Seismic response analysis of reinforced concrete frames using inelasticity‐separated fiber beam‐column model

Evaluating the inelastic seismic response of structures accurately is of great importance in earthquake engineering and generally requires refined simulation, which is a time‐consuming process. Because the material nonlinearity generally occurs in a small part of the whole structure, many researches focus on taking advantage of this characteristic to improve the computational efficiency and the inelasticity‐separated finite element method (IS‐FEM) proposed recently provide a generic finite element formulation for solving this kind of problems efficiently. Although the fiber beam‐column element is widely used for the simulation of reinforced concrete (RC) framed structures, the inelastic deformation is often detected in a large part of the numerical model under earthquake excitation so that it is hard to achieve high efficient computation when applying the IS‐FEM to the inelastic response analysis of RC fiber models directly. In this paper, a new numerical scheme for seismic response analysis of RC framed structures model by fiber beam‐column element is proposed based on the IS‐FEM. To implement the RC fiber model for use in IS‐FEM and improve the computational performance of proposed scheme, a method of identifying the local domains with severe section inelasticity level is proposed and a modified Kent‐Park concrete material model is developed. Because the Woodbury formula is adopted as the solver, the global stiffness matrix can keep unchanged throughout the analysis and the main computational effort is only invested on a small matrix representing local inelastic behavior. The numerical examples demonstrate the validity and efficiency of the proposed scheme.     

Nonlinear seismic analysis of reinforced concrete frames using the force analogy method

A method of nonlinear seismic analysis for RC framed structures considering full‐range factors, including stiffness and strength degradation, geometric nonlinearity, and structural member failure, is established based on the fundamental concept of the force analogy method. The strong material nonlinearity, large geometric deformation, and internal forces redistribution due to the member failure can be depicted by the proposed local plastic mechanisms, the rotation hinges at the member ends and the slide hinges assigned to the columns, of which the measurement relationships are moment versus plastic rotation and shear force versus shear plastic deformation, respectively. They are capable of evaluating the exact response of RC structures. Because only unchanging initial stiffness matrices are used through the whole computation process, the state‐space formulation was used for solving the equations of motion. The advantages of the force analogy method, such as high efficiency and stability, are still retained. The exactness of the proposed local plastic mechanisms is verified against a group of tests data, and the application of the proposed procedure is performed to an RC framed structure to simulate the full‐range nonlinear response by increasing the excitation step by step until failure of partial structural members appear. Copyright © 2014 John Wiley & Sons, Ltd.     

Smart restorable sliding base isolation system

A modern base isolation system is proposed for the aseismic control of structures. It is composed of steel-Teflon Flat Sliding Bearings, to support the gravity loads while allowing large horizontal displacements, and simply connected Shape Memory Alloy (SMA) truss elements, to provide the necessary horizontal stiffness as well as a proper restoring capability. The system is referred to as Smart Restorable Sliding Base Isolation System (SRSBIS). Depending on the arrangement of the auxiliary SMA elements, SRSBIS can exhibit a geometric nonlinearity in addition to the nonlinearity of materials. In this paper, the dynamic characteristics of SRSBIS are first examined in terms of the force-displacement behavior, effective period of vibration, and equivalent damping. After that, the earthquake response of buildings equipped with SRSBIS, designed in accordance with a direct displacement-based approach, is evaluated through extensive nonlinear time-history analyses. The effects of the design parameters on the system behavior are then investigated within a comprehensive parametric study and the seismic performances of SRSBIS are finally compared to those of similar practical isolation systems. Based on the results, it is shown that SRSBIS can be suitably used for the seismic protection of structures.     

Simplified design method and seismic performance of space trusses with consideration of the influence of the stiffness of their lower supporting columns

Static and dynamic force performance of two types of space truss structures i.e. square pyramid space truss (SPST) and diagonal on square pyramid space truss (DSPST), are studied to determine the effect of stiffness of their lower supporting members. A simplified model for the supporting columns and the equivalent spring mass system are presented. Furthermore, the feasibility of the simplified model is demonstrated through theoretical analysis and examples of comparative analysis of the simplified model with the entire model. Meanwhile, from the elastic analysis under frequently occurring earthquakes and elasto-plastic analysis under seldom occurring earthquakes subjected to TAFT and EL-Centro seismic oscillation it is shown that the simplified method can be encompassed in the results from the normal model. It also showed good agreement between the two methods, as well as greatly improved the computational efficiency. This study verified that the dynamic effect of the supporting structures was under considered in space truss design in the past. The method proposed in the paper has important significance for other space truss structures.     

地震作用下大跨度悬索桥几何非线性影响分析

大跨度悬索桥几何非线性主要来自3个方面：缆索垂度效应、梁柱效应、大位移引起的几何形状变化。鉴于地震波高频成分振幅大,低频成分振幅小的特点,很难对地震作用下大跨度悬索桥几何非线性的影响做出定性判断。目前大跨度桥梁的几何非线性研究主要集中在斜拉桥,且不同的学者得出了不同的结论。本文以逐级加大振幅的Ⅳ类场地多条地震波为激励,通过对称与非对称的2座典型大跨度悬索桥的几何非线性影响对比分析,探讨了几何非线性对大跨度悬索桥重要地震响应量的影响程度及其原因,并提出了相应的抗震设计参考建议。     

Simplified seismic sidesway collapse analysis of frame buildings

This paper presents the development and assessment of a simplified procedure for estimating the seismic sidesway collapse margin ratio of building structures. The proposed procedure is based on the development of a robust database of seismic peak displacement responses of nonlinear single‐degree‐of‐freedom systems for various seismic intensities and uses nonlinear static (pushover) analysis without the need for nonlinear time history dynamic analysis. The proposed simplified procedure is assessed by comparing its collapse capacity predictions on 72 different building structures with those obtained by nonlinear incremental dynamic analyses. The proposed simplified procedure offers a simple, yet efficient, computational/analytical tool that is capable of predicting collapse capacities with acceptable accuracy for a wide variety of frame building structures. Copyright © 2013 John Wiley & Sons, Ltd.     

竖向刚度不同的混合结构连续倒塌机制分析

为了探究上部钢结构-下部混凝土结构这类竖向刚度不同的混合结构抗连续倒塌机制,利用拆除构件法,应用ANSYS/LS-DYNA对初始失效后的剩余结构进行非线性静力(Pushdown方法)分析,研究其剩余结构的倒塌破坏模式、荷载变形关系,以及初始失效柱位置的不同和钢框架层数对结构抗连续倒塌性能的影响。结果表明:剩余结构的倒塌破坏模式带有典型的延性变形特征,且在倒塌过程中出现位移和应力分布不连续现象;除边柱失效后剩余结构的倒塌过程仅经历了梁机制外,其余剩余结构的倒塌过程均经历了梁机制、压拱机制和悬链线机制;剩余结构的竖向承载力与初始失效柱高度呈负相关,与钢框架层数呈正相关;为剩余结构提供足够的侧向约束作用以及提高结构冗余度和备用荷载路径数量,可以有效提高剩余结构的抗连续倒塌能力。     

Assessment of seismic design response factors of concrete wall buildings

To verify the seismic design response factors of high-rise buildings, five reference structures, varying in height from 20- to 60-stories, were selected and designed according to modern design codes to represent a wide range of concrete wall structures. Verified fiber-based analytical models for inelastic simulation were developed, considering the geometric nonlinearity and material inelasticity of the structural members. The ground motion uncertainty was accounted for by employing 20 earthquake records representing two seismic scenarios, consistent with the latest understanding of the tectonic setting and seismicity of the selected reference region (UAE). A large number of Inelastic Pushover Analyses (IPAs) and Incremental Dynamic Collapse Analyses (IDCAs) were deployed for the reference structures to estimate the seismic design response factors. It is concluded that the factors adopted by the design code are adequately conservative. The results of this systematic assessment of seismic design response factors apply to a wide variety of contemporary concrete wall buildings with various characteristics.     

ISO-834标准火灾作用后钢管混凝土的轴压刚度和抗弯刚度

火灾后钢管混凝土的轴压刚度和抗弯刚度是钢管混凝土结构变形性能和抗震分析的重要指标，也是火灾后钢管混凝土修复和加固的重要依据之一，本文利用数值方法计算了标准火灾作用后钢管混凝土轴压构件和纯弯构件荷载-变形关系曲线，分析了受火时间、材料强度、含钢率、截面尺寸等因素的影响规律，最后推导了标准火灾作用后钢管混凝土轴压刚度和抗弯刚度的简化计算公式，所得结果可供有关钢管混凝土结构工程设计时参考。     

Discussion on ‘an investigation into the effects of damping and nonlinear geometry models in earthquake analysis’ by Andrew Hardyniec and Finley Charney

The discussed paper explores how various assumptions for damping and geometric nonlinearity affect the seismic collapse behavior of steel‐frame buildings. The recommended damping scheme is questioned, and an alternative is suggested. Additional explanation is sought to justify the differences observed between the P‐delta and co‐rotational models for geometric nonlinearity. Copyright © 2016 John Wiley & Sons, Ltd.     

大跨度斜拉桥地震响应非线性时程分析

以有限元分析理论为基础,结合某大跨度斜拉桥工程实例,利用ANSYS软件建立有限元模型,通过修正后的El Centro波分别考虑横向、竖向及纵向输入,采用时程分析方法对其进行地震反应分析.计算分析表明:考虑几何非线性后,结构的内力和位移响应明显增大,且对主梁和索塔内力与位移的影响程度及规律也不尽相同,须区别对待分析.同时表明该桥抗震性能良好,地震荷载不控制设计.由此得出结论,对于斜拉桥这类柔性体系, 不可忽视结构几何非线性的影响.     

高层钢结构基于均匀损伤设计的整体抗震能力提高方法

本文主要研究如何通过合理设计来提高高层钢结构的整体抗震能力。首先,给出了高层钢结构的非线性计算模型;其次,建立了高层钢结构在强地震动作用下的倒塌失效模式的极限状态判别准则;然后,通过模态pushover分析,研究了高层钢结构在水平地震作用下的损伤规律;最后,重点研究了高层钢结构的整体抗震能力的提高方法,提出了均匀损伤的设计方法,该方法通过消除结构的薄弱层,来达到提高高层钢结构的整体抗震能力的目的。通过对两栋20层的高层钢框架结构进行极限时程分析和极限pushover分析,验证了文中提出的均匀损伤的设计方法的可行性。本文的工作可为高层钢结构的抗地震倒塌设计提供参考依据。     

上海浦东国际机场T2航站楼弹塑性时程分析

上海浦东机场T2航站楼结构为复杂大跨混合结构,本文采用NosaCAD2005有限元程序建立结构分析模型,模型主要由非线性杆单元组成,包括梁、柱和二力杆单元,梁、柱采用三段变刚度杆模型,以受弯为主的梁单元截面弯矩-曲率关系采用二折线和三折线模型,柱和二力杆截面采用纤维模型。通过多遇和罕遇烈度下的弹塑性时程分析,研究了该结构的变形、内力、破坏情况的发展历程。计算结果表明,该结构可以满足"小震不坏,大震不倒"的设防要求。     

System identification and damage evaluation of degrading hysteresis of reinforced concrete frames

In this study, signal processing approaches and nonlinear identification are used to measure seismic responses of reinforced concrete (RC) structures using the shaking table test. To analyze structural nonlinearity, an equivalent linear system with time‐varying model parameters, singular spectrum analysis to elucidate residual deformation, and wavelet packet transformation analysis to yield the energy distribution among components are adopted to detect the nonlinearity. Then, damage feature extraction is conducted using both the Holder exponent and the Level‐1 detail of the discrete wavelet component. Finally, the modified Bouc‐Wen hysteretic model and the system identification process are employed to the shaking table test data to evaluate the physical parameters, including the stiffness degradation, the strength deterioration and the pinching hysteresis. Finally, the identified stiffness and strength degradation functions from the test data of RC frames in relation to the degree of ground shaking, damage index and the identified nonlinear features are discussed. Based on the proposed method, both signal‐based and model‐based identifications, the relationship between the damage occurrence and severity of structural damage can be identified. Copyright © 2010 John Wiley & Sons, Ltd.     

Seismic behavior of single‐story asymmetric‐plan buildings under uniaxial excitation

The critical parameters that influence the nonlinear seismic response of asymmetric‐plan buildings are identified by evaluating the effects of different asymmetries that may characterize the structure of a building as well as exploring the influence of the ground motion features. First, the main findings reported in the literature on both the linear and nonlinear dynamic response of asymmetric‐plan buildings are presented. The common findings and the conflicting conclusions reached in different investigations are pointed out. Then, the results of comprehensive nonlinear dynamic analyses performed for evaluating the seismic response of systems characterized by different strength and stiffness configurations, representative of a large class of asymmetric‐plan buildings, are reported. Findings from the study indicate that the building response changes when moving from the linear to the nonlinear range, so that the seismic behavior of asymmetric‐plan buildings, apart from the source of asymmetry, can be always classified as irregular. Additionally, it was observed that as the seismic demands cause amplification of system nonlinearity with increasing earthquake intensity, the maximum displacement demand in the different resisting elements tends to be reached with the same deformed configuration of the system. The resultant of the seismic forces producing such a maximum demand is located at the center of resistance and corresponds to the collapse mechanism of the system that provides the maximum lateral strength in the exciting direction of the seismic action. Copyright © 2008 John Wiley & Sons, Ltd.     

Accuracy of nonlinear static procedures for the seismic assessment of shear critical structures

The nonlinear behavior of reinforced concrete (RC) members represents a key issue in the seismic performance assessment of structures. Many structures constructed in the 1980s or earlier were designed based on force limits; thus they often exhibit brittle failure modes, strength and stiffness degradation, and severe pinching effects. Field surveys and experimental evidence have demonstrated that such inelastic responses affect the global behavior of RC structural systems. Efforts have been made to consider the degrading stiffness and strength in the simplified nonlinear static procedures commonly adopted by practitioners. This paper investigates the accuracy of such procedures for the seismic performance assessment of RC structural systems. Refined finite element models of a shear critical bridge bent and a flexure‐critical bridge pier are used as reference models. The numerical models are validated against experimental results and used to evaluate the inelastic dynamic response of the structures subjected to earthquake ground motions with increasing amplitude. The maximum response from the refined numerical models is compared against the results from the simplified static procedures, namely modified capacity spectrum method and coefficient method in FEMA‐440. The accuracy of the static procedures in estimating the displacement demand of a flexure‐critical system and shear‐critical system is discussed in detail. Copyright © 2015 John Wiley & Sons, Ltd.     

竖向地震下双塔连体建筑的分析和设计

首先输入多条实际竖向地震记录,用时程分析考察了塔楼高度和连体跨度不同的多个算例。然后将其抽象成塔楼和连体桁架组成的双自由度体系,运用频域分析方法,得到竖向地震作用的变化规律：11随着桁架对塔楼频率比增加,连体地震放大作用越明显;2）当连体对塔楼质量比较小且两者频率比相近1,连体地震反应进一步加强。现行抗震规范的重力系数法提出的大跨度结构竖向地震的实用计算公式对于本文研究结构并不完全适用。提出考虑塔楼和桁架协同地震作用的实用算式,并对一个超高层工程实例进行竖向地震作用分析,与时程分析结果吻合较好。     

Seismic performance and probabilistic collapse resistance assessment of steel moment resisting frames with fluid viscous dampers

This paper evaluates the seismic resistance of steel moment resisting frames (MRFs) with supplemental fluid viscous dampers against collapse. A simplified design procedure is used to design four different steel MRFs with fluid viscous dampers where the strength of the steel MRF and supplemental damping are varied. The combined systems are designed to achieve performance that is similar to or higher than that of conventional steel MRFs designed according to current seismic design codes. Based on the results of nonlinear time history analyses and incremental dynamic analyses, statistics of structural and non‐structural response as well as probabilities of collapse of the steel MRFs with dampers are determined and compared with those of conventional steel MRFs. The analytical frame models used in this study are reliably capable to simulate global frame collapse by considering full geometric nonlinearities as well as the cyclic strength and stiffness deterioration in the plastic hinge regions of structural steel members. The results show that, with the aid of supplemental damping, the performance of a steel MRF with reduced design base shear can be improved and become similar to that of a conventional steel MRF with full design base shear. Incremental dynamic analyses show that supplemental damping reduces the probability of collapse of a steel MRF with a given strength. However, the paper highlights that a design base shear equal to 75% of the minimum design base shear along with supplemental damping to control story drift at 2% (i.e., design drift of a conventional steel MRF) would not guarantee a higher collapse resistance than that of a conventional MRF. At 75% design base shear, a tighter design drift (e.g., 1.5% as shown in this study) is needed to guarantee a higher collapse resistance than that of a conventional MRF. Copyright © 2014 John Wiley & Sons, Ltd.     

Iterative implicit integration procedure for hybrid simulation of large nonlinear structures

A fully implicit iterative integration procedure is presented for local and geographically distributed hybrid simulation of the seismic response of complex structural systems with distributed nonlinear behavior. The purpose of this procedure is to seamlessly incorporate experimental elements in simulations using existing fully implicit integration algorithms designed for pure numerical simulations. The difficulties of implementing implicit integrators in a hybrid simulation are addressed at the element level by introducing a safe iteration strategy and using an efficient procedure for online estimation of the experimental tangent stiffness matrix. In order to avoid physical application of iterative displacements, the required experimental restoring force at each iteration is estimated from polynomial curve fitting of recent experimental measurements. The experimental tangent stiffness matrix is estimated by using readily available experimental measurements and by a classical diagonalization approach that reduces the number of unknowns in the matrix. Numerical and hybrid simulations are used to demonstrate that the proposed procedure provides an efficient method for implementation of fully implicit numerical integration in hybrid simulations of complex nonlinear structures. The hybrid simulations presented include distributed nonlinear behavior in both the numerical and experimental substructures. Copyright © 2010 John Wiley & Sons, Ltd.     

预应力组合网架结构的自振特性分析及现场测试

本文采用子空间迭代法计算了预应力组合网架的自振频率与振型,分析总结了结构的自振特性及其影响因素,诸如索预应力、跨高比、边界条件、板和梁肋偏心、附加质量以及节点刚度的影响,并回归得出预应力组合网架基本周期简化计算公式。同时使用“脉动法”对天津一中新建活动中心楼层预应力组合网架进行了现场动力测试,结果表明预应力组合网架动力计算所采用的计算模型合理、计算分析结果可信,最后使用自由振动法及半功率点法得出了预应力组合网架结构的阻尼比,此值可作为钢与混凝土预应力组合网架结构的参考阻尼比。