurred while punching failure of SCCS occurred; that the SUCS possessed much higher ultimate capacity, rigidity and ductility than the SCCS with the same thickness did; that the specimen with sufficient perfobond rib shear connectors exhibited the best mechanical performance among the three SUCSs. Elaborate finite element models of the SUCSs were established in ABAQUS, which can reproduce the load-deflection curves obtained from the tests. Parametric study is conducted adopting the established finite element models.
EXPERIMENTAL STUDY ON THE AXIAL BEHAVIOR OF GRID JOINTS AND SPLICES OF SUSPENDED CEILINGS
JIANG Huan-jun, WANG Yong, WU Chen
2022, 39(7): 30-38, 80.   doi: 10.6052/j.issn.1000-4750.2021.04.0264
[Abstract](209) [FullText HTML](49) [PDF 5303KB](33)
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Suspended ceiling system is a type of nonstructural component suffering significant damage during earthquakes. The failure of the ceiling grid joints and splices is one of the major reasons for the ceiling damage. A series of tests on main tee splices, main-cross tee joints and peripheral joints under axial monotonic and cyclic loadings were conducted. The failure modes, load-bearing capacity, deformation capacity, and hysteretic behavior of different joints and splices were investigated. The fragility curves of the joints and splices were established based on the test data. The test results indicate that the failure mode of the main tee splices is the pulling out of the splices, that the failure mode of the main-cross tee joints is the buckling of the joints, and that the failure mode of the peripheral joints is the pulling out of the joints. The types of peripheral joints and end grids have little effect on the failure modes and loading-bearing capacity of the peripheral joints. Seismic clips should be fixed with the ceiling perimeter using screws to improve the seismic capacity of the peripheral joints.
THE DESIGN OF INTER-STORY ISOLATED BUILDINGS BUILT ON TOP OF METRO DEPOTS
XIE Lin-lin, WANG Xin-yu, LI Ai-qun, MIAO Qi-song, GE Dong-dong, SUN Hai-lin
2022, 39(7): 39-48.   doi: 10.6052/j.issn.1000-4750.2021.03.0214
[Abstract](181) [FullText HTML](83) [PDF 5037KB](64)
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Inter-story isolation is an effective method to improve the seismic performance of buildings built on top of metro depots (i.e., large chassis). To identify the factors controlling the critical design indexes and guide the detailed design, 12 study cases were designed based on a real engineering project, which includes two inter-story isolated towers built on top of a metro depot. Among these cases, three schemes and four schemes were considered for the tower and isolation system, respectively. Based on a refined model, the influence of the stiffness ratio between the tower, the isolation system and the large chassis and the yield ratio of the isolation system on nine critical design indexes were analyzed. The design indexes include the horizontal seismic absorbing coefficient (β) under the design basis earthquake, maximum inter-story drift ratio (θmax) and maximum absolute floor acceleration (amax) under the maximum considered earthquake of towers and chassis, maximum displacement of isolation system (Dmax), maximum and minimum compressive stresses of the isolator under the maximum considered earthquake. Subsequently, the factors controlling each index were identified. For the tower, the stiffness and yield ratio of the isolation system are the controlling factors for the β and amax. The decrease of these two factors can achieve a good control effect, while the increase of the stiffness of the tower can control β and amax to a certain extent. The increase of the stiffness of the tower and the decease of the stiffness and the yield ratio can control θmax to a certain extent, but such a control effect tends to stabilize when these two factors reach a certain extent. For the chassis, the schemes of the tower and isolation system has little impact on the design indexes. For the isolation system, the controlling factors for Dmax are the stiffness and yield ratio of the isolation system. The decrease of these factors leads to a significant increase of Dmax. The stiffness of the tower is the controlling factor for the maximum compressive stress of the isolators because the gravity increases with the stiffness. The increase of the stiffness of the tower and the decrease of the stiffness of the isolation system can significantly control the tensile stress of the isolators, and the control effect caused by the increase of the stiffness of two is more significant. The results provide a reference for the seismic performance control and design of inter-story isolated buildings built on top of metro depots.
HYSTERESIS MODEL AND EXPERIMENTAL INVESTIGATION OF ASSEMBLED SELF-CENTERING BUCKLING-RESTRAINED BRACES
JIN Shuang-shuang, LI Ying-kai, ZHOU Jian-ting, DU Ke, BAI Jiu-lin
2022, 39(7): 49-57.   doi: 10.6052/j.issn.1000-4750.2021.03.0218
[Abstract](182) [FullText HTML](59) [PDF 7210KB](50)
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To reduce the large residual deformation of buckling-restrained braces after strong earthquake, and facilitate structural repair, an assembled self-centering buckling restrained brace with combined disc springs (SC-BRB) is invented. The characteristics of the hysteretic curve can be effectively controlled by the yield force of the energy dissipation system and the pre-pressure of the self-centering system. The construction and mechanism of the novel SC-BRB were described, and the theoretical hysteretic model under cyclic loading was derived. Three different types of SC-BRBs were designed and fabricated. The residual displacement and hysteretic energy dissipation were analyzed through the quasi-static tests, and self-centering effect and failure mode were discussed. The experimental results show that the SC-BRB has flag shaped hysteretic curve and stable energy dissipation capacity. The combined disc spring self-centering system greatly reduces the residual deformation. The theoretical hysteretic model proposed in this paper agrees well with the experimental results. The novel SC-BRB is an effective self-centering damper with stable energy dissipation capacity.
PERFORMANCE STUDY OF MAIN STRUCTURE AND GLASS CURTAIN WALL OF HIGH-RISE BUILDING UNDER COMBINED ACTION OF WIND AND EARTHQUAKE
REN Chong-cui, LI Jian-hui, TANG Yi, LIU Jun-jin, YAN Ya-lin, HAO Wei, SUN Chao
2022, 39(7): 58-69.   doi: 10.6052/j.issn.1000-4750.2021.03.0223
[Abstract](244) [FullText HTML](125) [PDF 10868KB](41)
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The performance and interaction between main structure and glass curtain wall under the individual and combined actions of wind and earthquake was studied. Glass curtain wall is added to a 98 m high frame-core wall according to the standard. Three groups of 3D data are selected from seismic records, and the wind pressure data of different return periods are obtained through a 1∶440 scale wind tunnel model test. Then the effects of individual and combined actions of wind and earthquake on the behavior of main structure and glass curtain wall are studied by the dynamic elastoplastic analysis method. The results show that main structure has a greater impact on glass curtain wall than on main structure. Whether under the individual or combined actions of wind and earthquake, the story drift of main structure was larger than glass wall itself. Under the design and super-intensity earthquake loadings, with the increase of the effective load, the response of the main structure and the damage degree of the glass curtain wall are increasing, and the growth of structural deformation are greater than base shear. Under wind load, glass curtain wall was not fail, main structure was in good stage, and the base shear, top displacement and max story drift increased linearly. Compared with rare earthquake acting alone, when 1.1 times 100-year return period wind pressure is combined, torsional effect appears, and story drift ratio increased from 1.0 to 1.3. The nonlinear effect of main structure and glass curtain wall is greater than the sum of wind and earthquake. The top displacement and the max story drift were 121% and 106% of the sum of wind and earthquake. Under rare earthquake or combined with wind pressure, the failure of glass curtain wall is more likely to happen on the side parallel to earthquake main direction.
STUDY ON FATIGUE RHEOLOGICAL DAMAGE MODEL OF SILTSTONE UNDER CYCLIC LOADING
MIAO Sheng-jun, YANG Peng-jin, WANG Hui, LIANG Ming-chun, WANG Ya-xin
2022, 39(7): 70-80.   doi: 10.6052/j.issn.1000-4750.2021.03.0235
[Abstract](83) [FullText HTML](60) [PDF 8554KB](26)
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The fatigue test of siltstone under cyclic loading is carried out, aiming at the problem that the deformation law and the damage evolution characteristics of rock under cyclic loading cannot be described rigorously by the existing rheological models. According to the analysis of the test results, a damage variable established by Kachanov's creep damage theory is introduced into a viscoplastic element with strain trigger and stress threshold, then a new rheological constitutive model under cyclic loading is constructed through series with Burgers model and the viscoplastic element. In the meanwhile, the sine wave cyclic load stress function is used to replace the constant stress in the rheological differential constitutive equation. The one-dimensional and three-dimensional differential damage constitutive equation of rock is inferred by the integral method, and then the viscoelastic plastic rheological damage equation is inferred by a superposition principle. The parameters of the new rheological model are derived by fitted fatigue deformation curves of siltstone. The applicability verification shows that: the new rheological model can not only accurately reflect the attenuation and steady-state rheological deformation stage of siltstone, but also effectively describe the accelerated rheological stage when the upper limit of cyclic load is higher than the fatigue strength. Finally, the critical damage threshold and instability criterion of accelerated rheology are proposed, and the prediction methods of the start time, duration and fatigue life of accelerated rheology are developed. The model has certain theoretical significance for the long-term stability prediction of rock engineering.
SEISMIC ANALYSIS OF STEEL-CONCRETE COMPOSITE FRAME STRUCTURES BASED ON THE ULTIMATE BALANCE THEORY
WANG Yu-liang, ZHAO Min, HAO Ji-ping, XUE Qiang, JIANG Wei-shan
2022, 39(7): 81-88.   doi: 10.6052/j.issn.1000-4750.2021.03.0238
[Abstract](129) [FullText HTML](58) [PDF 4821KB](35)
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A simplified analysis method of steel-concrete composite frame structures under rare earthquake action is established based on the ultimate balance theory. The failure mechanism of composite frames is determined by theoretical analysis and experimental phenomena. Based on the ultimate balance theory and according to the distribution law of the deformation and internal force when the structure reaches the ultimate strength under earthquake action, the seismic strength of the composite frames is calculated when the top horizontal displacement of the frame is equal to H/50, H/40 and the lateral displacement corresponding to the limit load. The calculation results agree well with the low cyclic loading test results of 19 composite frames at home and abroad. It shows that the method can effectively predict the seismic strength of composite frame structures under rare earthquakes. A simplified method is proposed to control the deformation capacity and seismic strength of the composite frame at the same time to make the structure meet the seismic requirement under rare earthquakes.
PARAMETER IDENTIFICATION OF BROKEN LINE CONSTITUTIVE MODEL BASED ON SIGMA POINT GLOBAL ITERATION PARAMETRIC KALMAN FILTER
YANG Ji-peng, XIA Ye, SUN Li-min
2022, 39(7): 89-98.   doi: 10.6052/j.issn.1000-4750.2021.04.0242
[Abstract](105) [FullText HTML](34) [PDF 5357KB](34)
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The broken line constitutive model has few control parameters and clear physical meaning, but its mathematical expression is complex. Thusly, it is difficult to identify. Aiming at the parameter identification of the broken line constitutive model, a global iteration parametric Kalman filter algorithm based on Sigma point transform is proposed. The method proposed takes the parameters to be identified as the state vector to reduce the dimension of the state vector and the amount of calculation. Based on Sigma point Kalman filter, the Jacobian matrix is avoided, and the parameter identification of a discontinuous function constitutive model is realized. By setting the objective function for a global iteration, the optimal solution can be obtained. Because the next time response of the nonlinear system is related to the historical path, the measurement update is calculated from the initial time to the current time. Finally, under seismic loading, the isolated bearing system is simplified as a single degree of freedom with a bilinear model, and the pier is simplified as a single degree of freedom with a Takeda model. According to the method proposed, the broken line constitutive model parameters are identified based on different sampling rules, such as unscented Kalman filter (UKF), cubature Kalman filter (CKF) and spherical simplex-radial cubature quadrature Kalman filter (SSRCQKF). The results demonstrate that the method proposed can accurately identify the nonlinear parameters and has strong robustness. The convergence process and results of different filters are also different.
THE SEISMIC RESPONSE OF WATER SUPPLY NETWORKS IN RANDOM SEISMIC FIELDS BASED ON PHYSICAL MECHANISMS
MIAO Hui-quan, LI Jie
2022, 39(7): 99-108, 204.   doi: 10.6052/j.issn.1000-4750.2021.04.0243
[Abstract](383) [FullText HTML](148) [PDF 5668KB](48)
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Water supply networks are important components of lifeline engineering. Because of the influence of random earthquake motion fields, their seismic response and function also have obvious randomness. The influence of the complicated topological structure of water supply networks cannot be considered by the traditional seismic response analysis of buried pipelines. The traditional method is also difficult to be applied to analyze the random vibration of the nonlinear system. The physical response of pipelines has not been implemented into the functional analysis of water supply networks. To solve these three problems, this paper modifies the random physical model of seismic ground motion fields on the local engineering site, introduces a finite element method of buried pipe networks, combines the probability density evolution method, and realizes the random seismic response analysis of water supply networks. Furthermore, the transient flow theory is utilized, and the random seismic function analysis of water supply networks is completed. It lays foundation for the seismic reliability evaluation of water supply networks.
RESEARCH ON WIND PRESSURE FIELD OF LARGE-SPAN FLAT ROOF BASED ON DYNAMIC MODE DECOMPOSITION
FENG Shuai, XIE Zhuang-ning
2022, 39(7): 109-119.   doi: 10.6052/j.issn.1000-4750.2021.04.0247
[Abstract](137) [FullText HTML](87) [PDF 10626KB](53)
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The dynamic mode decomposition (DMD) method improved by embedded dimension and the proper orthogonal decomposition (POD) method are used to analyze the random wind pressure field of a large-span flat roof. The results show that the fuzzy dynamic features hidden in the wind tunnel test data can be discovered by using the Takens embedding theorem to increase the spatial dimension of the original snapshot matrix. The modal distributions of POD and DMD can reflect the main characteristics of typical vortices in a fluctuating pressure field. However, each mode of POD contains the information of multiple frequencies, which to a certain extent makes the mode of POD become the fluctuating coupling of multiple frequency bands. The mode decomposed by DMD method is a single-frequency mode and the stability of each mode can be obtained. At the same proportion, POD modes contain more energy than DMD modes. But when the same proportion of modes are used to reconstruct the fluctuating wind pressure field, the reconstruction results of DMD method can better describe and fit the local characteristics of the original fluctuating pressure field than those of POD method. This is because DMD method reconstructs the pressure field directly, while POD method mainly reconstructs the energy field. Therefore, the DMD method has more advantages in revealing the spatial-temporal evolution characteristics of a random wind pressure field.
STUDY ON SHEAR BEHAVIOR OF WEB-EMBEDDED U-SHAPED STEEL-CONCRETE COMPOSITE BEAM
YANG Yuan-long, SUN Tian-pei, HAN Jin-jun
2022, 39(7): 120-136.   doi: 10.6052/j.issn.1000-4750.2021.04.0251
[Abstract](126) [FullText HTML](27) [PDF 7144KB](41)
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The U-shaped steel-concrete composite beam has the advantages of high bearing capacity and good ductility, and its assembling construction technology also conforms to the current trend of assembly-type building structures. In this paper, nine web-embedded U-shaped steel-concrete composite beams (WUSCB) were designed with embedded connectors. The influence of parameters such as shear span ratio, concrete slab width, connector spacing and inclination angle, diameter of bottom longitudinal rebar, configuration of bottom studs and stirrups, depth-to-thickness ratio of steel web were considered. The specimen failure modes were analyzed and summarized. The mechanical properties such as shear capacity and ductility were analyzed based on the shear-deflection curves. The shear transfer mechanism of U-shaped steel web was studied based on the equivalent stress distribution in shear span. By using finite element software ABAQUS, a finite element model of WUSCB specimen was established and verified. Employing the finite element model, the four parameters including shear span ratio, concrete slab width, web depth-to-thickness ratio and bottom rebar ratio were analyzed. Based on the test results and finite element parameter analysis results, a shear bearing capacity design method of WUSCB was proposed. The method takes into account the contribution of concrete, U-shaped steel webs and bottom longitudinal reinforcements, and can be used to accurately predict the shear bearing capacity of WUSCB.
CONSTRUCTION OF FREE FIELDS IN BEDROCK-OVERBURDEN SITE SPACES BASED ON DESIGNED GROUND MOTIONS
HAN Lu, SONG Zhi-qiang, WANG Fei, LIU Yun-he
2022, 39(7): 137-146.   doi: 10.6052/j.issn.1000-4750.2021.04.0255
[Abstract](149) [FullText HTML](74) [PDF 5385KB](37)
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The propagation, transmission and reflection characteristics of seismic waves in overburden sites are extremely complex. The reasonable construction and expression of the free field of bedrock-overburden sites is the key to generating nonuniform ground motion input. The expressions between two directional ground motions at any point in an overburden site space and the incident SV and P waves are established. The time history and incident angle of the incident SV and P waves can be obtained from the measured ground motions in the horizontal and vertical directions of the ground surface. By considering the multiple reflections at the interface and the amplitude attenuation caused by soil damping, the free field of the bedrock-overburden site space is constructed. The results of the comparison with the measured array records at La Cienega site show that the simulated values of the two directional ground motions at different depths are consistent with the measured records. The time histories of the horizontal and vertical ground motions at any point in the free field are inconsistent. The spatial free field construction method proposed in this paper provides a basis for non-uniform ground motion input of overburden-dam systems.
DAMPING THEORY AND EXPERIMENTAL STUDY ON GRADED YIELDING METAL TUBE DAMPERS
WU Shan, HE Hao-xiang, LAN Bing-ji, CHEN Jian-wei
2022, 39(7): 147-157.   doi: 10.6052/j.issn.1000-4750.2021.04.0261
[Abstract](120) [FullText HTML](32) [PDF 6616KB](45)
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Conventional metal yielding dampers are usually designed only for medium and large earthquakes, which are difficult to dissipate energy under minor earthquakes. It is also difficult to observe the practical state after an earthquake and is inconvenient to replace them. A new metal tube damper is proposed. The steel strips with different yielding properties can dissipate energy separately, thus exhibiting a graded yielding behavior. Considering the influence of the semi-rigid joints at both ends of the strips, the performance parameters calculation formulas of the damper are derived. Quasi-static tests of the damper were carried out to reveal its failure characteristics. Refined finite element simulation of the specimens is carried out. The graded yielding characteristics of the damper are further verified by the stress nephogram. The performance parameters obtained from theoretical calculation, experiment and finite element simulation are compared. The results show that the damper could effectively achieve the design goal of graded yielding and has good deformation capacity and energy dissipation capacity. The accuracy of the performance parameter calculation formulas is high. The performance parameters of the damper obtained by the theoretical calculation and the finite element simulation are in good agreement with the experimental results. The rationality and accuracy of the refined finite element model are verified.
RESPONSE ANALYSIS OF FRAME STRUCTURES CONSIDERING THE NONLINEAR BEHAVIOR OF TWO TYPES OF PRECAST JOINTS
XU Wei-zhi, WANG Shu-guang, BEN Chi, SONG Bao-xi, LI Wei-wei
2022, 39(7): 158-169.   doi: 10.6052/j.issn.1000-4750.2021.04.0270
[Abstract](78) [FullText HTML](23) [PDF 6131KB](24)
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Precast concrete frame structures are widely used in China. At present, it is mainly designed and calculated according to the principle of equivalent cast-in-place. However, the difference in structural response caused by different nodal nonlinear behavior cannot be ignored. Considers the difference between the nonlinear behavior of two types of typical fabricated joints and cast-in-place joints and studies the influence of these differences on the seismic response of frame structures. For emulated connection joints, the force mechanism of the joints is analyzed based on their structural forms, and the differences between the cast-in-situ joint and the emulated joint in the test phenomenon is explained accordingly. Two types of non-dimensional hysteretic models of the joints are proposed. Existing test results verify the rationality of the proposed model. For non-emulated joints, the mechanical behavior of an unbonded post-tensioned prestressed hybrid precast concrete beam-column connection is systematically studied. The nonlinear dynamic time history analysis method is adopted to reveal the differences between precast frames and cast-in-place frames in terms of structural displacement responses, of beam-column ductility requirements, and of residual deformations. The research results have practical reference value for the application of precast frame structures in areas of high seismic intensity.
ANALYSIS OF THE WHOLE-PROCESS MECHANICAL RESPONSE OF TUNNEL SURROUNDING ROCK UNDER THE EFFECT OF ANCHORAGE SYSTEM
SUN Zhen-yu, ZHANG Ding-li, LIU Dao-ping, HOU Yan-juan, LI Ao
2022, 39(7): 170-182.   doi: 10.6052/j.issn.1000-4750.2021.04.0274
[Abstract](189) [FullText HTML](72) [PDF 4869KB](46)
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The tunnel anchoring system is an important means to control the deformation of surrounding rock, whose scientific design lies in the full understanding of its mechanism. In this paper, the whole process of the response of tunnel surrounding rock with the action of the anchorage system is analyzed. Based on the space effect of the tunnel face, the displacement releases of surrounding rock at bolt and anchor cable installation and the effect of their relative lengths are considered. According to the relationship between the anchorage zone and the plastic zone of the interaction between the anchorage system and the surrounding rock, six mechanical analytical models of the whole process evolution mechanism of anchorage system are proposed and analyzed respectively. The solutions of tunnel deformation, plastic radius and stress field of surrounding rock under the action of anchoring system are obtained. The correctness and reliability of the proposed model are verified through a comparison with numerical simulations using typical examples. Furthermore, the deformation control effect of the anchorage system and its influencing factors are analyzed, and the respective tasks and objectives of rockbolts and anchor cables are defined. The safety reserve function of anchor cable is clarified, giving a new understanding of deformation control principle of anchorage system. The research results lay a theoretical foundation for the quantitative design of tunnel anchorage system and provide a new idea for the control of large deformation of tunnel surrounding rock.
FRACTURE TEST AND SIZE EFFECT ANALYSIS OF LOW-HEAT CEMENT FULLY-GRADED CONCRETE
GAO Xiao-feng, HU Yu, YANG Ning, WU Kun, LI Qing-bin
2022, 39(7): 183-193.   doi: 10.6052/j.issn.1000-4750.2021.04.0276
[Abstract](133) [FullText HTML](21) [PDF 4979KB](42)
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This paper analyzes the size effect of the fracture parameters of low-heat cement fully-graded concrete. Wedge-splitting specimens with effective heights of 0.75 m, 1.5 m, and 2.25 m were cast on the construction site of a dam project, and tests were carried out to obtain the stable double-K fracture parameters of low-heat cement fully-graded concrete. Based on the test results, theoretical methods were used to derive the size independent unstable and initiation toughness of fully-graded concrete, and to predict the maximum and initiation horizontal loads of a specimen with an arbitrary dimension. The study found that when the ratio of ligament height to the maximum aggregate dimension is greater than or equal to 6.0, the double-K fracture parameters tend to be stable. The size effect model and its evolution forms can be used to determine the size independent unstable and initiation toughness of fully-graded concrete, quantitatively to analyze the influence of strength and toughness on crack propagation, and by introducing an equivalent geometric parameter, the prediction equations for the maximum load and crack initiation horizontal load of arbitrary size specimens can be established respectively.
STUDY ON SEISMIC BEHAVIOR OF STEEL FRAME WITH CLADDING PANEL AND ENERGY DISSIPATING CONNECTIONS
CHONG Xun, ZHU Dong, JIANG Qing, HUANG Jun-qi, FENG Yu-long, SONG Lei
2022, 39(7): 194-204.   doi: 10.6052/j.issn.1000-4750.2021.04.0279
[Abstract](82) [FullText HTML](58) [PDF 6402KB](34)
Abstract:
An energy dissipating cladding panel connecting method for steel frames was proposed. In order to study the effect of this new kind of connecting method on the seismic behavior of the main structure, quasi-static cyclic tests were carried out on two steel frames with X- or U-shaped steel dampers as the energy dissipating connections and one bare steel frame counterpart. The quasi-static cyclic tests of the two kinds of dampers were carried out as well. The test results indicated that local buckling occurred on the X-shaped dampers during the fatigue loading stage, and the final failure was governed by the fracture of the core board; the U-shaped dampers only presented slight cracks in the fatigue loading stage and showed better fatigue performance; the hysteresis loops of the two kinds of dampers were plump and showed hardening stages, and the X-shaped damper showed a more obvious hardening effect owing to the membrane effect of the core board; the failure modes of the three steel frames were similar, and the damage mechanism of the steel frame was not altered by the cladding panels; cracks occurred on the cladding panel of GKJ-1 in the final loading stage due to the membrane effect of the X-shaped dampers, and the final failure mode of the specimen was governed by the broken of the connecting bolt between the cladding panel and the beam; no damage was observed in the U-shaped dampers and cladding panel of GKJ-2; the cladding panels with energy dissipating connections could increase the stiffness, strength and hysteresis energy of the steel frame.
EXPERIMENTAL STUDY ON HYSTERETIC PERFORMANCE OF SINGLE-SIDE YIELDING PRECAST CONCRETE BEAM-COLUMN CONNECTION WITH REPLACEABLE ENERGY DISSIPATION BARS
ZHU Yun-qing, WU Jing, TONG Chao, LIU Dong-sen, XIE Lu-qi
2022, 39(7): 205-216, 256.   doi: 10.6052/j.issn.1000-4750.2021.04.0280
[Abstract](175) [FullText HTML](69) [PDF 6250KB](48)
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A new type of coupler for connecting bars, non-slipping threaded sleeve assembly, is proposed, and based on this, replaceable energy dissipation connection is assembled. An axial low-cycle reversed loading test was carried out, indicating the reliability of load transfer and excellent energy dissipation performance. An innovative single-side yielding beam-column connection with replaceable energy dissipation bars (REDB-SYBC) is developed by placing the energy dissipation connection in the bottom of the beam end of the prefabricated concrete frame. The quasi-static test was carried out to evaluate the seismic behaviors of the connection, such as damage distribution, failure pattern, hysteretic characteristics, and energy dissipation capacity. The hysteretic curves of the specimens are stable and full without pinching, showing a good seismic performance. The experimental results show that: the single-side yielding deformation pattern of the REDB-SYBC connection minimizes the deformation of the adjacent floor slabs and gives full play to the advantage of energy dissipation capacity of connectors at beam bottom, and makes the main damage and failure occur on the energy dissipation bars. That realizes the design goal of damage concentration and the seismic design principle of “strong column and weak beam”. The energy dissipation bars can be replaced by the inner space of the non-slipping threaded sleeve assembly. The seismic behaviors of the repaired specimens are basically the same as those of the original specimens.
A STUDY ON FORMING MECHANISM OF SHEAR BANDS AND VISUAL SHEARING TESTS OF SAND
WANG Zi-han, ZHANG Ruo-yu, JING Xiao-kun, XIAO Cheng-zhi, HUANG Da
2022, 39(7): 217-226.   doi: 10.6052/j.issn.1000-4750.2021.04.0283
[Abstract](223) [FullText HTML](89) [PDF 5036KB](37)
Abstract:
By visual reformation on traditional shear instrument, and combining digital image deformation measurement technology, it studies the forming mechanism and expansion processes of shear bands of sand samples with different sizes in shearing tests. The effects of sample sizes on sand strength are concluded. With the typical sample size, the evolution laws of shear bands (especially for secondary shear bands) in different shearing courses and various normal stresses are summarized. And the force analyses of arch damage areas discovered in tests are carried out. The strength parameters of primary and secondary shear bands are compared. The results show that sample sizes have influences on strength parameters. When the ratios of long to short side are greater than 2, test results deviate from average. When the ratios of long to short side are greater than 4, serious errors are caused. The shear failure areas are not always developed along horizontal shearing gap. The upward arch secondary shear bands are gradually formed in middle and lower part of upper boxes, and shear failure areas are developed along the primary and secondary shear bands. The arch failure areas decrease with the increasing shear displacements and decreasing normal stresses. The normal and tangential stresses on secondary shear bands are larger than those on primary shear bands. The strength indexes of primary and secondary shear bands are basically the same, which indirectly proves the rationality of the existence of secondary shear bands.
SIZE EFFECT NUMERICAL ANALYSIS ON PURE TORSIONAL FAILURE OF RC COLUMNS
JIN Liu, ZHU Hua-jie, DU Xiu-li
2022, 39(7): 227-236.   doi: 10.6052/j.issn.1000-4750.2021.04.0288
[Abstract](109) [FullText HTML](27) [PDF 6146KB](44)
Abstract:
Under the action of earthquake, the reinforced concrete (RC) columns may subject to torsional moment, and the existence of torsion will change the failure mode of RC columns. In order to study the size effect of RC columns on pure torsional failure, a numerical model of RC columns on pure torsional failure was established by using the three-dimensional meso-scale numerical simulation method, considering the meso-heterogeneity of concrete and the bond-slip action between reinforcements and concrete. The influence of structural size, longitudinal reinforcement ratio, stirrup ratio and cross-sectional shape on torsional failure of RC columns was investigated. The results show that: the tested RC columns show brittle failure patterns, the nominal torsional strength presents obvious size effect; the longitudinal reinforcement presents little influence on the size effect; columns with square cross-section present stronger size effect than the ones with circular shape; stirrups can improve the torsional strength, while they would weaken the size effect on torsional strength. Finally, a prediction formula for nominal torsional strength in the full-size range was established by modifying Bažant’s size effect law.
STUDY ON INFLUENCES OF TYPHOON NON-STATIONARITY ON DYNAMIC RESPONSE OF OFFSHORE WIND TURBINE WITH STEEL LATTICE FLOATING FOUNDATION
YAN Bo-wen, ZHU Heng-li, HUANG Xu, ZHANG Hao, WANG Yu-hang, ZHOU Xu-hong, YANG You-fa
2022, 39(7): 237-246.   doi: 10.6052/j.issn.1000-4750.2021.09.0717
[Abstract](32) [FullText HTML](7) [PDF 7860KB](17)
Abstract:
This study proposed a new type of steel lattice floating foundation for offshore wind turbines, and investigated the motion and dynamic responses of the steel lattice floating foundation for the offshore wind turbine during the passage of typhoon winds. A new type of steel lattice floating foundation was initially designed, considering a 5 MW wind turbine proposed by National Renewable Energy Laboratory (NREL). The dynamic response characteristics of the floating foundation were analyzed by Blade Element Momentum (BEM) theory, potential flow theory and Morison equation under the coupled typhoon wind-wave loads, using Holland typhoon model and the field data of super-typhoon "Mangkhut" (1822). The results show that the dynamic responses of the steel lattice floating foundation were significantly affected by strong typhoon, which were predominantly greater than those under synoptic strong wind conditions and featured with apparent non-stationarity. The dynamic responses of the floating foundation were in a good correspondence with the trend of the non-stationary wind speed. When the wind direction constantly changed, a greater torque was resulted at the bottom of the wind turbine tower, and increased yaw motions were also observed. It proves the effects of non-stationary typhoon winds on the stability of steel lattice floating foundation are indispensable and provides a theoretic basis and analysis methodology for the safety evaluation of steel lattice floating foundation for offshore wind turbines under typhoon winds.
OTHER ENGINEERING DISCIPLINES
RESEARCH ON ANALYTICAL METHOD OF CIRCULAR CYLINDRICAL SCATTERED WAVE PRESSURE SUBJECTED TO UNDERWATER EXPLOSION
YAN Qiu-shi, ZHANG Zhi-jie, WANG Pi-guang, BAO Xin, LI Shu-tao
2022, 39(7): 247-256.   doi: 10.6052/j.issn.1000-4750.2021.04.0249
[Abstract](143) [FullText HTML](84) [PDF 5143KB](32)
Abstract:
In order to improve the anti-blast and protection design of offshore structures such as bridges and wharves, this paper proposes an efficient analytical method for calculating the circular cylindrical scattered wave pressure subjected to underwater explosion, aiming at the common cylindrical structures with constant cross-sections in offshore structures. Based on the theory of diffracted waves, this paper derives the time-domain solution of the scattered wave pressure of the cylindrical structure by the method of separation of variables in the cylindrical coordinate system according to the water body state equation and boundary conditions; The calculation accuracy of the scattered wave pressure time-domain solution proposed in this paper is verified by numerical simulation comparison. The numerical example shows that the calculation errors of the two methods are within the engineering allowable range. Based on the time-domain substructure analysis method that considers the compressibility of water, by comparing the analytical methods proposed in this paper without considering the compressibility of water, the influence of water compressibility on scattered wave pressure is analyzed.

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