The modified dynamic‐based pushover analysis of steel moment resisting frames

A modified dynamic‐based pushover (MDP) analysis is proposed to properly consider the effects of higher modes and the nonlinear behavior of the structural systems. For this purpose, first, a dynamic‐based story force distribution (DSFD) load pattern is constructed using a linear dynamic analysis, either time history (THA) or response spectrum (RSA). Performing an initial pushover analysis with the DSFD load pattern, a nonlinearity modification factor (NMF) is calculated to modify the DSFD load pattern. The envelope of the peak responses of the structure obtained from 2 pushover analyses with the modified DSFD load pattern as well as the code suggested first mode load pattern are considered as the final demand parameters of the structural system. The efficiency of the proposed MDP procedure is investigated using the results of nonlinear THA besides some existing pushover procedures. For this purpose, the 2‐dimensional 9‐, 15‐, and 20‐story, SAC steel frame building models are considered for parametric studies using OpenSees program. The results indicate that the proposed MDP‐THA and MDP‐RSA methods can significantly improve the performance of the pushover analysis. Considering the accuracy and calculation efforts, the MDP‐RSA method is strongly suggested as an efficient and applicable method to estimate the nonlinear response demands of steel moment resisting frames.     

延性钢框架设计方法研究

介绍了1994年美国Northridge地震和1995年日本Kobe地震中钢框架结构断裂模式,指出利用钢框架结构梁柱新型延性节点进行延性设计是预防脆性断裂的主要途径;然后讨论了钢框架非线性分析的各种方法,以及钢框架延性设计的步骤和注意事项。     

基于位移的抗震设计研究进展

基于位移的抗震设计方法被认为是现阶段实现基于性能的抗震设计理论最为有效的一条途径,受到了国内外学者的广泛关注。对该方法的产生背景、分类、近年来国内外的研究进展情况进行了总结和介绍,并重点从非线性位移反应谱和推覆分析法两方面介绍地震位移需求估算的研究进展情况。最后,对该方法目前存在的问题和今后的研究方向进行了分析。     

The seismic behaviour of steel moment-resisting frames with stiffening braces

The present paper deals with the seismic behaviour of steel structures which are designed in the attempt of exploiting the dual characteristics of moment resisting frames (MRFs) and concentrically braced frames (CBFs) as lateral force resisting systems. Three prototype frames are studied within the context of Eurocode 8 (EC8) provisions; these are MRFs which are traditionally designed, against ultimate seismic actions (ULS), without checking serviceability limit state rules (SLS-interstory drift limits). To fulfill these requirements concentrical braces are inserted in the frames, which are not considered in the collapse resistance of the structural system. The non-linear behaviour of these systems under ultimate seismic environment is studied and compared to the one of the unbraced MRFs. The influence of second order effects is also investigated.     

Seismic performance of stiffness-based designed buckling-restrained braced frame and special moment-resisting frame dual systems

Conventional procedure for designing dual systems, proposed in seismic regulations, encompasses some limitations such as not putting a required minimum stiffness value for the secondary system. This research investigates the stiffness limit value required for the secondary system for designing buckling-restrained braced frame (BRBF) and special moment-resisting frame (SMRF) dual systems. Non-linear static and time history analyses were carried out on the sample dual structures with different heights and different relative stiffness ratios of the primary system to the secondary system. A stiffness-based designing approach is employed to ensure that the designed system comprises the predefined relative stiffness ratios. It is demonstrated that the suitable stiffness combination ratio is gained when the BRBF and SMRF subsystems have 65% and 35% of the total stiffness, respectively. Implementation of the suitable relative stiffness ratio in the dual systems designed according to the presented approach, leads to a uniform plasticity profile in the height of structures.     

Seismic response of steel braced frames with shape memory alloy braces

In this paper, the seismic performance of steel frames equipped with superelastic SMA braces was investigated. To do so, buildings with various stories and different bracing configurations including diagonal, split X, chevron (V and inverted V) bracings were considered. Nonlinear time history analyses of steel braced frames equipped with SMA subjected to three ground motion records have been performed using OpenSees software. To evaluate the possibility of adopting this innovative bracing system and its efficiency, the dynamic responses of frames with SMA braces were compared to the ones with buckling restrained braces. After comparing the results, one can conclude that using an SMA element is an effective way to improve the dynamic response of structures subjected to earthquake excitations. Implementing the SMA braces can lead to a reduction in residual roof displacement and peak inter-story drift compare to the buckling restrained braced frames.     

Seismic performance of composite moment-resisting frames achieved with sustainable CFST members

The main objective of the research presented in this paper is to study the bending behaviour of Concrete Filled Steel Tube (CFST) columns made with Rubberized Concrete (RuC), and to assess the seismic performance of moment-resisting frames with these structural members. The paper describes an experimental campaign where a total of 36 specimens were tested, resorting to a novel testing setup, aimed at reducing both the preparation time and cost of the test specimens. Different geometrical and material parameters were considered, namely cross-section type, cross-section slenderness, aggregate replacement ratio, axial load level and lateral loading type. The members were tested under both monotonic and cyclic lateral loading, with different levels of applied axial loading. The test results show that the bending behaviour of CFST elements is highly dependent on the steel tube properties and that the type of infill does not have a significant influence on the flexural behaviour of the member. It is also found that Eurocode 4 is conservative in predicting the flexural capacity of the tested specimens. Additionally, it was found that the seismic design of composite momentresisting frames with CFST columns, according to Eurocode 8, not only leads to lighter design solutions but also to enhanced seismic performance in comparison to steel frames.     

对结构静力弹塑性分析方法的几点改进

探讨了结构静力弹塑性分析方法的基本原理，指出了该方法目前存在的缺陷，基于模态Pushover法（MPA）提出了根据振型参与重量来确定对结构地震反应起主要影响的振型数以及两阶段的侧向力加载模式，并对确定结构目标位移的方法作了一些改进。采用动力时程分析法和改进的静力弹塑性方法，对一个优化钢框架结构的地震反应进行了数值模拟分析，其结果表明，采用本文改进的静力弹塑性分析方法对结构进行推覆分析，能较准确地模拟结构的地震反应，具有易操作、计算精度高的优点。     

静力弹塑性分析方法中不同加载模式的对比研究

Pushover分析方法是一种逐渐得到广泛研究与应用的评估结构抗震性能的简化方法,已经被我国现行建筑结构抗震设计规范采用.侧向加栽模式的选取是Pushover分析方法中的一个关键问题,不同结构的高阶振型对Pushover分析结果的影响程度不同.本文通过拟合规范的反应谱曲线,对三个钢筋混凝土结构分别选取了适用Ⅱ类场地的2条地震动记录和1条人工波,对比了典型地震动下非线性时程分析和采用5种不同侧向力分布模式的Pushover分析的层间位移角,以及推覆分析各工况下的结构推覆曲线、等效周期和等效阻尼比.通过振型质量参与系数体现高阶振型对结构反应的贡献.研究发现,随着结构层数的增加,高阶振型的影响变大,侧向加载模式的选取变得很重要.     

斜屋面西式瓦屋面施工技术

结合具体工程实践,对斜屋面西式瓦屋面施工技术进行了总结,介绍了该技术施工特点和技术原理,着重阐述了施工工艺流程、操作要点及质量控制措施,并对其应用效果作了具体说明,对今后同类屋面工程具有指导作用。     

基于能量的模态pushover分析方法

提出了一种基于能量的模态pushover分析方法,解决了高阶模态能力曲线失稳的问题。该方法利用基于结构变形吸收能量的等效位移,计算结构在地震作用下的非线性总体变形,替代模态pushover中基于顶点位移的变形解法,采用基于能量原理的等效单自由度体系,结合等强度谱计算目标位移,以目标位移对应的能量指标求出相应的结构性态反应,采用SRSS方法组合得到结构的最大反应。以9层钢框架结构为例对所提出方法进行了验证,结果表明:该方法可以考虑高阶效应,不会出现能力谱折返的失效情况,而且与时程分析法相比,该方法计算效率高且具有较好的精度。     

Direct displacement‐based design of steel‐braced reinforced concrete frames

This study investigates a direct displacement‐based design procedure for dual system structures composed of reinforced concrete frames and steel bracings. In this procedure, in order to establish the design displacement profile before any analysis, strength proportions between bracings and frames are assigned. By using the displacement profile and damping characteristics of the structural components, the structure can be represented as an equivalent single‐degree‐of‐freedom system. The effective period and secant stiffness of the structure are then calculated, and finally, after the base shear was computed, the design process can be implemented. Structures with 4, 8 and 12 stories have been designed using this methodology, and in order to validate it, seven accelerograms have been used for nonlinear time‐history analysis of the above structures. The results demonstrate the efficiency of this procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

Progressive collapse resisting capacity of moment frames with viscous dampers

In this paper, the effect of viscous dampers on reducing progressive collapse potential of steel moment frames was evaluated by nonlinear dynamic analysis. Parametric studies were conducted first to evaluate the effects of dampers installed in a steel beam‐column subassembly with varying natural period and yield strength on the reduction of progressive collapse potential. Then 15‐story moment‐resisting frames with three different span lengths were designed with and without viscous dampers, and the effect of viscous dampers was investigated by nonlinear dynamic analysis. According to the parametric study, the vertical displacement generally decreased as the damping ratio of the system increased, and the dampers were effective in both the elastic and the elasto‐plastic systems. It was also observed that the effect of the damper increased as the natural period of the structure increased and the strength ratio decreased. The analysis results of 15‐story analysis model structures showed that the viscous dampers, originally designed to reduce earthquake‐induced vibration, were effective in reducing vertical displacement of the structures caused by sudden removal of a first‐story column, and the effect was more predominant in the structure with longer span length. Copyright © 2011 John Wiley & Sons, Ltd.     

单跨混凝土框架倒塌机理分析

以一单跨混凝土框架为例,采用Pushover方法分析了其倒塌机理,结合已往地震中该类建筑的破坏特征,研究了现浇板及结构地坪的影响,并简单介绍了目前针对该类建筑的几种常用加固方法,以指导工程实践。     

Assessment of progressive collapse-resisting capacity of steel moment frames

In this study the progressive collapse-resisting capacity of steel moment resisting frames was investigated using alternate path methods recommended in the GSA and DoD guidelines. The linear static and nonlinear dynamic analysis procedures were carried out for comparison. It was observed that, compared with the linear analysis results, the nonlinear dynamic analysis provided larger structural responses and the results varied more significantly depending on the variables such as applied load, location of column removal, or number of building story. However the linear procedure provided more conservative decision for progressive collapse potential of model structures. As the nonlinear dynamic analysis for progressive collapse analysis does not require modeling of complicated hysteretic behavior, it may be used as more precise and practical tool for evaluation of progressive collapse potential of building structures.     

北京饭店消能减振抗震加固的静力弹塑性分析

以SAP2000软件为计算工具,并选用General型Frame单元模拟消能支撑,对北京饭店西楼消能减振抗震加固前后的结构进行静力弹塑性分析。采用两种不同的侧向荷载分布方式,计算了结构的基底剪力顶点位移曲线,并采用能力谱方法,证明加固后的结构符合抗震设计规范要求。     

基于能力谱法的钢框架抗震性能评估

介绍了能力谱法基本原理与技术路线,结合我国地震烈度设防规定,采用SAP2000有限元程序,针对一个9层钢框架结构,利用能力谱法进行了分析,得到了结构的层间信息以及塑性铰发展机制,并研究了钢框架静力推覆曲线和性能点随框架柱刚度变化的规律。结果表明,随着梁,柱刚度的增加,结构在强震作用下的对应性能点的基底剪力增大,顶点位移减小,说明结构能力谱法是结构抗震性能分析的有效方法,设计人员可以依据能力谱法评估结果调整构件来满足工程抗震需要。     

圆钢管拱桁架屋盖结构静力性能有限元分析

通过考虑十种不同的荷载工况组合,对某体育馆的圆钢管拱桁架屋盖结构进行了承载力分析,从而得到了结构杆件的内力分布、支座反力,并考虑两种不同的位移荷载工况,以了解结构的整体变形情况,分析结果表明,该拱桁架结构的强度及变形能满足要求,可为结构选型、构件截面设计提供参考。     

钢筋混凝土框架结构基于时变的抗震性能研究

钢筋混凝土结构在使用过程中由于钢筋锈蚀抗震性能退化。为了研究钢筋混凝土框架结构在正常使用环境下随使用时间的增加其抗震性能的退化规律,采用通用有限元分析软件ABAQUS对锈蚀钢筋混凝土框架进行多尺度建模以提高计算精度并保证计算效率。基于锈蚀钢筋混凝土构件及单榀框架的试验数据,验证了多尺度建模方法的正确性。采用多尺度模型对4层钢筋混凝土框架结构进行了静力推覆分析及弹塑性时程分析,对比不同使用时间的钢筋混凝土框架结构的地震反应和损伤情况。结果表明：当使用时间为25a时,结构的抗震性能与新建结构接近;当使用时间超过50a时,随着使用时间的增加,结构的承载能力及刚度退化明显,在地震作用下的位移响应逐渐增大,地震损伤范围不断扩大;相比新建结构,当使用时间为50、75a和100a时,结构的抗侧承载力分别降低了6.2%、14.1%及18.1%,罕遇地震作用下的最大层间位移角分别增大了9.2%、19.8%及25.1%。     

Effect of soft‐storey mechanism caused by infill elimination on displacement demand in nonlinear static procedure using coefficient method

In recent earthquakes, many buildings have been damaged due to the soft‐storey mechanism failure. The seismic design codes for buildings do not contain enough criteria to predict the real displacement of such buildings. This paper focuses on evaluating the nonlinear displacement of buildings that fail in soft‐storey mechanism form. Results show that the nonlinear static procedure with coefficient method, which is described in Chapter 3 of ASCE/SEI 41‐06, does not have sufficient accuracy for estimation of structure displacement demand in such buildings. In this paper, the coefficient methodology is used for evaluating the target displacement for 5‐storey, 8‐storey and 15‐storey special moment resisting steel frames. For this purpose, dynamic nonlinear time‐history analysis has been applied for the mentioned structures having a soft‐storey mechanism failure form. The numerical results of storey displacement and interstorey drift were compared with those values obtained from the coefficient method described in Chapter 3 of ASCE/SEI 41‐06. Copyright © 2012 John Wiley & Sons, Ltd.