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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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2023 No. 2, Publish Date: 2023-02-01
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2023, 40(2): .  
[Abstract](54) [FullText HTML](25) [PDF 1547KB](26)
Abstract:
OVERVIEWS
UNIFIED COMPUTATIONAL THEORY OF FRACTURE MECHANICS IN SHELL AND AIRCRAFT STRUCTURAL DESIGN
ZHUANG Zhuo, WANG Heng, NING Yu, WANG Xiang, LIU Zhan-li, ZHANG Zhi-nan
2023, 40(2): 1-7.   doi: 10.6052/j.issn.1000-4750.2022.06.ST02
[Abstract](107) [FullText HTML](11) [PDF 8441KB](74)
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The fracture mechanics theory and methodology have played an irreplaceable role in aircraft structure design. According to fracture criterion, it is divided into preventing and driving crack propagation. The crack arrest is to prevent aircraft structure from catastrophic failure, which is the last safety defense line; for example, the fracture arrested design for wing and fuselage of important structures, damage tolerance design for wide spread fatigue, and so on. The driving crack propagation is the key technology to realize quick separation of structures; for example, interstage separation of carrier rocket, separation between satellite and rocket, escape and life-saving of pilot and astronaut, and so on. The plate and shell are main structural forms of aircraft. There is an important scientific significance and engineering worth for investigating fracture mechanics in plate and shell. The authors have proposed the unified computational theory of fracture mechanics in shell and developed the corresponding extended finite element method. Based on the theory and method, the fracture propagation and arrest analysis are expressed in a large deformation curved shell. The successful applications are exhibited for designing wing monolithic structural component of domestic large airplane, Tianhe kernel cabin structure and opening canopy life-saving system of the advanced trainer.
METHODOLOGIES
RESEARCH ON EQUILIBRIUM AND CONFORMING THEORY OF THE FINITE ELEMENT METHOD IN ELASTICITY
FU Xiang-rong, CHEN Pu, SUN Shu-li, YUAN Ming-wu
2023, 40(2): 8-16.   doi: 10.6052/j.issn.1000-4750.2021.08.0647
[Abstract](141) [FullText HTML](36) [PDF 4355KB](64)
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Element formulations in finite element analysis may follow different approaches. A classification of elements in equilibrium and compatibility is presented. Analysis and comparison of some classic plane elements show that, non-conforming, conforming and super conforming elements can be constructed based on the compatibility theory, and analytical trial functions can be employed to help the construction of equilibrium elements. The researches of compatibility focus on the boundary conforming between elements, which conform bases of simplex conforming, non-simplex conforming, non-conforming and super conforming elements. The researches of equilibrium focus on the equilibrium principle in element or between elements, which emphasize high-precise completeness of analytical trial functions and weight functions. The benchmark tests show that although all kinds of elements have their own advantages and shortcomings, elements that satisfy both the equilibrium inside elements and the compatibility between elements deliver generally better performance.
DEEP LEARNING METHOD FOR FLOW FEATURE RECOGNITION BASED ON DIMENSIONLESS TIME HISTORY
ZHAN Qing-liang, GE Yao-jun, BAI Chun-jin
2023, 40(2): 17-24.   doi: 10.6052/j.issn.1000-4750.2021.08.0638
[Abstract](222) [FullText HTML](92) [PDF 5375KB](76)
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The characteristics of the flow field influence the flow-induced vibration state of structures, it thusly has a crucial significance to study the flow features around structures. However, in the case of the flow field with medium and high Reynolds numbers, the wake is highly complex, and it is not easy to extract and recognize complex features through traditional mathematical and physical methods. This paper proposes a deep learning method that uses the dimensionless time history of the flow variables to identify the flow features. The method eliminates the influence of different incoming flow speeds and only uses the time-varying features of the dimensionless time history for feature recognition, which improves the scope of the method. Two different flow time-history deep learning models are used to extract and identify the wakes of three types of prisms. Comparison results proved that unified time history maintains the critical features of wake caused by objects of different shapes. Furthermore, the unified time history can be used for the feature extraction of the flow field and improve the accuracy of the flow field feature extraction by the model. It is a feasible new method for flow field feature extraction.
CIVIL ENGINEERING
EXPERIMENTAL RESEARCH ON DISTORTIONAL BEHAVIOR OF COLD-FORMED THIN-WALLED Σ-SHAPED STEEL BUILT-UP SECTIONS UNDER ECCENTIRC COMPRESSION
HE Zi-qi, YANG Guang, ZHOU Xu-hong, PENG Sai-qing
2023, 40(2): 25-35.   doi: 10.6052/j.issn.1000-4750.2021.08.0626
[Abstract](66) [FullText HTML](21) [PDF 10727KB](15)
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To study the distortional buckling and interactive behavior of cold-formed steel composite sections with Σ-shaped web channels, and evaluate the applicability of current Chinese and North American codes, 22 members were designed and fabricated for compression-bending test. The main parameters including Σ-shaped stiffener, opening position, eccentric compression direction with respect to the strong & weak axis and the eccentricity are investigated to obtain the influence of each parameter on buckling behavior, failure mode and ultimate bearing capacity of the specimen. The test results indicate that all the specimens present distortional buckling or interaction buckling involving distortional mode; The stiffened-web can effectively prevent local buckling of the web; The holes in the web have slight effect on buckling mode; The eccentric compression locations with respect to the strong & weak axis have a significant effect on buckling behaviour of the specimen. Comparing the experimental results with the calculated bearing capacity results according to current Chinese and North American specifications, including GB 50018−2002, JGJ/T 421−2018 and NAS 100−2016, it is found that the calculations with respect to the strong axis adopting Chinese and North American specifications are all conservative; When the specimens are under eccentric compression with respect to the weak axis, the calculated results employing GB 50018−2002 and NAS 100−2016 are both conservative, while the ratio of the test results to the calculation results of JGJ/T 421−2018 averages 1.64, which is too conservative. Therefore, it is proposed that the bearing capacity of eccentric compression with respect to the weak axis should be calculated in accordance with the overall built-up cross-section when the two Σ-shaped channels of composite column work well together.
EXPERIMENTAL STUDY ON RESIDUAL STRESS OF Q235 STEEL WALLBOARD-Q460 HIGH STRENGTH STEEL COLUMN STRUCTURAL SYSTEM
GUO Da-peng, ZHOU Chao, WANG Deng-feng, WANG Yuan-qing
2023, 40(2): 36-46, 55.   doi: 10.6052/j.issn.1000-4750.2021.08.0630
[Abstract](172) [FullText HTML](58) [PDF 5341KB](31)
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The wallboard-column structural system on the side of box-type steel structures plays a main bearing role. The residual stress distribution of the high strength steel column supported by stressed skin wallboards is affected by the welding with wallboards, as a result, it is quite different from the welded H-section of an individually working member. In order to investigate the residual stress distribution of Q235 steel wallboard-Q460 high strength steel column structural systems, an experimental study was conducted using hole-drilling method, including six structural system specimens and two independent Q460 high strength steel welded H-section specimens. Based on the experiment results, the magnitude and shape of residual stress distribution over the entire section were obtained. The effects of the welding connection between wallboards and column, sectional dimensions and the interaction among component plates on residual stress distribution were analyzed. The self-equilibrium of residual stress occurring in each plate was examined. The welding between wallboards and column reduces the maximum tensile residual stress in the middle of the column rear flange to a certain extent, and reduces the distribution range of the compressive residual stress in rear flange, but has no obvious influence on the front flange and web. The tensile residual stress amplitude is not directly related to the sectional dimensions. The compressive residual stress amplitude decreases with the increase of the plate width-thickness ratio. There is an interaction between the residual stresses of the component plates. The residual stresses of front flange, web and rear flange-wallboards composite plate can be considered to satisfy self-equilibrium respectively. An accurate and reliable residual stress distribution mathematical model for Q235 steel wallboard-Q460 high strength steel column structural system was proposed, which lays a foundation for subsequent research on the stability of high strength steel columns supported by stressed wallboard skin.
EXPERIMENTAL RESEARCH AND THEORETICAL ANALYSIS OF POLYGON-KEY ASSEMBLY CONNECTION
WANG Wei, LI Ai-qun, WANG Xing-xing
2023, 40(2): 47-55.   doi: 10.6052/j.issn.1000-4750.2021.08.0667
[Abstract](179) [FullText HTML](33) [PDF 4782KB](53)
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To improve the shear performance of assembly connections in precast RC shear wall structures, a novel polygon-key assembly connection (PKA connection) is proposed. Pseudo-static tests are carried out to study the shear performance of the PKA connections. Specimens’ parameters considered in the tests consist of polygon-key inclination angles, polygon-key heights and axial compression ratios. Shear capacity, stiffness, and failure mode of the PKA connections are investigated. Furthermore, theoretical analyses of the PKA connections are performed, equations for calculation of PKA connections’ shear capacity are deduced, and the theoretical analysis results are validated by the test results. The results show that the polygon-keys can effectively improve shear capacity of the PKA connections. Compared with parallel assembly connections, peak loads of the PKA connections are enhanced by more than 15%. When polygon-key inclination angles are within the range of 45° ~ 90°, peak loads of the PKA connections change slightly. When polygon-key heights are within the range of 5 cm ~ 7 cm, cracking loads and peak loads of the PKA connections change slightly. With an increase in the axial compression ratio, peak loads of the PKA connections gradually increase. Based on the shear-friction theory, calculated peak loads of the PKA connections are in good agreement with the test results.
INFLUENCE OF DAMPING MODELS ON STRUCTURAL DYNAMIC RESPONSE ANALYSES UNDER SUBWAY-INDUCED VIBRATIONS
TIAN Yuan, HUANG Yu-li, WANG Yi-xing, LU Xin-zheng, XU Zhen
2023, 40(2): 56-65.   doi: 10.6052/j.issn.1000-4750.2022.08.0729
[Abstract](51) [FullText HTML](26) [PDF 5258KB](35)
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In the elastic dynamic response analysis of a structure, damping has an important influence and directly determines the energy dissipation and decay behavior of the structure. An accurate understanding of the applicable conditions of different damping models is of great significance for the analysis of practical engineering problems. The main characteristics of dynamic structural response analyses under subway-induced vibration excitations are: The subway vibration excitation intensity is small, and the structure usually remains elastic. Thus, the dynamic response of the structure is directly affected by the damping, and a reasonable damping energy dissipation is essential for the reliability of the analysis results; the frequency domain of subway-induced vibration is wide, and it is easy to excite the high-order vertical vibration pattern of the structure. Hence, the damping behavior of each order needs to be reasonably considered in the analysis. Different damping models are based on different basic assumptions and have different applicable conditions. Viscous damping and hysteretic damping are two types of commonly adopted damping models. In order to clarify the characteristics of different damping models in the structural dynamic response analysis under subway-induced vibration excitations, one typical representative for each type of damping models (Rayleigh damping and universal rate-dependent damping, respectively) is selected, and four common types of typical structures (concrete frame structure, steel frame structure, concrete shear wall structure, and steel frame-braced core tube structure) were analyzed. The results show that: When Rayleigh damping is used, the reference frequency range needs to be reasonably defined according to the structural dynamic characteristics and the external excitation frequency distribution. Compared with the Rayleigh damping model with the reference frequency range covering the main frequency of the external excitations, the model with the reference frequency range covering only the first 10 orders of vertical vibration mode is too narrow. In the cases of this paper, the vertical peak acceleration of the latter is 49% and 92% less than that of the former; the universal rate-dependent damping only requires direct definition of the expected damping-frequency relationship. The peak vertical roof accelerations of cases using the universal rate-dependent damping are 75%-156% of those adopting the Rayleigh damping model with a wide reference frequency range. The influence of damping models may differ for different structures and different locations of the same structure.
EXPERIMENTAL STUDY ON SHEAR STRAIN ENERGY AND MAXIMUM SHEAR STRAIN CHARACTERISTICS OF RED SANDSTONE
WANG Yun-fei, MA Yong-chao, LI Zhi-chao, WANG Li-ping, RONG Teng-long
2023, 40(2): 66-73.   doi: 10.6052/j.issn.1000-4750.2021.06.0470
[Abstract](119) [FullText HTML](48) [PDF 4781KB](30)
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Direct shear tests of dry and saturated red sandstone samples under different normal stresses were carried out in rock shear test system to determine shear strength, shear strain energy and maximum shear strain characteristics. The influences of normal stress and saturated water on shear strength, shear strain energy density, and shear strain of red sandstone were analyzed in detail. Results show that the shear force-shear displacement curve includes evidently linear and yielding sections in dry and saturation states, respectively. The shear strength and the shear displacement increase significantly when the normal stress is 10 MPa~20 MPa. The shear displacement slightly changes when the normal stress is 20 MPa~40 MPa. Red sandstone demonstrates significantly lower cohesion and internal friction angle under compression and shear stress than under triaxial compression stress. Saturated water weakens the cohesion and internal friction angle under triaxial stress path but only weakens the internal friction angle under compression and shear stress path. When the normal stress is less than 20 MPa, shear strength degradation rate increases linearly with the increasing of normal stress. When the normal stress is 20 MPa~40 MPa, shear strength degradation rate fluctuates at certain value. A good linear relationship exists between peak shear strain energy density and normal stress, and the effect of saturated water on peak shear strain energy density increases with the increasing of normal stress. The peak shear strain energy density of dry and saturated red sandstone samples remains constant at 1.4579 and 1.0033 MJ/m3, respectively, and the degradation rate of peak shear strain energy density is 31.18%. According to the variation in the peak shear strain energy density with normal stress, empirical strength criteria of shear strain for dry and saturated red sandstone samples were established when 20 MPa normal stress was taken as turning stress. The conclusions demonstrated certain reference significance for engineering design and stability analysis of red sandstone engineering.
SIMULATION METHOD OF LOW CYCLE RECIPROCATING LOADING OF PIER COLUMN CONSIDERING BOND-SLIP EFFECT
GAO Jian-feng, LI Jian-zhong, LIANG Bo
2023, 40(2): 74-84.   doi: 10.6052/j.issn.1000-4750.2021.08.0612
[Abstract](149) [FullText HTML](61) [PDF 7021KB](76)
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Based on the stress-slip model of concrete proposed by fib Model Code, the slip of rebar was derived and formulated to consider the bond-slip phenomenon occurring both in the column and in the footing. Furthermore, the stress-strain constitutive model of the tensile rebars located within the plastic zone of the column was modified to incorporate the rebar slips in the column and in the footing. In this way, the effect of bond-slip on the seismic responses of the column can be equivalently considered. The feasibility of this method was verified by experimental results. Besides, the comparison was made of the results between the proposed method and the Zero-Length Section Element (ZLSE) method. It can be concluded that the lateral stiffness, the cumulative hysteretic energy, and the residual displacement are all overestimated without considering the bond-slip phenomenon. Apart from that, the strength degradation of the column is unable to reflect objectively. Both the ZLSE method and the proposed equivalent method have the capability to resolve the issue of strength degradation. However, the former method yields the numerical results prominently susceptible to the rebar diameter, while the latter one can efficaciously capture the reciprocating loading process of the column affected by the bond-slip phenomenon.
STUDY ON SHAKING TABLE TEST OF FREESTANDING STONE CAVE DWELLING
ZHANG Feng-liang, PAN Wen-bin, LIU Zu-qiang, HU Xiao-feng, ZHAO Xiang-bi
2023, 40(2): 85-96.   doi: 10.6052/j.issn.1000-4750.2021.08.0614
[Abstract](103) [FullText HTML](123) [PDF 5709KB](16)
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According to the on-site investigation, taking the typical three-arch freestanding stone cave dwelling in Jingle County, Shanxi Province as the research object, the paper designed and manufactured a 1/4 model, and then carried out a shaking table test for it. The natural vibration frequency, damping ratio, acceleration amplification factor, maximum relative displacement, lateral displacement angle, base shear force and structural energy dissipation were analyzed. Test results show that the weak parts under the earthquake action are the dome and the middle kiln leg at the entrance of the side cave. With the increase of the peak acceleration of input seismic wave, the natural vibration frequency of the model decreases and the damping ratio increases. The dynamic amplification coefficients of the model changes little with the increase of the input peak acceleration. The largest dynamic amplification coefficient in the x-direction and y-direction occurs at the arch roof and kiln roof, respectively. When the input peak acceleration is 70 gal (frequent earthquakes), 200 gal (fortification earthquakes) and 440 gal (rare earthquakes), the maximum lateral displacement angle of the model occurs in the arch roof, which is 1/1618, 1/491 and 1/255, respectively. When the input peak acceleration is 600 gal, the maximum lateral displacement angle occurs in the kiln roof, which is 1/102. When the input peak acceleration is 800 gal, the maximum torsion angle of the model is 0.0037 rad. The bottom shear force and energy dissipation of the model increase with the increase of the peak acceleration of input seismic wave.
STUDY ON SEISMIC PERFORMANCE AND HYSTERETIC MODEL OF ROTATIONAL DAMPER FOR ENERGY-DISSIPATIVE PRECAST CONCRETE JOINTS
WU Cong-xiao, LIE Wen-chen, WU Chang-gen, LI Chang-hong, LI Ding-bin, WU Cong-yong
2023, 40(2): 97-111.   doi: 10.6052/j.issn.1000-4750.2021.08.0623
[Abstract](283) [FullText HTML](62) [PDF 7277KB](97)
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A novel rotational damper named torsional steel-tube damper is proposed, which can be implemented to the beam-column connection with energy dissipated in precast concrete structures. Five damper specimens with different parameters are designed and tested under quasi-static cyclic loading. Test results show that the specimens rotate around the pin shaft and have excellent rotational deformation. The limit angle is more than 0.06 rad, and the ductility factor is larger than 4.0 required by the specification. The hysteretic curves of the specimens are plump, and apparent isotropic hardening behaviour can be observed. The equivalent viscous damping factors of the specimens are about 0.5, indicating that the damper has good energy dissipation capacity. The specimen with a larger wall thickness and outer diameter and smaller effective tube length has larger rotational strength. Under cyclic loading with a constant amplitude, all fatigue performance parameters of the specimens are basically within the specification requirements of ±15%, and the specimen has good anti-fatigue performance. The modified Bouc-Wen model is introduced to simulate the cyclic behaviour of the damper, and the quantum particle swarm optimization algorithm is used to identify the model parameters. The identification results show that the modified Bouc-Wen model can well adapt to the specimens' isotropic hardening behaviour and has higher simulation accuracy than that of Bouc-Wen model. The modified model can be used for the seismic analysis of monolithic structures.
HEALTH ASSESSMENT OF TIBETAN ANCIENT WOOD STRUCTURES BASED ON THE PREDICTED VALUE OF STRAIN MONITORING DATA
YANG Na, LI Tian-hao, ZHAO Gong-min
2023, 40(2): 112-123, 134.   doi: 10.6052/j.issn.1000-4750.2021.08.0636
[Abstract](114) [FullText HTML](57) [PDF 6777KB](37)
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In order to increase the safety redundancy of the Tibetan ancient wood structures (TAWS), this paper proposes a prediction method to predict their health status based on short-term strain monitoring data. The corridor structure is taken as the research object, with the Sobel operator and the convolutional neural network method being used to deal with various data anomalies from sensors. The strain monitoring data components are determined by polynomial regression and power spectral density. The prophet algorithm is used to predict short-term temperature induced strain, and the Gumbel extreme value theory is used to predict human induced strain under different return periods. The superposition results of the strain monitoring data prediction values under different return periods are used to determine the structural positions that desire more attention and repair, so that the preventive protection requirements and minimum disturbance requirements can be fulfilled.
STUDY ON Nu -Mu CORRELATION CURVES OF CONCRETE FILLED DOUBLE SKIN STEEL TUBULAR (CFDST) BEAM-COLUMNS WITH EXTERNAL STAINLESS STEEL TUBE
ZHANG Ying, ZHAO Hui, WANG Rui, CHEN Peng
2023, 40(2): 124-134.   doi: 10.6052/j.issn.1000-4750.2021.08.0637
[Abstract](182) [FullText HTML](75) [PDF 5968KB](33)
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Concrete filled double skin steel tubular (CFDST) members with external stainless steel tubes present the merits of CFDST members and stainless steel, and have a wide application prospect in bridge piers, in offshore platforms and, in transmission towers. For this purpose, totally 225 CFDST beam-columns with outer stainless steel tubes were systematically analyzed using a fiber-based model in this work. The influences of the parameter on the typical N/Nu-M/Mu curve were investigated, and the obtained curves were compared with those of CFDST members with carbon steel. Finally, the correlation curve equation of N/Nu-M/Mu was proposed. The study results showed that: the fiber-based model program developed could well predict the compression-bending capacity and the development of N/Nu-M/Mu curve of CFDST members with external stainless steel tube; the shape of N/Nu-M/Mu curve is affected by the concrete strength, by the ratio of the diameter to the thickness of the inner steel tube, by the yield strength of steel, by the hollow ratio, by the nominal steel ratio and, by slenderness ratio; due to an obvious strain-strengthening effect of stainless steel, the N/Nu-M/Mu curves of the CFDST members with external stainless steel tubes are close to the steel members when compared to those of the CFDST members with external carbon tubes; and the characteristic-point and N/Nu-M/Mu formulas for CFDST members with outer stainless steel based on the test and parametrical results were suggested by modifying the formulas used for the companion with outer carbon steel, the calculation results by the formulas modified indicate a good agreement with the program-calculated results.
HIGH-PRECISION THREE-DIMENSIONAL FINITE ELEMENT METHOD FOR ANALYSIS OF SLIDING CABLE STRUCTURES
CHEN Shi-zai, YANG Meng-gang
2023, 40(2): 135-144, 189.   doi: 10.6052/j.issn.1000-4750.2021.08.0642
[Abstract](215) [FullText HTML](77) [PDF 5054KB](52)
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To overcome the shortcomings of limited application range and low precision in the existing analysis methods for sliding cable structures, a general and high-precision three-dimensional finite element method for sliding cables is proposed. Based on the catenary theory and Euler-Eytelwein equation, the governing equations of the three-dimensional sliding cable elements with known unstressed cable length and with known tensile forces are respectively developed, accounting for the thermal effect and sliding friction. The tangent stiffness matrix of the element is derived directly from the governing equations by using matrix differential. A refined analysis procedure of sliding cable structures for the whole process from tensioning to later loadings is proposed, with the capability of automatically using all types of cable elements and accurately analyzing the friction at each sliding point. The reliability and effectiveness of the proposed method are verified by three computational examples and, by the comparison with the pertinent existing theoretical solutions and, with the pertinent numerical results and experimental ones. The computational results show that the three-dimensional finite element method proposed is accurate and reliable with high computational efficiency and is very suitable for the high-precision nonlinear analysis of various sliding cable structures in engineering practice.
COMPRESSIVE PERFORMANCE STUDY OF GROUT-FILLED GFRP TUBE REPAIRING CORRODED JOINTS
CHANG Hong-fei, GAO Yu-hang, ZUO Wen-kang, LI Zhao-wei, YAN Xiao-yu
2023, 40(2): 145-156.   doi: 10.6052/j.issn.1000-4750.2021.08.0644
[Abstract](112) [FullText HTML](66) [PDF 5932KB](37)
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Steel welded circular hollow section (CHS) joints are widely adopted, and the corrosion induced degradation threaten the safety and reduce the residual life of them after long-term service. To study the performance of grout-filled GFRP tube repairing corroded circular hollow section (CHS) T-joints, a total of six specimens, including uncorroded, corroded unrepaired and grout-filled GFRP tube repaired CHS T-joints were tested under brace axial compressive loading. The experimental results show that the corroded joints with around 10% chord weight loss ratio may lead to about 20% reduction of the ultimate strength. The grout-filled GFRP tube repairing is effective to prevent the ovalization of the chord, by which the joint failure mode changed from chord plasticization into chord punching shear. The ultimate strength and initial stiffness of the repaired chord corroded joints are enhanced by 100% and 50%, respectively, which are higher than those of the corresponding uncorroded ones. Based on the verified finite element models, further parametric analyses indicate that the diameter ratio of the brace to the chord, the thickness of the GFRP tube and the section hollow ratio of the repaired chord are critical parameters that determine the repairing effect. By contrast, the length of the repairing cover and the strength of the grouting layer are found to be less influential. By optimizing the configuration of the grout-filled GFRP tube repairing, the ultimate strength of the corroded joint with 28% chord weight loss ratio can be enhanced by more than 1.5 times to its corresponding uncorroded one. Finally, suggestions are proposed for the repairing of joints with different corrosion ratios, to achieve a 20% ultimate strength enhancement than uncorroded joints after repairing. The current study can provide a reference for both repairing and improving performance of corroded steel tubular joints after long-term service.
PROPERTY EVOLUTION AND LIQUEFACTION STAGE CHARACTERISTICS OF SATURATED SAND UNDER CYCLIC LOADING
ZHANG Xin-lei, YI Rui-bo, JI Zhan-peng, GAO Hong-mei, WANG Zhi-hua
2023, 40(2): 157-167.   doi: 10.6052/j.issn.1000-4750.2021.08.0648
[Abstract](241) [FullText HTML](84) [PDF 5514KB](69)
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Correctly evaluating the property evolution of saturated sand in the liquefaction process is the key to solving the problem of large deformation of liquefiable soil. The undrained triaxial tests of saturated sand were conducted to study the relationship between shear stress and shear strain, the excess pore water pressure development rate and, the growth of liquidity during the liquefaction. The investigation results showed that the transformation process of saturated sand from solid phase to liquid phase displayed a significant stage characteristic. The liquefaction process of saturated sand could be divided into four stages: solid stage, solid-liquid transition stage, thixotropic fluid stage and, stable fluid stage according to pore pressure ratio development rate which is related to the residual shear strain of soil. Confining pressure and cyclic stress ratio would affect the duration of each stage in the process of soil liquefaction. The lower the confining pressure and the higher the cyclic stress ratio, the easier for saturated sand to transform from solid stage to fluid stage. A linear relationship between the required cycles of saturated Nanjing fine sand from one stage to another and the corresponding pore pressure ratio was found in this study.
RESEARCH ON LATERAL RIGIDITY OF SHARPLY CURVED BRIDGE PIER IN MODERN TRAM LINE
XIE Kai-ze, ZHAO Jia, ZHAO Wei-gang, WANG Xin-min
2023, 40(2): 168-178.   doi: 10.6052/j.issn.1000-4750.2021.08.0649
[Abstract](165) [FullText HTML](59) [PDF 5327KB](32)
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The lateral rigidity of a sharply curved bridge (SCB) pier has an important impact on regularities of the track in modern tram lines. A spatial calculation model for SCB-CWR (continuous welded rail) interaction is established by the grounds of the finite element method. Taking the example of a curved steel-concrete composite bridge with spans of 35 m+40 m+40 m+35 m, the effects of different factors on TAI (track alignment irregularity) are analyzed. The results show that the coupling between longitudinal and lateral SCB-CWR interactions can cause middle and long wave TAI. The amplitude of TAI shows a positive correlation with longitudinal rigidity of a pier, with the variation range of rail temperature and, with the maximum force of fastener longitudinal resistance, but a negative correlation with lateral rigidity of a pier, with curve radius and, with the yield displacement of fastener longitudinal resistance. The most significant factor is curve radius. When the radius increases from 150 m to 600 m, the amplitudes of TAI determined by the mid-chord offset method and by the differential offset method reduce by more than 60%. The lateral rigidity thresholds of piers for common curved continuous beam bridges in modern tram lines are ascertained respectively. The thresholds of steel-concrete composite bridges are 1.2~2.0 times greater than that of reinforced concrete bridges. Optimizing design stress-free rail temperature or using small resistance fastener which can effectively reduce the amplitude of TAI and the lateral rigidity thresholds of piers are recommended to be applied during the design of CWR on SCB.
ENERGY FACTOR BASED SEISMIC DESIGN AND EVALUATION METHOD FOR TENSION-ONLY BRACED BEAM-THROUGH STEEL FRAMES
ZHANG Rui-bin, WANG Wei
2023, 40(2): 179-189.   doi: 10.6052/j.issn.1000-4750.2021.08.0651
[Abstract](121) [FullText HTML](36) [PDF 6103KB](51)
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In order to realize the damage-control behavior of tension-only concentrically braced beam-through steel structural systems, the energy factor seismic demand index probability model of the structural system in the damage control stage is firstly established, and then the seismic design and evaluation method is proposed based on the energy factor incorporating the probability model of the seismic demand. A typical three-story tension-only concentrically braced beam-through steel structural system is selected to demonstrate the proposed design and evaluation process. The analysis results show that the structure designed through the seismic design and evaluation process proposed in this paper can achieve damage-control performance, that is, the damage is concentrated in the tension-only braces which can be easily replaced and the main frame remains elastic, thus no obvious residual deformation after earthquakes. Furthermore, the rationality of the method is verified by time history analysis.
EXPERIMENTAL STUDY ON THE SEISMIC PERFORMANCE OF JOINTS BETWEEN SIDEWALLS AND FLOORS IN PARTIALLY PREFABRICATED SUBWAY STATION
FENG Shuai-ke, GUO Zheng-xing, LIU Yi, PAN Qing, XU Jun-lin, WANG Guo-liang, XING Qiong
2023, 40(2): 190-201, 212.   doi: 10.6052/j.issn.1000-4750.2021.08.0655
[Abstract](148) [FullText HTML](33) [PDF 5864KB](28)
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A novel joint between the sidewall and the station floor was proposed for partially prefabricated subway stations. The internal force transmission between the partially precast sidewall and corresponding subway station floor was achieved through overlapping U-bars extending from them respectively. To investigate the seismic performance of the assembly joint, three full-scale precast joint specimens with different positions of the lap connection and one full-scale cast-in-place concrete joint specimen for comparison were designed and produced based on an actual engineering project. Quasi-static tests and finite element analysis were conducted on these four full-scale joint specimens. The critical seismic performance associated with the joints, including the failure pattern, bearing capacity, hysteretic characteristics, and mechanical performance of U-bars overlapping connection were analyzed. The results show that the local concrete compression failure inside the hook of the U-bars and the brittle fracture of the loop are the two main failure modes in the lap connection of assembly joints. Both failure modules can be attributed to the degradation of the bond between reinforcement and concrete. When the U-bars are overlapped in the haunched segment, the bearing capacity, failure pattern, and hysteretic characteristics of assembly joints are similar to those of the cast-in-place concrete joints. If failure of reinforcing steel bars bonding can be prevented, the U-bars overlapped outside the haunched segment can effectively increase the shear resistance of the joints.
EFFECT OF FREEZING AND THAWING ON FRACTURE PERFORMANCE OF CONCRETE AT POLAR LOW TEMPERATURE
XIE Jian, YAN Ming-liang, LIU Yang
2023, 40(2): 202-212.   doi: 10.6052/j.issn.1000-4750.2021.08.0656
[Abstract](136) [FullText HTML](85) [PDF 5453KB](53)
Abstract:
In order to study the durability performance changes of concrete after freeze-thaw cycles in polar and cold regions, freeze-thaw cycles and loading tests of 84 three-point bending beams were carried out by the slow-freezing method. The test was conducted with the lower limit temperature (down to −80 ℃), the number of freeze-thaw cycles, the concrete strength, and the concrete type as the study parameters, and the changes in the basic mechanical properties of concrete and key fracture parameters were compared and analyzed before and after the freeze-thaw cycles. The study results show that: with the decrease of the lower limit temperature of freeze-thaw cycles and the increase of the number of freeze-thaw cycles, the basic mechanical properties as well as the cracking toughness and fracture energy of concrete show a decreasing trend, but the instability toughness and characteristic length show a opposite trend, indicating that the ability of concrete to resist cracking decreases after experiencing freeze-thaw cycles, but the deformation properties of concrete improve significantly; with the increase of concrete strength, the freeze-resistance durability has been improved to a certain extent; the fracture performance of seawater sea-sand concrete after freeze-thaw cycles is not lower than that of ordinary concrete. The concept of freeze-thaw damage accumulation is proposed, which can be used to reflect the variation of fracture parameters and the quantitative comparison of different freeze-thaw conditions.
VORTEX-INDUCED VIBRATIONS OF LONG-SPAN CONTINUOUS BRIDGES WITH STEEL TRUSS-STIFFENED BOX-GIRDER
ZHOU Tao, DENG Yu, CHEN Xiao-hu, WANG Wen-xi, ZHOU Ming-xing, HUA Xu-gang, CHEN Zheng-qing
2023, 40(2): 213-221.   doi: 10.6052/j.issn.1000-4750.2021.08.0661
[Abstract](166) [FullText HTML](36) [PDF 5819KB](42)
Abstract:
Vortex-induced vibrations (VIVs) are one of the most critical issues for continuous beam bridges with long spans. The proposed 4th Bridge at Macao is a continuous-beam bridge made of steel truss-stiffened box girders with variable height and asymmetric configuration, and the bridge girder has a width of approximately 50 m and complex aerodynamic shape owing to various accessory components. The VIV performance of the 4th Bridge at Macao is studied by wind tunnel tests on 1∶70 sectional models, and the effects of wind attack angles, turbulence intensity, structural damping, wind barrier are compared. Two typical cross sections at the L/2 and L/3 of the main span are tested. The results shown that the cross-section of truss-stiffened box-girder may generate VIVs under negative wind attack angle, and the VIV of two cross-sections at negative attack angles are different, implying the effect of truss on VIV is significant. The results also shown that the asymmetry of the cross-section may significantly affect the VIV performance of the continuous beam bridge with steel truss and variable cross-sections. The amplitude of the VIV response can be reduced effectively by lowering the permeability of the outer barrier and adopting a spoiler with a reasonable placement. Finally, the parameters of the wake oscillation model for the simulation of vortex-induced vibrations are identified based on the experimental results, which can accurately reflect the relation between the amplitude of VIV and the wind speed.
MECHANICAL RESPONSE OF SIMPLY SUPPORTED REINFORCED CONCRETE SLABS UNDER FIRE
DING Fa-xing, WANG Wen-jun, JIANG Bin-hui, YU Zhi-wu
2023, 40(2): 222-231.   doi: 10.6052/j.issn.1000-4750.2021.08.0664
[Abstract](440) [FullText HTML](179) [PDF 5821KB](74)
Abstract:
The tensile membrane theory for the cracking state of reinforced concrete (RC) slabs does not explain the mechanism that enables the slabs to bear the load under a large deformation before the cracking at slab bottom. Therefore, three-dimensional solid finite element (FE) models of simply supported one-way RC slabs and two-way RC slabs in both heat transfer analysis and thermo-mechanical coupling analysis were established using the ABAQUS software, based on reasonable thermal parameters and thermo-mechanical coupling constitutive of materials. Using the verified model, the stress variation law of concrete and steel bars and the mechanical response of simply supported RC slabs under fire were further investigated. The results show that: simply supported RC slabs undergo intense stress redistribution, and their responses show four stages, namely elastic, elastic-plastic, plastic and, tensile cracking stages. In elastic-plastic and plastic stages, the bidirectional compression of bottom concrete, namely inverted arch effect, makes the fire resistance of two-way RC slab excellent; there is no cracking in the fire area of the slabs until the tensile cracking stage; Compared with one-way RC slabs, the time for two-way RC slabs to enter the plastic and tensile cracking stage is postponed, and the deformation rate in the plastic and tensile cracking stage is also slowed down. Therefore, the two-way RC slabs have better fire resistance.
MECHANICAL ENGINEERING
SEMI-ANALYTICAL MODEL AND TEST METHOD OF CONE INDENTATION BASED ON ELASTOPLASTIC PROPORTIONAL SUPERPOSITION
ZHANG Si-yu, CAI Li-xun, SI Shu-qian, CHEN Hui, LIU Xiao-kun
2023, 40(2): 232-246.   doi: 10.6052/j.issn.1000-4750.2021.09.0684
[Abstract](136) [FullText HTML](37) [PDF 5840KB](14)
Abstract:
A load vs. displacement model LDM-PS is proposed, and a conical indentation test method for obtaining the stress-strain relationship of the material under the Ramberg-Osgood law (R-O law) is proposed by the grounds of energy density equivalence, considering the proportional superposition of strain energy between linear law pure elasticity and power law pure plasticity in conical indentation. For 80 set materials, the load-displacement curve (forward prediction) predicted by LDM-PS is in a close agreement with the results of Finite Element Analysis (FEA), and the load-displacement curve obtained by FEA is taken as the experimental simulation curve. Two kinds of cone angle conical indenters are used to carry out single conical indentation (double conical indentation) twice on the surface of smooth material, and the R-O law parameters can be solved by parabolic law regression of the two loading vs. displacement curves of double conical indentation at the loading stage. The stress vs. strain curve of R-O law predicted by LDM-PS (inverse prediction) is in a close agreement with the condition curve of FEA. The stress vs. strain relationship, Young's modulus and strength predicted by the new method are in a good agreement with the results of the traditional uniaxial tensile test.
OTHER ENGINEERING DISCIPLINES
EXPERIMENTAL INVESTIGATION OF PLASMA FLOW CONTROL ON A FLYING WING MODEL BASED ON MICROSECOND PULSED EXCITATION
NIU Zhong-guo, LIANG Hua, JIANG Jia-li
2023, 40(2): 247-256.   doi: 10.6052/j.issn.1000-4750.2021.08.0615
[Abstract](109) [FullText HTML](47) [PDF 6006KB](8)
Abstract:
In order to improve the aerodynamic performance of flying wing layout aircrafts at high attack angles , an experimental study of microsecond pulsed dielectric barrier discharge (μs-DBD) plasma flow control was carried out in low-speed and transonic wind tunnels, using both full and half models of a flying wing. Flow visualization and force measurements are deployed to reveal the main mechanisms of plasma flow control and, to analyze the effects of excitation frequency and voltage on the stall characteristics of the flying wing model. The effectiveness of μs-DBD plasma in manipulating low-speed to subsonic flows is successfully verified, with the highest test Mach number and Reynolds number tested being 0.6 and 3.05×106, respectively. Results show that μs-DBD plasma perturbs the model airfoil flow field by unsteady micro-scale compressive wave. These wave perturbations weaken the front separation vortex of the model and suppresses the flow separation by frequency coupling, thus leaving dimensionless frequency as a key parameter which influences the effectiveness of plasma flow control. In a low-speed wind regime (wind speed: 30 m/s), the optimal dimensionless frequency range is 0.35 to 1.06, accompanied by more than 25% in the maximum lift coefficient and 4 degrees postponement in the stall attack angle. As a comparison, in the transonic regime of Mach 0.6, the favorable dimensionless frequency drops to 0.22 and 0.44, with the maximum lift coefficient increased by 4.72% and 4.77%, respectively, and the stall attack angle postponed by 1 and 2 degrees, respectively. Additionally, since the excitation voltage of plasma affects the intensity of the compressive wave perturbation, the higher the excitation voltage is, the better the effect of plasma flow control will be.

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