To investigate the shear performance of Italian poplar laminated veneer lumber(LVL)beams with opening in the bending-shear region,six standard specimens were designed and tested under four-point bending.The shear failure mechanisms of the LVL beams with opening under various parameters were analyzed.Using the extended finite element method and ABAQUS software,a finite element model of perforated beam with virtual cracks was developed.Parametric analyses were performed considering variations in the diameter-to-height ratio,opening shape,and opening center eccentricity,using the validated model.The results show that the unperforated beam experiences bending failure due to tensile cracking at the mid-span.In contrast,beams with circular opening experience longitudinal shear failure at the ends due to stress concentration around the opening perimeter.The maximum transverse tensile strain around the opening perimeter forms an angle of approximately 45°or 225°relative to the longitudinal axis of beam,consistent with the crack initiation angle.As the diameter-to-height ratio increases to 0.5,both cracking and ultimate load capacities of the beams with circular opening significantly decrease,exhibiting more brittle shear failure.When the diameter-to-height ratio increases from 0.3 to 0.4 and 0.5,the ratio of cracking to ultimate load capacity increases from 0.79 to 0.80 and 0.81,respectively.Using carbon fiber reinforced polymer(CFRP)wrapping around the openings effectively suppresses crack propagation and enhance the structural performance of the perforated beams.For the beam with a diameter-to-height ratio of 0.4,the ultimate load decreases by 17.9％and 5.22％,respectively,for one and two layers of CFRP wrapping,compared to the unperforated beam.When comparing circular-opening beam(diameter-to-height ratio of 0.3)to those with square-opening of the same diameter,the square-opening beam shows a 19.35％and 7.81％reduction in cracking and ultimate load capacity,respectively.Increasing the opening center eccentricity is found to improve both cracking and ultimate load capacities.The prediction formulas for the cracking and ultimate load capacities of LVL beams with opening were proposed.The prediction for cracking load is relatively conservative,and the average error between the predicted and experimental results for the ultimate load is 8％.
Carbon fiber-reinforced polymer-steel composite bars (C-FSCBs) and coral sea-sand aggregate seawater concrete (CSSC) are attractive choices as construction materials for island and atoll engineering construction. Understanding the bond behavior between the C-FSCB and CSSC is crucial for evaluating the mechanical properties of C-FSCB-reinforced CSSC structures. In this study, the bond-slip behavior between the C-FSCB and CSSC was experimentally assessed via pullout tests. The influence of various factors on the bond behavior was discussed, and the bond mechanism between the C-FSCB and CSSC was analyzed. The results indicate that, unlike steel bars, the low rigidity of fiber-reinforced polymer caused surface fiber stripping (i.e., shear damage) of the C-FSCB after interface slip, consequently reducing the squeezing fragmentation of concrete between the ribs. As the diameter and bond length of the C-FSCB increased, the bond strength decreased. Compared to specimens with C-FSCBs, the bond strength of specimens with steel bars of the same diameter increased by 17.9%. The degree of coarse aggregate fracture at the CSSC interface in the splitting failure was much higher than that of normal concrete. Based on existing research data, a formula for calculating the bond strength of C-FSCBs in CSSC has been established to determine the anchorage length of C-FSCBs, and the calculated values accurately predicted the test values.
Combining the advantages of partially encased composite structure (PEC) and corrugated steel web, a new type of composite PEC beam with corrugated web was proposed in this paper, namely corrugated webbed PEC (CWPEC) beam. In order to investigate the structural performance of the proposed CWPEC beams, four specimens were designed and fabricated. Four-point bending tests were carried out to study their flexural performance and failure modes. The failure process, load-displacement curve and strain distribution of the tested specimens were analyzed. Experimental results showed the high load carrying capacity and superior ductility of the proposed concept. Parametric study indicated that the concrete strength was increased from C30 to C50, the ultimate load slightly increased by 3.38%. The flange strength decreased from Q355 B to Q235, the ultimate load reduced by 9.17%. The flange width decreased from 250 mm to 200 mm, the ultimate load decreased by 22.21%. As comparison, the increase of steel flange width is more efficient to improve section moment capacity. Further analysis verified that the flexural strength of CWPEC beam was mostly provided by flanges with little contribution from the corrugated web. Finally, based on the quasi-plane assumption, prediction formulas for cracking moment and ultimate moment of CWPEC beams were proposed.
A suitable constitutive model for describing the damage behavior of ultra-high performance concrete (UHPC) under various loading histories plays a vital role in analyzing its structural performance. In this work, a consistent elastoplastic damage model is developed for UHPC containing coarse aggregate (UHPC-CA) subjected to static and fatigue loads, in which the driving and alleviating effects induced by the inclusions of coarse aggregate and steel fiber are considered. For damage evolution, based on the acting mechanism of the non-uniformity of stress wave propagation determined by the loading rate on the mechanical responses of UHPC-CA, the loading rate is skillfully integrated into the damage evolution rule to achieve the consistent description of mechanical behaviors of UHPC-CA under static and fatigue loading conditions. Regarding plasticity growth, an empirical plastic deformation model is adopted to improve the computational efficiency of structural nonlinear analysis. To verify the applicability of the proposed model, a user-defined UMAT subroutine is further developed for the subsequent numerical implementation. The comprehensive comparisons between the numerical predictions and independent experimental results at both the material level and structural level solidly demonstrate the capacity of the consistent model to capture the main features concerning the mechanical performance of UHPC-CA subjected to different loading paths.
Irregular buildings that occupy a certain proportion on regional scales are prone to suffer serious damage from earthquakes due to the influence of lateral-torsional coupling effect. However, the current regional seismic damage simulation methods are mainly based on two-dimensional simplified models, which cannot take into account the spatial characteristics of irregular buildings. In addition, the refined finite-element method is unsuitable for the simulation of a host of buildings on a regional scale. This paper proposes a moderately refined seismic damage simulation method for building groups with high efficiency to consider the spatial irregularity characteristics of structures. The moderately refined layer element model is established to simulate the nonlinear behavior of each story of the building with irregular plan configurations. For the elevation-irregular structures, the proposed model can also be used by properly combining the elements representing various stories in series. Additionally, a simplified approach of considering P-∆ effect is incorporated by adding equivalent lateral forces to nodes and the method for determining the hysteretic parameter and backbone curve parameters of the proposed model is illustrated. Then, a two-level accelerated dynamic analysis method is proposed to reduce computation time for seismic damage simulation in region, which involves a perturbation nonlinear dynamic governing equation for a single structure and an OpenMP parallel solution strategy for structure groups. Finally, the two individual numerical examples and the seismic damage simulation for a region are performed to demonstrate the validity and efficiency of the proposed method.
In order to investigate the hysteretic behaviour of concrete-filled double tubular(CFDT)columns,the quasi-static tests on 12 square CFDT members with inner circular steel tubes were completed.The influence of the axial load ratio(0.2,0.4 and 0.6)and the diameter-thickness ratio(30,44.5 and 57)of inner circular steel tubes on the failure modes of specimens,horizontal load-displacement curves and seismic performance were examined.Based on the fiber beam element subroutine iFiberLUT and ABAQUS software,a numerical model was developed to predict the test results and analyze the effects of various parameters on the horizontal load-displacement skeleton curves.The test results show that the circumferential local buckling of outer steel tube in the lower zone of columns gradually become obvious with the increase of the axial load ratio,while the diameter-thickness ratio of inner steel tube exhibit slight effect on the deformation capacity of columns.Within the parameters of this study,all horizontal load-displacement hysteretic loops are relatively full,and the average value of displacement ductility coefficient and viscous damping coefficient of all specimens are 0.326 and 0.6 respectively,showing a superior deformation and energy dissipation capacity.With an increase in the axial load ratio,the bearing capacity,the ductility and horizontal stiffness of specimens decrease,but the strength degradation is slight.When the axial load ratio increases from 0.2 to 0.6,the cwerage peak load decreases by 53.4％.The parameter analysis indicate that with an increase in the width-thickness ratio,the improvement of the diameter-thickness ratio of outer steel tube can lead to a more obvious increase in the peak loak of members,but increasing the axial load ratio can mitigate the influence of the diameter-thickness ratio of inner steel tube on the bearing capacity.
The interface bonding effect can determine the overall mechanical properties of the reinforced components to a large extent. This paper proposed an improved interface treatment method between FRP grid-ECC composite layer and concrete that could quantify the interface roughness, and the effect of this method on the interface bonding behavior was investigated through the double-shear test. Four groups of twelve specimens, including one group without interface treatment and three groups with different interface treatment rates, were tested to reveal their bond-slip relationship. The test results demonstrated that the improved method was effective, with the ability to inhibit interface peeling; moreover, as the interface treatment rate increased, the bonding effect enhanced, and the failure mode gradually transitioned from critical fracture to composite layer fracture. Furthermore, the bond-slip model and the bearing capacity formula for the improved method were established, and the predicted values were well matched to their corresponding test results.
Stainless steel tube-confined steel-reinforced recycled concrete columns (SSTCSRRC) have the potential to be widely used in engineering structures due to their advantages of aesthetic appearance and reutilization of waste materials. However, there is currently little research work on this new type of thin-walled stainless steel composite columns. This paper investigates the behaviour of SSTCSRRC stub columns under axial compression. Tests on seven circular and seven square stub columns were carried out, and the main variables include the thickness of the stainless steel tube, the recycled brick aggregate (RBA) replacement ratio and the specimen type. The results indicate that the confinement effect of the stainless steel tube improves the ultimate strength and ductility of the columns, and the ultimate strength decreases with an increase in RBA placement ratio. A high RBA placement ratio or using cross-shaped section steel can significantly improve the ductility of the columns. A finite element (FE) model was developed to simulate the axial compressive behaviour of SSTCSRRC stub columns. Based on the numerical data of 130 FE models, the design formulas for axial compressive strength and stiffness of SSTCSRRC stub columns were proposed.
Based on the design concepts of damage control and concentrated energy consumption of key energy-consuming components, this paper puts forward an earthquake-resilient prefabricated column foot joint. Expounds the structural composition, advantages and seismic design requirements of this new type column foot joint in detail. After comprehensively considering the mechanical mechanism of the column foot joint, the load-bearing capacity correction coefficient and the height ratio of lateral force-resisting shear member (LRSM) inflection point are introduced, and the design theory is established accordingly, including the dimension of LRSMs, the number of connecting bolts and the stiffness of connecting beams. The rationality and applicability of the proposed design theory are verified by 18 groups of 90 finite element models, and several test specimens. The research shows that the design theory proposed in this paper can accurately predict the yield load and initial stiffness of the new type column foot joint, and effectively control the bolt slip time and the connecting beam failure time. The new column foot joint designed according to this design theory has excellent bearing capacity and ductility. The plastic damage of this joint can be basically controlled on the lateral force-resisting energy-consuming device (LRECD), which has the premise of earthquake-resilient.
There has been extensive discussion as to whether the scope of site classification II is too broad in current Chinese seismic code. To address this issue, this study aims to optimize the site classification scheme for Chinese seismic code using clustering analysis of site amplification. Firstly, we estimate the empirical site amplification factors of KiK-net stations by the residual analysis method, and classify them by the site classification scheme of Chinese seismic code. Next, we perform k-means clustering analysis on the stations of site class II, considering site amplification factors, equivalent shear wave velocities and thicknesses of sedimentary layers as explanatory variables, and obtain two clusters with distinct site amplification effects. Finally, we use correlation analysis and Receiver Operating Characteristic (ROC) curve to guide the optimization of site classification scheme, and suggest dividing site class II into two subclasses, IIa and IIb, by a threshold of 15m for the thickness of sedimentary layer. The proposed optimized classification scheme would be beneficial for improving the seismic design code and could be further applied to the development of ground motion models and seismic hazard analysis.
Bobbin friction stir welding (BFSW) is a variant of the conventional friction stir welding (CFSW); it can weld the upper and lower surface of the work-piece in the same pass. This technique involves the bonding of materials without melting. In this work, the influence of tool design on the mechanical properties of welding joints of 6061-T6 aluminum alloy with 6.25 mm thickness produced by FSW bobbin tools was investigated and the best bobbin tool design was determined. Five different probe shapes (threaded straight cylindrical, straight cylindrical with 3 flat surfaces, straight cylindrical with 4 flat surfaces, threaded straight cylindrical with 3 flat surface and threaded straight cylindrical with 4 flat surfaces) with various dimensions of the tool (shoulders and pin) were used to create the welding joints. The direction of the welding process was perpendicular to the rolling direction for aluminum plates. Tensile and bending tests were performed to select the right design of the bobbin tools, which gave superior mechanical properties of the welded zone. The tool of straight cylindrical with four flats, 8 mm probe and 24 mm shoulders diameter gave better tensile strength (193 MPa), elongation (6.1%), bending force (5.7 KN), and welding efficiency (65.4%) according to tensile strength.
In order to study the low-cycle fatigue behaviour of stainless-clad(SC)bimetallic steel,research on the SC bimetallic steel S31603+Q355B and its corresponding substrate conventional mild(CM)steel Q355B was further expanded in this study from an energy-based perspective on the basis of existing test data.The concept of standard hysteresis loop was clarified,the cyclic strain energy and Masing properties of the metals were analyzed,and a new energy-based fatigue life prediction model was proposed.The results show that the strain amplitude is the main factor affecting the strain energy and low-cycle fatigue life of the SC bimetallic steel and the substrate CM steel.Cyclic hardening was observed in both the SC bimetallic steel and the corresponding CM steel,but it mainly occurred within the first several cycles,followed by visible cyclic softening features.The two steels exhibited cyclic stability during the entire cyclic loading process,and the steady-state process accounted for most of the cycling period.The proposed energy-based low-cycle fatigue life prediction model can effectively fit the fatigue life curves of both the SC bimetallic steel and the substrate CM steel,which can be used as an alternative to strain-fatigue life analyses.
为进行弹性半空间场地下结构动力特性的试验研究,提出以Fourier谱幅值与频率成反比、带通的平稳随机荷载作为实时耦联动力试验的激励;建立了综合运用经验小波变换(EWT)、随机减量法(RDT)和Hilbert变换进行实测结果的模态参数识别技术;土-结构相互作用体系中土体采用数值子结构模拟,地上结构采用物理子结构.对钢结构模型采用三种不同配重分别进行刚性基础和土-结构相互作用的模态参数识别试验,结果表明,所提平稳荷载激励下的实时耦联动力试验具有良好的稳定性;试验数据经EWT和RDT可得标准的自由振动信号,较好识别了体系的动力特性.因此,所提的试验和参数识别方法合理.刚性基础下框架结构的各阶模态阻尼比基本相同,且与结构的自振频率无关;在弹性半空间辐射阻尼的影响下,结构模态阻尼比远大于刚性基础下的阻尼比,且与结构的自振频率相关.
When double-skin composite（DSC） shear wall is applied to prefabricated steel structure buildings, concrete needs to be cast on the construction site. The onsite casting of concrete suffers from many deficiencies including low construction efficiency, complex construction process, a large amount of wet work and high labor cost, and thus does not meet the requirements of building industrialization. Therefore, the monolithic precast double-skin composite（MPDSC） shear wall is developed, that is, the standardized shear wall components are prefabricated in the factory while only a small amount of welding and post grouting technology are used for direct assembly on site so that the construction efficiency is effectively improved. In order to study the seismic performance of MPDSC shear wall, taking the connection mode of horizontal joint boundary elements and axial compression ratio as the main parameters, one traditional DSC shear wall and four MPDSC shear wall specimens were designed, and their quasi-static tests were carried out. The test results indicate that the failure mode of the MPDSC shear wall is typical compression bending failure: the boundary elements and the steel plate at the bottom of the wall buckle, the bending wave is distributed from the top of the stiffened plate on the upper part of the foundation beam to the height of 100-200 mm away from it, and the filled concrete is crushed. The hysteretic loop of the MPDSC shear wall is shuttle shaped, the peak load is about 5% higher than that of the DSC shear wall, the ductility coefficient is more than 3, and when the axial compression ratio is 0.2 and 0.4, the average yield displacement angles are 1/186 and 1/157 respectively, and the average failure displacement angles are 1/53 and 1/35 respectively, which meet the limit value of elastic and elastic-plastic displacement angle in JGJ/T 380—2015 ‘Technical specification for steel plate shear walls’. The connection mode of horizontal joint boundary element has little effect on the seismic performance of the MPDSC shear wall, when the horizontal joint is located in the middle of the shear wall, so the trilateral connection of boundary element, which is relatively simple for construction, can be used for field assembly.
为了实现工程结构的准确、高效模拟,提出了完全基于深度学习的结构全过程响应智能计算框架,从数据侧到模型侧综合考虑了结构自身构造信息以及任意加载制度,能够适用于材料、构件甚至是结构体系等多层次力学响应预测问题.并根据结构计算场景特点制定了结构静态特征统一数据接口模式,保真结构原始信息输入,有效减少人工干预.在此基础上,引入了注意力机制与深度交叉网络,提出了结构静态特征表示学习模型PADCN(注意力机制预处理的深度交叉网络,pre-attention deep&cross network),能够兼顾结构静态特征的记忆性与泛化性,挖掘不同构造信息的耦合关系.将PADCN模型与动态特征预测模型Mechformer相集成,并与设计的通用数据接口衔接,形成了端到端数据驱动的结构响应智能计算框架.为验证框架的有效性,以钢板剪力墙结构为载体开展数值试验,其中提出了适用于结构计算领域的数据增广算法,以缓解结构工程数据量匮乏的问题.结果表明:基于该框架的智能模型成功预测了不同构造的钢板剪力墙试件的全过程非线性响应,模拟精度优于精细有限元模型.同时,计算效率为传统数值方法1 000倍以上,证明该智能计算框架具有卓越的准确性与高效性.
总应变裂缝模型作为国际结构混凝土协会混凝土模式规范中推荐的混凝土本构关系,可以较准确地模拟混凝土开裂破坏全过程中的力学行为及裂缝分布.基于该模型分析了约束效应和横向开裂效应对混凝土受力性能的影响.为对该模型进行验证校核,进行了两根大尺寸钢筋混凝土梁的三点与四点加载试验.针对该试验及已有研究中箍筋约束混凝土柱的受压试验,进行了基于总应变旋转裂缝模型的有限元模拟.模拟所得荷载-位移、荷载-应变曲线以及开裂模式与试验结果的误差基本在15％以内.在此基础上,预测了箍筋约束混凝土轴压及大偏心受压下的承载力,所得结果与经验回归模型所得压弯破坏包络线相一致.
开槽密拼混凝土叠合板的预制板无外伸钢筋,通过开槽密拼构造连接,在槽口内放置附加钢筋再后浇混凝土可形成板间的有效传力;该构造形式能够有效解决装配式混凝土结构中预制构件外伸钢筋冲突的难题.为了研究开槽密拼混凝土叠合板的受力性能,共设计3个叠合板试件,研究开槽密拼混凝土叠合板的破坏模式、荷载-位移发展规律、承载力、刚度以及变形能力.结果表明:在正常使用状态下,相比于无拼缝混凝土叠合板,开槽密拼混凝土叠合板的刚度、屈服荷载和荷载-位移发展规律与其基本一致;在极限状态下,由于拼缝处叠合面的分离,导致开槽密拼混凝土叠合板的极限荷载以及变形能力有所下降,但仍满足设计需求;此外,增强附加钢筋的端部锚固可以进一步提升开槽密拼混凝土叠合板的承载力.给出了开槽密拼混凝土叠合板的受弯承载力与抗弯刚度计算方法,并结合典型工程案例对该结构的实用性展开分析,结果表明,开槽密拼混凝土叠合板不仅可以满足受力性能的设计需求,还能有效提升构件拼装速度,减少现场人工作业量,缩短施工周期,降低建造成本.
The deep buried straight wall round arch structure in the rock medium is taken as the research object in this study, to study the dynamic response, failure mode and damage mechanism of the deep buried underground structure under the impact of the explosion. A scaled test study of the underground structure under the ground impact of multiple explosion in the top with a scale of 1∶20 and a proportional explosion distance of 1.69 were designed and carried out. The macroscopic phenomena and measured data of the test were analyzed, and the results show that under the initial explosion and the repeated explosion, the surface of the surrounding rock model and the vicinity of the prefabricated loading hole are seriously damaged. In contrast, the damage of the underground structure is relatively minor, the overall structure produces downward bending deformation, and an axial crack occurs on the inner surface of the vault. Under the ground impact generated by the explosion, the deep buried underground structure model mainly performs overall vibration, and the acceleration response is significant. The peak accelerations of the vault and floor of the prototype structure can reach up to 107.05g and 97.15g, respectively. In the initial explosion, the damage of the upper part of the surrounding rock and the axial crack at the vault lead to a decrease in the local stiffness. And the crushed area and cracks of the surrounding rock formed by the initial explosion aggravate the attenuation and leakage of the shock wave energy during repeated explosions, resulting in the reductions of the ground shock pressure on the structure, the structural strain and the acceleration response at the base plate position. It is also found that at the floor of the prototype structure, the maximum spectral acceleration in the range of the natural vibration period of the human body exceeds 10g, which poses a safety threaten to the usage of underground structures.
In order to investigate the seismic performance of structure with energy dissipation cladding panels(EDCP),a 1/2-scale two-story and one-span reinforced concrete(RC)frame structure was designed and fabricated.EDCP were only equipped along the Y-direction,forming a'damping structure'in this direction and a'seismic structure'counterpart in the X-direction.Two natural ground motions were selected as inputs,and unidirectional shaking table tests under service level earthquake(SLE),design basis earthquake(DBE),and maximum considered earthquake(MCE)were conducted in the two directions of the test structure.The dynamic properties and seismic responses of the two structures were then compared.The test results show that the damage degree and seismic response of the damping structure are lesser than those of the seismic structure under DBE and MCE,indicating a satisfactory control effect.The damage of the two structures both focuses on the ends of beams and the roots of first story columns,indicating that the EDCP does not influence the damage pattern of the main structure.Throughout the test,the U-shaped steel dampers exhibit an expected crawler-type deformation and basically keep undamaged.Even under MCE,the cladding panels remain intact,indicating that this kind of structure can effectively control the damage to the cladding panels.
To select the economical and rational structural form for Dalian Suoyuwan Football Stadium,comparative analysis of three schemes was conducted:the double-layer orthogonal wheel-spoke cable structure,the upper-layer crossed wheel-spoke cable structure,and the double-layer crossed wheel-spoke cable structure.The results reveal that the upper-layer crossed wheel-spoke cable structure demonstrates better economical and mechanical advantages,which makes it the final structural system adopted for Dalian Suoyuwan Football Stadium.To investigate the feasibility of the tensioning construction scheme for the upper-layer crossed wheel-spoke cable structure,a 1∶20 scaled experimental model was designed and fabricated.The tensioning experiment was performed,and the tensioning process was further analyzed using the nonlinear finite element method.The results indicate that the experiment can accurately simulate the actual tensioning process,the construction scheme established based on ground assembly and overall lifting is feasible because of the stable and controllable process,and the traction lengths of active cables for experiment can serve as valuable references for practical construction.
