Seismic behavior of reduced beam section joints considering concrete floor effect

This study investigates the seismic impact of concrete floors on reduced beam section beam-to-column joints through four quasi-static cyclic tests. We examine mechanical properties, failure modes, and processes against specific criteria. Additionally, we analyze hysteretic response, energy dissipation, stiffness, capacity, and stress–strain mechanisms. Moreover, the ABAQUS platform was used to reproduce the specimen nonlinear finite element model to compare and analyze the test results. The results showed that the specimens exhibit excellent energy dissipation capacity and ductility (with a coefficient of 5.00); the column-bar connection characteristics affect the maximum capacity and plastic hinge behavior in the reduced beam area. The reduced section of beam's upper flange could not improve the overall seismic performance of the joint. The observed failure sequence is as follows: concrete floor cracking, beam flange yielding, reinforcement fracture, lower flange yielding in the reduced beam area, and overall joint failure. This sequence confirms that the joint fulfills the design criteria of a “strong column-weak beam” by achieving the target of plastic hinge outward movement.     

装配式钢框架节点带Z字形悬臂梁段和削弱梁段连接的抗震性能研究

为研究装配式钢框架节点带Z字形悬臂梁段和削弱梁段拼接的抗震性能,采用拼接区和削弱梁段共同耗能设计了4个试件。对4个试件进行了低周往复加载试验以及单调及往复加载的有限元分析。通过对试件的破坏模式和拼接区的滑移情况进行了分析,研究了以梁端弯矩 转角表征的滞回曲线、骨架曲线、耗能能力、转动能力等。结果表明：试件主要利用削弱梁段的塑性变形和拼接区的滑移实现耗能;其失效模式为螺孔或者焊缝处撕裂、削弱梁段处局部屈曲和削弱梁段处弯扭失稳;为保证节点充分发挥耗能能力,应增大削弱梁段处的侧向约束,防止发生弯扭失稳;为满足现场安装方便的要求和应对工厂加工精度不足的现状,可以在悬臂梁段翼缘开大孔;为降低工厂加工难度,可以将方钢柱内隔板替换为三角形垂直加劲肋。     

A simplified analytical story drift evaluation of steel moment frames with radius-cut reduced beam section

A simplified analytical procedure is presented to estimate the elastic story drift of steel frames with the radius-cut RBS (reduced beam section) moment connections. Due to the geometric configuration of the radius-cut RBS, the mathematical formulation is complicated when applying the conjugate beam method to compute the component of story drift contributed by the beam. In this study, the problem is circumvented by replacing the original radius-cut RBS with an equivalent beam of constant width. The equivalence between the two is established by imposing the equal flange elongation criterion over the RBS region. This approach is justified by a finite element analysis. The story drift components contributed by the column, the panel zone, and the beam are then formulated into a closed form solution for a typical beam-column subassembly. The derived results can readily be used by designers to estimate the magnitude of RBS frame story drift and the effect of the stiffness variations.     

Seismic performance of steel frames with reduced beam section connections

Reduced beam section (RBS) moment resisting connections are among the most economical and practical rigid steel connections developed in the aftermath of the 1994 Northridge, California, earthquake. Although extensive experimental testing and some numerical simulations have shed light on the behavior of this type of connection, system level studies of RBS steel frames are still quite limited. As part of this research, nonlinear pushover and transient analyses of 4-, 8-, and 16-story frames with RBS connections are conducted with the objective of developing a better understanding of RBS frame behavior and exercising as well as critiquing the recently published FEMA-350 design specifications. The analyses confirm that in spite of inherently low overstrength, RBS frames are capable of economically providing good seismic performance in regions of high seismic risk. Other structural behavior issues with design implications are also discussed.     

翼缘削弱的型钢混凝土框架抗震性能研究

为了研究翼缘削弱的型钢混凝土框架的抗震性能,对一榀两跨三层型钢混凝土框架模型进行了低周反复荷载试验。框架模型按"强柱弱梁"原则设计,且对节点核心区附近梁端工字形型钢的上、下翼缘采取狗骨式削弱,并适当增加最大削弱部位纵向钢筋的配筋率。通过对框架模型顶层施加低周反复水平荷载,观察了框架模型的破坏过程,测得框架模型的荷载-位移滞回曲线和骨架曲线以及各阶段的荷载和位移值,并分析了框架模型的延性、耗能、强度降低、刚度退化以及破坏机制。试验结果表明:框架模型的承载能力、变形能力和耗能能力高,延性大(延性系数大于7),满足延性框架的抗震要求。进一步分析了翼缘削弱在型钢混凝土框架中的具体作用。分析结果表明:翼缘削弱不仅能将塑性铰从梁端根部转移到翼缘削弱部位,从而降低节点核心区所受的剪力以及梁柱连接焊缝的应力,而且有利于框架形成梁铰耗能机构,从而提高框架的整体耗能能力。翼缘削弱能有效提高型钢混凝土框架的抗震性能,可在型钢混凝土     

Seismic design of reduced beam section steel moment connections with bolted web attachment

Recent test results on reduced beam section (RBS) steel moment connections showed that specimens with a bolted web connection tend to perform poorly due to premature brittle fracture of the beam flange at the weld access hole. The measured strain data appeared to indicate that a higher incidence of base metal fracture in bolted web specimens is related, at least in part, to the increased demand on the beam flanges due to the web bolt slippage and the actual load transfer mechanism which is significantly different from that usually assumed in connection design. In this paper, the practice of providing web bolts uniformly along the beam depth was brought into question. A new seismic design procedure, which is more consistent with the actual load path identified from analytical and experimental studies, is proposed. A pilot test specimen designed by following the proposed procedure exhibited sufficient cyclic connection rotation capacity without fracture.     

Experimental behaviour of steel reduced beam section to concrete-filled circular hollow section column connections

In this paper, five specimens of connections of reduced beam section (RBS) steel beam to concrete-filled steel tubular (CFST) circular hollow section (CHS) column using an external ring were tested. The experiments considered the hysteretic behaviour under combined constant axial load and cyclic lateral load. For comparison, three specimens of a weak-column without an RBS configuration steel beam to CFST column connection were tested under the same conditions. The axial load level of the CFST column, width of connection stiffening ring and RBS configuration were considered as the experimental parameters of their seismic behaviour. It was found that the lateral load (P) versus lateral deformation (Δ) hysteresis curves exhibited no obvious strength deterioration and stiffness degradation. The energy dissipation of the RBS connections is significantly improved when compared with weak-column connections. The concrete filled CHS columns failed as a weak-column connection and their energy dissipation capacity was reduced. It can be concluded that the RBS connections exhibit good seismic performance.     

Shape optimization of reduced beam section under cyclic loads

Optimal shapes are found for a reduced beam section of a cantilever H-beam subjected to forced cyclic displacement at the free end. The beam is discretized to finite elements, and a commercial software package called ABAQUS is used for elastoplastic analysis. The numerical results are first compared with experimental results to verify the accuracy. The objective function to be maximized is the dissipated energy throughout the loading history. The constraint is given for the maximum equivalent plastic strain at the welded section. Global optimal solutions are searched for by a heuristic approach called simulated annealing, which is successfully combined with ABAQUS. It is shown that the energy dissipation capacity is significantly improved by optimizing the flange shape.     

Instability of beams with reduced beam section moment connections emphasizing the effect of column panel zone ductility

Column panel zone (PZ) ductility significantly affects the failure mode of beams with reduced beam section (RBS) moment connections. Even though good hysteretic behaviour is expected in connections with strong PZs, their flexural strength considerably deteriorates due to beam instability. In contrast, weak PZs are prone to high shear deformation, resulting in brittle fracture of connections. This study aims to question the provisions specified in the codes for the design of PZs. To this end, a numerical analysis was conducted on a series of subassemblies with various PZ properties. Use of lower deep sections is another major concern. It is indicated in this study that partial shear yielding in PZs can improve the hysteretic response of specimens by avoiding premature instability in beams. The results show that the PZ ultimate shear strength commonly prescribed in the design codes does not extend to an adequate safety margin. Furthermore, a new parameter is expressed for controlling an RBS beam as regards instability. This parameter is able to appropriately model the behaviour of RBS beams. The results are generally in good agreement with the existing experimental data.     

基于椭球面屈服模型的钢框架梁柱节点断裂分析

为研究钢框架梁柱节点受力情况,对节点进行基于椭球面屈服模型的数值模拟和断裂分析,结果显示:模拟结果吻合较好,建议的屈服模型对预测钢框架节点开裂具有一定的适用性。翼缘削弱,塑性铰外移,断裂指数CI达到峰值,初始裂纹形成于翼缘对接焊缝中部。可用系数K=1.87近似等效考虑模拟过程中焊接缺陷和残余应力不利影响。     

Seismic performance of the Accordion-Web RBS connection

A new type of Reduced Beam Section (RBS) connection, “Accordion Web RBS (AW-RBS)”, is presented in this research. RBS connections are commonly known as connections with reduced flange width within a limited area near the column face. However, the AW-RBS decreases the web contribution in moment strength and a reduced section is developed in the beam. In an AW-RBS, the flat web is replaced by corrugated plates (L-shape folded plates, used here) at the expected location of the beam’s plastic hinge. While the corrugated web has adequate shear strength, its provided moment strength and flexural stiffness are negligible. Two relatively identical specimens including AW-RBS connections have been tested under cyclic loading. Both specimens provide at least 8% story drift, without any significant strength loss, which is more than current requirements for qualifying connections in special moment frames. The accordion effect of the corrugated web and the cyclic performance of the connection are verified by analytical results. According to the analytical and experimental results, the inelastic rotations of the connection are mostly provided by reliable and ductile rotation at the reduced region rather than in the connection plates or panel zone.     

削弱型钢框架梁柱节点研究现状

指出加强型节点和削弱型节点是目前实现延性钢框架的主要措施,重点介绍了两种削弱型节点：狗骨式节点和腹板开圆孔型节点,分别描述了两种节点的结构形式、受力特点、削弱参数及抗震性能,以期指导实践。     

梁端楔形翼缘连接钢框架低周反复荷载试验研究

提出了梁端楔形翼缘连接节点,通过2跨2层梁端楔形翼缘连接钢框架试件的低周反复加载试验,研究了结构在地震作用下的滞回性能、耗能机制、耗能能力、刚度退化和破坏形态。结果显示,试件破坏模式为延性,破坏时的顶点位移角达到了1/29,整体延性系数在4.7以上,梁上塑性铰出现在翼缘变化处,表明梁端楔形翼缘连接钢框架具有良好的抗震性能。对试件进行了静力弹塑性分析,节点域用转动弹簧来考虑其剪切变形,采用双线性特性塑性铰的计算结果与试验结果较一致。     

基础联系梁设计方法

结合工程实例，介绍了基础联系梁设计方法，阐述了基础联系梁的设计理论和设计方法，提出了设计理论方法中的一些基本假定，以便在设计中正确运用。     

Cost-benefit evaluation of self-centring concentrically braced frames considering uncertainties

Self-centring concentrically braced frame (SC-CBF) systems have been developed to reduce post-earthquake damages in braced frames. However, due to special details required by the SC-CBF system, the construction cost of an SC-CBF is expected to be higher than that of a conventional CBF. In this study, the seismic performance and economic effectiveness of two prototype buildings utilising SC-CBFs are assessed and compared with buildings utilising conventional CBFs by evaluating the annual probabilities of exceeding various damage levels, expected annual losses, life cycle costs (under seismic hazard) and economic benefit of using SC-CBFs considering prevailing uncertainties. The results of this study show that the SC-CBF buildings have lower drift-related losses but higher acceleration-related losses. The SC-CBF is found to be beneficial for the 6-storey configuration, but not for the 10-storey configuration. For the 6-storey buildings studied here, if the construction cost of the SC-CBF is assumed to be twice that of the CBF, the pay-off time is expected to be 12 to 21 years, with a probability of 68%, considering the uncertainties in the demand, capacity, loss parameters and initial construction costs. Finally, appropriate probabilistic engineering demand parameter model formulation is critical for generating accurate loss analysis results.     

考虑加载制度影响的狗骨式连接钢框架子结构抗震性能试验研究

为研究加载制度对狗骨式连接钢框架结构变形能力及累积耗能能力的影响,设计了5榀单跨狗骨式连接钢框架子结构,对其进行单向加载、等位移循环加载、标准加载及近场地震动作用下的拟静力试验。结果表明：所有框架出现的塑性铰均在钢梁端部的翼缘削弱位置,避免了钢梁端部焊缝的过早脆性断裂;狗骨式连接钢框架结构滞回曲线饱满、变形能力及延性性能优良。此外,加载制度对狗骨式连接钢框架子结构的层抗侧刚度、水平承载力退化、极限变形能力及累积耗能能力均有显著影响。等位移循环时,加载位移幅值越小,狗骨式连接钢框架子结构的层抗侧刚度及承载力退化越趋于缓慢,其层间累积延性系数及等效能量耗散系数越大。     

Blind bolted moment connection to sides of hollow section columns

This paper presents the results of an experimental programme for a new blind bolted connection to unfilled hollow section (HS) columns under static loading. In this connection, channels with side plates connect beam flanges to the side face of HS columns. This is a simple alternative connection to typical face connections, i.e. the extended endplate connection or the T-stub connection (with T-stubs connecting the top and bottom flanges of the beam to the face of the column). The channel side plate connection was found to be much stiffer than a typical face connection and has the potential to achieve a rigid connection status for braced frames according to the EC3 classifications. Comparison of the test results and three dimensional finite element (FE) modelling indicates that the FE analyses can be used to predict the connection behaviour with sufficient accuracy. The preliminary investigation for the channel side plate connection shows promising results and forms the basis for the development of other blind bolted side connections for applications in the low rise construction industry.     

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.     

桩基承台间联系梁配筋计算方法探讨

分析了几种计算联系梁截面配筋的方法,并指出了这几种方法的优缺点,提出了考虑联系梁受弯时联系梁截面配筋的计算方法,并结合工程实例比较了这几种方法的异同,为考虑联系梁受弯时联系梁截面配筋计算方法的选择提供指导。     

钢筋砼T形截面梁的截面延性系数计算

采用接近钢筋砼受弯构件实际受力情况的基本假定,对Ｔ形截面延性进行了分析,推导了较为精确的Ｔ形截面受弯构件截面延性系数的计算公式。