Concentric X-braced frames with HSS bracing

Concentrically braced frames are stiff, strong systems frequently used to resist wind and seismic loading; in regions of high seismicity in the US special concentrically braced frames (SCBFs) are used. CBF configurations vary, but in low rise or other structures with modest levels of demands single-story, X-configured braced frames (X-braced) are commonly used. The brace sections used also vary but hollow structural sections (HSS) are the most common in the U.S. Although important, in part because low-rise structures sustain large demands, few research programs have focused on the single-story X-brace configuration. A large research program was undertaken to understand and improve the response of SCBFs with selected testing on single-story X braced SCBFs. The test matrix consisted of two, full-scale planar X-braced frame experiments and one nearly-full-scale three-dimensional X-braced frame. The tests were designed using a new design and detailing philosophy, called the Balanced Design Method. In this paper, application of this design method to the frame is investigated, with a focus on the center-splice connection. The results show that the ultimate inelastic deformation capacity of the system is less dependent on the specific design detail at this splice. Additionally, the bi-directional load testing indicated that the out-of-plane demands did not impact the system performance.     

多层框架结构远程协同拟动力试验研究

拟动力试验尤其结合子结构技术,可用来进行大规模的结构试验。该技术的一个延伸就是将异地多个实验室的试验资源通过互联网连接在一起协同进行结构远程试验。在课题组业已开发的网络化结构实验室平台NetSLab的基础上针对多层剪切型房屋结构模型开发了一个标准化的开放式多自由度体系远程协同拟动力试验程序,包括控制中心、真实试验机、虚拟试验机和远程观察器四个模块,各个模块之间通过网络通讯平台传输试验控制信号及反馈数据。为了验证该程序的可行性及有效性,进行了十层钢管混凝土组合框架结构在三个水准地震作用下的远程拟动力试验。整体框架结构被划分成两个子结构,底部两层进行试验,其余各层进行非线性模拟,同时考虑各个子结构之间边界条件的模拟。试验结果表明,钢管混凝土组合体系在地震作用下表现出良好的抗震性能,远程协同试验程序为研究大型复杂结构的抗震实验提供平台,可以达到提高综合试验能力及资源共享的目的。     

多层钢框架半刚性端板连接的循环荷载试验研究

为研究多层钢框架半刚性梁柱端板连接的抗震性能,对8个不同构造端板连接足尺试件进行了循环荷载试验研究, 分析了端板厚度、螺栓直径、端板外伸加劲肋、柱腹板加劲肋、平齐式和外伸式等因素对节点承载力、转动刚度、极限转动 能力、耗能能力、延性和极限破坏状态的影响。试验结果表明,半刚性梁柱端板连接具有良好的延性和耗能能力,可以应用 于多层抗震钢框架中。根据试验结果及相关分析,提出了多层抗震钢框架中端板连接的标准构造为:两端外伸,设置柱腹 板加劲肋和三角形端板加劲肋,柱翼缘在端板外伸边缘上下各100mm范围内局部加厚,厚度与端板厚度相同。对提高端 板连接节点的抗震性能提出了宜采用大直径螺栓、中等厚度端板的设计建议。本文还在"强节点,弱构件"抗震设计一般原 则的基础上提出了"强连接,弱板件"的端板连接抗震设计概念。     

多层多跨钢筋混凝土平面框架拟静力倒塌试验研究#br#

建筑结构的破坏具有离散性和系统性的特点,该特性决定结构抗地震倒塌的研究需多参数、多层次考虑问题。文章结合结构地震倒塌破坏模式的研究,完成了三榀钢筋混凝土平面框架的低周反复荷载试验,通过对模型框架破坏过程、破坏形态、滞回耗能及刚度退化的分析,探讨轴压比和梁柱线刚度比对RC框架结构抗震性能的影响,以期为后续结构地震倒塌破坏机理的研究提供参考。分析结果表明：降低结构的竖向荷载和梁柱线刚度比,有利于梁端塑性铰的充分发育,从而更易实现理想的“梁铰”破坏机制;试验框架的最终破坏是由底层柱下端塑性铰充分发育后、混凝土突然压溃所致,底层构件的耗能能力得到充分发挥,而中间层构件和顶层构件所耗散的能量较少;KJ-2的峰值荷载及极限荷载比KJ-1的峰值荷载及极限荷载分别大约9.9%和8.7%、等效黏滞阻尼系数比KJ-1大约16.5%,但位移延性系数比KJ-1小约57.1%,说明增大结构的竖向荷载可以提高其承载能力及耗能能力,但会降低延性及变形能力,同时,一定程度地增大竖向荷载,有利于强化结构的初始抗侧刚度,延缓刚度退化趋势,但在层间位移角较大情况下P-Δ效应的影响凸显;结构梁柱线刚度比的增大可以提高其耗能能力,但会降低结构的承载能力、延性及初始抗侧刚度;对于轴压比及梁柱线刚度比较小的“梁铰”结构,临近倒塌时的层间位移角可达1/25,此时结构仍具有一定的竖向承载能力。     

Elastic buckling load of multi-story frames consisting of Timoshenko members

The objective of this paper is to propose a method for the evaluation of the elastic critical buckling load of columns in frames consisting of members susceptible to non-negligible shear deformations, such as built-up members in steel frames, based on Engesser's approach. To that effect, a stability matrix is proposed and three general stability equations are derived for the cases of unbraced, partially braced and braced frames. Indicative graphic interpretation of the solutions for the stability equations of the braced and unbraced cases is shown. Slope-deflection equations for shear-weak members with semi-rigid connections are also derived and used for the presentation of a complete set of rotational stiffness coefficients, which are then used for the replacement of members converging at the bottom and top ends of the column in question by equivalent springs. All possible rotational and translational boundary conditions at the far end of these members, as well as the eventual presence of axial force, are considered. Five examples are presented, dealing with braced, unbraced and partially braced frames, with rigid and semi-rigid beam to column connections, loaded with concentrated or uniformly distributed loads, in a symmetrical or non-symmetrical pattern. In all cases the proposed approach is in excellent agreement with finite element results.     

多层钢框架中梁柱端板连接的强度和刚度

端板连接的构造特点决定了其在具有较强承载能力的同时还具有一定的柔性,有别于传统的刚接和铰接。针对这一现象,本文论述了多层钢框架结构中梁柱端板连接的强度和刚度问题,包括连接的构造形式、端板和螺栓的计算方法、节点域柱腹板的受力状态以及加劲肋的作用,根据端板连接的简化力学模型提出了确定连接极限承载力和转动刚度的方法,其中转动刚度主要与节点域剪切刚度和端板抗弯刚度有关。最后,结合连接的荷载.位移曲线特点推导出单向加载和循环加载下连接的简化弯矩转角关系,并与相关数据结果作了对比验证,该方法简单实用且比较准确,可供结构计算和节点设计参考。     

Buckling strength of multi-story sway, non-sway and partially-sway frames with semi-rigid connections

The objective of this paper is to propose a simplified approach to the evaluation of the critical buckling load of multi-story frames with semi-rigid connections. To that effect, analytical expressions and corresponding graphs accounting for the boundary conditions of the column under investigation are proposed for the calculation of the effective buckling length coefficient for different levels of frame sway ability. In addition, a complete set of rotational stiffness coefficients is derived, which is then used for the replacement of members converging at the bottom and top ends of the column in question by equivalent springs. All possible rotational and translational boundary conditions at the far end of these members, featuring semi-rigid connection at their near end as well as the eventual presence of axial force, are considered. Examples of sway, non-sway and partially-sway frames with semi-rigid connections are presented, where the proposed approach is found to be in excellent agreement with the finite element results, while the application of codes such as Eurocode 3 and LRFD leads to significant inaccuracies.     

附加减震钢框架的加固混凝土框架结构抗震性能试验研究

为提高既有混凝土框架抗震性能,在不显著增加既有结构构件受力的同时,在混凝土框架外部增设钢框架并设置屈曲约束支撑。设计并制作1榀纯混凝土框架和2榀设置附加减震钢框架的混凝土框架,通过低周往复加载试验,研究其开裂和破坏状态、滞回曲线、骨架曲线、刚度退化、等效阻尼比以及钢筋混凝土梁、附加钢框架的应变发展等。试验结果表明：增设附加减震框架后,结构破坏机制更加合理,屈曲约束支撑耗能性能稳定,加固后结构的滞回曲线饱满;采用外部附加钢框架加固钢筋混凝土框架,可提高既有混凝土框架结构的受剪承载能力至3倍以上,既有结构、外部附加钢框架和屈曲约束支撑可协同工作,在设防目标下可避免混凝土柱发生压剪脆性破坏;最后对附加减震框架改进连接构造设计提出了建议。     

A survey of glazing system behavior in multi-story buildings during hurricane andrew

A focused survey of glazing system behavior in multi-story buildings in the direct aftermath of Hurricane Andrew was conducted. Seventeen buildings and four building complexes were examined between 26 August and 30 August, 1992. The buildings surveyed spanned a 32 km (19 mile) distance from Miami on the north to Cutler Ridge on the south. With few exceptions, glazing systems performed poorly and damage to building contents was extensive. The following specific observations were made: (1) impacts from windborne debris were a dominant cause of glass failure; (2) wall system anchorages sometimes failed; (3) prevention of ‘blow-through’ after internal pressurization significantly mitigated storm damage to building interiors; and (4) outer-lite-only failures occurred on some insulating glass units. Results of the survey underscore the vital importance of maintaining the integrity of a building envelope during a severe windstorm. Windborne debris must be considered in the design of architectural glazing systems, as must proper anchorages of glazing systems to building framing members.     

Iterative system buckling analysis,considering a fictitious axial force to determine effective length factors for multi-story frames

Traditional elastic buckling analysis, based on the system buckling approach, is a convenient tool for the evaluation of effective length factors of columns, in the stability design of multi-story frames. This method is superior to other analytical approaches, such as the isolated subassembly and story-based approaches, in that the inter-story and inter-column interactions are inherently taken into account. Nevertheless, use of the conventional critical load expression, in combination with results of elastic buckling analysis, may yield an excessively large effective length in members having relatively small axial forces. The present paper proposes an iterative elastic buckling analysis to determine reasonable effective length factors of columns in multi-story frames. In this paper, numerical procedures for an iterative buckling analysis using a modified geometric stiffness matrix, are described to obtain the effective length factors of the columns in multi-story frames. The axial force term in the geometric stiffness matrix is modified by adding a fictitious axial force to make the columns buckle along with the overall buckling of the frame. Iterative eigenvalue analysis is performed using the modified geometric stiffness matrix, to obtain the effective length factors of each column using the critical load expression. Example frames presented in this paper demonstrate that the proposed method not only provides excellent outcomes by amending the weakness associated with traditional elastic buckling analysis for determining the effective length factor, but is also a competitive alternative in the design of multi-story frames.     

钢框架梁柱节点力学性能研究

在美国的Northridge地震和日本阪神地震中,钢框架梁柱刚性连接节点发生严重的脆性破坏现象,显示出节点构造还不尽合理,需对其进行构造改进.文中提出三种改进方式,通过对改进后节点的有限元计算分析,结果表明:在反复荷载作用下,改进节点强度和刚度较好,能够满足我国抗震规范的要求;塑性铰外移,改善节点区的力学性能;加载到极限状态时,节点域变形很小,满足强节点弱杆件的抗震设计原则;且节点构造简单,易于工地现场施工.     

多层砌体填充墙框架结构抗震性能试验研究

为了研究砌体填充墙沿框架层不连续布置对框架结构抗震性能的影响,进行了3榀两层单跨砌体填充墙框架结构模型、1榀单层单跨砌体填充墙框架结构模型、1榀两层单跨框架结构模型和1榀单层单跨框架结构模型的对比试验,分析了各试件的破坏特征、滞回曲线、骨架曲线、位移延性、刚度退化、承载力退化和耗能性能等抗震性能指标。结果表明：无论是单层单跨还是两层单跨的砌体填充墙框架结构,其水平峰值荷载和初始刚度比相应的纯框架结构均有较大幅度的提高,且其刚度退化程度比相应纯框架结构要缓慢;砌体填充墙的存在提高了框架结构的抗侧刚度和水平峰值荷载,使框架结构的变形由剪切型逐渐转变为弯剪型;砌体填充墙参与了结构的滞回耗能,填充墙框架的位移延性和累积耗能能力明显优于框架;砌体填充墙沿框架层不连续布置会引起框架结构层间侧移刚度和层间受剪承载力发生突变,影响框架结构的破坏形态,但由于砌体填充墙参与了框架结构的滞回耗能,故其仍具有较好的抗震性能。     

多层厂房仓库的火灾扑救

以某实业公司厂房仓库火灾为例,分析了该类建筑的火灾特点,并从接警调度、战术运用、跨战区增援、器材装备运用、战斗过程和其他相关方面探讨了扑救类似火灾应注意和加强的方面。     

多层钢管混凝土组合框架结构抗震性能的比较研究

钢-混凝土组合结构能够充分发挥钢材和混凝土的优点,具有良好的抗震性能,越来越广泛地应用于高层建筑中.目前,应用较多的主要有钢管混凝土组合结构,为分析研究钢管混凝土组合结构的抗震性能,分别对2栋5层钢筋混凝土框架结构和钢管混凝土组合框架结构进行了地震反应弹塑性时程分析,并对多种地震波输入下的两类结构的加速度和位移反应进行了对比.理论计算分析结果表明:与钢筋混凝土结构相比,钢管混凝土结构具有较好的抗震性能.     

钢框架梁柱改进型节点力学性能分析

发生在美国的Northridge地震和日本的阪神地震中,大量的钢框架梁柱节点发生严重的脆性破坏,显示出节点构造方面还存在一定的问题.通过对节点的有限元计算对比分析,得到在反复荷载作用下,构造经过改进的节点,其强度和刚度较好,能够满足我国抗震规范的要求;塑性转动能力较好,可以满足抗弯钢框架连接塑性转动能力的要求;加载到极限状态时,节点域变形很小,满足强节点弱杆件的抗震设计原则;且构造简单,易于现场施工.     

Initial postbuckling behavior of thin-walled frames under mode interaction

An L frame made up by beam and column having channel cross sections, has been analyzed in a previous work by two of the authors [14]. Depending on the aspect ratio and the joint configuration, it has been proved that the structure can exhibit two simultaneous buckling modes. Here using the asymptotic theory of elastic bifurcation that takes into account mode interaction, the initial slope of the bifurcated paths has been determined. Three cases of joint configurations, which are the more common used in welded connections, have been considered. For each case three admissible bifurcated paths have been found. Two of them show a slope having the same order of magnitude of the ones found in the absence of mode interaction while the remaining exhibits a slope largely steepest. Selecting, for each joint case, the bifurcated path with the higher slope and between them the smallest one, it is found that it is associated to the path which bifurcates at the higher critical load. This means that the stiffer structure is also the less imperfection sensitive. Finally for each one of the cases studied, the effect of initial imperfection has been considered and the real load carrying capacity of the frames has been determined. Finally some results have been compared with those obtained using the FE code ABAQUS.     

底部框架、框剪砖房抗震承载力研究

底框，框剪多层砖房在临街建筑中往往应用很多，由于该种建筑底部太柔，变形集中，构成薄弱楼层，受力复杂。因此，主要对其抗震性能进行了研究，采用剪力分配法求该种建筑地震荷载时，用底部地震增大系数进行修正。     

Compressive behavior of dual-gusset-plate connections for buckling-restrained braced frames

This work conducts compression tests and finite element analyses for steel dual-gusset-plate connections used for buckling-restrained braced frames (BRBFs). Compared to a single-gusset-plate connection, dual gusset plates sandwiching a BRB core reduce gusset plate size, eliminate the need for splice plates, and enhance connection stability under compression. The experimental program investigated ultimate compression load by testing ten large dual-gusset-plate connections. Out-of-plane deformation of the gusset plate in the test resembled that of a buckled gusset plate with low bending rigidity provided by the BRB end. The general-purpose nonlinear finite element analysis program ABAQUS was applied for correlation analysis. A parametric study of the dual-gusset-plate connection was performed to study the effects of plate size, presence of centerline stiffeners, and beam and column boundaries on ultimate compression load. The ultimate compression load of the dual-gusset-plate connection could not be predicted based on the AISC-LRFD approach due to beam flange out-of-plane deformation. The ultimate compression load of the dual-gusset-plate connection was reasonably predicted using a column strip length from the Whitmore section to the workpoint of the beam and column centerlines and a buckling coefficient of K = 2.     

Seismic behavior of CFRSTC composite frames considering slab effects

This paper reports on an experimental and numerical investigation conducted on the seismic behavior of concrete-filled rectangular steel tubular columns (CFRSTC) composite frames. The experimental study was conducted by subjecting two full-scale composite frames to simulated seismic loads. Both frames were composed of CFRSTC and steel beams. One specimen was placed on a reinforce concrete (RC) floor slab and the other was not. The purpose of the test was to investigate the elasto-plastic performance of the CFRSTC composite frame system and to examine the effects of composite action on the behavior of composite frames. The test results showed that the stiffness, strength and energy-dissipating capacity of the CFRSTC frame increased significantly with the presence of the floor slab. Compared with a bare steel beam, the composite beam experienced a decrease in the rotation capacity from 0.046 rad to 0.026 rad. The shear deformation of the panel zone grew because of the composite action, which delayed the fracture of the beam. Finite element (FE) models were established to simulate the tested frames. The results of the FE model fit well with that of the test model in terms of stiffness, strength, hysteretic behavior and component deformation.