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.     

Seismic performance of moment resisting steel frame subjected to earthquake excitations

This study presents static and dynamic assessments on the steel structures. Pushover analysis (POA) and incremental dynamic analysis (IDA) were run on moment resisting steel frames. The IDA study involves successive scaling and application of each accelerogram followed by assessment of the maximum response. Steel frames are subjected to nonlinear inelastic time history analysis for 14 different scaled ground motions, 7 near field and 7 far field. The results obtained from POA on the 3, 6 and 9 storey steel frames show consistent results for both uniform and triangular lateral loading. Uniform loading shows that the steel frames exhibits higher base shear than the triangular loading. The IDA results show that the far field ground motions has caused all steel frame design within the research to collapse while near field ground motion only caused some steel frames to collapse. The POA can be used to estimate the performance-based-seismic-design (PBSD) limit states of the steel frames with consistency while the IDA seems to be quite inconsistent. It is concluded that the POA can be consistently used to estimate the limit states of steel frames while limit state estimations from IDA requires carefully selected ground motions with considerations of important parameters.     

Seismic response of self‐centering precast concrete frames with hysteretic dampers

With the rapid development of cities and the invasion of major natural disasters such as earthquakes, the resilience city as a new design concept has been paid more and more attention. As an important branch of self‐centering seismic resisting system, self‐centering concrete frame system has been studied by many scholars. These studies prove that self‐centering concrete frame structure has excellent self‐centering ability but poor energy dissipation capacity. Adhering to the working principle of self‐centering structure and considering the development concepts of building industrialization and modularization, this paper proposed a kind of self‐centering precast concrete frame with hysteretic damper (SCPCHD). In order to verify its energy dissipation capacity and seismic performance, elaborate finite element models were established and elastoplastic dynamic time history analyses were carried out. The results showed that the SCPCHD frame has a similar interstory displacement response to the reinforced concrete (RC) frame and the energy dissipation performance of its joint is obviously superior to the RC frame under rare earthquake because the SCPCHD frame has low damage characteristics and excellent damping device. In summary, this paper proves the feasibility and superiority of the SCPCHD frame, providing reliable support for further research.     

Seismic performance of steel MRF building with nonlinear viscous dampers

This paper presents an experimental study of the seismic response of a 0.6-scale three-story seismicresistant building structure consisting of a moment resisting frame (MRF) with reduced beam sections (RBS), and a frame with nonlinear viscous dampers and associated bracing (called the DBF). The emphasis is on assessing the seismic performance for the design basis earthquake (DBE) and maximum considered earthquake (MCE). Three MRF designs were studied, with the MRF designed for 100%, 75%, and 60%, respectively, of the required base shear design strength determined according to ASCE 7-10. The DBF with nonlinear viscous dampers was designed to control the lateral drift demands. Earthquake simulations using ensembles of DBE and MCE ground motions were conducted using the real-time hybrid simulation method. The results show the drift demand and damage that occurs in the MRF under seismic loading. Overall, the results show that a high level of seismic performance can be achieved under DBE and MCE ground motions, even for a building structure designed for as little as 60% of the base shear design strength required by ASCE 7-10 for a structure without dampers.     

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.     

Seismic collapse assessment of reinforced concrete moment frames using endurance time analysis

In this paper, seismic collapse of reinforced concrete moment frames is assessed using endurance time (ET) analysis. A set of 30 frames that incorporate deterioration of concrete components is used for this assessment. Application of ET method for collapse assessment of structures is explained, and its accuracy for this purpose is evaluated by comparing its results with incremental dynamic analysis results. Input motions for ET analysis are generated based on ASCE7‐05 design spectrum, and also accelerograms used for incremental dynamic analysis are spectrally matched to the same spectrum. Distribution of different engineering demand parameters over frames height and their values at collapse occurrence are compared for two methods. Results show that spectral accelerations in which collapse occurs in both analyses are very similar for most of the frames, and ET method can appropriately predict the collapse mechanisms of the structures especially for taller frames. Accuracy of ET method in collapse assessment of reinforced concrete moment frames is satisfactory, and this method can be used as a good estimator for study of collapse mechanisms with much less computational effort. Copyright © 2014 John Wiley & Sons, Ltd.     

Quantification of seismic performance factors of steel diagrid system

This study is carried out to evaluate the response modification, overstrength, and deflection amplification factors for steel diagrid system. To quantify these factors, the rational procedure introduced in Federal Emergency Management Agency (FEMA) P695, which is based on low probability of structural collapse and encompasses nonlinear static and dynamic analyses, is used. To this end, a series of diagrid structures with various slopes of external braces are designed. Nonlinear static analyses are performed to obtain system overstrength and period‐based ductility. Incremental dynamic analyses are then performed to assess collapse margin ratio (CMR) of the archetypes. The effects of spectral shape of different ground motions are considered in CMR values to obtain an adjusted CMR (ACMR), for each archetype. The values of calculated ACMRs are compared with the acceptable values of FEMA P695 to assess reliability of presumed seismic performance factors of diagrid systems. The results show that values of calculated ACMRs for steel diagrid systems designed using the response modification factor equal to 4.50 are acceptable. It is also observed that as the slope of the peripheral diagonal elements increases, the overstrength and the collapse margin ratios decrease, and the ductility of system increases.     

Seismic fragility curves for mid-rise reinforced concrete frames in Kingdom of Saudi Arabia

This article is concerned with the development of seismic fragility curves for typical mid-rise plane reinforced concrete moment-resisting frames in Kingdom of Saudi Arabia (KSA), which is considered as low-seismicity area. Two structural models; four- and eight-storey moment-resisting frames were considered. Three cities with different seismic intensities, Abha, Jazan and Al-Sharaf, were selected to cover various values of mapped spectral accelerations in KSA. The 0.2-s spectral accelerations range from 0.21 to 0.66 g, while the 1.0-s spectral accelerations range from 0.061 to 0.23 g. The structural models were designed under dead, live and seismic loads of these cities according to the Saudi Building Code. Incremental dynamic analysis was performed under 12 ground motions using SeismoStruct. Five performance levels, namely, operational, immediate occupancy, damage control, life safety and collapse prevention were considered and monitored in the analysis. Fragility curves were developed for the structural models of the three cities considering the five selected performance levels.     

基于IDA的高面板堆石坝抗震性能评价

抗震性能分析能够有效估计结构在地震作用下的危险性,逐渐成为抗震安全性评价的重要方法,但由于结构的复杂性,该方法在面板堆石坝方面的应用还处于起步阶段。随着强震区大量高面板堆石坝的建设,这些高坝的安全性是必须要考虑的重大问题,因此对大坝进行抗震性能分析至关重要。增量动力分析(IDA)法作为一种抗震性能分析方法,能够全面、深入地分析在不同强度地震作用下结构性能的变化。将IDA法引入到高面板堆石坝安全评价领域,建立了高面板堆石坝地震破坏性能评价方法。根据场地条件选取了15条不同的强震动记录,以地震峰值加速度PGA为地震动参数,采用坝体地震震后变形、坝坡稳定性、面板防渗体安全为抗震性能评价指标,选取合适的性能参数,建议了高面板堆石坝各评价指标的破坏等级划分标准,通过大量非线性有限元计算,得到各性能参数的地震易损性曲线,分析了大坝在不同强度地震作用下发生破坏的概率,成果可为高面板堆石坝抗震性能设计和安全风险评估提供参考和依据。     

基于屈服点谱法的中心支撑钢框架抗震性态评估

屈服点谱(Yield Point Spectra,YPS)是以位移-加速度表述的反应谱形式。YPS可以用于对现有结构进行抗震评估,确定结构在给定地震作用下的峰值位移和延性。本文按照我国设计规范分别设计了6层、9层、12层3个人字形中心支撑钢框架结构,利用YPS对3个结构进行非线性静力分析,得到结构在设防地震和罕遇地震下的峰值位移和层间位移角,并与SAP2000动力时程分析得到的结果进行对比,评估人字形中心支撑钢框架在设防地震和罕遇地震下的抗震性态,评价了YPS方法用于中心支撑钢框架抗震性态评估的可靠性。     

Seismic performance analysis and evaluation of tall structures using grille-type steel plate composite shear walls

Grille-type steel plate composite (GSPC) shear wall is an innovative wall system consisting of concrete cores, steel faceplates, steel tie plates, and steel channels with more advantages than conventional reinforced concrete (RC) walls, including better ductility, higher bearing capacity, and easy-modular characteristics. This paper mainly discusses the seismic performance and damage resistance of GSPC walls to the entire structure from the aspect of the structural level. Three nonlinear numerical models of high-rise structures with different structural heights and types were established by PERFORM-3D software to study the influence of GSPC walls on the change in structural internal forces and deformations compared with RC walls. One of these structures was selected to conduct the seismic fragility analysis based on the incremental dynamic analysis and to assess the structure's seismic performance with GSPC walls. Finally, the seismic damage prediction method was used to evaluate the damage levels of the GSPC wall structure. Results indicate that the structures with GSPC walls suffer more significant seismic forces than those with RC walls, although they experience lesser structural deformations. Moreover, GSPC walls can effectively improve the structure's collapse and seismic damage resistance.     

Numerical collapse simulation based critical state analysis for framed-wall structure subjected to earthquakes

With the rapid developments of the constitutive theory, numerical methods, and computer software and hardware, full attention has been paid to establishing nonlinear structural models and investigating the nonlinear behavior, damage performance, and failure criterion of the structures. Consequently, this study introduces a precise analysis with a highly accurate level of simulation for an existing framed-wall structure excited with strong ground motions. The incremental dynamic analysis (IDA) technique has been adopted to investigate the nonlinear behavior of the structure. The damage evolution and collapse pattern have been well captured in the structure based on the adopted damage model. The results showed that the maximum interstory drift (ISD) position varies at different seismic loads due to the damage initiation and propagation variation. The IDA curves show the end of the elastic stage at 0.70, 0.50, 0.70, and 0.20 g at San Francisco, Italy, Northridge, and San Fernando ground motions, respectively. Also, different collapse patterns of the structure have been observed at different ground motions and also at different intensities for the same ground motion. Therefore, the high-rise building design should account for multiple collapse patterns. Moreover, a new IDA-based technique is proposed to estimate the structure's maximum seismic capacity (MSC) and ensure it through the collapse analysis. The structure adopted in this study reaches its MSC at the San Francisco event at an intensity of 2.50 g. However, the MSC decreased by 40% at Italy and Northridge events and 60% at the San Fernando event. Since the seismic capacity of the structure is considered an essential ingredient in the design process, therefore, the findings of this study are supposed to lay the basis for the performance-based seismic design of the structure.     

Cyclic behaviour of hinged steel frames enhanced by masonry columns and/or infill walls with/without CFRP

Abstract

This paper investigates the in-plane seismic behaviour of hinged steel frames that are enhanced with masonry columns and/or infilled walls. First, eight half-scaled hinged steel frame specimens were constructed according to the realistic structural system of Bund 18, which is a historical building in Shanghai, China. Then, cyclic loads were exerted on these frames. The test results indicated that the seismic behaviours of the hinged steel frames can be significantly improved with the use of masonry columns and/or infilled masonry walls as well as with proper strengthening due to carbon fibre-reinforced polymer (CFRP) sheets. A simplified model was developed to simulate the seismic behaviours of these frames. In this model, infilled walls and CFRP sheets were replaced by diagonal struts, and the steel members and their surrounding elements were treated as composite members. Finally, this model was verified by experimental results.     

Influence of seismicity level and height of the building on progressive collapse resistance of steel frames

Influences of building height and seismicity level on progressive collapse resistance of buildings are investigated in this paper. For the height, 4‐story, 8‐story and 12‐story steel special moment resisting frames are focused. The obtained results indicate that taller buildings are safer against progressive collapse. To study the influence of seismicity level, different four‐story structures having special moment resisting frame systems are designed for different levels of seismicity, namely, very high, high, moderate and low. The structures are evaluated, using nonlinear dynamic method and two main scenarios of the codes, including sudden removal of a corner and a middle column in the first floor. Some graphs are presented for progressive collapse resistance of the structures, depending on their seismic base shears. It is shown that the structures designed for greater seismic base shears are more resistant against progressive collapse. Copyright © 2016 John Wiley & Sons, Ltd.     

The influence of out‐of‐straightness imperfection in physical theory models of bracing members on seismic performance assessment of concentric braced structures

In physical theory models, the hysteretic response of concentric braces is simulated by modelling the bracings with two nonlinear fibre‐section beam–column elements connected together with an initial out‐of‐straightness imperfection (?₀). The width of such imperfection is the parameter governing the numerical prediction of the brace buckling. In this paper, the accuracy of different formulations of ?₀ is investigated and validated against monotonic and cyclic experimental results from literature carried out on different bracing configurations. Correlations and measures of scatter between the predicted response and experimental performance are evaluated. A statistical analysis on both X‐braced and inverted‐V‐braced frames based on Monte Carlo simulation is presented and discussed for the following reasons: (a) in order to account for the dispersion of the nonlinear dynamic‐evaluated seismic performance due to epistemic uncertainties associated with examined formulations for camber width and (b) to provide modelling correction factors of simulated interstorey drift demand. The analysis shows that the formulations used for ?₀ affect the drift demand, the collapse mechanism and have a noticeably impact on the seismic response parameters at collapse. In particular, inverted‐V‐braced frames are more influenced than X‐braced configurations, because the prediction of brace–beam interaction is very sensitive to ?₀. Copyright © 2014 John Wiley & Sons, Ltd.     

Approximate method of estimating seismic performance of high‐rise buildings with oil‐dampers

When subjected to long‐period ground motions, many existing high‐rise buildings constructed on plains with soft, deep sediment layers experience severe lateral deflection, caused by the resonance between the long‐period natural frequency of the building and the long‐period ground motions, even if they are far from the epicenter. This was the case for a number of buildings in Tokyo, Nagoya, and Osaka affected by the ground motions produced by the 2011 off the Pacific coast of Tohoku earthquake in Japan. Oil‐dampers are commonly used to improve the seismic performance of existing high‐rise buildings subjected to long‐period ground motion. This paper proposes a simple but accurate analytical method of predicting the seismic performance of high‐rise buildings retrofitted with oil‐dampers installed inside and/or outside of the frames. The method extends the authors' previous one‐dimensional theory to a more general method that is applicable to buildings with internal and external oil‐dampers installed in an arbitrary story. The accuracy of the proposed method is demonstrated through numerical calculations using a model of a high‐rise building with and without internal and external oil‐dampers. The proposed method is effective in the preliminary stages of improving the seismic performance of high‐rise buildings.     

翼缘削弱的型钢混凝土框架抗震性能研究

为了研究翼缘削弱的型钢混凝土框架的抗震性能,对一榀两跨三层型钢混凝土框架模型进行了低周反复荷载试验。框架模型按"强柱弱梁"原则设计,且对节点核心区附近梁端工字形型钢的上、下翼缘采取狗骨式削弱,并适当增加最大削弱部位纵向钢筋的配筋率。通过对框架模型顶层施加低周反复水平荷载,观察了框架模型的破坏过程,测得框架模型的荷载-位移滞回曲线和骨架曲线以及各阶段的荷载和位移值,并分析了框架模型的延性、耗能、强度降低、刚度退化以及破坏机制。试验结果表明:框架模型的承载能力、变形能力和耗能能力高,延性大(延性系数大于7),满足延性框架的抗震要求。进一步分析了翼缘削弱在型钢混凝土框架中的具体作用。分析结果表明:翼缘削弱不仅能将塑性铰从梁端根部转移到翼缘削弱部位,从而降低节点核心区所受的剪力以及梁柱连接焊缝的应力,而且有利于框架形成梁铰耗能机构,从而提高框架的整体耗能能力。翼缘削弱能有效提高型钢混凝土框架的抗震性能,可在型钢混凝土     

高强钢组合K形偏心支撑框架抗震性能对比分析

为研究不同强度组合的高强钢组合K形偏心支撑框架结构的抗震性能,设计了一组不同强度(Q345、Q460、Q690钢材)组合的5层K形偏心支撑框架结构算例Q345-5、Q460-5和算例Q690-5,选取10条地震动记录对其进行动力时程分析,得到各算例在不同水准地震作用下的耗能梁段转角和层间位移角。研究表明:8度罕遇地震作用下,高强钢组合K形偏心支撑框架的层间位移角比传统K形偏心支撑钢框架大,各算例耗能梁段全部进入塑性变形阶段;塑性层间位移角到达规范限值时,算例Q460-5框架梁开始进入塑性变形阶段,算例Q690-5框架柱、框架梁和支撑均处于弹性变形阶段,还可以承受更大的地震作用;达到定义的极限状态时,与传统偏心支撑钢框架相比,算例Q460-5能够承受的地震作用和耗能梁段转角更小;算例Q690-5承受的地震作用和耗能梁段转角更大。