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.

Behavior of ductile steel X-braced RC frames in seismic zones

A satisfactory ductile performance of moment-resisting reinforced concrete concentric braced frame structures (RC-MRCBFs) is not warranted by only following the provisions proposed in Mexico’s Federal District Code (MFDC-04). The nonlinear behavior of low to medium rise ductile RC-MRCBFs using steel X-bracing susceptible to buckling is evaluated in this study. The height of the studied structures ranges from 4 to 20 stories and they were located for design in the lakebed zone of Mexico City. The design of RC-MRCBFs was carried out considering variable contribution of the two main lines of defense of the dual system (RC columns and steel braces). In order to observe the principal elements responsible for dissipating the earthquake input energy, yielding mappings for diff erent load-steps were obtained using both nonlinear static and dynamic analyses. Some design parameters currently proposed in MFDC-04 as global ductility capacities, overstrength reduction factors and story drifts corresponding to diff erent limit states were assessed as a function of both the considered shear strength and slenderness ratios for the studied RC-MRCBFs using pushover analyses. Additionally, envelopes of response maxima of dynamic parameters were obtained from the story and global hysteresis curves. Finally, a brief discussion regarding residual drifts, residual drift ratios, mappings of residual deformations in steel braces and residual rotations in RC beams and columns is presented. From the analysis of the obtained results, it is concluded that when a suitable design criterion is considered, good structural behavior of RC-MRCBFs with steel-X bracing can be obtained. It is also observed that the shear strength balance has an impact in the height-wise distribution of residual drifts, and an important “shake-down” eff ect is obtained for all cases. There is a need to improve design parameters currently proposed in MFDC to promote an adequate seismic performance of RC-MRCBFs.

型钢组合加固震损RC框架抗震性能试验研究

震损RC框架需在震后得到快速修复,考虑采用加强局部构造及提高整体结构抗震能力的方法,以恢复甚至提高震损框架的抗震能力。结合框架在地震作用下的受力特性及破坏模式,先对柱采取外包角钢与缀条的局部加固,后对整体框架分别采取薄壁钢板剪力墙、斜支撑、V形屈曲约束支撑方式进行加固,并对加固后试件进行低周往复加载试验。结果表明:组合加固后试件抗震性能改善明显,将原框架的“强梁弱柱”转为符合抗震要求的“强节点弱构件,强柱弱梁”破坏。破坏时支撑及薄壁钢板先破坏,能有效避免主体框架过早破坏。试件加固后承载能力、初始刚度、延性及累积耗能均比未加固试件提高显著,且承载力及刚度退化均较缓慢,最后破坏为累积损伤所致。采用V形屈曲约束支撑加固的试件由于其具有多重耗能能力,其抗震性能及延性均好于其他两种组合加固方式的试件,综合考虑试件加固后的抗震性能及破坏模式,建议选用此种方法加固。

Effectiveness of two conventional methods for seismic retrofit of steel and RC moment resisting frames based on damage control criteria

This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation methods, concentric chevron bracing（CCB） and cylindrical friction damper（CFD） were selected. The performance assessment procedure of the frames is divided into two distinct phases. First, the limit state probabilities of the structures before and after rehabilitation are investigated. In the second phase, the seismic risk of structures in terms of life safety and financial losses（decision variables） using the recently published FEMA P58 methodology is evaluated. The results show that the proposed retrofitting methods improve the serviceability and life safety performance levels of steel and RC structures at different rates when subjected to earthquake loads. Moreover, these procedures reveal that financial losses are greatly decreased, and were more tangible by the application of CFD rather than using CCB. Although using both retrofitting methods reduced damage state probabilities, incorporation of a site-specific seismic hazard curve to evaluate mean annual occurrence frequency at the collapse prevention limit state caused unexpected results to be obtained. Contrary to CFD, the collapse probability of the structures retrofitted with CCB increased when compared with the primary structures.

Seismic performance of a reinforced concrete building retrofitted with self-centering shape memory alloy braces

Self-centering earthquake-resistant structures have received increased attention due to their ability to reduce post-earthquake residual deformations and,thus,repair time and cost.This stimulated the development of recentering shape memory alloy(SMA)dampers that use superelastic nitinol wires to dissipate energy and self-center the structure.However,there are still a few case studies applications on full-scale RC buildings in the literature.Moreover,general guidelines or even simplified approaches for the practical design of SMA damped braces are still lacking.This paper focuses on evaluating the effect of using self-centering shape memory alloy dampers for buckling-restrained braces applied for the seismic retrofit of a complex RC building structure.A design method originally proposed for elastoplastic dampers was implemented to size the SMA dampers to be placed on selected spans and stories of a building.The effectiveness of the design procedure was demonstrated by nonlinear time-history analyses under different sets of earthquake strong ground motions.The analysis results show that the recentering shape memory alloy bracing system is effective in limiting the maximum transient inter-story drifts and reducing the residual inter-story drifts after strong seismic events,due to its excellent recentering behavior together with its not negligible energy dissipation capacity.

Seismic Design Loads of Truss Arch Frames with Ceilings subjected to Vertical and Horizontal Earthquake Motions

Spatial structures such as a gymnasium and an exhibition hall often use ceilings because of enhancing sound effects and reducing heating bills. Although the ceiling members fell down on a large scale due to the seismic motion according to the past great earthquake disaster reports, structural engineers particularly do not carry out the seismic design. The study gives structural engineers the equivalent static loads for the design of the earthquake-proof design of the ceiling system. In particular, it is significant to investigate the dynamic behavior and the applied seismic loads for the complicated vibration of the long span arch building structures with RC columns.

防屈曲支撑加固既有RC框架结构抗震性能研究

参照建于20世纪70年代末的具有代表性的8层RC框架结构,按照1∶2.5的比例进行缩尺,制作一个两榀两层三跨的RC框架子结构模型。采用外贴防屈曲支撑RC框架的方式分别加固子结构模型每榀的中间跨,两榀框架的加固方式分别为植筋加固和抗剪键加固。对加固后的模型进行拟静力抗震性能试验,试验研究的结果表明,两种加固方法均安全可靠;防屈曲支撑加固后RC框架结构的抗震性能明显提高,在规范允许的变形条件下,地震能量主要被防屈曲支撑耗散,试验结果表明防屈曲支撑在地震作用时耗散的地震能量占到结构总耗能的66.9%以上。另外,根据FEMA356中基于性能的抗震设计方法,采用Perform-3D软件对框架结构模型进行非线性分析,分析结果与试验结果吻合良好。

Y形偏心钢支撑RC框架结构滞回性能试验研究

为了研究耗能段与RC框架梁采用不同连接节点形式对Y形偏心钢支撑RC框架结构滞回性能的影响,进行了2榀1/3缩尺Y形偏心钢支撑RC框架的低周反复荷载试验。介绍了试验过程,分析了试件在循环荷载作用下的破坏机理、滞回性能、延性、刚度退化规律以及耗能能力。试验结果表明:应用Y形偏心钢支撑加固RC框架合理可行,Y形偏心钢支撑承担了结构80%以上的水平荷载;U型外包钢与框架横梁连接的试件连接节点承载能力较高,耗能段耗能充分,结构的滞回曲线饱满;钢板与框架横梁底部连接的试件滞回曲线捏缩,耗能段耗能不充分,结构整体耗能能力差;U形外包钢与框架横梁连接的试件,耗能段破坏导致结构失效;钢板与框架梁底部连接的试件,连接节点破坏导致结构失效。

多遇地震下填充墙侧向刚度对RC框架结构抗震性能的影响

目前,我国RC框架结构抗震设计通常采用纯框架模型:将填充墙作为非结构构件,不考虑其抗侧力作用仅将墙体重量当作外荷载加到计算模型上,通过减小结构自振周期考虑填充墙对结构整体刚度增大作用。然而,多遇地震下填充墙具有一定的抗侧刚度,在其影响下纯框架计算模型是否合理有待商榷。针对该问题,建立考虑填充墙布置的RC框架结构计算模型,并进行线性动力时程分析。对计算结果进行分析表明:当填充墙均匀布置时,从框架部分承担水平地震作用力方面考虑纯框架模型是合理的,而从框架柱轴压力方面考虑又是不合理的;当填充墙不均匀布置时,结构抗震性能的各个指标均有很大的不同,纯框架模型是不合理的。

倒V形钢支撑加固RC框架的PUSHOVER分析

为揭示倒V形钢支撑加固RC框架在罕遇地震作用下的性能,建立了4层RC框架结构及在RC框架结构上后加钢支撑的结构模型,并对模型进行了PUSHOVER分析.从基底剪力-顶点位移曲线、楼层位移曲线及出铰顺序等方面对结构在罕遇地震作用下的抗震性能进行了评估.结果表明,在罕遇地震作用下,后加倒V形钢支撑的RC框架结构达到性能点时的基底剪力较原RC框架结构大,顶点位移较原RC框架结构小;钢支撑作为第一道抗震防线能吸收大部分的地震能量,对梁、柱构件能起有效的保护作用;此外,钢支撑对抗连接倒塌也有较大的现实意义.

基于FEMA P-58的RC框架结构抗震及减隔震性能评估

该文采用FEMA P-58理论进行RC框架结构抗震及减隔震性能评估。设计了一栋典型多层RC框架结构,并在此基础上添加屈曲约束支撑以及隔震支座形成BRB-框架结构与隔震框架结构,采用OpenSees软件建立了3个结构的有限元模型,选取合适的地震动记录并调幅,对三个结构进行了非线性结构响应分析。针对多遇地震、基本地震、罕遇地震、极罕遇地震4个地震动强度,使用FEMA P-58理论中基于强度的方法,对三个结构在四个地震强度下进行性能评估,并针对各性能指标的评估结果进行对比分析。地震损失评估结果显示,采用隔震框架结构与BRB-框架结构可以有效降低建筑物在地震作用下的维修成本与维修时间。与普通框架相比,在罕遇地震作用下隔震结构的维修成本与维修时间可降低65%与58%,BRB-支撑框架结构可降低47%与34%。

RC框架-钢管混凝土腋撑结构抗震性能分析

腋撑是设置于梁柱节点区域的短斜撑,用于提高结构抗水平力作用性能。与普通框架支撑相比,腋撑能提高建筑的有效使用空间,提高建筑的使用功能。腋撑可采用钢支撑、混凝土支撑以及耗能支撑等形式。钢管混凝土腋撑相比于钢腋撑,其轴向承载力较高;相比于混凝土腋撑和耗能腋撑,其施工更为方便。以新沂市某中学教学楼为背景工程,分别构建RC框架和RC框架-钢管混凝土腋撑结构模型,计算两种结构的振型、自振周期、能力曲线以及刚度退化速率等动力性能指标,通过对比分析,探讨增加钢管混凝土腋撑后对结构抗震性能的影响。研究表明,增设钢管混凝土腋撑后,结构的水平极限承载力和初始刚度大幅提高,层间位移明显减小,RC框架-钢管混凝土腋撑结构是一种抗震性能较好的新型结构。

耗能梁段与RC框架梁连接节点滞回性能的有限元分析

为了系统研究耗能梁段与RC框架梁连接节点的滞回性能,基于文献[11]所进行的低周往复加载试验,以S-5试件为BASE试件,设计了螺杆布置位置、螺杆数量、U型板侧边加胶、底板长度、螺杆钢材强度等级5个系列9个试件。采用ABAQUS对S-5及系列试件的滞回性能进行了模拟,分析了相关设计参数对连接节点滞回性能、承载力、抗侧刚度、耗能的影响规律。研究结果表明:耗能梁段与RC梁之间的连接可采用螺杆加外包钢的构造方式,螺杆位置、底板长度、螺杆钢材强度等级对此类节点的力学性能影响相对较小。但螺杆数量需合理确定,其数量过少将导致螺杆承载力不足,节点易发生脆性破坏。U型侧板同RC梁侧面增设结构胶可改善节点的刚度、承载力及耗能能力。

轴压比对Y型偏心支撑RC框架抗震性能的影响

针对Y型支撑加固多高层混凝土框架工程中框架轴压比的不同,对不同轴压比的Y型偏心支撑砼框架的滞回性能进行了非线性有限元分析。结果表明,随着轴压比的增大,结构的承载力呈先上升后下降的趋势;轴压比的增大能提高结构初始刚度,同时使结构后期刚度下降加快。最后,对Y型支撑加固混凝土框架工程中关于轴压比提出设计建议。

内填Y形偏心钢支撑加固RC框架结构设计方法

随着使用时间的增长,RC框架结构会出现结构性能劣化、使用条件改变、抗震设防烈度提高等变化,结构会存在抗侧刚度不足,需要对其进行加固补强.Y形偏心钢支撑抗侧刚度高,耗能段独立于框架之外,耗能能力好,内填Y形偏心钢支撑加固RC框架结构效果好.在试验研究的基础上,提出了基于耗能段与框架梁连接节点承载能力的Y形偏心支撑加固RC框架的简化设计方法和构造措施.主要包括:耗能段与RC框架梁连接节点的构造和设计;耗能段的选取与设计,耗能段与支撑之间的连接构造;钢支撑的确定和设计,钢支撑与梁柱连接节点的构造和设计以及内填Y形钢支撑的布置.提出的简化设计方法可为类似工程的抗震加固提供设计依据.

基于MARC的钢筋混凝土框-撑结构动力时程分析

文章根据动力时程分析和非线性有限元分析的方法,运用MSC.Marc软件研究了钢筋混凝土框-撑结构的动力反应。对钢筋混凝土框-撑结构和普通钢筋混凝土框架结构进行了对比分析,主要研究了钢筋混凝土框-撑结构的位移、速度、加速度及内力等地震反应能力。

防屈曲耗能支撑在某RC框架结构加固改造中的应用

本文以某高校科研办公楼6层RC框架结构加固改造为例,简述了工程所采用的增大截面法、粘贴碳纤维布以及防屈曲消能支撑的加固方法。采用静力推覆分析方法,分析防屈曲消能支撑的使用对该RC框架结构抗震性能的影响。结果表明,屈曲消能支撑的设置提高了结构在罕遇地震作用下的变形能力,在保护主体结构构件和防止结构倒塌方面起到关键作用。工程实践也表明防屈曲消能支撑施工安装便捷,施工周期短。其优良的耗能性能和优越的工程价值备受工程界所关注,应用将越来越广泛。

耗能梁段与带楼板RC框架梁连接节点滞回性能的有限元分析

基于文献[1]所进行的耗能梁段与带楼板RC框架梁连接节点的低周往复加载试验研究,采用非线性有限元程序ABAQUS对试件B-2进行模拟验证,并以B-2为BSAE试件,设计了U型板侧边注胶、螺杆强度、螺杆布置位置、螺杆直径等6个系列12个试件。对影响连接节点性能的主要设计参数进行分析,研究了此类连接节点的承载力、刚度及滞回性能,提出了相应的设计建议。

Y型偏心钢支撑加固弱柱RC框架的滞回性能试验

为研究Y型偏心支撑加固弱柱RC框架的滞回性能,进行了2榀、1/3缩尺的Y型偏心钢支撑加固RC框架的低周往复加载试验,其中1榀试件的RC框架为强梁弱柱型,另外1榀对比试件为强柱弱梁型。重点研究采用Y型偏心钢支撑加固强、弱柱RC框架结构的破坏过程及破坏特征,分析了两类加固框架的滞回性能、延性、刚度退化、耗能等抗震性能。试验结果表明采用Y型偏心钢支撑加固弱柱框架后,仍可获得较高的水平承载力、抗侧刚度,以及良好的变形和耗能能力。

Y型偏心钢支撑加固弱柱RC框架结构的滞回性能模拟及参数分析

为了系统研究Y型钢支撑加固RC框架的滞回性能,采用通用有限元程序ABAQUS对试验试件RCF-YB2进行了模拟验证。在此基础上,系统分析了低周往复荷载作用下框架柱截面、框架柱纵筋配筋率及框架柱配箍率对此类加固结构的滞回性能、水平承载力、抗侧刚度、耗能能力的影响。研究结果表明,框架柱截面对结构的水平承载力、抗侧刚度、耗能影响显著;框架柱纵筋配筋对结构的水平承载力、抗侧刚度、耗能影响较小;框架柱配箍率对结构的水平承载力、抗侧刚度、耗能能力影响可忽略。