Tensile strength equation for HSS bracing members having slotted end connections

In the previous study, the authors investigated the effect of w/t ratios on the behaviour of bracing members under symmetric cyclic loading in compression and tension. In this study, 11 bracing members with slotted end sections made of cold‐formed square hollow structural sections (HSS) were tested. The w/t ratios ranged from 8 to 28. Unlike the test results of other former studies obtained under compression‐oriented cyclic loading, the results of this study showed that bracing members having a smaller w/t ratio (<14) had less deformation and less energy dissipation capacity, and a shorter fracture life compared with other specimens. Such inferior behaviour resulted from early fracture at the slotted end section. This study compares tensile strength obtained from the design equations in the AISC LRFD manual and Eurocode 3 using the actual strengths of the tested specimens. This study found that for preventing early fracture in HSS bracing members, design fracture strength should be larger than design yield strength. Design strength equations are proposed for bracing members in special concentrically braced frames (SCBF). The proposed design equations are verified by experimental tests conducted under symmetric cyclic loading in tension and compression using two HSS bracing members designed according to the proposed equation. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Evaluation of performance of non‐invasive upgrade strategy for beam–column sub‐assemblages of poorly designed structures under seismic type loading

Beam–column sub‐assemblages are the one of the most vulnerable structural elements to the seismic loading and may lead to devastating consequences. In order to improve the performance of the poorly/under‐designed building structures to the critical loading scenarios, introduction of steel bracing at the RC beam–column joint is found to be one of the modern and implementable techniques. In the present work, a diagonal metallic single haunch/bracing system is introduced at the beam–column joints to provide an alternate load path and to protect the joint zone from extensive damage because of brittle shear failure. In this paper, an investigation is reported on the evaluation of tae influence of different parameters, such as angle of inclination, location of bracing and axial stiffness of the single steel bracing on improving the performance through altering the force transfer mechanism. Numerical investigations on the performance of the beam–column sub‐assemblages have been carried out under cyclic loading using non‐linear finite element analysis. Experimentally validated numerical models (both GLD and upgraded specimen) have been further used for evaluating the performance of various upgrade schemes. Cyclic behaviour of reinforcement, concrete modelling based on fracture energy, bond‐slip relations between concrete and steel reinforcement have been incorporated. The study also includes the numerical investigation of crack and failure patterns, ultimate load carrying capacity, load displacement hysteresis, energy dissipation and ductility. The findings of the present study would be helpful to the engineers to develop suitable, feasible and efficient upgrade schemes for poorly designed structures under seismic loading. Copyright © 2016 John Wiley & Sons, Ltd.     

Seismic response of steel structures with seesaw systems using viscoelastic dampers

Vibration control systems are being used increasingly worldwide to provide enhanced seismic protection for new and retrofitted buildings. This paper presents a new vibration control system on the basis of a seesaw mechanism with viscoelastic dampers. The proposed vibration control system comprises three parts: brace, seesaw member, and viscoelastic dampers. In this system, only tensile force appears in bracing members. Consequently, the brace buckling problem is negligible, which enables the use of steel rods for bracing members. By introducing pre‐tension in rods, long steel rods are applicable as bracing between the seesaw members and the moment frame connections over some stories. Seesaw mechanisms can magnify the damper deformation according to the damper system configuration. In this paper, first, the magnification factor, that is, the ratio of the damper deformation to the story drift, is delivered, which includes the rod deformation. Results of a case study demonstrate that the magnification factor of the proposed system is greater than unity for some cases. Seismic response analysis is conducted for steel moment frames with the proposed vibration control system. Energy dissipation characteristics are examined using the time‐history response results of energy. The maximum story drift angle distributions and time‐history response results of displacement show that the proposed system can reduce the seismic response of the frames effectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Active control of building seismic response by energy dissipation

Active energy dissipation is proved to be very effective for abating seismic effects on buildings. The implementation of this concept in seismic design of buildings is studied by response simulations of a single storey building subjected to earthquake motion. Active energy dissipaters can be installed as part of the building lateral load bracing, and they regulate the strength and stiffness of the bracing during the building's response to the seismic events. The energy is dissipated when the bracing load exceeds the axial strength provided by the dissipater, and the bracing telescopes in and out. The design parameters of active energy dissipaters are described using the simulated response of a single storey building to ground pulse and harmonic ground excitation. The feasibility of the energy dissipater is demonstrated by the development and construction of a full-scale prototype device called an Active Slip Bracing Device (ASBD). The device utilizes Coulomb friction. The active characteristics are implemented by a computer controlled clamping mechanism on the friction interface. The ASBD's control of the strength and stiffness is investigated.     

Steel frames with bracing mechanism and hysteretic dampers

A new earthquake resistant structural system for multi‐storey frame structures, based on a dual function of its bracing components, is developed. This consists of a hysteretic damper device and a cross‐bracing mechanism with a kinetic closed circuit, working only in tension, so that cable members can be used for this purpose. Solutions are presented regarding the connections' design of three types of structural frame system, that are concerned throughout the study: braced moment free frame, braced moment resisting frame with moment free supports, and with moment resisting supports. The dynamic behaviour of the system is investigated on the basis of an SDOF model, and based on the response spectra method an approximate design approach of the controlled structures is shown. From the time history analysis of the structural systems for the El Centro earthquake the areas of appropriate stiffness relations of the frames to the hysteretic dampers and the cable braces are deduced, so that the energy dissipation of the system may be controlled by the damper‐cable bracing mechanism. Based on the results of these studies, a predesign approach is developed for the implementation of the control system in frame structures. Copyright © 2003 John Wiley & Sons, Ltd.     

格构式输电铁塔组成杆件对极限承载力影响的研究

对输电铁塔中数量较多、构造复杂的交叉斜材体系利用大型通用有限元程序ANSYS建立了有限元模型，并对其极限承载能力以及承载力的影响因素进行了全面的非线性分析。结果表明主材、斜材和附材对交叉斜材体系极限承载能力的影响程度各不相同，其中斜材影响最大。根据分析结果，针对沈阳地区某输电塔结构提出了加固改造方案，并给出了加固后输电铁塔抵抗静力推覆作用和抗震能力的提高程度。     

循环荷载特征对焊接工字形钢支撑低周疲劳性能的影响

通过14根铰支焊接工字形支撑在不同特征的循环轴向位移荷载下的低周疲劳试验，研究了循环轴向位移荷载的位移幅值、平均位移幅值及加载次序等因素对钢支撑低周疲劳及耗能性能的影响。研究发现，对称循环荷载中幅值越小，支撑翼缘局部屈曲发展越晚，其耗能及承载力退化也越平缓。文中提出了支撑在幅值6δ≤Δδ≤12δy的对称循环荷载下的疲劳寿命经验公式。试验表明，循环荷载的位移幅值是支撑疲劳损伤及耗能退化的最主要影响因素，过载峰效应及适当的平均压位移幅值改善了钢支撑低周疲劳及耗能性能。     

Dynamic behaviour of CLASP-type buildings

This paper deals with the dynamic behaviour of pin-jointed, steel-framed buildings which derive stiffness from bracing and cladding, and their response to earthquake loading. The first part of the paper considers the best way to obtain an analytical model, using the natural frequencies and mode-shapes measured on a CLASP building in Nottingham employing eccentric-mass vibrators. The second part is a study of a key section of a CLASP hospital now under construction in Algeria, in which the earthquake-induced forces in the bracing are calculated. The final part is concerned with studies on two-storey and three-storey CLASP-type models, using different bracing arrangements.     

CONTROL OF BUILDING VIBRATIONS WITH ACTIVE/PASSIVE DEVICES

Two linear optimal control laws and a non-linear control strategy are critically evaluated. They are implemented in a ten-story frame structure. For the linear control laws, both an active bracing system and a hybrid mass damper are considered as control devices, while the non-linear control law can be implemented with either an active or semi-active bracing system. The active and semi-active systems are compared to a passive bracing system with linear viscous dampers and to a hybrid system consisting of a passive bracing and a hybrid mass damper. Dimensionless indices based on the reduction of the maximum story drift and on the maximum control force required are introduced to compare the efficiencies of different control strategies. While the linear optimal control laws exhibit an excellent performance, the non-linear control law, in addition to its simplicity and robustness, appears to be more efficient when the allowable control force is within a certain limit. Furthermore, one attractive feature of the latter is that it can be implemented with semi-active devices to minimize the power requirement.     

Seismic behaviour of hybrid systems made of PR composite frames coupled with dissipative bracings

The paper investigates the dynamic behaviour of hybrid systems made of partially restrained (PR) steel–concrete composite frames coupled with viscoelastic dissipative bracings. A numerical model that accounts for both the resisting mechanisms of the joint and the viscoelastic contribution of the dissipative bracing is introduced and briefly discussed. The model is first validated against experimental outcomes obtained on a one‐storey two‐bay composite frame with partial strength semi‐rigid joints subjected to free vibrations. A number of time‐history analyses under different earthquake ground motions and peak ground accelerations are then carried out on the same type of frame. The purpose is to investigate the influence of the type of beam‐to‐column connection and property of the viscoelastic bracing on the performance of the hybrid system. The inherent stiffness of the bare PR frame and the plastic hysteresis of the beam‐to‐column joints, which always lead to only limited damage in the joint, are found to provide a significant contribution to the overall structural performance even under destructive earthquakes. This remark leads to the conclusion that the viscoelastic bracing can be effectively used within the hybrid system. Copyright © 2008 John Wiley & Sons, Ltd.     

On‐line hybrid test method for evaluating the performance of structural details to failure

A test environment to evaluate the seismic performance of gusset plate connections intended for steel braced frames is proposed. The developed test method combines the substructuring techniques with finite element analysis methods in an on‐line hybrid scheme. Numerical substructure analysis is conducted on bracing members, while bracing connections are treated as experimental substructures. A force‐displacement combined control imposed with the aid of 2 jacks ensures physical continuity between the analysis and test. The rotational behavior of gusset plate connections subjected to large inelasticity and varying axial loading until fracture is investigated. Two gusset plate details were designed and tested to verify the efficiency of the proposed method. The test method is rational, and smooth operation is achieved. The test results revealed the advantage of the developed on‐line hybrid test method in exploring the ultimate capacity of bracing connections.     

Passive and active control of three‐dimensional buildings

The majority of the recent research effort on structural control considers two‐dimensional plane structures. However, not all buildings can be modelled as plane structures, thus limiting the capability of the proposed procedures only to regular and symmetrical structures. A new procedure is developed in this paper to analyse three‐dimensional buildings utilizing passive and active control devices. In the building model, the floors are assumed rigid in their own plane resulting in three degrees of freedom at each floor. Two types of active control devices utilizing an active tuned mass damper and an active bracing system are considered. The effect of passive mass dampers and active control force in the equations of motion is incorporated by using the Hamilton's principle. The passive parameters of the dampers as well as the controller gain is then optimized using a genetic based optimizer where the H₂, H_∞ and L₁ norms are taken as the objective functions. Copyright © 2000 John Wiley & Sons, Ltd.     

一种改进的斜支撑体系支护某超大深基坑的变形分析

济南某商业广场超过50000 m^2的基坑采用一种改进的斜支撑支护体系进行支护,与普通斜支撑支护型式不同,该支护体系包括支护桩、斜撑、立柱与支撑桩。本文采用FLAC^3D显式有限差分数值计算分析方法,并结合支护桩水平位移测斜数据,对该支护体系的变形特性进行分析研究,从中论证各支护单元在3个开挖阶段的运动学效应。研究结果表明,该斜支撑支护体系可以把各支护单元以及它们之间的土体充分调动起来,相互之间积极协调,以抵挡基坑开挖带来的土压力,从而减小基坑周围土体位移,保障周围道路、地下设施及周边建筑的正常运行。     

Cyclic behavior and failure mechanism of self‐centering energy dissipation braces with pre‐pressed combination disc springs

A new type of bracing system composed of friction energy dissipation devices for energy dissipation, pre‐pressed combination disc springs for self‐centering and tube members as guiding elements is developed and experimentally studied in this paper. The mechanics of this system are explained, the equations governing its hysteretic responses are outlined and large‐scale validation tests of two braces with different types of disc springs are conducted under the condition of low cyclic reversed loading. The experimental results demonstrate that the proposed bracing system exhibits a stable and repeatable flag‐shaped hysteretic response with an excellent self‐centering capability and effective energy dissipation throughout the loading protocol. Furthermore, the maximum bearing force and stiffness are predicted well by the equations governing its mechanical behavior. Fatigue and destructive test results demonstrate that the proposed bracing system can maintain stable energy dissipation and self‐centering capabilities under large deformation cyclic loading even when the tube members exceed the elastic limit and that a larger bearing capacity is achieved by the system that has disc springs without a bearing surface. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance evaluation of retrofitting strategies for non-seismically designed RC buildings using steel braces

Recent major earthquakes around the world have evidenced that research in earthquake engineering must be directed to the vulnerability assessment of existing constructions lacking appropriate seismic resisting characteristics. Their retrofit or replacement should be made in order to reduce vulnerability, and consequent risk, to currently accepted levels. In this work, the efficiency of ductile steel eccentrically-braced systems in the seismic retrofitting of existing reinforced concrete (RC) buildings is studied. The retrofit technique studied consists in a bracing system with an energy dissipation device, designed to dissipate energy by shear deformation. The numerical model was calibrated with cyclic test results on a full-scale structure. The models used for the RC frame and masonry represent their real behavior and influence in the global structural response. The steel bracing system was modeled with strut rigid elements. The model for the energy dissipater device reproduces rigorously the behavior of the shear-link observed in the cyclic tests, namely in terms of shear, drift and energy dissipation. With the calibrated numerical model, a series of non-linear dynamic analyses were performed, for different earthquake input motions, intending to study: the influence of the retrofitting system in the response of bare and infilled structures; the influence of the location and strength of the retrofitting system.     

Design of dampers for structures based on optimal control theory

The aim of this paper was to propose a design guideline for using visco‐elastic dampers for the control of building structures subjected to earthquake loading as well as suspension roof structures subjected to wind loading. The active control algorithm was used to calculate the control forces. Based on the single‐mode approach the control forces were transformed to the forces which visco‐elastic dampers can provide. Application of the method to the design of the building structure with passive damping devices in the bracing system and to the suspension roof with dampers was studied. Through the application of optimal control theory a systematic design procedure to implement dampers in structures is proposed. Copyright © 2000 John Wiley & Sons, Ltd.     

Mechanical compression release device in steel bracing system for retrofitting RC frames

1 Introduction Braced steel frames are commonly used to resist seismic loads. Their seismic behavior was extensively studied during the past decades (Bertero et al.., 1989; Roeder, 1989; Jain, 1978). Their design is governed by the buckling behavior of the bracing members (ASCE, 1994,2002; CSA, 1994). To prevent or delay the seismic buckling of compressive members in concentrically braced frames in steel structures, a great number of methods have been proposed. These include the use of sp…     

建筑结构的屈曲约束支撑对其抗震加固性能的影响

当前方法采用伸臂桁架加固建筑结构时,未考虑建筑结构的屈曲约束支撑力的影响,伸臂桁架与建筑结构的连接不牢固,导致其对建筑结构的抗震加固性能较差。故此,深入分析建筑结构的屈曲约束支撑对其抗震加固性能的影响,设计建筑结构抗震加固方案,利用高强螺栓节点经由连接钢板实现屈曲约束支撑与建筑结构的铰接固定。分别从支撑变形同建筑结构层间位移的关系、建筑结构支撑承载力、多遇地震影响下屈曲约束支撑框架的位移验算,以及罕遇地震影响下屈曲约束支撑的弹塑性位移验算方面,分析屈曲约束支撑对建筑结构抗震加固性能影响。经实验分析得出,建筑结构加入屈曲约束支撑后第一扭转周期同第一平动周期的比值降低0.14,X、Y两个方向的砌体墙同建筑结构的刚度比值降低6.9、8.0,最大顶点位移值降低15.4 mm、29.3 mm,抗震加固性能大大提高。     

Performance-based assessment of an innovative braced tube system for tall buildings

In this paper, an innovative seismic lateral force resisting system for tall buildings is introduced. In this system, a novel supplemental part, ribbed bracing system (RBSyst), is attached to Braced Tube System, creating a modified BTS. RBSyst is a supplemental part which is attached to the conventional bracing members to eliminate buckling problem. The behavior of RBSyst under tensile force is similar to that of the conventional braces. However, in compression, it prevents the braces from buckling by length reduction. In order to evaluate the efficiency of this new BTS system by performance-based assessment, two typical 40-story tall buildings with different story modules equipped with this proposed bracing system are modeled numerically. Then, the seismic behavior of these 3-dimensional models are evaluated by nonlinear time history analysis under maximum considered earthquakes and service-level earthquakes. The results of the analysis demonstrate that the performance of the tall buildings equipped with this new BTS system is within the acceptable limits under both service-level and maximum considered earthquake ground motions. Additionally, it is shown that RBSyst part can effectively enhance the seismic behavior of BTS systems.