Analytical Model for Viscous Wall Dampers

By now, many civil engineering researchers have extensively studied the application of earthquake energy dissipation systems in seismic‐resistant buildings. Earthquake energy dissipation systems play an important role in enhancing the sustainability of structures against seismic excitation. Frame buildings are strengthened by installing damper devices as supplemental structural members. This article presents the finite‐element‐based development of an analytical model for a viscous wall damper (VWD) device, an alternative to other earthquake energy dissipation systems, which can diminish the effect of earthquakes on structures and improve the seismic performance of multistory buildings subjected to ground motion. The constitutive law of VWDs has been formulated and integrated to develop a finite element model of VWD compatible with the reinforced concrete (RC) structure analytical model. Then, the finite element algorithm has been developed for inelastic analysis of RC buildings equipped with VWD devices capable of detecting damage to both structural members and damper connections under dynamic loading. Based on the developed system, the special finite element program was codified and verified by applying it to a real model of a RC building with supplementary VWD devices. Influence of VWDs on seismic performance of the RC building during earthquake excitation was evaluated. The proposed analytical model for VWD is verified by using experimental test data and analysis result proved that this energy dissipation system succeeds by substantially diminishing and dissipating a structure's induced seismic responses. Also the parametric study indicated that the damping coefficient is very effective on performance of VWD.     

Reliability evaluation in nonlinear analysis of reinforced concrete structures

Modern building codes provide a basis for development of advanced nonlinear models for analysis and design of reinforced concrete (RC) structures. Application of nonlinear models permits direct evaluation of reliability of the whole structure at the stage of a structural analysis. In this paper a probabilistic method for reliability evaluation of plane frame structures with respect to ultimate limit states is proposed. The method is based on a combination of the nonlinear finite element structural model and the first-order reliability method (FORM). Implementation of the FORM for nonlinear analysis of RC structures is considered. Uncertainties associated with the structural model are taken into account and their influence on structural reliability is examined via sensitivity analysis.     

Assessment of RC columns subjected to horizontal and vertical ground motions recorded during the 2009 L’Aquila (Italy) earthquake

In the aftermath of recent earthquakes there has been substantial field evidence demonstrating that the collapse of several existing structures was caused by the effects of the vertical component of seismic ground motions. Such field evidence has not yet been supported by comprehensive analytical assessment and experimental tests. The present work focuses on preliminary analyses of the seismic response of reinforced concrete (RC) members subjected to horizontal (HGMs) and vertical (VGMs) ground motions recorded during the 2009 L’Aquila (Italy) earthquake. Normalised axial loads in beam-columns as well as the peak ground acceleration ratios between horizontal and vertical ground accelerations are emphasised as they are considered parameters of paramount importance for the assessment of structural components and systems subjected to combined horizontal and vertical ground motions (HVGMs).Results of extensive parametric nonlinear dynamic analyses carried out on simplified structural models are discussed in detail. The sample models comprise cantilever RC columns and a two-storey, two-bay plane frame designed for gravity loads. The structural response quantities for the performed analyses are expressed in terms of axial loads, axial deformations, bending moment-axial load interaction and shear demand/capacity ratios. It is found that the variation of axial loads is significant in columns under HVGMs, especially in compression. For values of normalised axial loads (ν) corresponding to actual RC columns in framed building structures, e.g., normalised axial load ν>0.10, the average increase of the compression load ranges between 174% (ν=0.20) and 59% (ν=0.50). For high values of normalised axial loads the computed axial load-bending moment pairs lie beyond the threshold interaction curves and, in turn, the RC members may fail. The shear demand-to-supply ratio is also detrimentally affected by the high fluctuations of axial loads in the columns. Net tensile forces were computed for columns with low-to-moderate axial gravity preload. In multi-storey framed buildings, the response of central columns is significantly affected by the HVGMs. Reliable seismic performance assessment of framed systems requires that combined HGMs and VGMs should be accounted for in the analyses. Further experimental and numerical research is needed to formulate efficient mechanical models to evaluate the shear capacity of structural members of existing RC framed buildings under earthquake loading.     

Macroscopic FE model for tracing the fire response of reinforced concrete structures

A macroscopic finite element model for tracing the fire response of reinforced concrete (RC) structural members is presented. The model accounts for critical factors that are to be considered for performance-based fire resistance assessment of RC structural members. Fire induced spalling, various strain components, high temperature material properties, restraint effects, different fire scenarios and failure criteria are incorporated in the model. The validity of the numerical model is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. Case studies are conducted to demonstrate the use of the computer program for tracing the response of RC members under standard and design fire exposures. Through the results of the case studies, it is shown that the fire scenario has a significant effect on the fire resistance of RC columns and beams. It is also shown that macroscopic finite element models are capable of predicting the fire response of RC structural members with an adequate accuracy for practical applications.     

Progressive collapse performance analysis of precast reinforced concrete structures

In this paper, the progressive collapse performance analysis of precast reinforced concrete (RC) structures is performed. A numerical simulation framework for precast RC structures is developed on the basis of the OpenSEES software, where the fiber frame element is used for beam and column type members and Joint2D element is used for the beam‐to‐column connections. The conjugated material models are then introduced, and a min–max failure criterion is imposed on the original models to reflect the steel fracture and concrete crushing when the structure is undergoing progressive collapse. In addition, to overcome the computational difficulties arisen from progressive collapse behavior, two enhanced nonlinear solutions , that is, the consistent quasi‐Newton algorithm and the explicit KR‐α algorithm, are employed, respectively, for static and dynamic analysis. A 10‐storey prototype precast RC structures is designed to verify the developed numerical framework, and the progressive collapse resisting mechanism of the structures is investigated through both static pushdown analysis and dynamic column‐removal analysis. Finally, influences of some typical parameters in precast RC structures on their progressive collapse performance are studied.     

钢筋混凝土构件动力加载试验数据库

钢筋混凝土结构在地震作用下会产生应变率效应,受该效应影响,结构的抗震性能将产生变化。因此,在对钢筋混凝土结构进行抗震性能分析及设计时应考虑应变率效应的影响。对国内外已有研究的钢筋混凝土构件在不同加载速率下的相关试验进行力学模型等效和试验数据处理,分析了钢筋混凝土构件在不同加载速率下力学性能的一般变化趋势,并以此为基础建立了钢筋混凝土构件动力加载试验数据库,该数据库界面友好、检索方便,包含了钢筋混凝土梁、柱、节点和剪力墙构件的数据。     

高强钢绞线网-聚合物砂浆加固混凝土梁的非线性分析

高强钢绞线网-聚合物砂浆加固法是一种新型的加固方法,它具有耐火、耐腐蚀、耐老化的优点。本文通过有限元模拟,对钢筋混凝土梁的抗剪加固进行非线性全过程分析。分析结果表明,通过合理的建立有限元模型,可以较好的模拟高强钢绞线网-聚合物砂浆加固混凝土梁的受剪性能。分析结果和试验结果均表明高强钢绞线网-聚合物砂浆加固法可有效提高抗剪刚度、开裂荷载、极限承载力,验证了用ANSYS进行有限元分析的可行性和优越性。     

单自由度体系地震残余变形分析及计算

地震残余变形是结构可修复能力的重要指标,准确分析结构的残余变形对于震后结构性能的评估与控制具有重要意义。基于对不同单自由度(SDOF)体系的弹塑性地震响应的统计分析,研究了不同参数对地震残余变形的影响,其中滞回特性、屈服后刚度、地面峰值加速度(PGA)以及最大弹塑性变形对残余变形的影响较大;同时结合理论分析提出了分别适用于弹塑性Kinematic滞回模型和Takeda滞回模型的残余变形简化计算方法。该方法是以先获得结构的最大弹塑性变形为基础的,能与传统的确定结构最大变形性能的抗震分析方法(Pushover方法)较好地结合。最后,以一钢筋混凝土单柱桥墩为例,详细阐述了所提出的方法进行单自由度体系结构的地震残余变形计算及震后结构性能评估的过程,分析表明基于Takeda模型的结构残余变形的计算结果偏于安全。     

Effect of elaborate plastic hinge definition on the pushover analysis of reinforced concrete buildings

Due to its simplicity, lumped plasticity approach is usually used for nonlinear characterization of reinforced concrete (RC) members in pushover analysis. In this approach, the inelastic force deformation of hinges could be defined as either the nonlinear properties suggested in FEMA‐356 and ATC‐40 or defined hinges quantified on the basis of the properties of RC members. However, the nonlinear response of RC structures relies heavily on the inelastic properties of the structural members concentrated in the plastic hinges. To provide a comparative study, this paper attempts to show the results of pushover analyses of RC structures modeled on the basis of the FEMA nonlinear hinges and defined hinges. Following the validation of the adopted models, the force–deformation curves of the defined hinges are determined in a rigorous approach considering the material inelastic behavior, reinforcement details and dimensions of the members. For the case studies, two four‐story and one eight‐story frames are considered in order to represent low‐rise and mid‐rise buildings with different ductility. Nonlinear responses of both models are elaborated in terms of the inter‐story drift, hinging pattern, failure mechanism and the pushover curve. It is confirmed that FEMA hinges underestimate the strength and more importantly the displacement capacity, especially for the frame possessing low ductility. Copyright © 2012 John Wiley & Sons, Ltd.     

钢筋混凝土框架结构梁柱刚域对抗震性能的影响

在钢筋混凝土框架结构地震反应分析中,梁柱节点区域因具有相对较大的刚度而设置一定范围的刚域,其设定方法对结构的地震响应和损伤发展历程具有明显的影响。采用基于柔度法的纤维有限元方法考察了不同的刚域设置方法对结构地震反应和损伤发展的影响,并结合我国抗震设计的实际情况给出了相应的设计建议。     

基于机器学习的钢筋混凝土柱失效模式两阶段判别方法增强出版（附加材料可在文章详情页“评审附件”下载）

钢筋混凝土柱在侧向地震力作用下具有弯曲、剪切和弯剪三种失效模式。不同的失效模式下钢筋混凝土柱具有不同的地震损伤特征。因此,准确地判别钢筋混凝土柱的失效模式对于准确评估钢筋混凝土结构的抗震性能具有重要意义。利用已有的钢筋混凝土柱滞回加载试验数据,采用机器学习方法,提出了一种钢筋混凝土柱失效模式两阶段判别方法。其中,第一阶段以钢筋混凝土柱的基本设计参数为输入变量,采用机器学习中的回归算法,建立钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形预测模型。第二阶段以钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形作为输入变量,采用机器学习中的分类算法,对钢筋混凝土柱的失效模式进行自动判别,实现了准确判别钢筋混凝土柱失效模式的目的。研究结果表明：极端随机树、AdaBoost、随机森林和梯度提升算法分别对受弯承载力、受剪承载力、弯曲变形和剪切变形的预测效果最佳;极端随机树、梯度提升算法和最近邻居法分别对弯曲失效、剪切失效和弯剪失效具有最佳的分类效果;相比已有的钢筋混凝土柱失效模式分类方法,提出的两阶段分类方法具有与真实失效模式最为接近的分类结果,分类精度可以达到96%。     

Seismic fragility analysis of reinforced concrete structures considering reinforcement corrosion

钢筋锈蚀是影响钢筋混凝土结构耐久性的一个重要因素，会引起结构的自振周期延长、地震需求变化及抗震能力衰减，使得锈蚀钢筋混凝土结构的地震易损性分析不同于未锈蚀钢筋混凝土结构。以一栋按我国规范设计的RC框架结构为研究对象，分别建立了未锈蚀和锈蚀结构的非线性有限元模型并进行了模型验证。分别采用云图法和条带法计算得到了钢筋混凝土结构在未锈蚀和锈蚀两种工况下的地震易损性曲线和函数参数，对锈蚀钢筋混凝土结构地震易损性分析的特殊性及其对地震易损性分析结果的影响进行了分析。分析结果表明：不考虑钢筋锈蚀引起的结构自振周期延长会错误估计锈蚀钢筋混凝土结构的地震易损性水平。采用云图法分析锈蚀钢筋混凝土结构的地震易损性会出现锈蚀结构的极限状态失效概率低于未锈蚀结构的情况。而条带法比云图法可以更好地反映钢筋锈蚀对钢筋混凝土结构地震易损性的影响。忽略钢筋锈蚀引起的结构抗震能力衰减会低估锈蚀钢筋混凝土结构地震易损性水平，建议在锈蚀钢筋混凝土结构地震易损性分析中采用基于Pushover的极限状态定义方法。     

A machine-learning-based two-step method for failure mode classification of reinforced concrete columns

钢筋混凝土柱在侧向地震力作用下具有弯曲、剪切和弯剪三种失效模式。不同的失效模式下钢筋混凝土柱具有不同的地震损伤特征。因此，准确地判别钢筋混凝土柱的失效模式对于准确评估钢筋混凝土结构的抗震性能具有重要意义。利用已有的钢筋混凝土柱滞回加载试验数据，采用机器学习方法，提出了一种钢筋混凝土柱失效模式两阶段判别方法。其中，第一阶段以钢筋混凝土柱的基本设计参数为输入变量，采用机器学习中的回归算法，建立钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形预测模型。第二阶段以钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形作为输入变量，采用机器学习中的分类算法，对钢筋混凝土柱的失效模式进行自动判别，实现了准确判别钢筋混凝土柱失效模式的目的。研究结果表明：极端随机树、AdaBoost、随机森林和梯度提升算法分别对受弯承载力、受剪承载力、弯曲变形和剪切变形的预测效果最佳；极端随机树、梯度提升算法和最近邻居法分别对弯曲失效、剪切失效和弯剪失效具有最佳的分类效果；相比已有的钢筋混凝土柱失效模式分类方法，提出的两阶段分类方法具有与真实失效模式最为接近的分类结果，分类精度可以达到96%。     

锈蚀钢筋混凝土结构地震易损性分析

钢筋锈蚀是影响钢筋混凝土结构耐久性的一个重要因素,会引起结构的自振周期延长、地震需求变化及抗震能力衰减,使得锈蚀钢筋混凝土结构的地震易损性分析不同于未锈蚀钢筋混凝土结构。以一栋按我国规范设计的RC框架结构为研究对象,分别建立了未锈蚀和锈蚀结构的非线性有限元模型并进行了模型验证。分别采用云图法和条带法计算得到了钢筋混凝土结构在未锈蚀和锈蚀两种工况下的地震易损性曲线和函数参数,对锈蚀钢筋混凝土结构地震易损性分析的特殊性及其对地震易损性分析结果的影响进行了分析。分析结果表明：不考虑钢筋锈蚀引起的结构自振周期延长会错误估计锈蚀钢筋混凝土结构的地震易损性水平。采用云图法分析锈蚀钢筋混凝土结构的地震易损性会出现锈蚀结构的极限状态失效概率低于未锈蚀结构的情况。而条带法比云图法可以更好地反映钢筋锈蚀对钢筋混凝土结构地震易损性的影响。忽略钢筋锈蚀引起的结构抗震能力衰减会低估锈蚀钢筋混凝土结构地震易损性水平,建议在锈蚀钢筋混凝土结构地震易损性分析中采用基于Pushover的极限状态定义方法。     

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.     

结构三维弹塑性分析方法及其在建筑物震害研究中的应用

介绍了作者研究开发的结构三维弹塑性分析方法及其在建筑物震害研究中的应用。采用杆系模型 ,包括梁、柱、墙单元、拉压杆单元、弹簧单元和阻尼单元 ,可建立各种结构计算模型 (质点系模型、平面或空间框架模型 )。对柱和墙单元等压弯杆件 ,采用了“多弹簧模型”和“纤维模型”来考虑变动轴力和双向弯曲荷载之间的耦合作用 ,能够表达压弯杆件在多轴荷载作用下的力学特性 ,从而比较真实地模拟结构弹塑性地震反应。为了表达各种荷载作用下杆件或弹簧的力和变形关系 ,作者开发和引进了多种材料恢复力模型 ,这些恢复力模型模拟了材料的非线性。在结构分析过程中也采用近似方法考虑了几何非线性。采用以上计算模型 ,作者开发了结构三维弹塑性分析计算机程序 ,用于分析遭受地震作用的建筑物 ,其结果与实际的地震破坏吻合较好 ,能够说明结构的破坏机制。     

结构三维弹塑性分析方法及计算机程序CANNY

介绍了作者研究开发的结构三维弹塑性分析方法及其在建筑物震害研究中的应用。采用杆系模型,包括梁,柱,墙单元,拉压杆单元,弹簧单元和阻尼单元,可建立各种结构计算模型（质点系模型,平面或空间框架模型）。对柱和墙单元等压湾杆件,采用了“多弹簧模型”和“纤维模型”来考虑变动轴力和双向弯曲荷载之间的耦合作用,能够表达压弯杆件在多轴荷载作用下的力学特性,从而比较真实地模拟结构弹塑性地震反应。为了表达各种荷载作用下杆件或弹簧的力和变形关系,作者开发和引进了多种恢复力模型,这些恢复力模型模拟了材料的非线性。在结构分析过程中也采用近似方法考虑了几何非线性。采用以上计算模型,作者开发了结构三维弹塑性分析计算机程序CANNY,用于分析遭受地震作用的建筑物,其结果与实际的地震破坏吻合较好,能够说明结构的破坏机制。     

FRP-strengthened RC slabs anchored with FRP anchors

An abundance of tests over the last two decades has shown the bending capacity of flexural members such as reinforced concrete (RC) beams and slabs to be enhanced by the bonding of fibre-reinforced polymer (FRP) composites to their tension face. The propensity of the FRP to debond, however, limits its effectiveness. Different types of anchorages have therefore been investigated in order to delay or even prevent debonding. The so-called FRP anchor, which is made from rolled fibre sheets or bundles of lose fibres, is particularly suitable for anchoring FRP composites to a variety of structural element shapes. Studies that assess the effectiveness of FRP anchors in anchoring FRP strengthening in flexural members is, however, limited. This paper in turn reports a series of tests on one-way spanning simply supported RC slabs which have been strengthened in flexure with tension face bonded FRP composites and anchored with different arrangements of FRP anchors. The load-deflection responses of all slab tests are plotted, in addition to selected strain results. The behaviours of the specimens including the failure modes are also discussed. The greatest enhancement in load and deflection experienced by the six slabs strengthened with FRP plates and anchored with FRP anchors was 30% and 110%, respectively, over the unanchored FRP-strengthened control slab. The paper also discusses the strategic placement of FRP anchors for optimal strength and deflection enhancement in FRP-strengthened RC slabs.     

Probabilistic response evaluation for RC flexural members subjected to blast loadings

The probabilistic responses of the maximum displacement and displacement ductility factor for a reinforced concrete (RC) flexural member against potential blast loadings are evaluated through a nonlinear dynamic analysis of its equivalent single-degree-of-freedom (SDOF) system. Monte-Carlo simulation is used in the analysis. Some differences are observed between the actual responses of the RC member and those of the equivalent SDOF system due to the complex behaviours of reinforced concrete structural members under blast conditions. Two non-dimensional indices are defined to quantify the differences and their expressions are generated through a large amount of numerical and statistical analyses. The approach of utilizing the indices into a probabilistic response assessment of RC flexural members accounting for different kinds of uncertainties is illustrated via four numerical examples which are verified through nonlinear dynamic finite element analysis. It is concluded that the probabilistic response of RC flexural members obtained from the developed approach have a similar distribution with those from probabilistic nonlinear finite element analysis.     

输电塔线体系的风(雨)致振动响应与稳定性研究

根据输电塔线体系在风(雨)激励下破坏的实际状况,建立了"三塔两跨"有限元分析模型,其中,输电塔采用三自由度梁单元,导(地)线采用索单元;提出雨荷载的计算方法以及与风湍流共同作用于输电塔线体系的荷载组合原则;分析输电塔、导(地)线和结构体系的结构动力特性及其相互关系;采用数值模拟方法,建立设计与灾害荷载的不同工况组合,分别在时域和频域内对输电塔的动力响应规律进行分析;采用结构主要组件(如主立柱杆件和输电线)强度分析的方法,分析结构强度的变化和灾害发生的可能性原因。研究表明:输电塔线体系的运动耦合性对结构动力特性有不容忽视的影响;降雨对输电塔线体系的响应具有明显影响,且有与风湍流同时作用的激励特征;结构体系发生连续倒塔破坏的原因是风雨共同作用,结构局部动态受压失稳造成的。