05 December 2024, Volume 45 Issue 12

    

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Special topic in seismic resistance of structures
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  Experimental study on lateral overstrength capacity of RC structures designed with DBJ/T 15-92—2021 ‘Technical specification for concrete structures of tall building’

  LING Yuhong, ZHANG Haopeng, ZHOU Jing, FANG Xiaodan

  Journal of Building Structures. 2024, 45(12): 1-18. https://doi.org/10.14006/j.jzjgxb.2023.0671

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  In order to study the lateral overstrength capacity and safety reserve of reinforced concrete (RC) structure, the low-cyclic reversed loading tests of the scaled plane structural specimens were conducted, as well as the pushover analysis of the prototype building structure. Taking seismic structural level as the parameter, the allowable stress method was adopted to design three twelve-storey RC frame structures and three twelve-storey RC frame-shear wall structures. One-bay plane structure at bottom three-stories was selected to conduct the seismic test of twelve (1/4 scaled) specimens, which included two batches of specimens constructed by two groups at various periods. Taking the building height, slab flange and infill wall as the parameters into consideration, the structural models were established with using the Perform-3D to conduct the pushover analysis, the change mechanism of different parameters was researched, such as the overstrength coefficient of lateral-force resisting system and the lateral ductility. The low-cyclic reversed loading experimental results indicate that the main damage mechanism of the twelve scaled plane specimens is compression and bending damage. The hysteresis curves are full, the ductility is relatively large. The average of yielding overstrength coefficient is 2.21 for frame structure specimens and 2.26 for frame-shear structure specimens. The tendency indicates that the overstrength capacity is higher and the ductility is better for specimens designed with higher seismic structural level. Pushover analysis results indicate that the lateral force-resisting capacity at performance-point of RC structures after encountering an earthquake of rare intensity exceeds the yielding load, rather than the peak load, which illustrates that the overstrength capacity satisfies the seismic design requirements of not damaged after a fortification intensity earthquake, and reparable or not collapsed after a rare earthquake. The recommended value of yielding overstrength coefficient is 2.0 for the RC seismic structures designed with DBJ/T 15-92—2021 ‘Technical specification for concrete structures of tall building’.
  
  
Special topics in seismic resistance of structures
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  Shaking table test and dynamic analysis on a tower structure in traditional style building

  XUE Jianyang, LING Huaiquan, QI Liangjie, SONG Jianglan, LU Mingyu

  Journal of Building Structures. 2024, 45(12): 19-30. https://doi.org/10.14006/j.jzjgxb.2023.0786

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  To investigate the dynamic response and seismic performance of the tower structure in a traditional style building under earthquake motions, a specimen of Xi’an Tianren Chang’an Tower with a scale ratio of 1/15 was designed and fabricated and subjected to simulated seismic shaking table tests. The dynamic characteristics of the specimen, such as natural frequency, damping ratio, and stiffness degradation rule, were obtained through white noise frequency sweeping. The dynamic responses, including acceleration amplitude factor, floor displacement, inter-story drift ratio and shear force, were investigated under different earthquake intensities. The results indicate that the damage is relatively minor under rare earthquake excitation, mainly concentrates in concrete cracking near the column base. The natural frequency and stiffness slowly decrease with increasing peak acceleration, while the damping ratio increases. The acceleration amplitude factors at the top are notably higher than those of other stories.  The overall distribution of shear force shows a decreasing trend with increasing height, with the dim stories being larger than the bright stories on the same story. The OpenSees software was used to establish the model and simulate the main results, and the seismic performance of the prototype structure was evaluated. It is shown that under the 8-degree frequent occurrence earthquake waves, the maximum inter-story drift is 1/782, and the base shear coefficients in both directions are 3.57% and 3.78%, respectively. Under the rare occurrence earthquake waves of 8-degree, the maximum inter-story drift is 1/128, which meets the requirements of the current design code.
  
  
Special topic in seismic resistance of structures
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  Seismic performance of steel frame structure with self-centering cable braces

  XU Gang, GUO Tong, LI Aiqun, LAI Zhengcong, ZHANG Hengyuan, WANG Kairui, DANG Longji

  Journal of Building Structures. 2024, 45(12): 31-41. https://doi.org/10.14006/j.jzjgxb.2023.0824

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  In order to improve the seismic resilience of the braced frame structure, a novel self-centering cable brace has been proposed to effectively prevent compression buckling. It features a self-centering friction damper whose working principle has been analyzed both theoretically and experimentally, displaying a flag-shaped force-displacement curve with stable energy dissipation and self-centering capabilities. Based on this, three-story scale model steel frames with self-centering cable braces was designed, including models with prestressed dampers and without prestress, alongside a conventional steel frame model for comparison. Shaking table tests were conducted followed by the development of finite element models that accurately simulated the experimental process. Parametric studies were carried out and the results indicate that model with prestressed dampers shows almost no residual deformation post-earthquake, and the residual deformation in model without prestress is significantly less than that in conventional steel frame model. The displacement response is critically influenced by the level of initial prestress, the model with prestressed dampers exhibits less displacement than both conventional steel frame model and model without prestress. Furthermore, the maximum base moment in models with prestressed dampers and without prestress is reduced by 32.5% and 45.6%, respectively, compared to conventional steel frame model. With increasing seismic intensity, the floor acceleration amplification factor is observed to decrease progressively. The addition of energy dissipation elements is found to notably increase the residual displacement and seismic force on the structures, with the type of column base having a significant effect on the maximum displacement and residual deformation.
  
  
Special topics in seismic resistance of structures
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  Experimental study on seismic behavior of BRB-RC frame sub-structure with controllable bending failure mode

  ZHANG Jiaguang, HAO Shufei, ZHAO Junxian, ZHANG Shaojun, SONG Jiayu, LIU Yuanzhen

  Journal of Building Structures. 2024, 45(12): 42-55. https://doi.org/10.14006/j.jzjgxb.2023.0720

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  To effectively prevent the buckling-restrained braced reinforced concrete (BRB-RC) frame substructure from shear or flexural-shear failure caused by frame action prior to the BRB, a controllable failure mode design method based on a novel sliding gusset connection was proposed. The method addresses problems of the current siding gusset connection, such as the limited bearing capacity of the anchorage plate and the unreasonable design of the shear capacity of substructure beams. Quasi-static  tests were conducted on five full-scale BRB-RC subassemblages, one with a traditional connection and the others with the proposed sliding gusset connection to verify the effectiveness of the sliding gusset connection and the design method. The failure modes, hysteresis behavior and energy dissipation capacity of sub-structure were investigated. It is shown that the sliding gusset connection has stable performance and could significantly reduce the shear force of the sub-structure beam and plastic damage level. The energy dissipation proportion of the BRB significantly increases. The additional rebars and longitudinal distribution rebars at the beam end can effectively enhance the shear capacity of the sub-structure beam within gusset plate region, thus realizing the bending failure mode.
  
  
Special topic in seismic resistance of structures
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  Seismic performance of castellated beam-to-column end-plate joints with dual hinge mechanism

  BI Ran, XU Feng, JIA Lianguang, WANG Qinghe, WANG Chungang

  Journal of Building Structures. 2024, 45(12): 56-71. https://doi.org/10.14006/j.jzjgxb.2023.0625

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  In this paper, a castellated beam-to-column end-plate (CBE) joint was proposed to address the problem of brittle fracture of welds caused by high stresses in solid web beam-to-column end-plate connections and the development of plastic deformations in frame beams. Cyclic loading tests of 12 CBE joints were conducted to investigate the effects of floor, end-plate and opening parameters on the failure mode and hysteresis performance of the joints. The development of plasticity and the dual hinge failure mechanism of CBE joints were clarified. It is shown that the dual hinge failure mechanism is superior to the plastic hinge failure mechanism of the end-plate. A larger opening rate allows the beam to form a plastic hinge earlier than the connection, thus protecting the joint zone. Compared with solid-web joints, CBE joints demonstrate larger plastic deformation capacities (improved by about 14%) and smoother stiffness degradations. The ductility coefficient and energy consumption of the joints are 42% and 30% higher than those of solid-web joints, respectively. In addition, a calculation method for the bending bearing capacity of CBE joints was proposed. The calculation results are in good accordance with the experimental results and finite element analysis results.
  
  
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  Study on seismic performance of beam-end flange reinforced joints of concrete-filled centrifugal precast concrete column-steel beam

  ZHANG Xizhi, DI Yao, GUO Guanghai, ZHANG Shaohua, LI Xingqian, PU Yuta, LIANG Jian

  Journal of Building Structures. 2024, 45(12): 72-83. https://doi.org/10.14006/j.jzjgxb.2023.0608

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  In the joint of centrifugal precast concrete column and steel beam (RCS), stress concentration at the joint of flange and through partition commonly occurs due to the variable cross-section, and the weld between cylinder and beam end is prone to brittle fracture under earthquake action. To mitigate this issue, pseudo-static tests of three full-size joints with different structures of beam end flanges were designed and conducted in this paper. The influence of different beam end strengthening forms on the seismic performance of the joints was studied. The results show that beam hinge failure occurs at all joints. The joint hysteresis curves are full and the energy dissipation capacity is good. Compared with the normal RCS joint, the displacement ductility coefficient and bearing capacity of the joints with side plate widening and arc expansion are increased by 14.95%, 35.51%, 30.79% and 31.48% respectively. The ductility and bearing capacity of the joint can be effectively improved by the side plate widening and arc expansion. The arc expansion method can alleviate the stress concentration at the transition section and avoid premature joint failure and can better enhance the bearing capacity and seismic performance of the joints compared to the side plate widening method. Therefore, it is recommended for use in the RCS frame system in high intensity earthquake areas.
  
  
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  Experimental study on seismic performance of earthquake-damaged prefabricated groove frame beam with high ductile concrete

  KOU Jialiang, MA Ming, CAO Lanyue, ZHOU Heng

  Journal of Building Structures. 2024, 45(12): 84-96. https://doi.org/10.14006/j.jzjgxb.2023.0829

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  In this paper, an experimental study was conducted involving one earthquake-damaged frame beam and three earthquake-damaged prefabricated frame beams to investigate the seismic performance of earthquake-damaged prefabricated groove connection frame beams reinforced with high ductility concrete (HDC). The beams were subjected to low-cyclic reversed loading tests to analyze the failure modes and seismic performance. The results show that HDC forms a constraint effect to effectively restrain the cracking and damage component. The bearing capacity of the HDC-reinforced earthquake-damaged frame beam increases by 66.7%, the displacement ductility coefficient increases by 88%, and the cumulative energy dissipation increases by 12.1% compared to the original prefabricated frame beam. These improvements demonstrate that the seismic performance of earthquake-damaged prefabricated groove frame beams can be substantially restored, while also enhance the brittle failure characteristics of the original structure. Additionally, the presence of lateral and bottom steel plates significantly influences the stiffness and bearing capacity of the prefabricated groove frame beams. Based on the observed failure characteristics, the shear capacity of the earthquake-damaged prefabricated groove frame beams was calculated using a tension-compression bar model, and the calculated results were found to be in good agreement with the experimental outcomes.
  
  
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  Hysteresis behaviours of circular steel reinforced concrete-filled stainless steel tubular columns

  WANG Zhibin, HUANG Shutian, PENG Guihan, LIN Wanfu, LI Xinlei

  Journal of Building Structures. 2024, 45(12): 97-110. https://doi.org/10.14006/j.jzjgxb.2023.0590

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  In this paper, the hysteresis tests of six circular steel reinforced concrete-filled stainless steel tubular (SRCFSST) columns and three circular concrete-filled stainless steel tubular (CFSST) columns were carried out to study the hysteresis behaviors of SRCFSST columns. The main parameter investigated in the tests was the axial load ratio. The tests reveal that the typical damage mode of circular SRCFSST columns is compression-bending damage, including profiled steel buckling, steel tube buckling, and concrete crushing. When the axial load ratio is relatively low, the stainless steel tube can be subjected to tensile rupture. Compared to circular stainless steel tubular concrete specimens, the peak load, displacement ductility coefficient, equivalent damping ratio, cumulative energy dissipation, and flexural stiffness of steel reinforced concrete-filled stainless steel tubular columns improve by an average of 34.2%, 10.3%, 20.4%, 144.8%, and 3.0%, respectively. The composite column was simulated using a finite element (FE) model, and a parametric study was conducted using the verified FE model. The parametric study show that the ultimate load-carrying capacity of the columns increases with higher steel content ratio of the internal steel section, higher steel content ratio of the stainless steel tube section, higher yield strength of the steel section, higher yield strength of the stainless steel, higher concrete strength, and larger radius of gyration of the steel section. However, it also found that the peak load decreases with the increasing slenderness ratio and axial load ratio. Finally, the P-Δ restoring force model of the composite column was recommended, and it is shown that the P-Δ restoring force model can accurately predict test results.
  
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  Research on seismic performance of weld box-shaped columns fabricated of Q345FR and Q460FR steel

  WANG Yanbo, XU Siyi, HAI Letian

  Journal of Building Structures. 2024, 45(12): 111-124. https://doi.org/10.14006/j.jzjgxb.2023.0609

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  This paper conducted an experimental study on seismic performance of weld box-shaped columns made of Q345FR and Q460FR fire-resistant steels to enhance the application of fire-resistant steel structure in seismic regions. Through a validated numerical model, a parametric study was subsequently performed to clarify the influence of axial load ratio, slenderness and plate width-to-thickness ratio on the seismic behavior. The fire-resistant steels demonstrate an obvious cyclic-softening behavior. Columns with cross-section of ‘Level 1’ in GB 50011—2010 exhibit a failure mode of elastic-plastic local buckling in plate components. The hysteretic curves and drift angle are favorable for utilization in steel frames. The columns studied herein exhibit similar seismic performance with that of existing Q460C weld columns. The increase in plate slenderness and axial load ratio tends to decrease the flexural capacity and energy-dissipation ability. Based on the test and numerical results, a normalized hysteretic model for the columns was established studied. The proposed model can provide a reasonable prediction accuracy due to the consideration of cumulative damage, axial load ratio and plate slenderness.
  
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  Research on seismic performance of waste glass autoclaved aerated concrete masonry walls

  WEN Bo, WANG Huaizheng, WANG Xuefeng, ZHANG Haiyan, WANG Maoyu

  Journal of Building Structures. 2024, 45(12): 125-136. https://doi.org/10.14006/j.jzjgxb.2023.0549

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  In this paper, to improve the utilization rate of waste glass and expand its application in the field of construction, waste glass was ground into powder to replace quartz sand in the preparation of autoclaved aerated concrete blocks. Experimental research and finite element analysis were conducted on the seismic performance of waste glass autoclaved aerated concrete masonry walls. An orthogonal quasi-static test was designed for four walls made of waste glass autoclaved aerated concrete masonry, considering three factors: height-width ratio, vertical compressive stress, and mortar strength. It is shown from the tests that the failure mode of waste glass autoclaved aerated concrete masonry walls is shear failure. The ductility is significantly improved by the addition of glass powder, with the ductility coefficient of waste glass autoclaved aerated concrete masonry walls ranging from 4.74 to 6.00, demonstrating good seismic performance. It is shown from the numerical simulation that the shear resistance of the walls can be improved by increasing vertical stress, reducing the height-width ratio, and improving mortar strength. Among these factors, the height-width ratio is found to have the greatest influence.
  
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  Experimental study on seismic performance of brick wall strengthened with single-side polypropylene mesh-polymer mortar face

  ZHANG Fengliang, MA Dong, LIU Zuqiang, HU Pengchun, MAO Jingyan, XUE Jianyang, AN Zhanyi

  Journal of Building Structures. 2024, 45(12): 137-147. https://doi.org/10.14006/j.jzjgxb.2023.0812

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  To improve the seismic performance of brick masonry rural building, a strengthening method using single-side polypropylene mesh-polymer mortar face was proposed, considering the actual application situation of rural building. Eight scaled specimens were designed and quasi-static tests were carried out. The variable parameters of the specimens included the form of the strengthening face, the thickness of the strengthening face and the strength of the masonry mortar. The failure patterns and horizontal load-displacement curves of the specimens were obtained. The bearing capacity, ductility, stiffness and energy dissipation capacity of the specimens were analyzed. It is shown  that the failure patterns of brick walls strengthened with a single-side polypropylene mesh-mortar face under low cyclic reversed loads include shear-compression failure, shear-friction failure, and a combination of shear-compression and shear-friction failure, with the hysteretic curves being full fusiform. After strengthening with the single-side polypropylene mesh-mortar face, the peak load, displacement ductility coefficient, initial stiffness and maximum energy dissipation coefficient of the brick wall increase by 23%, 84%, 22% and 151%, respectively, indicating an effective improvement in the seismic performance of the brick wall. As the thickness of the strengthening face and the strength of the masonry mortar increase, the bearing capacity, initial stiffness and energy dissipation capacity of the strengthened brick wall show improvement. Based on the experimental study, a calculation method of the shear capacity for brick wall strengthened with a single-side polypropylene mesh-polymer mortar face was put forward, and average ratio between the calculation results and the experimental results is 0.99 and the variation coefficient is 0.059，indicating that the calculation results and the experimental results agree well.
  
special topics in fire resistance of structures
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  Fire resistance performance of multi-ribbed composite walls#br#

  WANG Zelin, CHEN An, SUN Jing

  Journal of Building Structures. 2024, 45(12): 148-159. https://doi.org/10.14006/j.jzjgxb.2024.0012

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  To investigate the fire resistance performance of multi-ribbed composite walls, two full-scale multi-ribbed composite walls were subjected to single-and double-sided fire tests, respectively. The temperature fields, displacements, fire resistances and failure modes of the walls were obtained. It is observed from the test that, under single-sided fire, a significant temperature gradient formed inside the wall along the thickness direction. When damaged, the temperatures of the autoclaved aerated concrete blocks and the concrete of the ribbed beams and ribbed columns on the surface unexposed to fire are 90℃ and 109℃, respectively. The failure mode is compressive-bending instability caused by thermal bending. For the wall under double-sided fire, a low temperature area is formed at the center along the thickness of the autoclaved aerated concrete blocks. When the wall fails, the temperature in this area is 193℃. The failure mode is axial compression failure caused by material strength degradation. Therefore, there is a significant temperature gradient between the autoclaved aerated concrete blocks inside the wall and the concrete of the ribbed beams and ribbed columns under both fire conditions. The interfacial cracking between the autoclaved aerated concrete blocks and the concrete of ribbed beams and columns has a negligible effect on the integrity of the walls. Under an axial compression ratio of 0.5, the walls under single- and double-sided fire conditions reach the fire resistances of 181min and 91min, respectively. The finite element model of multi-ribbed composite wall was established and a parametric study was conducted considering the axial compression ratios and fire conditions. It is found that the peak of thermal expansion of the multi-ribbed composite wall decreases as the axial compression ratio increases. When subjected to the same axial compression ratio and fire time, the axial thermal expansion of the wall under double-sided fire is larger than that under single-sided fire.
  

  
  

  
  
  
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  Research on mechanical properties of Q550D high-strength structural steel during heating and cooling stages of fire

  JIANG Binhui, WANG Fuxin, WANG Mengjie, LI Guoqiang

  Journal of Building Structures. 2024, 45(12): 160-169. https://doi.org/10.14006/j.jzjgxb.2024.0056

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  To study the mechanical properties of high-strength structural steel in fire, this paper investigated the mechanical properties of domestic Q550D high-strength structural steel during the fire heating and cooling stages, including the elastic modulus, yield strength, ultimate strength, ultimate strain, and elongation at break, by using the steady state test method. A cooling stage influence coefficient was adopted to reflect differences in the mechanical properties of steel between the cooling and heating stages. The results indicate that the mechanical properties of Q550D steel at the cooling stage are related to not only the test temperature but also the peak heating temperature. When the peak heating temperature is within 600℃, the difference in mechanical properties between the cooling and heating stages of Q550D steel is relatively small. However, as peak heating temperature further increases, especially when peak heating temperature exceeds 700℃, the significant differences appear on the mechanical properties between the cooling and heating stages, the yield strength and ultimate strength decreased significantly, and the ultimate strain increases significantly. Additionally, a high-temperature mechanical property model for high-strength steel during the cooling stage was established, and the proposed formula for calculating the mechanical property parameters of Q550D steel at the fire cooling stage was fitted well.
  
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  Experimental study on mechanical properties of corroded Q355 weathering steel at high temperature

  ZHANG Zongxing, TIAN Chenrui, JIANG Jian, YE Jihong, XIAO Luping, XU Yuxuan

  Journal of Building Structures. 2024, 45(12): 170-180. https://doi.org/10.14006/j.jzjgxb.2024.0104

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  In order to study the evolution of mechanical properties of corroded steel at high temperature, high temperature tensile tests were conducted on 12 mm thick Q355 weathering steel that had been in service for 10 years. The damage morphology, stress-strain curve and mechanical property degradation law of corroded steel at different temperatures were discussed. A numerical analysis model considering the surface morphology of corroded steel was established using three-dimensional reverse reconstruction technology. The development law of surface stress of corroded steel at different temperatures was studied, and the surface stress concentration coefficient and damage law of corroded steel at different temperatures were compared. The results show that the surface of the corroded steel is uneven and features pits of different sizes. With the increase in the degree of rust, the strength and ductility of steel at room temperature gradually decrease, with ultimate strength and elongation decreasing by 20% and 39%, respectively. As temperature increases, the influence of corrosion on the elastic modulus of steel is intensified, and the surface stress concentration of the specimens gradually decreases. When the temperature reaches 900 ℃, the mechanical properties of steel with different degrees of corrosion are found to be basically the same. High temperature significantly reduces the influence of corrosion damage, but the influence of rust on the ductility of steel still exists.
  
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  Experimental study on fire resistance performance of bolted glued laminated bamboo spliced connections subjected to axial loading

  WANG Mingqian, DAI Lu, XU Qingfeng, HAN Chongqing, CHEN Lingzhu, LENG Yubing

  Journal of Building Structures. 2024, 45(12): 181-188. https://doi.org/10.14006/j.jzjgxb.2024.0080

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  In this paper, nine axially loaded bolted glued laminated bamboo connection specimens were designed and tested at normal temperature and in fire to investigate the fire endurance of spliced connections subjected to axial loading. The test parameters included connection type, bolt end distance and load ratio. The fire endurance was determined based on the test results. The results indicate that the bolt end distance has an important influence on the failure modes of the specimens tested at normal temperature. Splitting failure perpendicular to the bamboo grain direction and longitudinal shear failure occurr in the glued laminated bamboo components when the specimens in fire are close to ultimate failure. A higher load ratio can lead to more notably bending deformation in the bolts of the specimens in fire. The load ratio plays an important role in the fire endurance of the connections. When the load ratio increases from 0.3 to 0.5, the fire endurance of the connections with slotted-in steel plates and a bolt end distance of 7 and 10 times the bolt diameter, and the connections encased with steel plates with a bolt end distance of 7 times the bolt diameter, decreases by 27.6%, 32.9% and 37.2%, respectively. The bolt end distance has a significant impact on the fire endurance of the slotted-in steel plate connections. When the bolt end distance increases from 7d (d is the bolt diameter) to 10d, the connection fire endurance with load ratios of 0.3 and 0.5 increases by 25.1% and 15.9%, respectively. The fire endurance of the bolted glued laminated bamboo connections subjected to axial loading meets the requirements of current timber structure design standards for similar types of bolted connections. The charring rate of the glued laminated bamboo decreases with the extension of fire exposure time. The average charring rate of the glued laminated bamboo is close to the nominal linear charring rate (0.90 mm/min) prescribed by T/CECS 1101—2022 ‘Standard for design of engineered bamboo structures’. 
  
  
Fundamental theories and general technologies
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  Automatic measurement of structural steel bar size based on ArUco assisted stitching and lightweight semantic segmentation network

  GAO Chenhao, CHEN Wang, JIANG Shang, ZHANG Jian

  Journal of Building Structures. 2024, 45(12): 189-202. https://doi.org/10.14006/j.jzjgxb.2023.0538

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  To address the issue of large rebar dimensions that cannot be covered by a single camera field of view in processing and inspection, a method for measuring the geometric shape (length and angle) of rebar using computer vision technology was proposeed. A partitioned camera measurement system was proposed. The partitioned cameras were utilized to simultaneously capture images and stitch together a panoramic view based on binary encoded ArUco markers. For real-time computing requirements, a lightweight semantic segmentation network, named as ghost-Unet, was proposed to balance the efficiency and accuracy of rebar contour recognition. To ensure computational accuracy, a robust straight-line detection algorithm was utilized for segmenting and fitting the rebar contours. The measurement results indicate that in the laboratory, the average length measurement error is 2.92mm when measuring vertical rebar with the optical axis of camera perpendicular to the plane. The average length measurement error is 4.27mm when measuring horizontal rebar with the optical axis of camera at an angle much less than 90° to the plane due to a rebar thickening issue in the orthographic correction stage. In the field, the average length measurement error is 3.08mm, and the angle error is within 0.7°. 
  
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  Experimental study on size effect of shear capacity of BFRP-reinforced concrete short beams

  SONG Bo, JIN Liu, ZHANG Jiangxing, DU Xiuli

  Journal of Building Structures. 2024, 45(12): 203-212. https://doi.org/10.14006/j.jzjgxb.2023.0537

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  The size effect of the shear capacity of concrete short beams can be effectively weaken by the reasonable arrangement of shear web reinforcement. Shear tests were conducted on eight BFRP-reinforced concrete short beams with  cross-sectional heights of 300mm to 1200mm (including four short beams without web reinforcement and four short beams with horizontal and vertical web reinforcement ratios of 0.5%). The development trends of the failure mode, load-deflection curve, and web reinforcement strain with changes in beam section height were analyzed, and the size effect of shear capacity of BFRP-reinforced concrete short beams without and with web reinforcement was revealed.It is  shown by tests that when the cross-sectional height increases from 300mm to 1200mm, the nominal shear strength of test beams without web reinforcement decreases by 52.3%, while the nominal shear strength of test beams with a web reinforcement ratio of 0.5% still decreases by 45.7%. The results indicate that BFRP-web reinforcement has not significantly suppressed the size effect behavior. Compared with the calculation results of relevant design codes in other countries, the shear capacity design method proposed by the author in previous research can reasonably reflect the size effect of BFRP-reinforced concrete short beams. The calculation results are in good agreement with the experimental results.
  
  
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  Study on axial compression behavior of 6A13-T6 high-strength aluminum alloy square section columns

  ZHONG Changjun, FENG Ruoqiang, LI Huyang

  Journal of Building Structures. 2024, 45(12): 213-222. https://doi.org/10.14006/j.jzjgxb.2023.0407

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  To investigate the force performance of 6A13-T6 aluminum alloy square cross-section axial compression members and to promote engineering applications, the material performance test, axial compression performance test of extruded square cross-section members, and finite element analysis were carried out with aluminum alloy members for curtain walls as the object of research, and the mechanical properties of the materials, the failure modes of the members and the methods of calculating the bearing capacity were investigated, as well as the evaluation and reliability analysis of the results of bearing capacity prediction obtained from the Chinese, American and Australian specifications and the direct strength method. The predicted results of Chinese, American, and Australian specifications and the predicted results of the direct strength method were evaluated and analyzed for reliability. The results show that the non-proportional yield strength f0.2 of 6A13-T6 aluminum alloy is as high as 340MPa, and the elongation after fracture is 14.5%; the large width-to-thickness ratio of the plates makes the members show obvious local buckling phenomenon at failure; as the length of the members increases, the failure mode of the members is changed from local buckling to coupled local-integral buckling, and the bearing capacity decreases significantly. The stiffening effect of the shaped part of the section can be conservatively disregarded in the bearing capacity calculation of the members. In general, the bearing capacity assessment using the relevant specifications is conservative, and the direct strength method has the best prediction effect, which is recommended to be used for the bearing capacity assessment. In addition, the reliability of each of the above bearing capacity prediction methods is greater than 2.5 but only meets the relevant requirements of the American and Australian specifications. To meet the requirement of the target reliability of 3.7 in the Chinese specification, the resistance sub-coefficient can be revised to 1.40.
  
  
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  Study on shear resistance of precast concrete sleeve grouting joint with double-interface

  QIN Chaogang, GAO Zhiyao, YANG Long, WU Tao

  Journal of Building Structures. 2024, 45(12): 223-235. https://doi.org/10.14006/j.jzjgxb.2023.0540

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  In this paper, direct shear tests were conducted on 22 Z-shaped specimens to analyze the shear performance of the concrete-grout-concrete double interface in the grouted sleeve connection of precast components. The failure modes, shear strength, shear stiffness, and shear-slip curve variations of the shear interface were examined. Several parameters such as interface roughness, reinforcement ratio, fullness of sleeve grouting, and grout layer thickness were considered in the tests. It is shown that the double-interface shear cracks start at the bonding interface, develop along the interface regularly and run through the grout layer after cutting the keyway. In the elastic and elastoplastic stages, the shear force is balanced by the cohesion force, the bar friction force and the pin force, and only the bars provide the shear resistance after the cracks penetrates. The ultimate shear and shear stiffness of the double interface are improved by increasing the interface roughness, reinforcement ratio and grouting thickness. The ultimate shear strength, residual shear strength, and shear stiffness are reduced by about 10%, 15% and 20% with the absence of 65% sleeve grouting material, respectively. Based on the performance parameters of the characteristic points of the shear-slip curve, a two-interface shear-slip constitutive model was established. The cohesive force and friction coefficient affected by different interface roughnesses were determined. Based on the theory of beams on elastic foundation, the expression of pin force influenced by the thickness of the grout layer was derived. Finally, the calculation formula for double-interface shear bearing capacity under different factors was established, and the calculated results matched well with the experimental data.
  
  
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  Experimental study on shear and flexural performance of section steel plug-in welding composite joint for composite reinforcement concrete prefabricated square piles

  XU Quanbiao, XUE Chaoyue, CHEN Gang, ZHANG Xuwei, GONG Shunfeng

  Journal of Building Structures. 2024, 45(12): 236-245. https://doi.org/10.14006/j.jzjgxb.2023.0525

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  A composite connection joint for section steel plug-in welding of concrete prefabricated piles was designed to improve the connection performance of concrete prefabricated piles. The shear and flexural experiments of thirteen composite joints and pile bodies of composite reinforcement concrete prefabricated square piles with section side lengths of 300mm, 450mm and 600mm were conducted to compare the shear and flexural bearing capacities, deformation capacity and failure characteristics of the section steel plug-in welding composite joints and pile bodies. The results show that the shear failure mode for the pile bodies is the oblique section shear failure in the flexural shear section, and for the joints is the oblique section shear failure in the flexural shear section and the steel bar pier heads being pulling off at the joint. The main flexural failure mode for the pile bodies is the tensile fracture of the steel bars in the tensile zone of the section, and for the joints is the steel bar pier heads being pulled off at the joint. For the shear specimens, many vertical cracks are observed in the pure flexural section, along with an obvious oblique abdominal shear crack in the flexural shear section. While for the flexural specimens, the vertical cracks in the pile bodies are numerous and evenly distributed, with bifurcation phenomena. The shear and flexural bearing capacities, and deformation capacity of 300mm and 450mm square pile joints are close to those of the pile bodies. For the 600 mm square pile joint, adding anchoring rebars to the end plate at the joint can effectively enhance the flexural bearing capacity and deformation capacity of the joint.
  
  
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  Settlement calculation method of combined grouted bored piles considering influence of length-diameter ratio

  HU Tao, DAI Guoliang, WAN Zhihui, FANG Bowen, GONG Weiming,

  Journal of Building Structures. 2024, 45(12): 246-257. https://doi.org/10.14006/j.jzjgxb.2024.0015

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  The length-diameter ratio has important influences on the bearing behavior of combined grouting bored piles. Based on the field test data of bored piles in the Jinghang Grand Canal Bridge on Ningliang Expressway, the effects of combined grouting, length-diameter ratio and bearing layer on the load transfer characteristics of bored piles were analyzed. On this basis, the calculation method for settlement for combined grouting bored piles based on the load transfer method and spherical permeation grouting theory was established, considering the influences of length-diameter ratio and an enlarged pile tip, and the rationality of the calculation method was varified by an engineering example. The results show that combined grouting effectively improves the ultimate bearing capacity of bored piles under the premise of pile length optimization. The load transfer characteristics of the combined grouting bored pile are greatly affected by the length-diameter ratio and the type of bearing layer. The initial slope of the side load transfer curve of the combined grouting bored pile with different length-diameter ratios can vary by up to 380%. Compared with existing prediction methods, the proposed calculation method can better predict the actual load-settlement characteristics of the combined grouting bored pile, which provides a reference for the scientific optimization and design of the combined grouting bored pile while ensuring the safety of the prediction results.