On the design of new ductile knee bracing

An approximate method is presented that can be used to determine the nonlinear behavior of a new structural bracing system called the ‘Chevron Knee Bracing’ (CKB). In this framing system, an especial form of diagonal brace connected to a knee element instead of a beam-column joint is investigated. The diagonal element provides lateral stiffness during a moderate earthquake. However, the knee element is designed to have three plastic joints or two yielded specimens in flexural and shear yielding mode, respectively, for dissipation of the energy caused by a strong earthquake. This article demonstrates the transformation of a complex problem into a new, practical set of design charts and graphs. To severe purpose, first, an optimal shape and angle for the diagonal-knee element is considered based on the studying of the elastic and inelastic behavior of the system. Then, by use of the main graphs and charts designed accordingly, the dynamic response of this model is properly investigated. Finally, the correctness of the results is ascertained, using example problems. The comparison of the results between the technique presented in this paper and the exact finite element methods and/or experimental results shows very good agreement and very suitable conformity.     

钢结构中V形支撑的抗震性能影响因素的定量分析

事实上,根据设计和荷载规范进行抗震设计时,需要确定地震反应修正系数R、高强度系数Ω0和变形放大系数Cd。针对结构的横向支撑系统,也即V形支撑(CKB)对上述系数进行评估。这类支撑系统中的V形构件在支撑系统内形成弯曲或剪切塑性铰,有助于系统的能量耗散。采用基于低概率结构倒塌的FEMAP695方法进行研究,包含非线性静动力学分析。通过静力弹塑性分析研究这种支撑的高强度和延性。通过增量动力分析(IDA)获得原始模型的抗倒塌储备系数(CMRs),并对其进行修改,得到每个原始模型调整后的抗倒塌储备系数(ACMR)。计算得到的ACMRs满足考虑了整体系统倒塌的不确定性的FEMAP695的要求,证明了CKB系统假定的抗震性能影响因素的有效性。     

Seismic performance of friction dampers using flexure of rc shear wall system

Shear wall systems in high‐rise apartments are governed by the flexural behaviour of members such as a cantilever beam. The installation of the damper‐brace system in a structure governed by flexural behaviour is not suitable. Because of the relatively high lateral stiffness of the shear wall, a load is not concentrated on the brace and the brace cannot perform the role of a damping device. In this paper, a friction damper that applies the flexibility of a shear wall is proposed in order to reduce the deformation of the structure. To evaluate the performance of the proposed friction damper, a nonlinear time history analysis is executed by the SeismoStruct analysis program, and a multiple vertical linear element model is used for simulating flexural behaviour of the shear wall. It is found that the control performance of the proposed friction damper is superior to that of a coupled wall with a rigid beam. In conclusion, this study verified that the optimal control performance of the proposed friction damper is equal to 45% of the maximum shear force induced in the middle floor beam with the rigid beam. Copyright © 2009 John Wiley & Sons, Ltd.     

On the Evaluation of the Use of EKBs to Improve Seismic Performance of Steel Frames

In this paper a new eccentric and knee bracing system named Eccentrically Knee Brace (EKB) is introduced and its merits to increase seismic performance of the steel frames is investigated. To assess the seismic behavior of this system compared to other steel braced systems, numerical modeling using finite element software is implemented. Subjected to moderate earthquakes, the knee element exclusively dissipates the seismic energy through plastic shear distortion, while the other structural elements remain in elastic range. Under severe earthquakes, plastic deformation of the knee element will be halted by the stopper subsequently causing yielding of the link element. Finally, a simplified analytical model is derived to predict the bilinear behavior of the EKBs.     

Parametric computational study on butterfly-shaped hysteretic dampers

A parametric computational study is conducted to investigate the shear yielding, flexural yielding, and lateral torsional buckling limit states for butterfly-shaped links. After validating the accuracy of the finite element modeling approach against previous experiments, 112 computational models with different geometrical properties were constructed and analyzed including consideration of initial imperfections. The resulting yielding moment, corresponding critical shear force, the accumulation of plastic strains through the length of links as well as the amount of energy dissipated are investigated. ‚€ƒThe results indicate that as the shape of the butterfly-shaped links become too straight or conversely too narrow in the middle, peak accumulated plastic strains increase. The significant effect of plate thickness on the buckling limit state is examined in this study. Results show that overstrength for these links (peak force divided by yield force) is between 1.2 and 4.5, with straight links producing larger overstrength. Additionally, proportioning the links to delay buckling, and designing the links to yield in the flexural mode are shown to improve energy dissipation.     

含可更换剪切型耗能梁段的钢框筒结构抗震性能研究

地震作用下,传统钢框筒结构难以实现强柱弱梁的设计理念,大震下柱端往往先于梁端出现塑性铰。针对这一问题提出了含可更换剪切型耗能梁段的钢框筒结构,即在裙梁中设置可更换的剪切型耗能梁段,大震作用下结构利用剪切型耗能梁段良好的弹塑性变形能力进行耗能,其余构件仍处于弹性状态或部分发展塑性。设计了一组算例结构,包括传统钢框筒结构和含可更换剪切型耗能梁段的钢框筒结构,采用SAP2000有限元分析软件对算例结构进行了弹性和弹塑性地震反应分析,对比了传统钢框筒结构和不同耗能梁段布置形式的含可更换剪切型耗能梁段的钢框筒结构在多遇地震、罕遇地震和极罕遇地震作用下的抗震性能和破坏模式。结果表明:在裙梁中设置剪切型耗能梁段对结构整体刚度的影响较小,含可更换剪切型耗能梁段的钢框筒结构改变了传统钢框筒结构的耗能机制,主要通过耗能梁段的剪切变形代替裙梁端部塑性铰耗能。罕遇地震作用下耗能梁段全部进入塑性耗能,震后仅需替换损伤严重的耗能梁段即可快速恢复结构的使用功能。极罕遇地震作用下,传统钢框筒结构达到极限状态,而含可更换剪切型耗能梁段的钢框筒结构的耗能梁段进一步发展塑性,其余构件保持弹性,结构具有足够的安全储备。     

Lateral-torsional buckling analysis of cantilever beam with tip lateral elastic brace under uniform and concentrated load

The studies on the lateral-torsional buckling of cantilever steel beam with tip lateral elastic brace are rarely reported. The total potential energy is first established for the lateral-torsional buckling of cantilever steel beam with tip lateral elastic brace under uniform and concentrated load. The modal trial function of the lateral displacement and torsional angle are expressed as trigonometric function combination with six terms. By introducing new dimensionless parameters, the analytical solution of the dimensionless buckling equation for the lateral-torsional buckling of cantilever steel beam with tip lateral elastic brace is obtained. With the help of 1stOpt software which is mathematical optimization analysis software, the non-dimensional critical moment formula of the lateral-torsional buckling of cantilever beam with tip lateral elastic brace is obtained. Then, the accuracy of the formula is verified by ADINA finite element software. The results show that the given critical moment formula is of high accuracy. It provides convenient and simple design method for practical engineering.     

Shear slotted bolted connection

Slotted bolted connections (SBCs) have been developed and used as an axial friction damper in braced frames since 1980s. To employ the benefits of SBCs in moment resisting frames (MRFs), rotational slotted bolted connections have been developed more recently with limited application in members that flexural behavior is dominated to shear. In this paper, shear slotted bolted connection (SSBC) is introduced as a new type of friction dampers to employ the benefits of SBCs in lateral load resisting systems with predominant shear behavior members that dissipate energy by traditional yielding mechanisms. The SSBC is a modified bolted connection that dissipates energy through friction in which friction is activated by shear force. The applications of the proposed system as a shear link in link beams of eccentrically braced frames (EBFs), in the beams of MRFs, and coupling beams of coupled concrete shear walls are introduced. To show the efficiency of SSBC, an existing EBF with tubular link beam is equipped with SSBC, and its behavior is studied via models created in general purpose finite element program ABAQUS (SIMULIA, The Dassault Systèmes, Realistic Simulation, RI, USA) verified thoroughly against relevant test results. Also, three MRFs with different beam lengths are modified using SSBC, and their monotonic and cyclic behavior are investigated using validated finite element models. The results show that, as expected, SSBC is capable of working as a mechanical shear fuse dissipating energy effectively in both MRFs and EBFs without any material yielding.     

带跨层预应力斜支撑的高层钢框筒结构静力性能研究

对于高层钢框筒结构体系,风荷载起控制作用,结构顶层侧移、层间位移角不易控制,为提高钢框筒结构的抗侧能力,将柔性预应力索用于钢框筒结构,并运用SAP 2000有限元软件对跨层预应力支撑钢框筒结构和钢框筒结构的抗侧性能和剪力滞后效应进行分析、对比,进一步研究预应力支撑的初始预拉力、弹性模量、布置角度、截面直径和布置方式等参数对跨层预应力支撑钢框筒结构受力性能的影响。研究表明:对钢框筒结构施加预应力支撑,显著提高其抗侧能力,并改善结构局部的剪力滞后效应;跨层预应力支撑宜布置为45°左右的交叉剪刀形状;在实际钢框筒结构工程允许的范围内,预应力支撑应选取较大的弹性模量和直径。     

斜隅支撑体系的弹塑性性能分析

提出了一种新型耗能支撑框架钢结构体系——斜隅支撑框架体系,指出该体系具有延性好、抗侧移刚度大、震后容易修复的特点,分析了隅撑与梁柱的连接方式以及隅撑的布置方式对钢框架受力性能的影响。     

内置轻钢桁架混凝土组合剪力墙抗震性能试验研究

将冷弯薄壁型钢桁架配置在普通钢筋混凝土剪力墙中代替钢筋而形成轻钢桁架混凝土组合剪力墙。为研究该类墙体的抗震性能,对两组共6个内置轻钢桁架混凝土组合剪力墙进行拟静力试验,研究轴压比和斜撑体积配钢率对其滞回性能、变形性能、刚度退化以及耗能能力的影响。对比了低矮剪力墙和中高剪力墙的位移延性和耗能能力。结果表明：轴压比对该类剪力墙的变形能力和耗能能力均不利,应予以控制;斜撑体积配钢率对提高低矮墙的延性、耗能能力效果明显,但对承载力的提高作用较小;对中高剪力墙,斜撑体积配钢率的增加,对其耗能能力不利。     

Experimental Study on Low Cyclic Loading Tests of Steel Plate Shear Walls with Multilayer Slits

A new type of earthquake-resisting element that consists of a steel plate shear wall with slits is introduced. The infill steel plate is divided into a series of vertical flexural links with vertical links. The steel plate shear walls absorb energy by means of in-plane bending deformation of the flexural links and the energy dissipation capacity of the plastic hinges formed at both ends of the flexural links when under lateral loads. In this paper, finite element analysis and experimental studies at low cyclic loadings were conducted on specimens with steel plate shear walls with multilayer slits. The effects caused by varied slit pattern in terms of slit design parameters on lateral stiffness, ultimate bearing capacity and hysteretic behavior of the shear walls were analyzed. Results showed that the failure mode of steel plate shear walls with a single-layer slit was more likely to be out-of-plane buckling of the flexural links. As a result, the lateral stiffness and the ultimate bearing capacity were relatively lower when the precondition of the total height of the vertical slits remained the same. Differently, the failure mode of steel plate shear walls with multilayer slits was prone to global buckling of the infill steel plates; more obvious tensile fields provided evidence to the fact of higher lateral stiffness and excellent ultimate bearing capacity. It was also concluded that multilayer specimens exhibited better energy dissipation capacity compared with single-layer plate shear walls.     

Seismic Study of Buckling Restrained Brace System without Concrete Infill

Bracing is the one of the best-known means of seismic retrofitting. Buckling restrained brace (BRB) is a certain type of brace with great efficiency against lateral loading. This paper presents the results of a finite element analysis on a BRB in which casing has no concrete infill. The core segment of this brace is similar to the conventional BRB, but it has a different buckling restraining system. The aim of this paper was to perform a parametric seismic study on the effect of a gap and also the effect of friction between the core and the casing and to evaluate the buckling behavior of these braces in response to changes in the initial shape of the bracing system. The results show that the flexural stiffness of the casing system, regardless of size of the gap, can significantly affect the buckling behavior of bracing.     

设置屈曲约束支撑的斜交网筒结构延性有限元分析

斜交网筒结构具有较大的抗侧刚度,但其延性较差,通过设置屈曲约束支撑可改善斜交网筒结构延性。以30层的斜交网筒结构模型为研究对象,分别对普通斜交网筒结构和设置屈曲约束支撑斜交网筒结构进行静力弹塑性推覆（Pushover）分析。结果表明：屈曲约束支撑可有效改善斜交网筒结构延性。此外,对立面中部、立面角部、底部楼层、上部楼层共4种局部区域布置屈曲约束支撑的方案进行了结构延性分析。局部设置屈曲约束支撑斜交网筒结构的设计应确保斜柱处于弹性工作状态,屈曲约束支撑率先进入塑性耗能状态。建议采用立面中部布置屈曲约束支撑的方案,可实现在保证结构受剪承载力的前提下,较好地改善斜交网筒结构的延性,避免结构发生脆性破坏。     

Self‐centering viscoelastic diagonal brace for the outrigger of supertall buildings: Development and experiment investigation

This paper aims to improve the seismic performance of outriggers within supertall buildings and eliminate the defects of obvious degradation of stiffness, low energy dissipation capacity, and large residual deformation after the buckling of traditional diagonal members by presenting a new type of outrigger. The traditional profiled steel diagonal member is replaced with a self‐centering viscoelastic diagonal brace (SC‐VEDB) in the proposed outrigger, providing enhanced energy dissipation and self‐centering capacity. The new SC‐VEDB is composed of the inner and outer steel tubes, viscoelastic materials, and prestressed tendons. Energy dissipation capacity is produced by the shear deformation of viscoelastic materials, whereas prestressed tendons provide the self‐centering capacity. The working mechanism of SC‐VEDB is first theoretically analyzed. Following this, two specimens with a length of 2.2 m were designed, fabricated, and tested under low cyclic reversed loadings within different frequencies and pretension forces. The results confirm that the hysteretic curve of SC‐VEDB has a typical flag shape, which imparts the stable stiffness, good energy dissipation, and self‐centering capacities. The activation force of SC‐VEDB is mainly determined by the initial pretension force, and the post‐activation stiffness predominantly depends on the stiffness of the prestressed tendons. Moreover, SC‐VEDB has better repairability, and the initial hysteretic behavior of the component can be quickly recovered by replacing the damaged prestressed tendons. A refined finite element model for SC‐VEDB is established to predict its hysteretic behavior, and the numerical simulation corresponds well with the experimental results. The maximum relative error of the initial elastic stiffness and ultimate strength is approximately 4.6% and 1.3%, respectively, which verifies the accuracy of the SC‐VEDB numerical simulation method.     

新型抗震体系隅撑支撑框架结构研究

新型抗震隅撑支撑框架(knee-braced frame,KBF)是在梁柱连接的附近设一起耗能作用的隅撑,主支撑连接在此隅撑上构成的抗震结构体系。与偏心支撑体系EBF抗震结构体系对比,具有大震时框架结构不易损坏、维修方便的优点。采用有限元考察了不同的隅撑形式、不同高宽比下KBF结构的性能。在分析总结的基础上,系统地提出了KBF框架的抗震设计要求和有关的计算公式。     

两边连接屈曲约束钢板剪力墙受力机理与等效支撑模型

采用理论分析和有限元方法,针对两边连接屈曲约束钢板剪力墙的受力机理和传力规律进行研究。提出了钢板墙边缘约束区的概念并确定了边缘约束区的宽度,分析了钢板墙的屈服形状、钢板墙内各部分应力流的分布规律和钢板墙与梁连接处的受力特点等。在此基础上提出了两边连接屈曲约束钢板剪力墙等效支撑模型,对不同尺寸、不同层数的框架 屈曲约束钢板剪力墙结构和框架 等效支撑结构在水平荷载作用下的力学性能进行分析,并对两种结构的荷载 位移曲线进行了对比。分析表明,所提出的等效支撑模型在结构刚度和承载力方面具有较好的准确性,无论是单调加载还是反复加载均能准确地模拟两边连接屈曲约束钢板剪力墙结构的受力行为。     

预压弹簧自恢复耗能支撑非线性原理模型参数识别及试验验证

结合预压弹簧自恢复耗能（PS-SCED）支撑工作原理,提出由两组Bouc-Wen模型及一组线弹性模型共同构成的支撑非线性原理模型,并给出模型计算公式。基于PS-SCED支撑拟静力试验结果,利用遗传算法对PS-SCED支撑原理模型的7个控制参数进行参数识别,并将识别结果与PS-SCED支撑拟静力试验、ANSYS实体模型及PS-SCED支撑分段式简化模型分析结果进行对比研究。结果表明,PS-SCED支撑原理模型能够准确、细致的描述PS-SCED支撑的滞回响应特性,相比实体模型及支撑分段式简化模型,提出的原理模型对支撑恢复力、过渡段圆滑性、等效黏滞阻尼比及累积耗能的预测结果更加准确。     

内藏钢板支撑剪力墙屈服前刚度的有限元分析

介绍了内藏钢板支撑剪力墙这种新型抗侧力支撑体系的特点及性能,通过对其屈服前刚度的有限元分析,并结合试验资料对比分析,对《高层民用建筑钢结构技术规程》(JGJ 99-98)附录中内藏钢板支撑剪力墙构件屈服前刚度计算公式进行了验证,通过回归分析,提出了内藏钢板支撑剪力墙构件屈服前刚度的修正计算公式,可为进一步的研究和规程修订提供参考。     

Experimental and numerical investigation on full-scale tension-only concentrically braced steel beam-through frames

This paper presents an experimental investigation on two full-scale tension-only concentrically braced beam-through frames (TOCBBTFs) with through beam bolted connections. This type of TOCBBTF system features cold-formed square-tube section columns connected to H-section through beams by bolted end plate. It is commonly used in low-rise prefabricated buildings. Two two-story, four-span by one-span TOCBBTFs subjected to design vertical load were cyclically loaded horizontally to examine the seismic behavior. Stable behavior was observed up to a story drift angle of 1/10. The cyclic behavior was characterized by a linear response, followed by a slip range and a significant hardening response. Deteriorating pinched hysteresis was observed due to the occurrence of cyclic brace compression buckling and tension yielding. The structural damage evolution, ductility, stiffness and shear force distribution of the TOCBBTFs were investigated. Moreover, the finite element software ABAQUS was used to investigate the behavior of TOCBBTF by nonlinear analysis. Semi-rigid analysis produced the most reasonable prediction including initial lateral stiffness and peak story shear. The calibrated numerical models can be employed to launch further studies for this structural system.