Seismic response of multi-storey steel buildings with flexible connections

In the limit states design of steel building frames, usually simplifying assumptions are made with regard to the behaviour of beam-to-column connections. The Canadian standard for steel buildings recognizes three such sets of assumptions. One of them is the ‘special simple construction’ in which the beam-to-column connections are assumed to be completely free (pinned) to resist gravity loads and are assumed to be ‘rigid’ to resist the lateral loads due to earthquake or wind. Such connections are then designed for moments due to lateral loads only, and thus they are usually flexible. This paper is concerned with the influence of the connection flexibility and the strength on the overall strength and stiffness of steel building frames. The study considers 10 storey and 20 storey office buildings. The first part of the paper illustrates the analysis and design of the 10 storey building on the basis of ‘special simple construction’. By using realistic connection behaviour, the frames were subjected to equivalent static loads due to wind or earthquake and El Centro, 1940 earthquake excitation. In the nonlinear static analysis the building frames were subjected to specified gravity loads and incremental lateral loads until failure. In the nonlinear dynamic analysis the buildings were subjected to specified gravity loads and 70% of El Centro, 1940 earthquake excitation. For comparison purposes the frames were analysed twice, first assuming rigid connections and then with flexible connections. The static analyses results show that the connection flexibility increases the building deflections at specified loads, but the strength is only marginally affected. The dynamic analyses results show an increase in deflections and also generally an increase in column bending moments due to connection flexibility and the associated strength.     

腹板双角钢梁柱连接循环荷载试验研究

为了研究腹板双角钢梁柱连接的抗震性能,对四个连接试件进行了梁端循环位移加载试验。试验中考察了角钢高度、角钢与柱翼缘连接高强螺栓的直径和排列布置对连接的承载能力、滞回性能和破坏机理的影响,分析了这种连接的破坏模式和变形能力。试验结果表明:连接在循环荷载作用下表现出良好的延性,转角均超过0.04rad,连接的最终破坏均为角钢的塑性撕裂破坏;连接具有相当的抗弯能力,在结构分析中,须考虑节点抗弯强度对框架性能的影响,不能简单作为铰接处理;增大角钢的高度,能提高连接的强度;增大螺栓间距,减小螺栓直径,能提高连接的延性。最后,根据试验结果提出设计施工建议。     

超大承载力端板连接节点试验研究

在大跨或重载钢结构中,当梁柱之间需要采用螺栓连接时,如果普通构造的端板连接节点和大承载力端板连接节点不能满足承载力要求,则需要采用受拉区布置12颗或16颗螺栓的超大承载力端板连接节点。为研究该类型节点受力性能,进行4个超大承载力端板连接节点足尺试件的单调加载试验,得到各节点试件的弯矩-转角曲线,分析不同螺栓直径、端板厚度和螺栓布置形式下各节点的抗弯承载力、转动刚度和受拉区螺栓拉应变增量分布的特点。结果表明,在试验试件构造条件下超大承载力端板连接节点的弯曲失效模式为端板屈服后螺栓失效,端板厚度对节点承载力影响明显;各螺栓的拉应变增量分布不均匀,角部螺栓对节点抗弯承载力影响较小,建议在设计中移除或仅按抗剪螺栓考虑;建议节点域屈服承载力仍按照现行规范计算,该类节点的等效受拉螺栓数量取为7。     

螺栓端板连接节点加固后承载性能有限元分析

已有试验表明,螺栓端板连接梁柱节点具有良好的受力性能,但节点刚度较小,循环荷载作用下破坏模式以螺栓拉断为主。当建成的结构由于各种因素螺栓端板节点承载性能不能满足要求时,需要进行加固以提高节点刚度和承载力。改：善其抗震性能,本文提出了在柱腹板加斜向加劲肋,并对端板进行焊接的加固方案。有限元分析表明加固后节点的刚度、延性和承载力都得到提高。静力加载时,荷载一位移曲线在达到峰值后出现平缓的下降段;循环加载时,节点破坏模式是梁翼缘发生局部屈曲形成塑性较,滞回曲线饱满。由于使用了焊缝,节点有可能发生脆性破坏,加固中应尽量使用较小尺寸的焊缝,施工中也应保证焊缝的质量,减小残余应力。     

装配式钢管混凝土柱-双钢梁框架节点受力性能试验研究

针对一种适合装配式结构的钢管混凝土柱-双钢梁框架体系,对其2个典型平面节点和2个典型空间节点进行单调和循环加载试验,以研究加载模式和节点类型对节点破坏形态、承载力、刚度、延性及耗能能力的影响。结果表明：试件的破坏均发生在梁端,柱与节点域保持完好,满足“强柱弱梁、强节点弱构件”的抗震设计要求;试件的位移延性系数为2.6~3.6,能量耗散系数为1.7~2.2,耗能能力与型钢混凝土节点相当;加载模式(单调或循环)相同而节点类型(平面或空间)不同时,节点性能差异小;加载模式不同而节点类型相同时,节点性能差异大：循环荷载作用下的节点梁端焊缝发生拉裂破坏,位移延性系数较小。该种节点静力性能较好,但从提高抗断裂能力出发,需进一步改进构造,对焊缝分布进行优化设计。     

复式钢管混凝土柱与H形钢梁连接节点抗震性能试验研究

借鉴方钢管混凝土柱-钢梁外肋环板节点形式,将非梁柱连接面的柱两侧外肋环板改为竖贴于柱侧的竖向肋板并伸出与梁翼缘焊接,同时设置锚固腹板,形成复式钢管混凝土柱与H形钢梁连接节点。通过7个梁柱组合体试件的低周反复荷载试验,分析各试件的破坏过程及特征,并对试件的滞回性能、承载力、延性、耗能能力和承载力及刚度退化等抗震性能进行研究。研究结果表明：节点的破坏形态基本相同,梁端先屈曲,形成塑性铰;锚固腹板可有效提高节点的承载力和变形能力;竖向肋板外伸长度可提高试件的初始刚度,使梁端塑性铰外移,有效保护节点核心区;试件的滞回曲线呈明显的梭形,具有良好的承载力、延性及耗能能力;试件在整个加载过程中刚度退化现象明显,承载力退化很小,可应用于抗震设防地区。     

Experimental analysis on strength and failure modes of wood beam-column connections

This research experimentally examined the strength, failure modes, and behaviors of dowel-bearing and fiber-bearing wood beam-column connections and explored the effects of cyclic loading on the strength, failure modes, and behaviors of those connections. Base on limited numbers of exploratory laboratory tests (6 preliminary tests in total), the authors observed that the typical bolted connection (dowel-bearing type wood beam-column connection with fiberbearing surfaces) showed good behavior (large peak moment) under the monotonic loads, and the tenon joint connection (fiber-bearing wood beam-column connection) showed good behavior under cyclic loads. The cyclic property of loading reduced the strength of the dowel-bearing type wood beam-column connections, but increased the strength of fiberbearing type wood beam-column connections. More importantly, the authors identified a possible location of safety concern in current national design specifications (NDS) standards for the typical bolted connection (dowel-bearing connection with fiber bearing surface) under cyclic loading because the tested value was smaller than the NDS calculated value. But, because of the small amount of tests conducted, no final conclusion can be drawn based on those preliminary observations yet. A large number of repetitive laboratory tests should be conducted.     

带外加强环不等高梁-钢管混凝土柱组合节点抗震性能试验研究

对4个带外加强环不等高梁钢管混凝土柱节点试件进行了循环加载和单调加载试验,试件主要变化参数为节点两侧梁高度差,取值为 0、75、 150mm。为了研究节点域的受剪承载力,对试件按“强构件,弱节点”进行设计。对于所设计的4个节点试件,其破坏分为整个节点域剪切破坏和部分节点域剪切破坏。试验结果表明：加载方式对试件节点域剪切承载力影响不大;节点试件在正反两个方向加载形成不同的破坏模式,并且在反向荷载作用下其承载力略高于其在正向荷载作用下的承载力;节点两侧梁高度差对节点域破坏形式和承载力影响显著;在整个加载过程中,所有试件节点均未出现开裂;该类节点具有很好的变形能力和稳定的耗能能力,但随着两侧梁高度差的增加,耗能能力逐渐降低。     

高层钢框架新型梁柱节点抗震性能试验研究

本文提出了三种焊接孔扩大型梁柱节点,完成了8个足尺试件在四种反复荷载历程下的破坏试验。对节点破坏模式和滞回曲线的比较分析表明,焊接质量是防止节点脆性破坏的首要保证,明显的焊接缺陷容易导致裂缝过早开始扩展,从而降低节点延性和耗能能力。节点局部构造尤其是焊接孔形状尺寸对于节点应力集中情况和节点破坏模式有很大影响。本文提出的焊接孔扩大型节点可以不同程度地缓解局部应力集中,同时通过采用较长的焊接孔,使节点破坏模式转变为梁翼缘的局部屈曲,降低了对接焊缝发生脆性破坏的可能,对节点延性有较大的改善作用。焊接孔扩大型节点构造也便于加工制作,是一种值得推荐的新型节点形式。     

带翼缘钢填板-螺栓连接胶合木梁-柱节点转动性能试验研究

针对钢填板-螺栓胶合木梁-柱连接节点易发生木材横纹劈裂脆性破坏的问题,提出在钢填板上下端增设翼缘以降低木材横纹拉应力或约束木材横纹裂缝扩展,形成带翼缘钢填板-螺栓连接胶合木梁-柱节点形式。通过对其进行单调加载试验,获得了该连接节点的弯矩-转角关系曲线,对比分析了该类连接节点和采用不同加固技术的普通钢填板-螺栓连接节点的受弯承载力。研究表明：带翼缘钢填板-螺栓连接节点具有良好的变形能力,其相对受弯承载力较普通钢填板-螺栓连接节点提高最多可达129%,且高于采用自攻螺钉、碳纤维布和交叉胶合木等技术加固的普通钢填板-螺栓连接节点的受弯承载力。     

梅江会展中心张弦桁架抗连续倒塌分析

通过对天津梅江会展中心张弦桁架移除关键构件后的残余结构的承载力分析,得到张弦结构的支座、边索和边跨桁架支座处下弦杆等关键构件的破坏对结构承载力影响最大;为了模拟杆件失效前静力荷载产生的初始变形对结构连续倒塌的影响,采用考虑初始变形的全动力等效荷载瞬时卸载法模拟杆件失效。对支座、边索和边跨桁架支座处下弦杆失效进行连续倒塌动力分析,研究了纵向联系桁架对张弦结构抗连续倒塌的作用,得到平面张弦桁架通过纵向联系桁架组装成一整体,其整体性随着纵向联系构件抗弯刚度的增大而提高,共同作用效果明显。在此基础上,利用山墙的抗风柱,将边跨张弦桁架改变为多支点支承的普通桁架,设计时该抗风柱不仅承担水平风荷载,还承担竖向荷载,从而提高结构的抗连续倒塌能力。并根据该工程的特点提出集桁架支座、张拉端（锚固端）和桁架下弦管于一体的铸钢节点构造,不仅满足建筑要求,还使得该处节点承载力大大加强,可供相关工程参考。     

法兰连接L形钢管混凝土柱-H型钢梁全螺栓节点抗震性能研究

为降低多高层钢结构的梁柱间的装配难度,提出了法兰连接L形钢管混凝土柱-H型钢梁全螺栓装配节点,包括梁与柱连接和柱与柱连接,梁与柱现场全螺栓连接,柱与柱现场法兰连接。为研究连接件形式及加劲肋对该种节点抗震性能的影响,以改变连接件形式、加劲构造为主要变化参数,设计了4个该类型节点,通过低周反复加载试验和有限元分析获得了节点的破坏模式、滞回曲线、耗能能力和性能指标。研究结果表明：4个节点的滞回曲线均呈梭形,具有良好的耗能能力;节点正负方向的塑性转角超过0.05 rad,满足抗震规范要求;L形连接件与T形连接件均有足够的刚度传递荷载,4个节点的破坏模式、耗能能力与滞回曲线形状较为接近;连接件与梁翼缘之间的滑移提高了节点的延性、耗能能力与转动能力。     

宽肢组合异形柱-钢梁节点抗震性能试验研究

为研究适用于高层钢结构住宅体系的组合异形柱框架结构的翼缘加强型节点的抗震性能,设计了两种不同构造形式的足尺节点试件,即格构式宽肢组合异形柱节点和实腹式宽肢组合异形柱节点,并进行拟静力试验,研究了该类节点的破坏形态、滞回性能、承载能力、梁端转角、延性及耗能能力。试验结果表明：2个节点最终均在加强件端部发生了翼缘开裂而破坏;节点的受弯承载力是梁端全截面塑性承载力的1.10~1.13倍;钢梁转角是梁端总转角的主要组成部分,节点区转角只占梁端总转角的1.0%~1.8%,柱变形转角占9.2%~13.0%;节点的位移延性系数约为2.33~2.38,黏滞阻尼系数约为0.264~0.267。此外,2个节点的承载能力基本相当,格构式宽肢组合异形柱节点的抗震性能指标相对实腹式宽肢组合异形柱节点较好;但与传统翼缘加强型节点相比,其延性和耗能能力略有降低。     

水平-竖向-扭转荷载下吸力沉箱基础承载特性数值研究

海上风机吸力沉箱基础承受结构自重及环境因素引起的竖向、水平、扭转荷载,处于复合加载状态。以位于饱和黏土地基上长径比为0.25～1.0的单桶沉箱基础为对象,ABAQUS为计算工具,研究沉箱基础的承载特性,并考虑沉箱与地基土的摩擦接触作用。首先分析沉箱基础在单一的竖向荷载、水平荷载及扭转荷载作用下的极限承载力,并给出沉箱基础在这些荷载组合下的破坏包络面,其中倾覆力矩通过施加偏心水平荷载实现。结果表明,沉箱基础的竖向承载力可用改进的经典承载力公式计算,而水平承载力系数在给定的接触条件下随沉箱长径比增加而减少,扭转承载力与理论预测结果非常吻合;扭转荷载对沉箱的竖向承载力影响较大,但对水平承载力影响较小;不同扭转荷载下的V-H包络面可用椭圆曲线拟合。     

The behavior of top and seat bolted angle connections under blast loading

Abnormal loading generated by blast or impact may cause local damage in a building that may evolve to affect the whole structural system. Therefore, structures have to be designed to prevent such disproportional consequences. Connection is an important contributor to ductility and robustness of the structural steel systems in mitigating such consequences. Considering this importance, finite element analysis is used in this paper to study the behavior of top and seat bolted angle connections under blast loading. The two frequent angle connections including top and seat angle bolted connections with and without web angles are studied using the ANSYS finite element software. The finite element models are verified by comparing the predicted results obtained from the models and the values measured in the experimental tests. Simplified blast loading is then applied to the verified connection models and the behavior of these connections under blast loads is evaluated with the connection critical areas being determined. The connection failure modes as well as the applicability of the connection under blast loading are briefly discussed.     

Dynamic response of hollow section frames with bolted moment connections

The behaviour of moment-resisting steel frames under various types of loads is dependent on the type of beam-to-column connections and their flexibilities. The extended end-plate connection is a practical field bolted moment connection that can be adopted in moment-resisting steel frames with hollow structural steel (HSS) columns, by using high strength blind bolts. The objective of this work was to study the behaviour of blind bolted extended end-plate connections for HSS columns under cyclic loading. With proper detailing and modelling of such connections, it has been possible to investigate the effect of joint flexibility on the response of the frame when subjected to dynamic loading and then to compare its response to that of a rigid frame. It is concluded that the proposed bolted joint behaves in a predictable manner that can be modelled and analysed using standard frame analysis programmes. The study also showed that the inclusion of the connection flexibility in frame analysis is essential to obtain a more realistic frame behaviour.     

装配式钢管混凝土柱-盖梁节点抗震性能试验研究

装配式钢管混凝土柱-盖梁节点施工简单、工期短,逐渐在桥梁建设中广泛运用。提出一种带抗剪环的新型钢管混凝土柱-盖梁节点,介绍装配式节点在桥梁施工中的施工工序。设计7个钢管直径超过508mm 的大规模节点试件,通过低周反复荷载试验对6个抗剪环节点和1个钢筋笼节点进行了地震响应分析。对比分析节点的破坏形态、有效刚度、延性、滞回性能和极限承载能力等力学特性,得到如下结论：钢管混凝土柱出现初始撕裂时的位移随着构件的有效刚度增大而增大,盖梁的开裂情况则随着钢管混凝土柱埋深的增加而减少。埋深相近的情况下,抗剪环节点的极限荷载承载力大于钢筋笼节点;抗剪环节点的整体延性随着径厚比D/t的增大而减小。     

Tying capacity of web cleat connections in fire,Part 1: Test and finite element simulation

The tying capacity of connections between beams and columns is very important in maintaining structural integrity when beam deflections are high due to accidental loads such as fire, but has not so far been thoroughly studied. The project which is the subject of this paper has investigated the robustness of common types of steel connection when subjected to fire. The results reported here concern the performance of web cleat connections in fire, and are drawn largely from experimental investigations. During the testing programme, short cantilever stub beams were subjected to different combinations of shear and tying force. The rotational capacities and resistance to tying forces of their connections at high temperatures were investigated in the presence of other concurrent actions.Test results show that web cleat connections have excellent rotational ductility, and that their resistance reduces rapidly with increase of temperature. Web cleat connections can fail in a number of modes, the selection of which is highly dependent on the connection temperature. Finite element simulations of the test results have been shown to be able to reproduce the behaviour accurately up to the stage at which material failure happens. However, as the ultimate behaviour of connections is often controlled by material fracture, finite element analysis is limited in predicting the ultimate resistance of connections. Investigation of the behaviour of the connection, with some proposed modifications to the general finite element model, showed that finite element analysis can help to interpret the test results and expand the test observations to other similar applications.     

超薄壁冷弯型钢矩形截面钢管墙架柱-楼层梁连接抗震性能试验研究

冷弯薄壁型钢结构的墙架柱与楼层梁连接构成空间受力体系,考虑柱的轴压比和楼层连接处不同构造方式,对3组共6个矩形截面镀锌钢管墙架柱与楼层梁的连接试件进行了低周往复加载试验。研究结果表明：墙架柱的轴压比从0.2增加到0.4时,规程JGJ 227-2011推荐的连接构造试件的屈服、极限和破坏荷载较角钢加强型连接构造试件均降低约20%,但对角钢加强型连接影响较小;所有连接均发生延性破坏,极限状态时墙架柱损伤很小;柱轴压比对延性、耗能能力均有一定的影响,因此将未加强的连接用于多层房屋结构时,要引起足够重视;在角钢加强型连接中,角钢厚度对连接试件的承载力影响显著,故建议对多层冷弯薄壁型钢房屋中的墙架柱与梁连接,采用厚t≥2 mm的角钢,与规程JGJ 227-2011推荐的连接方式相比,其承载力明显提高,累积耗能能力及屈服耗能能力均较强,破坏前试验所经历的荷载循环级数增加。     

Test of screw fastened profiled roofing sheets subject to simulated wind uplift

Screw fastened light gauge steel profiled roofing sheets are predominantly subjected to wind suction, i.e., wind uplift, and may fail locally in the vicinity of screw fasteners under strong or sustained fluctuating wind uplift. A series of static tests was performed on three types of profiled roofing sheets to investigate their structural behaviour and profile effects under simulated wind uplift. The considered sheeting profiles were arc-tangent, trapezoidal and ribbed, and an alternate (or equivalent alternate) sheeting crest fastening system was adopted. It was found that structural behaviour of the roofing sheets under uplift loads was greatly dependent on the sheeting profiles including the shape and height of the crest. Both arc-tangent and trapezoidal type roofing sheets exhibited a large cross-sectional distortion stage and a deflection hardening stage, following a local plastic collapse in the vicinity of the screw fasteners at the central support. The ribbed roofing sheet, however, had a final failure mode of sudden fracture with cracks under the screw fastener head at the central support. The use of cyclone washers with screw fasteners reduced local plastic deformations and, in general, increased initial failure loads of the roofing sheets. Increasing the roofing span only slightly reduced the limit values of the reaction force per fastener at the central support due to the local failure characteristic of the screw fastened profiled roofing sheets.