Optimization of design parameters for controlled rocking steel braced dual-frames

A controlled rocking concentrically steel braced frame(CR-CSBF)is introduced as an alternative to conventional methods to prevent major structural damage during large earthquakes.It is equipped with elastic post-tensioned(PT)cables and replaceable devices or fuses to provide overturning resistance and dissipate energy,respectively.Although CR-CSBFs are not officially legalized in globally valid codes for new buildings,it is expected to be presented in them in the near future.The main goal of this study is to determine the optimal design parameters consist of the yield strength and modulus of elasticity of the fuse,the initial force of the PT cable,and the gravity load on the rocking column,considering different heights of the frame,spanning ratios and ground motion types for dual-configuration CR-CSBF.Nonlinear time-history analyses are performed in OpenSees.This study aims to define the optimal input variables as effective design parameters of CR-CSBFs by comparing four seismic responses consisting of story drift,roof displacement,roof acceleration and base shear,and also using the Euclidean metric optimization method.Despite the previous research,this study is innovative and first of its kind.The results demonstrate that the optimal design parameters are variable for various conditions.

Probabilistic safety assessment of self-centering steel braced frame

The main drawback of conventional braced frames is implicitly accepting structural damage under the design earthquake load, which leads to considerable economic losses. Controlled rocking self-centering system as a modem low-damage system is capable of minimizing the drawbacks of conventional braced frames. This paper quantifies main limit states and investigates the seismic performance of self-centering braced frame using a Probabilistic Safety Assessment procedure. Margin of safety, confidence level, and mean annual frequency of the self-centering archetypes for their main limit states, including PT yield, fuse fracture, and global collapse, are established and are compared with their acceptance criteria. Considering incorporating aleatory examined. Results of the investigation indicate that the provide the adequate margin of safety against exceeding and epistemic uncertainties, the efficiency of the system is design of low- and mid-rise self-centering archetypes could the undesirable limit-states.

Shaking table test and numerical analysis of a 1:12 scale model of a special concentrically braced steel frame with pinned connections

This paper describes shaking table tests of a 1：12 scale model of a special concentrically braced steel frame with pinned connections, which was fabricated according to a one-bay braced frame selected from a typical main factory building of a large thermal power plant. In order to investigate the seismic performance of this type of structure, several ground motion accelerations with different levels for seismic intensity Ⅷ, based on the Chinese Code for Seismic Design of Buildings, were selected to excite the model. The results show that the design methods of the members and the connections are adequate and that the structural system will perform well in regions of high seismicity. In addition to the tests, numerical simulations were also conducted and the results showed good agreement with the test results. Thus, the numerical model is shown to be accurate and the beam element can be used to model this structural system.

Peak displacement patterns for the performance-based seismic design of steel eccentrically braced frames

Performance-based seismic design(PBSD) aims to assess structures at different damage states. Since damage can be directly associated to displacements, seismic design with consideration of displacement seems to be logical. In this study, simple formulae to estimate the peak floor displacement patterns of eccentrically braced frames(EBFs) at different performance levels subjected to earthquake ground motions are proposed. These formulae are applicable in a PBSD and especially in direct displacement-based design(DDBD). Parametric study is conducted on a group of 30 EBFs under a set of 15 far field and near field accelerograms which they scaled to different amplitudes to adapt various performance levels. The results of thousands of nonlinear dynamic analyses of EBFs have been post-processed by nonlinear regression analysis in order to recognize the major parameters that influence the peak displacement pattern of these frames. Results show that suggested displacement patterns have relatively good agreement with those acquired by an exact nonlinear dynamic analysis.

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.

Seismic response of high-rise steel framed buildings with Chevron-braced designed according to Venezuelan codes

The object of this study is to determine the seismic response of regular high-rise steel buildings with chevron-braced frames. Mechanics models of three buildings of 14, 18 and 20 stories are studied, all of them with similar geometric characteristics in plant and elevation. These models are realized using prescriptions and parameters from venezuelan design codes. The seismic action is carry on through varius synthetic design spectrum compatible accelerograms defined by the seismic codes in this study, with three levels of intensity corresponding to three specific Limit States. Dynamic analysis is used to compute parameters of ductility, over strength and maximum displacements. From these results it can be concluded that chevron-braced frames presented a good overall performance and non V-braced frames show greater damage due to dynamic actions, validating non linear dynamic analysis as a very powerful tool to seismic-resistance design and chevron-braced frames as a very useful choice in improving the response of tall steel structures. since this lateral bracing system is absent from Venezuelan seismic codes.

Conceptual study of X-braced frames with different steel grades using cyclic half-scale tests

In this paper, an experimental and analytical study of two half-scale steel X-braced flames with equal nominal shear strength under cyclic loading is described. In these tests, all members except the braces are similar. The braces are made of various steel grades to monitor the effects of seismic excitation. Internal stiffeners are employed to limit the local buckling and increase the fracture life of the steel bracing. A heavy central core is introduced at the intersection of the braces to decrease their effective length. Recent seismic specifications are considered in the design of the X-braced frame members to verify their efficiency. The failure modes of the X-braced frames are also illustrated. It is observed that the energy dissipation capacity, ultimate load capacity and ductility of the system increase considerably by using lower grade steel and proposed detailing. Analytical modeling of the specimens using nonlinear finite element software supports the experimental findings.

钢支撑-钢筋混凝土掉层框架结构抗震性能试验研究

为改善坡地钢筋混凝土(RC)掉层框架结构抗侧刚度分布的不均匀性,设计了一栋在上接地层设置钢支撑的RC掉层框架结构,按1/4比例提取其顺坡向中榀框架下部5层子结构为试验对象,开展钢支撑-RC掉层框架拟静力试验,观测试件的破坏过程,并对比RC掉层框架试验所得试件的破坏形态,分析试件滞回性能、延性和刚度退化等抗震性能指标。结果表明:试件的最终破坏是以第4层柱底混凝土压溃,梁端混凝土剥落、底部钢筋断裂,顶层柱顶混凝土剥落为标志。与RC掉层框架试验结果相比,钢支撑-RC掉层框架试件上接地柱的破坏明显减轻,柱端破坏分布也更为均匀,避免了掉层框架结构“半层破坏模式”的出现,改善了结构的耗能和抗地震倒塌能力。但试件上接地层相邻上一层的变形和破坏程度较大,应对该楼层的柱端进行适当的抗震加强;设置钢支撑后,试件的滞回曲线较为饱满,并具有良好的延性(正、负向加载的位移延性系数分别可达5.13、5.69),正负向加载的刚度退化曲线也趋于对称。

双层带钢板暗支撑装配整体式混凝土剪力墙抗震性能研究

为研究带钢板暗支撑装配整体式混凝土剪力墙的抗震性能,设计制作1片双层带钢板暗支撑装配整体式混凝土剪力墙和1片双层带钢板暗支撑现浇混凝土剪力墙,其中装配整体式剪力墙内置钢板暗支撑在墙身与基础梁和上下墙身水平连接节点处采用双面角焊缝连接以适应施工时的安装尺寸冗余度要求。对试件进行低周反复加载试验,结果表明:采用双面角焊缝连接预制墙身内置钢板暗支撑可以适应较大的施工冗余度,并且保证暗支撑传力的可靠性;装配整体式剪力墙具有和现浇剪力墙等同的水平承载力、刚度退化水平和耗能能力;2个构件均为弯曲破坏,但装配整体式剪力墙在一层墙体后浇带与预制墙身接缝处也产生塑性铰。

四川大学博物馆结构设计重难点分析研究

四川大学博物馆采用钢框架结构体系,并设置屈曲约束支撑改善结构的抗震性能。介绍了四川大学博物馆的结构设计参数及抗震性能目标。针对结构设计中的重难点,开展了屈曲约束支撑的工作机理分析、框架柱计算长度与穿层柱分析、东侧大悬挑空间的相关分析。利用反应谱分析及时程分析探究了屈曲约束支撑工作机理,分析结果表明,屈曲约束支撑能够有效改善钢结构产生塑性铰的状况,起到保护主体钢框架的作用。针对东侧大悬挑空间的功能要求,设计采用了屋顶桁架结合钢拉杆吊挂东侧大楼梯的结构形式,通过结构防连续倒塌分析、楼板应力分析、楼盖舒适度分析、关键节点有限元分析等确保该部位结构设计安全合理。对整体结构受力机理和薄弱部位进行了研究,提出了重点部位的设计原则和加强措施。

火灾下LYP160屈曲约束支撑抗震性能研究

为研究屈曲约束支撑(buckling-restrained brace,BRB)及其体系在高温工况的抗震性能,对BRB芯材低屈服点LYP160钢材分别进行了常温和高温材料力学性能试验.通过与试验结果比较,建立了BRB热-力耦合精细化有限元分析模型,验证了该模型的准确性;对火灾下LYP160屈曲约束支撑的温度场、滞回曲线、骨架曲线和耗能能力等性能进行了对比分析;对不同工况(3种火灾工况和常温工况)下8层配置屈曲约束支撑钢框架(BRB structure,BS)和原结构(original structure,OS)分别进行了弹塑性动力时程分析.研究结果表明:3种火灾工况下BS的平均层间位移角较于OS分别降低了30.4%、33.2%和42%;OS柱塑性铰损坏严重,且更多出现在柱上,BS整体损坏程度较OS轻,更为安全可靠.

钢支撑架设滞后对地连墙基坑变形影响分析

为研究钢支撑滞后对深基坑支护体系变形的影响,以目前处于施工高峰期的北京地铁13号线、22号线某深基坑为例,通过监测数据分析钢支撑滞后并叠加多种不利因素工况下中立柱、相邻钢支撑轴力变化情况,以及围护结构的变形模式。结果表明:快速的土方开挖与支撑滞后情况下,宽大基坑中立柱隆起速率明显增加;同一断面内第2、3道支撑滞后会导致第1道支撑轴力快速上升;偏压影响下,同一断面内基坑两侧围护结构变形模式不同且墙顶位移方向相反;同基坑不同断面第1道支撑滞后与第2道支撑滞后其围护结构变形模式存在差异;不同壁厚基坑其地连墙敏感度明显不同。

某新型半导体显示产业钢厂房备料区抗震性能分析

以某新型半导体显示产业钢结构厂房备料区为工程背景,建立了厂房钢框架-支撑结构的非线性有限元模型,分别对多遇地震和罕遇地震下的结构抗震性能进行了分析。结果表明,结构整体指标均满足设计规范要求,第3层和第6层的层间位移角较大;罕遇地震下构件损伤主要集中在支撑,而结构底层角柱和中部楼层的边跨梁有轻微损伤;钢支撑能够有效提高结构刚度,减小梁柱的损伤。

东日本大地震后某校舍抗震加固改造与效果评估实验研究

2011年东日本大地震后,校舍建筑的抗震加固变得极为迫切。针对日本某校舍建筑的抗震加固工程展开计算分析及实验研究。首先阐述既有校舍建筑的结构特征及抗震鉴定结果,提出纵向采用钢支撑框架提高强度,首层横向新设剪力墙以及增厚楼梯间楼板的加固方案。随后,利用无线振动测试系统在校舍建筑抗震加固前后进行常时微动测试实验,分别从整体与局部角度分析加固前后校舍建筑加速度响应、固有周期以及振型等参数变化。最后,对比分析有限元计算及测试结果,阐述抗震加固方法及位置对原有建筑的性能影响,验证抗震加固方法的有效性。结果表明:采用钢支撑框架的加固方法有效提高既有校舍建筑的强度,加固后加速度响应值约降低至加固前的1/3,加固方法起到提高整体强度、改善刚度分布及结构整体性作用;固有周期以及加速度响应放大倍率的变化与该校舍抗震加固方法较吻合,表明基于振动测试的研究方法能够有效评估抗震加固措施的效果。研究成果可为既有校舍建筑的抗震加固方案选取及性能评估提供参考。

多层剪切型支撑钢框架整体稳定性的解析算法研究

剪切型支撑钢框架整体稳定计算需考虑钢框架与剪切型支撑之间的相互作用,还需要考虑同层柱间的相互支援以及层与层之间的支援作用,规范计算长度系数法无法考虑这些因素可能会造成不合理设计。提出了一种计算多层剪切型支撑钢框架整体稳定性的解析算法,首先分析了支撑刚度与结构临界承载力之间的关系,推导了层临界支撑刚度计算公式,接着利用弹簧-摇摆柱力学模型推导了任意支撑下框架柱临界刚度比系数计算公式,然后将各楼层的有效抗侧刚度及荷载刚度进行楼层间的组装,将求解剪切型支撑钢框架的临界承载力转化为求解结构的楼层有效抗侧刚度,最后基于轴力权重加权平均的方法推导了可直接求解多层剪切型支撑钢框架临界承载力的计算公式,该公式能够判断结构的薄弱层,可以定量地计算楼层之间相互支援程度,有效地弥补规范尚无法求解弱支撑钢框架柱计算长度系数的不足。

广州航空轮胎大科学装置主体结构设计

广州航空轮胎大科学装置作为科学试验、产业吸引的重要建筑,方案新颖奇特,为竖向及水平圆组合的造型。结构设计时,通过设置防震缝将其分割成两个独立的结构主体,同时考虑建筑造型、试验设备、超高大跨吊车等的相关需求。竖向圆为中部通高的六层钢框架-中心支撑结构,充分利用吊车支撑做成强支撑框架,减少中部30m高跃层柱的长度系数,同时充分利用建筑形体,在30m以上做成半圆柱面单层网壳结构,实现建筑效果的同时也节约了材料;水平圆为钢框架结构,针对屋面大跨楼盖,采用单向密肋实腹钢梁,钢梁截面最大高度为1.9m,以满足建筑净空和结构挠度等要求;幕墙与主体间采用桁架式铰接支座,实现外鼓幕墙造型;10台半埋式试验台基础采用灌注桩基础,并设置隔振沟以减轻动力试验对主体结构的影响。设计最终很好地实现了建筑功能及结构安全性和适用性。

莲花桥桥面板临时支撑钢架的稳定性分析

在桥梁施工过程中,临时支撑体系的稳定性直接影响到桥梁结构的安全施工。该文依托浙江省杭州市莲花桥工程,采用三维有限元分析软件Midas,开展桥面板临时支撑钢架的稳定性研究,分析支撑体系的变形特征和应力分布规律,评价支撑体系的稳定性,对支撑基础的承载力进行验算,提出临时支撑钢架结构的设计原则。研究成果为工程的安全施工提供参考。

高空斜撑钢梁卸载悬挑支模平台体系

本文结合工程实例,通过南宁市某医院项目三层梁板处长悬臂结构混凝土构件的施工应用,研究了高空斜撑钢梁卸载悬挑支模平台体系。结果表明,通过斜撑钢梁的设置进行悬挑支模平台的卸载,可保证现浇结构构件的安全施工。

新型H型钢前撑在复杂边界条件下深基坑的应用研究

前撑注浆钢管支护体系是近几年应用的一种新型基坑支护技术,已在长三角地区地下一层广泛应用与实践。与传统钢斜撑相比具有施工便捷、节省工期和对周边环境影响小等明显优势。以某杭州地区某复杂边界条件下深大基坑工程为例,从方案选型、施工技术要点、支护效果等方面对新型H型钢前撑体系进行了详细的分析和介绍,通过现场试验、数值模拟分析和现场监测等手段,进一步分析验证了H型钢前撑体系使用的可行性,为类似地质和边界条件下深大基坑工程设计提供参考。

三种中心支撑不同布置对平面钢框架抗侧性能影响分析

本文通过分析不同中心支撑布置对结构单元抗弯、抗剪刚度的影响,针对支撑布置水平夹角对结构单元抗剪刚度的影响,提出支撑与水平方向的夹角宜控制在30°~50°;针对三种不同中心支撑类型不同布置对结构抗侧性能的影响进行对比分析,结合SAP2000结构分析软件,计算了三种中心支撑不同布置位置下的结构最大侧移,研究了中心支撑布置对钢框架结构抗侧刚度的影响,为钢框架结构的设计提供参考。