Seismic behaviour of multistorey RC wall–frame system versus bare ductile frame system

The wall–frame systems have many known advantages, namely increase of the system's lateral strength and stiffness thereby allowing for a good tangential inter‐storey drift control, and the retention of a satisfactory energy dissipation capacity. However, rocking of the wall could occur as a result of uplifting wall base or concentrated plastic hinge deformations. Problems arising from this phenomenon have significant impact on the system behaviour and hence require extended study. This paper focuses on the wall‐rocking phenomenon due to the concentrated plastic hinge rotation at the wall base. To facilitate a comprehensive evaluation, a six‐storey three‐bay RC wall–frame structure is investigated with comparison to a bare ductile frame by means of earthquake simulation tests. The results revealed that, despite a superior performance over the ductile frame under low to moderate seismic actions, the wall–frame structure deteriorated more rapidly than the bare frame during advanced inelastic response. The increasingly significant rocking of the wall resulted in severe material damage at localized critical regions. Mitigating the wall rocking is seen to be a key to the further improvement of the system performance, and the extent to which this may be achieved by incorporating the three‐dimensional effects is explicitly illustrated by an analytical evaluation. Copyright © 2001 John Wiley & Sons, Ltd.     

Experimental study on a new type of earthquake resilient shear wall

Reinforced concrete (RC) shear walls have been extensively used as lateral load resisting structural members in tall buildings. However, in the past, strong earthquake events RC structural walls in some buildings suffered severe damage, which concentrated at the bottom and was very difficult to be repaired. The installation of the replaceable corner components (RCCs) at the bottom of the structural wall is a new method to form an earthquake resilient structural wall whose function can be quickly restored by replacing the RCCs after the strong earthquake because of the damage concentrating on RCCs. In this study, a new kind of replaceable energy‐dissipation component installed at the bottom corner of RC structural walls was proposed. To study the seismic performance of the new structural wall with RCCs, the cyclic loading tests on three new structural wall specimens and one conventional RC structural wall specimen were conducted. One of the new structural wall specimens experienced replacement and reloading process to verify the feasibility of replacement. The results show that the structural behavior of all specimens was flexure dominating. The damage in the new shear specimens mainly concentrated on RCCs. The replacement of RCCs can be implemented conveniently after the residual deformation occurred in the structure. Compared with the conventional structural wall specimen, the seismic performance of new structural wall specimens was improved significantly. Copyright © 2017 John Wiley & Sons, Ltd.     

Shake‐table test performance of an inertial force‐limiting floor anchorage system

A new floor connecting system developed for low‐damage seismic‐resistant building structures is described herein. The system, termed Inertial Force‐Limiting Floor Anchorage System (IFAS), is intended to limit the lateral forces in buildings during an earthquake. This objective is accomplished by providing limited‐strength deformable connections between the floor system and the primary elements of the lateral force‐resisting system. The connections transform the seismic demands from inertial forces into relative displacements between the floors and lateral force‐resisting system. This paper presents the IFAS performance in a shake‐table testing program that provides a direct comparison with an equivalent conventional rigidly anchored‐floor structure. The test structure is a half‐scale, 4‐story reinforced concrete flat‐plate shear wall structure. Precast hybrid rocking walls and special precast columns were used for test repeatability in a 22‐input strong ground‐motion sequence. The structure was purposely designed with an eccentric wall layout to examine the performance of the system in coupled translational‐torsional response. The test results indicated a seismic demand reduction in the lateral force‐resisting system of the IFAS structure relative to the conventional structure, including reduced shear wall base rotation, shear wall and column inter‐story drift, and, in some cases, floor accelerations. These results indicate the potential for the IFAS to minimize damage to the primary structural and non‐structural components during earthquakes.     

边缘约束构件对钢筋混凝土剪力墙抗震性能的影响

钢筋混凝土剪力墙是高层建筑中的主要抗侧力构件，边缘约束情况是影响剪力墙抗震性能的一个重要因素。为研究边缘约束构件对钢筋混凝土剪力墙抗震性能的影响，本文进行了三片边缘约束情况不同的钢筋混凝土剪力墙的低周反复试验，并对试验结果进行了分析，分析内容包括：破坏形态、水平承载力、位移延性系数、刚度退化、抗震耗能能力等方面。研究结果表明，合理地设置边缘约束能够扩大塑性破坏区域，提高试件的水平承载力，改善其抗震耗能性能。研究进一步发现，边缘纵筋配筋率在提高试件的水平承载力，改善其抗震耗能性能和刚度退化程度方面影响显著，而边缘配箍率对抗震性能的贡献在本次试验分析中表现得并不明显。     

Damage index based on stiffness degradation of low‐rise RC walls

Widely used damage indices, such as ductility and drift ratios, do not account for the influences of the duration of strong shaking, the cumulative inelastic deformation or energy dissipation in structures. In addition, the formulation and application of most damage indices have until now been based primarily on flexural modes of failure. However, evidence from earthquakes suggests that shear failure or combined shear‐flexure behavior is responsible for a large proportion of failures. Empirical considerations have been made in this paper for evaluating structural damage of low‐rise RC walls under earthquake ground motions by means of a new energy‐based low‐cycle fatigue damage index. The proposed empirical damage index is based on the results of an experimental program that comprised six shake table tests of RC solid walls and walls with openings; results of six companion walls tested under QS‐cyclic loading were used for comparison purposes. Variables studied were the wall geometry, type of concrete, web shear steel ratio, type of web shear reinforcement, and testing method. The index correlates the stiffness degradation and the destructiveness of the earthquake in terms of the duration and intensity of the ground motions. The stiffness degradation model considers simultaneously the increment of damage associated to the low‐cycle fatigue, energy dissipation, and the cumulative cyclic parameters, such as displacement demand and hysteretic energy dissipated. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic performance and damage evaluation of a reinforced concrete frame with hysteretic dampers through shake‐table tests

Passive energy dissipation devices are increasingly implemented in frame structures to improve their performance under seismic loading. Most guidelines for designing this type of system retain the requirements applicable to frames without dampers, and this hinders taking full advantage of the benefits of implementing dampers. Further, assessing the extent of damage suffered by the frame and by the dampers for different levels of seismic hazard is of paramount importance in the framework of performance‐based design. This paper presents an experimental investigation whose objectives are to provide empirical data on the response of reinforced concrete (RC) frames equipped with hysteretic dampers (dynamic response and damage) and to evaluate the need for the frame to form a strong column‐weak beam mechanism and dissipate large amounts of plastic strain energy. To this end, shake‐table tests were conducted on a 2/5‐scale RC frame with hysteretic dampers. The frame was designed only for gravitational loads. The dampers provided lateral strength and stiffness, respectively, three and 12 times greater than those of the frame. The test structure was subjected to a sequence of seismic simulations that represented different levels of seismic hazard. The RC frame showed a performance level of ‘immediate occupancy’, with maximum rotation demands below 20% of the ultimate capacity. The dampers dissipated most of the energy input by the earthquake. It is shown that combining hysteretic dampers with flexible reinforced concrete frames leads to structures with improved seismic performance and that requirements of conventional RC frames (without dampers) can be relieved. Copyright © 2014 John Wiley & Sons, Ltd.     

The seismic shear of ductile cantilever wall systems in multistorey structures

The distribution of seismic base shear demand among ductile flexural cantilever walls, comprising the lateral load resisting system of a multistorey building, is studied. It is shown that the base shear force demand depends on the sequence of hinge formation at the wall bases, and this in turn depends on the relative wall lengths. Hence, the routine elastic approach in which the shear forces are allocated per relative flexural rigidity or (when some consideration is given to plastic hinge formation) to moment capacity at the wall base, may appreciably underestimate the shear force demand on the walls, particularly the shorter (usually the more flexible) ones. A simple procedure yielding the results of ‘cyclic’ pushover analysis is proposed to predict the peak seismic wall forces for a given total base shear when plastification is confined to the wall base. The effects of plastic hinges developing at higher floors on (1) shear distribution among the walls and (2) the in‐plane floor forces are also considered. Two numerical examples are presented to demonstrate the main points made. Copyright © 2004 John Wiley & Sons, Ltd.     

Seismic behavior of asymmetric RC wall buildings: principles and new deformation‐based design method

The seismic design of multi‐story buildings asymmetric in plan yet regular in elevation and stiffened with ductile RC structural walls is addressed. A realistic modeling of the non‐linear ductile behavior of the RC walls is considered in combination with the characteristics of the dynamic torsional response of asymmetric buildings. Design criteria such as the determination of the system ductility, taking into account the location and ductility demand of the RC walls, the story‐drift demand at the softer (most displaced) edge of the building under the design earthquake, the allowable ductility (ultimate limit state) and the allowable story‐drift (performance goals) are discussed. The definition of an eccentricity of the earthquake‐equivalent lateral force is proposed and used to determine the effective displacement profile of the building yet not the strength distribution under the design earthquake. Furthermore, an appropriate procedure is proposed to calculate the fundamental frequency and the earthquake‐equivalent lateral force. A new deformation‐based seismic design method taking into account the characteristics of the dynamic torsional response, the ductility of the RC walls, the system ductility and the story‐drift at the softer (most displaced) edge of the building is presented and illustrated with an example of seismic design of a multi‐story asymmetric RC wall building. Copyright © 2005 John Wiley & Sons, Ltd.     

Single precast concrete rocking walls as earthquake force‐resisting elements

Precast concrete walls with unbonded post‐tensioning provide a simple self‐centering system. Yet, its application in seismic regions is not permitted as it is assumed to have no energy dissipation through a hysteretic mechanism. These walls, however, dissipate energy imparted to them because of the wall impacting the foundation during rocking and limited hysteretic action resulting from concrete nonlinearity. The energy dissipated due to rocking was ignored in previous experimental studies because they were conducted primarily using quasi‐static loading. Relying only on limited energy dissipation, a shake table study was conducted on four single rocking walls (SRWs) using multiple‐level earthquake input motions. All walls generally performed satisfactorily up to the design‐level earthquakes when their performance was assessed in terms of the maximum transient drift, maximum absolute acceleration, and residual drift. However, for the maximum considered earthquakes, the walls experienced peak lateral drifts greater than the permissible limits. Combining the experimental results with an analytical investigation, it is shown that SRWs can be designed as earthquake force‐resisting elements to produce satisfactory performance under design‐level and higher‐intensity earthquake motions. Copyright © 2016 John Wiley & Sons, Ltd.     

组合剪力墙的抗震研究与发展

剪力墙是高层建筑结构中的核心抗侧力部件,研制抗震性能好的剪力墙,是建筑抗震设计的关键技术之一。组合剪力墙包括不同材料和不同结构形式的组合,可以发挥不同材料和不同结构形式各自的优势,使剪力墙的延性和耗能能力得以提高,从而改善其抗震性能。本文对国内外一些新型组合剪力墙的抗震研究工作进行了归纳总结,并对其发展作一展望。     

Hybrid experimental performance of a full‐scale two‐story buckling‐restrained braced RC frame

This paper proposes a novel implementation of buckling‐restrained braces (BRB) in new reinforced concrete (RC) frame construction. Seismic design and analysis methods for using a proposed steel cast‐in anchor bracket (CAB) to transfer normal and shear forces between the BRB and RC members are investigated. A full‐scale two‐story RC frame with BRBs (BRB‐RCF) is tested using hybrid and cyclic loading test procedures. The BRBs were arranged in a zigzag configuration and designed to resist 70% of the story shear. The gusset design incorporates the BRB axial and RCF actions, while the beam and column members comply with ACI 318‐14 seismic design provisions. Test results confirm that the BRBs enhanced the RCF stiffness, strength, and ductility. The hysteresis energy dissipation ratios in the four hybrid tests range from 60% to 94% in the two stories, indicating that BRBs can effectively dissipate seismic input energy. When the inter‐story drift ratio for both stories reached 3.5% in the cyclic loading test, the overall lateral force versus deformation response was still very stable. No failure of the proposed steel CABs and RC discontinuity regions was observed. This study demonstrates that the proposed design and construction methods for the CABs are effective and practical for real applications. Copyright © 2016 John Wiley & Sons, Ltd.     

双向单排配筋混凝土低矮剪力墙抗震性能试验研究

双向单排配筋混凝土低矮剪力墙适用于多层住宅结构。对4个原型的剪跨比为1.0配筋混凝土低矮剪力墙进行了低周反复荷载试验研究,包括1个双向双排配筋混凝土低矮剪力墙和3个双向单排配筋混凝土低矮剪力墙。其中1个双向单排配筋混凝土低矮剪力墙加设暗支撑,用以研究暗支撑对这种新型墙体的作用。在试验研究的基础上,对比分析了各剪力墙的刚度及其衰减过程、承载力、延性、滞回特征、耗能能力及破坏特征。试验表明,经过合理设计,这种双向单排配筋混凝土低矮剪力墙可以满足多层住宅结构抗震要求。     

Seismic behaviour of steel plate shear wall systems with staggered web configurations

Unstiffened steel plate shear walls (SPSWs) are used as lateral load‐resisting systems in building structures. The energy dissipation mechanism of SPSWs consists of the tension yielding of web plates and the formation of plastic hinges at the ends of horizontal boundary elements. However, vertical boundary elements (VBEs) of high‐rise SPSWs may experience high axial forces under lateral loading. This study explores the effectiveness of staggering of web plates on the reduction of VBE forces and drift response of SPSWs during an earthquake event. An analytical study has been conducted to determine the base shear reduction factor so as to match the overstrength of staggered systems with conventional SPSWs. A design methodology has been proposed for staggered SPSWs. Six‐, 9‐, and 20‐storey staggered and conventional SPSWs with varying aspect ratios are considered in this study to compare their seismic response. These study frames are modelled and analysed in OpenSEES platform. Nonlinear static and dynamic analyses are performed to compare the drift response, hinge mechanisms, and steel tonnage. Staggered SPSWs showed uniform drift distribution and reduction in interstorey drift and axial force demand on the VBEs.     

The cause of unproportionately large higher mode contributions in the inelastic seismic responses of high‐rise core‐wall buildings

In the conventional seismic design of high‐rise reinforced concrete core‐wall buildings, the design demands such as design shear and bending moment in the core wall are typically determined by the response spectrum analysis procedure, and a plastic hinge is allowed to form at the wall base to limit the seismic demands. In this study, it is demonstrated by using a 40‐story core‐wall building that this conventional approach could lead to an unsafe design where the true demands—the maximum inelastic seismic demands induced by the maximum considered earthquake—could be several times greater than the design demands and be unproportionately dominated by higher vibration modes. To identify the cause of this problem, the true demands are decomposed into individual modal contributions by using the uncoupled modal response history analysis procedure. The results show that the true demands contributed by the first mode are reasonably close to the first‐mode design demands, while those contributed by other higher modes are much higher than the corresponding modal design demands. The flexural yielding in the plastic hinge at the wall base can effectively suppress the seismic demands of the first mode. For other higher modes, however, a similar yielding mechanism is either not fully mobilized or not mobilized at all, resulting in unexpectedly large contributions from higher modes. This finding suggests several possible approaches to improve the seismic design and to suppress the seismic demands of high‐rise core‐wall buildings. Copyright © 2012 John Wiley & Sons, Ltd.     

Dual‐plastic hinge design concept for reducing higher‐mode effects on high‐rise cantilever wall buildings

This paper explores the notion of detailing reinforced concrete structural walls to develop base and mid‐height plastic hinges to better control the seismic response of tall cantilever wall buildings to strong shaking. This concept, termed here dual‐plastic hinge (DPH) concept, is used to reduce the effects of higher modes of response in high‐rise buildings. Higher modes can significantly increase the flexural demands in tall cantilever wall buildings. Lumped‐mass Euler–Bernoulli cantilevers are used to model the case‐study buildings examined in this paper. Buildings with 10, 20 and 40 stories are designed according to three different approaches: ACI‐318, Eurocode 8 and the proposed DPH concept. The buildings are designed and subjected to three‐specific historical strong near‐fault ground motions. The investigation clearly shows the dual‐hinge design concept is effective at reducing the effects of the second mode of response. An advantage of the concept is that, when combined with capacity design, it can result in relaxation of special reinforcing detailing in large portions of the walls. Copyright © 2009 John Wiley & Sons, Ltd.     

中空暗缝RC剪力墙板拟静力试验及数值模拟分析

为明晰中空暗缝RC剪力墙抗剪机理和滞回性能,进行1榀1∶3缩尺单层、单跨中空暗缝RC剪力墙板拟静力试验,得到了试件破坏模式、滞回曲线、骨架曲线、刚度退化、强度退化、延性和耗能能力。通过数值模拟分析了混凝土强度、中空暗缝厚度、缝间墙配筋率对剪力墙板水平抗剪承载力的影响。研究结果表明:试件滞回曲线呈捏缩状,耗能能力一般,但具有较好的剪切变形能力;试件最终呈中空暗缝剪碎、缝间墙两端形成弯曲塑性铰的破坏模式;随着混凝土强度的提高和中空暗缝厚度的减小,试件水平抗剪承载力呈增加趋势;缝间墙配筋率对试件水平抗剪承载力及损伤状态的影响较小。     

装配式人工消能塑性铰框架-摇摆墙抗震性能研究

为提高装配式钢筋混凝土(RC)框架结构的抗震性能,并针对震后梁、柱构件损伤严重等问题,提出一种基于人工塑性消能铰的装配式混凝土框架-摇摆墙结构。人工消能塑性铰即梁、柱构件在梁端采用机械铰及附加耗能钢板连接的构造,基于该构造的框架结合底部铰接的剪力墙,形成人工消能塑性铰框架-摇摆墙结构。使用OpenSEES软件建立了人工消能塑性铰框架-摇摆墙模型及2组对比模型,选用24条天然地震波对3组结构模型进行双向地震响应分析,结果表明:人工消能塑性铰框架-摇摆墙结构可通过摇摆墙的构造,提升结构竖向连续刚度,使结构层间变形均匀,实现完全梁铰的理想屈服机制;在整体可控的变形模式下充分利用人工消能塑性铰滞回耗能,有效减小结构地震响应。     

Seismic behavior and strength capacity of steel tube‐reinforced concrete composite columns

The steel tube‐reinforced concrete (ST‐RC) composite column is a novel type of composite column, which consists of a steel tube embedded in RC. In this paper, the seismic behavior of ST‐RC columns is examined through a series of experiments in which 10 one‐third scale column specimens were subjected to axial forces and lateral cyclic loading. The test variables include the axial force ratio applied to the columns and the amount of transverse reinforcement. All specimens failed in a flexural mode, showing stable hysteresis loops. Thanks to the steel tube and the high‐strength concrete it is filled with, the ST‐RC column specimens had approximately 30% lower axial force ratios and 22% higher maximum bending moments relative to the comparable RC columns when subjected to identical axial compressive loads. The amount of transverse reinforcement made only a small difference to the lateral load‐carrying capacity but significantly affected the deformation and energy dissipation capacity of the ST‐RC columns. The specimens that satisfied the requirements for transverse reinforcement adopted for medium ductile RC columns as specified by the Chinese Code for Seismic Design of Buildings (GB 50011‐2010) and EuroCode 8 achieved an ultimate drift ratio of around 0.03 and a displacement ductility ratio of approximately 5. The design formulas used to evaluate the strength capacity of the ST‐RC columns were developed on the basis of the superposition method. The predictions from the formulas showed good agreement with the test results, with errors no greater than 10%. Copyright © 2013 John Wiley & Sons, Ltd.     

ASEISMIC CONSTRUCTION AND DESIGN METHOD FOR MULTI-STOREY COMPOSITE STRUCTURES

Using a newly introduced ductile low-rise shear wall with vertical keyways, a seismic resistance design approach for a practical type of composite structure, which consists of a reinforced concrete frame in the bottom floors and masonry structures in the upper floors, has been presented. The purpose of the new design approach is to improve the earthquake resistance of the whole structure by increasing the energy dissipation capacity in the bottom part of the structure. Non-linear analysis shows that, by adopting the newly proposed ductile low-rise shear wall in the bottom of the structure, the lateral deflection of the structure is not much more than that of a structure using conventional solid low-rise shear walls under a small or moderate earthquake excitation, and that even under the attack of a severe earthquake, a stable structural response can be expected for the proposed structure. Thus it is easy for such a structure to achieve the design objective of ‘minor damage in a small earthquake and prevention of collapse in a severe earthquake’ and the design method is of practical value for similar types of composite structures.     

Incorporating low‐cycle fatigue model into duration‐dependent inelastic design spectra

Seismic performance of structures is related to the damage inflicted on the structure by the earthquake, which means that formulation of performance‐based design is inherently coupled with damage assessment of the structure. Although the potential for cumulative damage during a long‐duration earthquake is generally recognized, most design codes do not explicitly take into account the damage potential of such events. In this paper, the classical low‐cycle fatigue model commonly used for seismic damage assessment is cast in a framework suitable for incorporating cumulative damage into seismic design. The model, in conjunction with a seismic input energy spectrum, may be used to establish an energy‐based seismic design. In order to ensure satisfactory performance in a structure, the cyclic plastic strain energy capacity of the structure is designed to be larger than or equal to the portion of seismic input energy contributing to cumulative damage. The resulting design spectrum, which depends on the duration of the ground motion, indicates that the lateral strength of the structure must be increased in order to compensate for the increased damage due to an increased number of inelastic cycles that occur in a long‐duration ground motion. Examples of duration‐dependent inelastic design spectra are developed using parameters currently available for the low‐cycle fatigue model. The resulting spectra are also compared with spectra developed using a different cumulative damage model. Copyright © 2004 John Wiley & Sons, Ltd.