基于纤维模型的空间网架支承体系的优化设计与分析

近年来,民用航空制造业的快速发展给大柱距空间网架结构带来新的契机。本文针对某大柱距厂房设计了无柱间支撑、柱间钢支撑和柱间消能支撑3种抗侧力结构体系。在此基础上,分别建立了3种结构体系的三维整体有限元模型,通过优化设计确立了钢支撑和消能支撑的具体设计参数,并进行了多遇地震作用下的弹性时程对比分析。最后,建立了结构弹塑性分析的纤维模型,对3种结构体系进行了罕遇地震作用下的弹塑性时程分析,对比研究了3种结构体系在大震作用下的倒塌机制。结果表明：采用纤维模型能够较为精确地进行结构的弹塑性时程分析;相较于不加柱间支撑结构体系,柱间钢支撑和柱间消能支撑结构体系在多遇地震作用下的结构层间位移分别衰减约32%和64%,在罕遇地震作用下的结构层间位移分别衰减约12%和46%,且均具有更好的倒塌机制。本文可供大柱距空间结构的设计与分析参考和借鉴。     

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

A composite shear wall concept based on concrete filled steel tube （CFST） columns and steel plate （SP） deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements： CFST columns; SP deep beams; and reinforced concrete （RC） strips. The RC strips are intended to allow the core structural elements - the CFST columns and SP deep beams - to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.     

非一致地震波动输入下大型钢筋混凝土框架结构-地基体系地震响应规律

为探索非一致地震波动输入对大型钢筋混凝土框架结构地震响应的影响,基于OpenSees软件平台建立二维钢筋混凝土框架结构\|地基动力相互作用有限元模型。将El-Centro地震波按P波波形分别以0°、15°、30°和35°角入射该有限元模型进行计算,对比分析框架柱内力和楼层层间位移的地震响应。研究发现非一致地震波输入方法对于大型钢筋混凝土框架结构建筑动力响应影响明显,随着地震波入射角的增大,钢筋混凝土框架结构底层柱的轴力幅值减小,剪力幅值增大,而弯矩幅值变化较小,楼层层间位移幅值也随之增大。研究结果对于大型钢筋混凝土框架结构抗震设计具有参考意义。     

Probabilistic seismic performance evaluation of SMA-braced steel frames considering SMA brace failure

This study explores seismic performance of steel frame buildings with SMA-based self-centering bracing systems using a probabilistic approach. The self-centering bracing system described in this study relies on superelastic response of large-diameter cables. The bracing systems is designed such that the SMA cables are always stressed in tension. A four-story steel frame building characterized until collapse in previous research is selected as a case-study building. The selected steel frame building is designed with SMA bracing systems considering various design parameters for SMA braces. Numerical models of these buildings are developed by taking into account the ultimate state of structural components and SMA braces as well as the effect of gravity frames on lateral load resistance. Nonlinear static analyses are conducted to assess the seismic characteristics of each frame and to examine the effect of SMA brace failure on the seismic load carrying capacity of SMA-braced frames. Incremental dynamic analyses (IDA) are performed to compute seismic response of the designed frames at various seismic intensity levels. The results of IDA are used to develop probabilistic seismic demand models for peak inter-story and residual inter-story drifts. Seismic demand hazard curves of peak and residual inter-story drifts are generated by convolving the ground motion hazard with the probabilistic seismic demand models. Results show that steel frames designed with SMA bracing systems provide considerably lower probability of reaching at a damage state level associated with residual drifts compared to a similarly designed steel moment resisting frame, especially for seismic events with high return periods. This indicates reduced risks for the demolition and collapse due to excessive residual drifts for SMA braced steel frames.     

Shake-table testing of a self-centering precast reinforced concrete frame with shear walls

The seismic performance of a self-centering precast reinforced concrete (RC) frame with shear walls was investigated in this paper. The lateral force resistance was provided by self-centering precast RC shear walls (SPCW), which utilize a combination of unbonded prestressed post-tensioned (PT) tendons and mild steel reinforcing bars for flexural resistance across base joints. The structures concentrated deformations at the bottom joints and the unbonded PT tendons provided the self-centering restoring force. A 1/3-scale model of a five-story self-centering RC frame with shear walls was designed and tested on a shake-table under a series of bi-directional earthquake excitations with increasing intensity. The acceleration response, roof displacement, inter-story drifts, residual drifts, shear force ratios, hysteresis curves, and local behaviour of the test specimen were analysed and evaluated. The results demonstrated that seismic performance of the test specimen was satisfactory in the plane of the shear wall; however, the structure sustained inter-story drift levels up to 2.45%. Negligible residual drifts were recorded after all applied earthquake excitations. Based on the shake-table test results, it is feasible to apply and popularize a self-centering precast RC frame with shear walls as a structural system in seismic regions.     

黏滞阻尼器用于层间位移角超限的既有建筑的优化研究

在水平地震作用下,结构产生较大的层间变形或者结构底部地震剪力较大导致了很多建筑发生破坏.对于既有建筑,可采用安装黏滞阻尼器的加固方法减小其层间位移角,而结构层间位移角和基底剪力等均受阻尼器的位置与参数影响.因此,阻尼器的位置及参数优化的研究有重要意义.对于层间位移角超过现行规范限值的既有建筑结构,文中综合考虑结构变形与...     

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.     

Consistent DOF reduction of tall steel frames

This paper presents an energy‐consistent approach for reducing the number of degrees‐of‐freedom (DOFs) in tall steel frames. In the present approach, the moment resistance of beams and columns in each story is represented by the moment resistance of a rotational spring and a beam‐column element, respectively. The shear resistance provided by braces in each story is represented by the shear resistance of a shear spring. Furthermore, the resistance to the overturning moment provided by axial resistance of columns in each story is represented by the moment resistance of a rotational spring. These representations are carried out by achieving the equivalence between the strain energy stored and dissipated in the elements in the full (unreduced) DOF models and the strain energy stored and dissipated in the corresponding elements in the reduced DOF models. The accuracy of the present approach is demonstrated through numerical examples, which compare the results of nonlinear time history analyses obtained using the full and reduced DOF models. In the numerical examples, the response is estimated for 20‐story and 40‐story steel frames with and without buckling‐restraint braces subjected to a suite of near‐fault and far‐fault ground motions. The present approach is useful in estimating the response of tall steel frames having non‐regular member arrangements to a suite of intense ground motions including near‐fault ones, where it is crucial to capture the influence of higher mode effects on collapse mechanisms. Copyright © 2017 John Wiley & Sons, Ltd.     

Shake table testing and numerical simulation of a self‐centering energy dissipative braced frame

The self‐centering energy dissipative (SCED) brace is a new steel bracing member that provides both damping to the structure and a re‐centering capability. The goal of this study was to confirm the behavior of SCED braces within complete structural systems and to confirm the ability to model these systems with both a state‐of‐the‐art computer model as well as a simplified model that would be useful to practicing engineers. To these ends, a three‐story SCED‐braced frame was designed and constructed for testing on a shake table. Two concurrent computer models of the entire frame were constructed: one using the opensees nonlinear dynamic modeling software, and a simplified model using the commercial structural analysis software sap2000 . The frame specimen was subjected to 12 significant earthquakes without any adjustment or modification between the tests. The SCED braces prevented residual drifts in the frame, as designed, and did not show any significant degradation due to wear. Both numerical models were able to predict the drifts, story shears, and column forces well. Peak story accelerations were overestimated in the models; this effect was found to be caused by the absence of transitions at stiffness changes in the hysteretic model of the braces. Copyright © 2013 John Wiley & Sons, Ltd.     

Seismic performance of modular steel frames equipped with shape memory alloy braces

The demand for modular steel buildings (MSBs) has increased because of the improved quality, fast on-site installation, and lower cost of construction. Steel braced frames are usually utilized to form the lateral load resisting system of MSBs. During earthquakes, the seismic energy is dissipated through yielding of the components of the braced frames, which results in residual drifts. Excessive residual drifts complicate the repair of damaged structures or render them irreparable. Researchers have investigated the use of superelastic shape memory alloys (SMAs) in steel structures to reduce the seismic residual deformations. This study explores the potential of using SMA braces to improve the seismic performance of typical modular steel braced frames. The study utilizes incremental dynamic analysis to judge on the benefits of using such a system. It is observed that utilizing superelastic SMA braces at strategic locations can significantly reduce the inter-storey residual drifts.     

Cyclic tests on a hybrid coupled wall utilizing a rocking mechanism

A new type of hybrid coupled wall system, consisting of rolled steel coupling beams, reinforced concrete (RC) wall piers, and concrete‐filled tube (CFT) short columns, is introduced. In this new system, the bases of the wall piers are connected to the base beams only through CFT short columns, unlike conventional coupled walls. Yield occurs in the coupling beams and the short columns; hence, in the RC wall piers, only minimum cracking appears. A total of four subassembly specimens, designed to fail in various collapse mechanisms, were cyclically loaded under constant axial force. A benchmark specimen showed ductile behavior with large energy dissipation until fracture occurred in the coupling beam. In the specimen designed to fail in shear in its CFT, substantial axial shortening was observed, but the overall behavior was ductile. Behavior of specimens with small amounts of section steel in the wall panel fringe, or with thin wall panels, also showed ductile behavior, but the strength and energy dissipation were significantly smaller than other two specimens. An analytical model was proposed for a frame analysis program using fiber elements to simulate elastic–plastic behavior of the system. Design methods to prevent shear failure of CFT and RC panels are suggested using the analytical and test results. Copyright © 2008 John Wiley & Sons, Ltd.     

碳纤维布增强混凝土框架抗震性能的有限元分析

利用碳纤维布（CFS）对一个9层钢筋混凝土框架的底层柱进行了加固,运用有限元程序对加固前后结构的整体抗震性能进行了动力分析.分析结果表明,利用碳纤维布加固底部框架柱有助于提高框架的整体抗震性能,从而减少框架在地震作用下的最大侧移和各层间位移.     

Cyclic Displacement Model for Reinforced Concrete Columns

Reinforced concrete (RC) structures in low to moderate seismic regions and many older RC structures in high seismic regions include columns with steel reinforcement details not meeting the requirements of modern seismic design codes. These columns typically fail in shear or in a brittle manner and their behavior must be accurately captured when RC structures are modeled and analyzed. The total lateral displacement of a low ductility or shear critical RC column can be represented as the sum of three displacement components: (1) flexural displacement, (2) displacement due to slippage of the reinforcing bars at column ends, and (3) shear displacement. In this study, these three displacement components are separately modeled and then combined together following a proposed procedure based on the expected overall behavior of the column and its failure mechanism. A simplified slip model is proposed. The main objective of this research is to develop an easy-to-apply method to model and capture the cyclic behavior of RC columns considering the shear failure mechanism. The proposed model is validated using the available data from RC column and frame experiments.     

Shaking table tests on reinforced concrete frames without and with passive control systems

An extensive experimental program of shaking table tests on reduced‐scale structural models was carried out within the activities of the MANSIDE project, for the development of new seismic isolation and energy dissipation devices based on shape memory alloys (SMAs). The aim of the experimental program was to compare the behaviour of structures endowed with innovative SMA‐based devices to the behaviour of conventional structures and of structures endowed with currently used passive control systems. This paper presents a comprehensive overview of the main results of the shaking table tests carried out on the models with and without special braces. Two different types of energy dissipating and re‐centring braces have been considered to enhance the seismic performances of the tested model. They are based on the hysteretic properties of steel elements and on the superelastic properties of SMAs, respectively. The addition of passive control braces in the reinforced concrete frame resulted in significant benefits on the overall seismic behaviour. The seismic intensity producing structural collapse was considerably raised, interstorey drifts and shear forces in columns were drastically reduced. Copyright © 2005 John Wiley & Sons, Ltd.     

Analytical investigations of seismic responses for reinforced concrete bridge columns subjected to strong near-fault ground motion

Strong near-fault ground motion, usually caused by the fault-rupture and characterized by a pulse-like velocity- wave form, often causes dramatic instantaneous seismic energy (Jadhav and Jangid 2006). Some reinforced concrete (RC) bridge columns, even those built according to ductile design principles, were damaged in the 1999 Chi-Chi earthquake. Thus, it is very important to evaluate the seismic response of a RC bridge column to improve its seismic design and prevent future damage. Nonlinear time history analysis using step-by-step integration is capable of tracing the dynamic response of a structure during the entire vibration period and is able to accommodate the pulsing wave form. However, the accuracy of the numerical results is very sensitive to the modeling of the nonlinear load-deformation relationship of the structural member. FEMA 273 and ATC-40 provide the modeling parameters for structural nonlinear analyses of RC beams and RC columns. They use three parameters to define the plastic rotation angles and a residual strength ratio to describe the nonlinear load- deformation relationship of an RC member. Structural nonlinear analyses are performed based on these parameters. This method provides a convenient way to obtain the nonlinear seismic responses of RC structures. However, the accuracy of the numerical solutions might be further improved. For this purpose, results from a previous study on modeling of the static pushover analyses for RC bridge columns (Sung et al. 2005) is adopted for the nonlinear time history analysis presented herein to evaluate the structural responses excited by a near-fault ground motion. To ensure the reliability of this approach, the numerical results were compared to experimental results. The results confirm that the proposed approach is valid.     

Seismic retrofitting of reinforced concrete frame structures using GFRP-tube-confined-concrete composite braces

This paper presents a new type of structural bracing intended for seismic retrofitting use in framed structures. This special composite brace,termed glass-fiber-reinforced-polymer(GFRP)-tube-confined-concrete composite brace,is comprised of concrete confined by a GFRP tube and an inner steel core for energy dissipation.Together with a contribution from the GFRP-tube confined concrete,the composite brace shows a substantially increased stiffness to control story drift, which is often a preferred feature in seismic retrofitting.An analysis model is established and implemented in a general finite element analysis program-OpenSees,for simulating the load-displacement behavior of the composite brace.Using this model,a parametric study of the hysteretic behavior(energy dissipation,stiffness,ductility and strength)of the composite brace was conducted under static cyclic loading and it was found that the area ratio of steel core to concrete has the greatest influence among all the parameters considered.To demonstrate the application of the composite brace in seismic retrofitting, a three-story nonductile reinforced concrete(RC)frame structure was retrofitted with the composite braces.Pushover analysis and nonlinear time-history analyses of the retrofitted RC frame structure was performed by employing a suite of 20 strong ground motion earthquake records.The analysis results show that the composite braces can effectively reduce the peak seismic responses of the RC frame structure without significantly increasing the base shear demand.     

圆钢管混凝土边框剪力墙抗震性能试验研究

圆钢管混凝土边框剪力墙是在普通混凝土剪力墙基础上研发的一种新型组合剪力墙。其将圆钢管混凝土柱和普通混凝土剪力墙进行了优势组合,形成多道抗震防线。为了解该组合剪力墙的抗震性能,进行了3个1/5缩尺试件的低周反复荷载试验,其中包括1个圆钢管混凝土柱框架结构、1个普通混凝土剪力墙和1个圆钢管混凝土边框剪力墙。在试验研究基础上,分析了圆钢管混凝土边框剪力墙的承载力、刚度及其退化过程、延性、滞回特性、耗能能力及破坏特征。研究表明:圆钢管混凝土边框剪力墙的抗震性能比普通混凝土剪力墙显著提高,且其承载力、抗震耗能能力均高于圆钢管混凝土柱框架和普通混凝土剪力墙承载力、抗震耗能能力之和,可用于高层和超高层建筑的抗震设计。     

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.     

Experimental and numerical studies on buckling restrained braces with posttensioned carbon fiber composite cables

There has been an increasing interest in using residual deformation as a seismic performance indicator for earthquake resistant building design. Self-centering braced structural systems are viable candidates for minimizing residual deformations following a major earthquake. Hence, this study proposes an alternative type of buckling restrained brace (BRB) with externally attached posttensioned (PT-BRB) carbon fiber composite cables (CFCCs). The steel core of the brace is used as an energy dissipator, whereas the CFCCs provide the self-centering force for minimizing residual story drifts. Three proof-of-concept specimens are designed, fabricated, and cyclically tested at different posttensioning force levels. The CFCC behavior to obtain cyclic response, including the anchorage system, is examined closely. A parametric study is also conducted to show the effect of the different configurations of PT-BRBs on the inelastic response. Furthermore, optimal brace parameters are discussed to realize design recommendations. The results indicated that the implementation of partially self-centering BRBs in building frames can lead to the target residual displacements. A stable behavior is obtained for the proposed PT-BRBs when subjected to the loading protocol specified in the American Institute of Steel Construction (AISC) 2016 Seismic Provisions.     

Seismic behavior of outrigger truss-wall shear connections using multiple steel angles

An experimental investigation on the seismic behavior of a type of outrigger truss-reinforced concrete wall shear connection using multiple steel angles is presented. Six large-scale shear connection models, which involved a portion of reinforced concrete wall and a shear tab welded onto a steel endplate with three steel angles, were constructed and tested under combined actions of cyclic axial load and eccentric shear. The effects of embedment lengths of steel angles, wall boundary elements, types of anchor plates, and thicknesses of endplates were investigated. The test results indicate that properly detailed connections exhibit desirable seismic behavior and fail due to the ductile fracture of steel angles. Wall boundary elements provide beneficial confinement to the concrete surrounding steel angles and thus increase the strength and stiffness of connections. Connections using whole anchor plates are prone to suffer concrete pry-out failure while connections with thin endplates have a relatively low strength and fail due to large inelastic deformations of the endplates. The current design equations proposed by Chinese Standard 04G362 and Code GB50011 significantly underestimate the capacities of the connection models. A revised design method to account for the influence of previously mentioned test parameters was developed.