考虑翼缘影响的异形柱框架节点抗裂性能分析

在钢筋混凝土异形柱框架节点受力分析的基础上,应用弹性理论推导出考虑翼缘尺寸影响的节点抗裂承载力计算公式,并给出了节点核心区截面有效验算宽度、截面有效高度的表达式.另外,对4个异形柱框架节点进行了低周反复荷载作用下受力性能试验研究,分析了异形柱节点内箍筋应变随荷载变化情况.试验结果表明:节点内箍筋的应变在节点开裂前较小,计算异形柱节点开裂承载力时,可以不考虑其影响;当节点开裂后,箍筋应变突然增大.该荷载为节点核心区的开裂承载力.最后,将提出公式的计算结果与试验结果进行对比,表明该公式具有较好的适用性.     

高强钢筋钢纤维混凝土框架中节点抗震性能试验研究

为研究配置高强钢筋梁柱节点抗震性能同时改善配置高强钢筋所引起的框架节点梁筋滑移量大的问题,在混凝土中加入钢纤维应用于节点的不同范围,对2个配置HRB600/HRB400钢筋的普通混凝土节点和2个配置HRB600钢筋的钢纤维混凝土节点进行低周反复荷载试验,探究钢筋强度、钢纤维范围对框架中节点抗震性能的影响。对比分析框架中节点的破坏特征,研究节点耗能能力、累积损伤、位移延性、梁筋滑移量等抗震性能指标。研究结果表明,所有试件均发生节点核心区剪切破坏,提高节点的梁钢筋等级能够显著提高节点的承载能力和耗能能力,但梁筋滑移量增加。在节点构件中采用钢纤维混凝土整体增强或局部增强均能够有效减少裂缝宽度和梁筋滑移,改善配置HRB600钢筋节点的破坏形态和滞回性能,提高耗能能力和延性性能,减轻累积损伤程度并减缓刚度退化。     

配矩形螺旋箍筋型钢高强混凝土短柱轴压性能试验研究

为研究配矩形螺旋箍筋型钢高强混凝土短柱轴压性能,以混凝土强度、体积配箍率和配箍形式为变化参数设计6个试件进行轴心受压加载试验。试验结果表明,所有试件的破坏形态和荷载-轴向位移曲线相似,配螺旋箍筋的试件变形性能要优于配普通箍筋试件,配矩形螺旋箍筋的试件极限承载力随混凝土强度、体积配箍率的增加而提高。在试验基础上,采用基于叠加理论的计算方法对配矩形螺旋箍筋型钢高强混凝土短柱轴压承载力进行计算,给出了相关设计建议,研究结果可为配矩形螺旋箍筋型钢高强混凝土短柱的工程应用提供科学依据。     

应用三维有限元法探讨RC梁柱节点的破坏机理

为了探究节点加强后RC梁柱节点的抗剪承载力、延性提高以及节点破坏模式由剪切破坏转变为梁弯曲破坏的实质,本文在RC节点的三维有限元分析的基础上探讨RC梁柱节点加强后的破坏机理。通过详细考察加固前后节点内部不同位置混凝土的应力-应变发展规律,探讨加强前后节点混凝土的宏观损伤发展过程;同时,通过考察核心混凝土的应力-应变关系及发展过程定量探讨加强钢板、梁柱主筋及箍筋对核心混凝土的约束作用。基于上述混凝土损伤过程的宏观分析,可以得出由于梁主筋的粘结加强、加强钢板以及箍筋对混凝土约束作用,使节点核心混凝土的实际强度增大、损伤延迟,RC节点由加强前的节点剪切破坏模式转变成梁端的弯曲破坏模式,从而提高RC梁柱节点的抗剪承载力和延性。     

用于RC框架-轻钢增层混合结构的新型外箍式节点抗震性能试验研究

RC框架-轻钢增层混合结构是一种上轻下重、刚度突变明显的复杂结构,为了保证结构整体协同工作,本文提出了一种能够有效减缓刚度突变和增强对上部结构约束的新型外箍式连接节点。通过对新型外箍式节点与传统植筋节点的1∶2缩尺模型拟静力试验研究,得到了试件破坏模式和荷载-位移滞回曲线,对比分析了其滞回特性、梁端塑性铰、骨架曲线、强度退化、刚度退化和耗能能力等抗震性能。结果表明:新型外箍式节点可以使梁端塑性铰远离梁根部,有效保护了节点核心区;新型节点通过外箍钢板的构造措施提高了试件的初始刚度、承载力和耗能能力,减缓了刚度与强度退化速度,表明新型节点的抗震性能大幅度优于传统植筋节点,研究成果可为RC框架-轻钢增层混合结构的节点设计提供一定参考。     

框桁式复合墙体抗震性能试验及有限元分析

提出一种新型框桁式复合墙,由钢筋混凝土外框和内部桁式杆件构成。为了研究其抗震性能,按1∶2的缩尺比例初步设计和制作了3个单片框桁式复合墙体,进行了拟静力试验,并采用ABAQUS软件建立了有限元非线性分析模型,重点分析了轴压比、混凝土强度、箍筋配箍率及纵筋配筋率对其承载力和延性的影响。结果表明,墙体桁杆先于外框墙肢产生变形和破坏,最终在墙肢底部与桁杆围成的三角形部位由于弯矩值达到极限而发生破坏,破坏顺序明确,可达到多级耗能的目的;三个试件的延性系数均小于2.5,各试件延性系数的不同说明桁杆截面形式是影响墙体承载力的重要因素;随着轴压比、混凝土强度和纵筋配筋率的增大,试件承载力有不同程度的提高,试件的延性系数随轴压比和纵筋配筋率的增大而减小,随混凝土强度的增大而增大;箍筋配箍率对试件荷载-位移曲线、承载力和延性系数的影响很小;各因素对各项抗震性能的影响程度不同。     

桥梁空间分析中预应力效应分析方法研究

预应力技术在桥梁中的广泛使用,使得桥梁结构受力状况复杂,对预应力混凝土桥梁进行空间分析是必要的;但由于预应力筋数量庞大且形状复杂,对预应力空间效应的模拟是预应力混凝土桥梁空间分析的难点。从预应力筋的实际作用机理出发,提出在预应力张拉阶段用等效节点荷载来模拟预应力对结构的作用;而在预应力管道灌浆后,将预应力筋作为结构的一部分,用实体退化单元进行结构分析,并用两算例对本文的方法进行了验证。结果表明,该方法能真正模拟预应力的空间效应,可用于预应力混凝土桥的空间分析。     

高层建筑结构边节点抗震性能研究

通过7根留有施工缝的高层建筑结构边节点的低周反复抗震性能试验,研究了轴压比、节点核心区的混凝土强度等级、柱中混凝土在梁中的延伸长度等对梁柱边节点抗震性能的影响,对构件的破坏特征、承载能力、延性性能、滞回曲线和骨架曲线进行了对比分析。试验结果表明:所有试验构件均为梁端受弯破坏;柱中混凝土在梁中的延伸长度对骨架曲线的形态、屈服荷载和最大荷载都没有显著影响;但是延伸长度对节点的延性性能是有影响的,延伸长度为0.5h(h为梁高)的边节点构件的位移延性系数小于延伸长度为1.0h和1.5h的构件。     

梁柱不同混凝土强度的高层框架节点试验和有限元分析

高层框架结构设计时，梁板与柱常常会采用不同的混凝土强度等级，柱的混凝土强度等级往往高于梁板。对于梁柱的节点，一般多采用与柱相同的强度等级，这给施工带来很大麻烦，如果采用与梁板相同强度等级混凝土时。虽然方便了施工，但降低了节点的抗震性能。本文的研究是通过对此类节点采取加强措施，以弥补混凝土强度等级降低的不利影响。通过节点模型试验，研究其受力性能及破坏机理，验证加强措施的有效性。并在试验研究的基础上，用有限元方法对受力复杂的节点进行分析，结果表明节点区混凝土存在应力集中和应力扩散现象以及存在混凝土侧向受拉的现象．证实了梁加腋和增设X型钢筋后节点受力性能得到了改善和加强。这些研究成果对目前高层建筑梁柱节点采用不同混凝土强度等级的设计、施工提供了有益的参考。     

新型外包加强型混合节点非线性数值模拟及参数分析

采用Abaqus有限元软件建立新型外包加强型混合节点模型,在验证模型正确性的基础上对其进行拟静力作用下的非线性分析,深入研究各个加载阶段的受力性能及破坏机制,并进行了相关参数对节点抗震性能的影响分析。结果表明,新型节点的最终破坏形态为梁端塑性铰破坏,外包混凝土及扩大包脚的嵌固作用使塑性铰远离节点核心区域,可以有效保护节点核心区和传力路径的连续性;滞回曲线较为饱满,具有较好的耗能能力和塑性变形能力;适当增大扩大包脚立面高度和水平长度,可以提高节点的初始刚度与承载力等性能,并根据相关参数研究给出了合理的设计建议范围,以便为工程设计提供参考。     

FRP-to-concrete interfaces between two adjacent cracks: Theoretical model for debonding failure

External bonding of fibre reinforced polymer (FRP) composites has become a popular technique for strengthening concrete structures all over the world. The performance of the interface between FRP and concrete is one of the key factors affecting the behaviour of the strengthened structure. Existing laboratory research has shown that the majority of reinforced concrete (RC) beams strengthened with a bonded FRP soffit plate fail due to debonding of the plate from the concrete. Two types of debonding failures have been commonly observed: plate end debonding and intermediate crack induced debonding. In order to understand and develop methods to predict such debonding failures, the bond behaviour between concrete and FRP has been widely studied using simple shear tests on FRP plate/sheet-to-concrete bonded joints and a great deal of research is now available on the behaviour of these bonded joints. However, for intermediate crack induced debonding failures, the debonding behaviour can be significantly different from that observed in a simple shear test. Among other factors, the most significant difference may be that the FRP plate between two adjacent cracks is subject to tension at both cracks. This paper presents an analytical solution for the debonding process in an FRP-to-concrete bonded joint model where the FRP plate is subject to tension at both ends. A realistic bi-linear local bond-slip law is employed. Expressions for the interfacial shear stress distribution and the load–displacement response are derived for different loading stages. The debonding process is discussed in detail. Finally, results from the analytical solution are presented to illustrate how the bond length affects the behaviour of such bonded joints. While the emphasis of the paper is on FRP-to-concrete joints, the analytical solution is equally applicable to similar joints between thin plates of other materials (e.g. steel and aluminium) and concrete.     

Nonlinear analysis of beam–column joints using softened truss model

The aim of this study is to expand the application of the nonlinear softened truss model for membrane elements on beam–column joints. The softened truss model employs three equations for equilibrium, three for compatibility and four equations for the constitutive laws of materials. The constitutive equations for both the concrete and steel are based on the actually observed stress–strain relationships. The model has three important attributes. The first is the nonlinear association of stress and strain. The second, and conceivably more noteworthy, is the softening of concrete in compression due to tensile strains in the perpendicular direction. The third is that the influence of the concrete tensile stresses between cracks on the average stress–strain relationship for reinforcing steel and the influence of orthogonal tensile stresses on the compression stress–strain relationship for concrete can be considered in the model. For beam–column joints, one of the most important factors influencing the behaviour is certainly the bond conditions of the beam bars. In this study, the softened truss model is expanded to take into account the influence of this important factor into account. In the revised version of the model, full strain compatibility does not exist between the steel reinforcement and the surrounding concrete and thus the factors influencing the bond-slip between concrete and reinforcement is adequately considered. The improved softened truss model is applied on 51 exterior beam–column joint tests. It is apparent from the results that the revised model gives very accurate predictions of the shear strength of joints and is an improvement on the existing version of the model proposed by Hsu.     

Effect of non-persistent joints distribution on shear behavior

The particle flow code 2D (PFC2D) is used to establish a coplanar, non-persistent joint model. Three joint distribution types, namely, both-side (type a), scattered (type b), and central (type c), are set according to their position. Numerical simulations of the direct shear test are conducted to investigate the effect of non-persistent joint distribution and connectivity on shear mechanical behavior. Simulation results are in good agreement with the analytical solutions to Jennings' criterion, and show: (1) type-c and type-b joints have high strength, whereas type-a joints have low strength. Shear strength and modulus increase with a decrease in joint persistency, and the shear displacement that correspond to shear strength increases with a decrease in persistency. (2) The brittle failure characteristics of the sample are evident when the intact rock bridge area is large. Reinforcement at both ends of the joint limits shear deformation, and shear strength can be effectively improved when joint persistency is large. The small-area dispersed reinforcement joint method cannot effectively improve shear strength. (3) The comprehensive shear strength parameters and the shear strength of the non-persistent joints can be predicted well using Jennings' criterion. Cohesion is the dominant factor that controls shear strength.     

A new theoretical approach for structural modelling of riveted and spot welded multi-spot structures

A general theoretical approach based on theory of elasticity is presented in order to define the structural behaviour of riveted and spot welded joints. The new closed form solutions lead to the definition of a joint element useful to FE models of riveted or spot welded multi-spot structures. The objective is an accurate evaluation of the local elastic stiffness of spot joints in FE analysis, which is fundamental to perform a reliable simulation of multi-joint structures and, consequently, a good estimate of loads acting on spots; this makes it possible to introduce structural stress or new general criteria allowing, for example, to predict fatigue behaviour. On the other hand, a low entry of degrees of freedom is needed when several spot joints are present in a complex structure. The goal is to reach a reliable spot region model which can be used as the basis to develop a spot element in FE analysis. In the present paper, based on new closed form solutions, a spot element is introduced, so as to precisely evaluate both local and overall stiffness both of spot welded joints and riveted joints. Based on the stress function approach and the Kirchhoff plate theory in linear elastic hypotheses, closed-form in-plane stress, displacement, moment and transverse shear force solutions are derived for a new bidimensional model, subjected to various types of loads. The capability to simulate spot welds or rivets depends on the definition of two elastic parameters intrinsic in closed form solutions, that tunes the theoretical model according to actual joint behaviour.The proposed joint element combines the precision in the simulation with a very limited number degrees of freedom in the overall finite element model of an actual multi-spot structure.The results obtained using the introduced theoretical framework and spot element approach perfectly match those obtained using very refined FE models and experimental data.     

高层钢-混凝土混合结构地震作用下的能量反应分析

针对目前高层建筑混合结构中常用的外钢框架-内混凝土核心筒混合结构,从地震能量输入和结构能量耗散的角度对其进行了地震作用下的能量反应分析.通过选取不同的地震动参数对混合结构的总输入能及其在滞回耗能和阻尼耗能之间的分配情况进行了研究,明确了地震动各参数的变化对混合结构能量反应的影响;通过分析不同地震波作用下混合结构的滞回耗能在外钢框架和内混凝土核心筒间的分布以及在结构层间的分部情况知,底层剪力墙是整个混合结构中滞回耗能比较集中的区域,地震破坏最为严重.通过本文研究知,地震反应的能量分析方法是一种能较好反应混合结构在地震作用下的地震反应全过程及其弹塑性性能的方法.     

甘肃北山地质处置库围岩节理抗剪强度经验估算

节理抗剪强度参数是地质处置库预选地段工程地质对比和围岩稳定性分析的重要指标。本文在旧井地段英云闪长岩节理分组的基础上,运用定向统计测量方法估测节理粗糙度系数,通过评价节理粗糙度系数的尺寸效应,确定节理抗剪强度经验估算有效长度,由JRC-JCS模型求得各组节理4个方向的抗剪强度参数,并评价了地质处置库围岩节理抗剪强度的各向异性特征。