Ductility demands on buckling-restrained braced frames under earthquake loading

Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center,Lehigh University to prepare for an upcoming experimental program.The analysis program DRAIN-2DX was used to model a one-bay,four-story prototype BRBF including material and geometric nonlinearities.The buckling- restrained brace(BRB)model incorporates both isotropic and kinematic hardening.Nonlinear static pushover and time- history analyses were performed on the prototype BRBF.Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results.Particular emphasis was placed on global ductility demands and ductility demands on the BRBs.These demands were compared with anticipated ductility capacities.The analysis results,along with results from similar previous studies,are used to evaluate the BRBF design provisions that have been recommended for codification in the United States.The results show that BRB maximum ductility demands can be as high as 20 to 25.These demands significantly exceed those anticipated by the BRBF recommended provisions.Results from the static pushover and time- history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5.Modifications to the testing protocol are recommended.

Experimental study on slender buckling-restrained knee braces with round steel bar cores

This study aimed to investigate a novel slender buckling-restrained knee brace damper (BRKB) for welded and weld-free steel framing systems. The proposed BRKB adopts steel bar cores connected by a central coupler and restrained by tube buckling restrainers with a cover tube supporter. The advantages of the proposed damper include easy assembly compared to conventional buckling restrained braces, and high architectural flexibility for the retrofitting of large-span weld-free or welded steel moment-resisting systems. Specifically, by increasing the number of contraction allowances, undesirable failure mechanisms that are global instability and local buckling of the restrainer ends can be effectively suppressed because the more uniform plastic deformation of the core bar can be achieved longitudinally. In this study, displacement-controlled compression and cyclic loading tests were carried out to investigate the deformation capacities of the proposed BRKBs. Structural performance metrics associated with both loading tests, such as strength capacities, strains at the cover tubes and buckling restrainers, and hysteretic behaviors of the proposed damper under cyclic loads, were measured and discussed. Test results revealed that the geometrical characteristics of the cover tubes and adopted contraction allowances at the dampers play essential roles in their load-bearing capacities.

防屈曲耗能支撑研究与应用的新进展

防屈曲耗能支撑是一种性能优良的新型耗能减震构件。本文阐述了防屈曲耗能支撑的构成和基本原理,根据约束构件的不同材料形式,将防屈曲耗能支撑划分为混凝土约束型防屈曲耗能支撑、全钢型防屈曲耗能支撑和装配式防屈曲耗能支撑。分别介绍了防屈曲耗能支撑的类型与性能、防屈曲耗能支撑框架分析与子结构试验,以及防屈曲耗能支撑在工程中的应用情况和标准化。指出了防屈曲耗能支撑研究和推广应用中存在的问题,给出了今后研究与应用的建议。

节点刚接与螺栓连接的屈曲约束支撑框架结构抗震性能

为研究刚接和螺栓连接两种不同梁柱节点连接方式的屈曲约束支撑框架(buckling restrained braced frame,BRBF)结构的抗震性能。首先设计了水平分担率分别为20%、30%、40%的8层梁柱节点刚接的BRBF结构(TM模型)为基本的研究模型,然后通过对梁柱节点转换得到相对应的3个8层梁柱节点螺栓连接的BRBF结构(SM模型),运用CLAP软件对模型进行静动力弹塑性分析。结果表明:梁柱节点从刚性连接改为螺栓连接后,结构首层和顶层失效时的最大破坏层剪力降低了1/2,两种模型均表现出中下部楼层变形突出的特征;在地震波作用下,SM模型的层间位移均明显大于TM模型,但两组模型的层间位移均控制在1/50(失效点)以内,且几乎都大于弹性层间位移角1/250,都呈现先增大后减小的规律;TM模型与SM模型的BRB吸收塑性变形能量基本相差不大,且都出现往中下部楼层集中的现象;两组模型滞回曲线饱满,但SM模型的滞回曲线面积大于TM模型,因此地震需求耗能更多。

防屈曲支撑框架体系按延性方法设计与按现行规范设计对比

简要介绍了我国抗震设计方法的历史沿革、结构延性设计的基本理念以及必要性,介绍了防屈曲支撑框架结构的概念、受力原理。引入了结构体系延性调整系数γRS,介绍了延性设计方法对梁柱节点、构件截面宽厚比、长细比以及层间位移的要求。本文主要是为了得到在抗震设计中采用本文方法设计工程项目时的经济指标,因此工作重点放在按照延性设计方法设计实际工程以及与按现行规范设计的比较中。论文给出了13层试设计算例设计对比。利用MTS软件分别按延性设计方法以及按现行规范对一个13层防屈曲支撑框架结构算例进行试设计,对按两种方法进行设计得出的各个结果进行对比,讨论按延性设计方法设计结构的优越性。

防屈曲支撑框架设计方法研究

采用数值手段,研究了防屈曲支撑框架和普通中心支撑框架在性能上的差异。基于弹塑性时程分析,由大量防屈曲支撑框架算例,建立支撑框架结构在大震下的层间位移角最大值随抗侧刚度比k变化的关系曲线,按照大震不倒的要求,获得k值的合理取值范围。分别对不同k值下支撑框架结构的设计进行研究,得到相应k值下允许设计的最弱框架(即框架设计的临界点),供结构设计参考。

含有屈曲约束支撑平面框架的抗震性能试验研究

为了研究含有屈曲约束支撑结构的抗震性能,对含有屈曲约束支撑和普通支撑的平面框架进行了试验研究。结合试件破坏现象及试验结果,对屈曲约束支撑的力学性能、破坏机理以及作用效果进行了分析探讨。同时,还对试验过程进行了数值模拟分析。试验及理论分析结果表明:与含普通支撑框架相比,含屈曲约束支撑的框架在提高承载力的同时,还具有更稳定的耗能能力;经过适当的设计,可以使屈曲约束支撑先于主体结构进入弹塑性状态,提高结构的抗震性能。