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1.
The present paper investigates the seismic reliability of the application of buckling restrained braces (BRBs) for seismic retrofitting of steel moment resisting framed buildings through fragility analysis. Samples of regular three‐storey and eight‐storey steel moment resisting frames were designed with lateral stiffness insufficient to comply with the code drift limitations imposed for steel moment resisting frame systems in earthquake‐prone regions. The frames were then retrofitted with concentrically chevron conventional braces and BRBs. To obtain robust estimators of the seismic reliability, a database including a wide range of natural earthquake ground motion records with markedly different characteristics was used in the fragility analysis. Nonlinear time history analyses were utilized to analyze the structures subjected to these earthquake records. The improvement of seismic reliability achieved through the use of conventional braces and BRBs was evaluated by comparing the fragility curves of the three‐storey and eight‐storey model frames before and after retrofits, considering the probabilities of four distinct damage states. Moreover, the feasibility of mitigating the seismic response of moment resisting steel structures by using conventional braces and BRBs was determined through seismic risk analysis. The results obtained indicate that both conventional braces and especially BRBs improve significantly the seismic behavior of the original building by increasing the median values of the structural fragility curves and reducing the probabilities of exceedance of each damage state. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

2.
This paper presents a simultaneous optimization procedure for both viscoelastic dampers (VEDs) and supporting braces installed in a structure. The effect of supporting braces on the control efficiency of VEDs is also investigated. To apply a general gradient‐based optimization algorithm, closed‐form expressions for the gradients of objective function and constraints are derived. Also, the constraint on the dynamic behavior of a structure is embedded in the gradient computation procedure to reduce the number of variables in the optimization. From numerical analysis of an example structure, it was found that when sufficient stiffness cannot be provided for the supporting braces, the flexibility of the brace should be taken into account in the design of the VED to achieve the desired performance of the structure. It was also observed that, as a result of the proposed optimization process, the size of the supporting brace could be reduced while the additional VED size (to compensate for the loss of the control effect) was insignificant. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

3.
Damage to buildings observed in recent earthquakes suggests that many old reinforced concrete structures may be vulnerable to the effects of severe earthquakes. One suitable seismic retrofit solution is the installation of steel braces to increase the strength and ductility of a building. Steel bracings have some compelling advantages such as their comparatively low weight, their suitability for prefabrication, and the possibility of openings for utilities, access, and light. The braces are typically connected to steel frames that are fixed to the concrete structure using post‐installed concrete anchors along the perimeter. However, these framed steel braces are not without some disadvantages such as heavier steel usage and greater difficulties during the installation. Therefore, braces without steel frames appear to be an attractive alternative. In this study, braces were connected to gussets furnished with anchor brackets, which were fixed by means of a few post‐installed concrete anchors. The clear structural system and the increased utilization of the anchors allowed the anchorage to be designed precisely and economically. The use of buckling‐restrained braces (BRBs) provides additional benefits in comparison with conventional braces. BRBs improve the energy dissipation efficiency and allow the limitation of the brace force to be taken up by the highly stressed anchorage. Cyclic loading tests were conducted to investigate the seismic performance of BRBs connected with post‐installed anchors used to retrofit reinforced concrete frames. The tests showed that the proposed design method is feasible and increases strength as well as ductility to an adequate seismic performance level. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

4.
The results of experimental tests carried out on reinforced concrete (RC) full‐scale 2‐storey 2‐bays framed buildings are presented. The unretrofitted frame was designed for gravity loads only and without seismic details; such frame was assumed as a benchmark system in this study. A similar RC frame was retrofitted with buckling‐restrained braces (BRBs). The earthquake structural performance of both prototypes was investigated experimentally using displacement‐controlled pushover static and cyclic lateral loads. Modal response properties of the prototypes were also determined before and after the occurrence of structural damage. The results of the dynamic response analyses were utilized to assess the existing design rules for the estimation of the elastic and inelastic period of vibrations. Similarly, the values of equivalent damping were compared with code‐base relationships. It was found that the existing formulations need major revisions when they are used to predict the structural response of as‐built RC framed buildings. The equivalent damping ratio ξeq was augmented by more than 50% when the BRBs was employed as bracing system. For the retrofitted frame, the overstrength Ω and the ductility µ are 1.6 and 4.1, respectively; the estimated R‐factor is 6.5. The use of BRBs is thus a viable means to enhance efficiently the lateral stiffness and strength, the energy absorption and dissipation capacity of the existing RC substandard frame buildings. The foundation systems and the existing members of the superstructure are generally not overstressed as the seismic demand imposed on them can be controlled by the axial stiffness and the yielding force of the BRBs. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

5.
This article examines the use of rocking steel braced frames for the retrofit of existing seismically deficient steel building structures. Rocking is also used to achieve superior seismic performance to reduce repair costs and disruption time after earthquakes. The study focuses on low‐rise buildings for which re‐centring is solely provided by gravity loads rather than added post‐tensioning elements. Friction energy dissipative (ED) devices are used to control drifts. The system is applied to 2‐storey and 3‐storey structures located in 2 seismically active regions of Canada. Firm ground and soft soil conditions are considered. The seismic performance of the retrofit scheme is evaluated using nonlinear dynamic analysis and ASCE 41‐13. For all structures, rocking permits to achieve immediate occupancy performance under 2% in 50 years seismic hazard if the braces and their connections at the building's top storeys are strengthened to resist amplified forces due to higher mode response. Base shears are also increased due to higher modes. Impact at column bases upon rocking induces magnified column forces and vertical response in the gravity system. Friction ED is found more effective for drift control than systems with ring springs or bars yielding in tension. Drifts are sufficiently small to achieve position retention performance for most nonstructural components. Horizontal accelerations are generally lower than predicted from ASCE 41 for regular nonrocking structures. Vertical accelerations in the gravity framing directly connected to the rocking frame are however higher than those predicted for ordinary structures. Vertical ground motions have limited effect on frame response.  相似文献   

6.
Multi‐storey main buildings constructed with a low‐rise podium structure possess some architectural merits but the setback features of such a building complex may lead to seismic response enlargement of the main buildings. This paper explores the possibility of using passive friction dampers to connect the podium structure to the main buildings to prevent their seismic response enlargement without violating the architectural features. A series of shaking table tests were carried out on one 3‐storey and one 12‐storey building models in fully‐separated, rigidly connected, and friction damper‐linked configurations. Four sets of seismic ground motions were selected as inputs to the shaking table. The control competence of two buildings linked with friction damper was evaluated by comparison of their responses with those from fully‐separated and rigidly connected cases. Experimental results showed that unfavourable seismic response amplification did occur in the building complex in the rigidly connected case. By contrast, friction damper showed effectiveness in reducing absolute acceleration and interstorey drift responses of both buildings if friction force level was appropriately applied. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

7.
The effectiveness of hysteretic passive devices to protect and mitigate the response of a structure under seismic loading is well established by both analytical and experimental research. Nevertheless, a systematic and well‐established methodology for the topological distribution and size of these devices in order to achieve a desired structural response performance does not exist. In this paper, a computational framework is proposed for the optimal distribution and design of yielding metallic buckling restrained braces (BRB) and/or friction dampers within steel moment‐resisting frames (MRF) for a given seismic environment. A Genetic Algorithm (GA) is used to solve the resulting discrete optimization problem. Specific examples involving two three‐story, four‐bay steel MRFs and a six‐story, three‐bay steel MRF retrofitted with yielding and/or friction braces are considered. The seismic environment consists of four synthetic ground motions representative of the west coast of the United States with 5% probability of exceedance in 50 years. Non‐linear time‐history analyses are employed to evaluate the potential designs. As a result of the evolutionary process, the optimal placement, strength and size of the dampers are obtained throughout the height of the steel MRF. Furthermore, the developed computational approach for seismic design based upon GAs provides an attractive procedure for design of MRFs with hysteretic passive dampers. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
Results from real‐time dynamic substructuring (RTDS) tests are compared with results from shake table tests performed on a two‐storey steel building structure model. At each storey, the structural system consists of a cantilevered steel column resisting lateral loads in bending. In two tests, a slender diagonal tension‐only steel bracing member was added at the first floor to obtain an unsymmetrical system with highly variable stiffness. Only the first‐storey structural components were included in the RTDS test program and a Rosenbrock‐W linearly implicit integration scheme was adopted for the numerical solution. The tests were performed under seismic ground motions exhibiting various amplitude levels and frequency contents to develop first and second mode‐dominated responses as well as elastic and inelastic responses. A chirp signal was also used. Coherent results were obtained between the shake table and the RTDS testing techniques, indicating that RTDS testing methods can be used to successfully reproduce both the linear and nonlinear seismic responses of ductile structural steel seismic force resisting systems. The time delay introduced by actuator‐control systems was also studied and a novel adaptive compensation scheme is proposed. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
Buildings are continually subject to dynamic loads, such as wind load, seismic ground motion, and even the load from internal utility machines. The recent trend of constructing more flexible high‐rise buildings underscores the importance of including viscoelastic dampers in building designs. Viscoelastic dampers are used to control the dynamic response of a building. If the seismic design is based only on the linear response spectrum, considerable error may occur when calculating the seismic response of a building; rubber viscoelastic dampers show non‐linear hysteretic damping that is quite different from viscous damping. This study generated a non‐linear response spectrum using a non‐linear oscillator model to simulate a building with viscoelastic dampers installed. The parameters used in the non‐linear damper model were obtained experimentally from dynamic loading tests. The results show that viscoelastic dampers effectively reduce the seismic displacement response of a structure, but transmit more seismic force to the structure, which essentially increases its seismic acceleration response. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

10.
This paper presents a 2-D numerical study on the nonlinear seismic response of buildings equipped with two types of energy dissipators, which dissipate energy activating two different mechanisms. Three types of reinforced concrete buildings with 3, 7 and 15 stories, respectively representative of short, medium and long period ranges, are considered. Dissipators are placed on steel diagonal braces at all the floors; their sliding threshold (or yielding) forces are taken as 100% of those generated by the equivalent static lateral forces recommended by EC8 for a ductile moment resisting frame. The input consists of six recorded earthquakes, 3 representatives of near-field earthquakes and 3 representatives of far-field earthquakes. Each input is considered once from the bedrock and once filtered by a common ground with several layers of different thicknesses. The responses of the buildings are discussed and compared emphasizing the filtering effects produced by the ground.  相似文献   

11.
Buckling is usually conceived as an unstable structural behavior leading to lateral instability of axially loaded members, if not properly supported. However, a pre‐bent strip would become an excellent seismic energy‐dissipative device if it is deformed in a guided direction and range. Geometrically large lateral deformation of the steel strips in buckling leads to inelastic behavior of the material and dissipates energy as a consequence. The purpose of this study is to propose a new type of seismic damper in the form of braces based on pre‐bent steel strips. The nonlinear elastic stiffness of monotonously loaded pre‐bent strips in both compression and tension is derived. The energy‐dissipative characteristics of the proposed damping device are investigated via component tests under cyclic loads. Experimental results indicate that the force–displacement relationship of pre‐bent strips in cyclic loads exhibits mechanical characteristics of displacement‐dependent dampers. A series of seismic performance tests has been conducted further to verify the feasibility and effectiveness of using the proposed device as seismic dampers. Encouraging test results have been obtained, suggesting feasibility of the proposed device for earthquake‐resistant design. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

12.
Performance analysis of the Pangu Plaza under earthquake and wind loads is described in this paper.The plaza is a 39-story steel high-rise building,191 m high,located in Beijing close to the 2008 Olympic main stadium.It has both fluid viscous dampers(FVDs) and buckling restrained braces or unbonded brace(BRB or UBB) installed.A repeated iteration procedure in its design and analysis was adopted for optimization.Results from the seismic response analysis in the horizontal and vertical directions show that th...  相似文献   

13.
A proper characterization of concrete strength is essential to correctly model existing RC structures, whose seismic performance is affected by the poor quality of materials. The purpose of this work is to evaluate the effect of incorrect assumptions for concrete strength and the adequacy of current Codes provisions (Eurocodes, FEMA). Even the effects of the non homogeneity of concrete strength within the building is considered due to its high variability; in fact, buildings can experience an irregular seismic response, both in plan and in elevation. In this work the effects of irregularity in plan due to the strength variability of concrete is analyzed on a case study, a four storey RC framed building, designed for vertical loads only. The variability of concrete strength has been evaluated using the data of an extensive investigation developed by REGIONE TOSCANA on a large sample of RC framed buildings.  相似文献   

14.
A methodology for the optimal design of supplemental viscous dampers for framed structures is presented. It addresses the problem of minimizing the added damping subject to a constraint on the maximal interstorey angular drift for an ensemble of realistic ground motion records while assuming linear behaviour of the damped structure. The solution is achieved by actually solving an equivalent optimization problem of minimizing the added damping subject to a constraint on a maximal weighted integral on the squared angular drift. The computational effort is appreciably reduced by first using one ‘active’ ground motion record. If the resulting optimal design fails to satisfy the constraints for other ground motions from the original ensemble, additional ground motions (loading conditions) are added one by one to the ‘active’ set until the optimum is reached. An efficient selecting process which is presented herein will usually require one or two records to attain an optimum design. Examples of optimal designs of supplemental dampers are presented for a 2‐storey shear frame and a 10‐storey industrial frame. The 2‐storey shear frame is required to withstand one given ground motion whereas the 10‐storey frame is required to withstand an ensemble of twenty ground motions. The resulting viscously damped structures have envelope values of interstorey drifts equal or less than the target drifts. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

15.
This paper evaluates the hysteretic behavior of an innovative compressed elastomer structural damper and its applicability to seismic‐resistant design of steel moment‐resisting frames (MRFs). The damper is constructed by precompressing a high‐damping elastomeric material into steel tubes. This innovative construction results in viscous‐like damping under small strains and friction‐like damping under large strains. A rate‐dependent hysteretic model for the compressed elastomer damper, formed from a parallel combination of a modified Bouc–Wen model and a non‐linear dashpot is presented. The model is calibrated using test data obtained under sinusoidal loading at different amplitudes and frequencies. This model is incorporated in the OpenSees [17] computer program for use in seismic response analyses of steel MRF buildings with compressed elastomer dampers. A simplified design procedure was used to design seven different systems of steel MRFs combined with compressed elastomer dampers in which the properties of the MRFs and dampers were varied. The combined systems are designed to achieve performance, which is similar to or better than the performance of conventional steel MRFs designed according to current seismic codes. Based on the results of nonlinear seismic response analyses, under both the design basis earthquake and the maximum considered earthquake, target properties for a new generation of compressed elastomer dampers are defined. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

16.
A displacement-based design procedure is proposed for proportioning hysteretic damped braces in order to attain, for the in-plan least seismic capacity direction and a specific level of seismic intensity, a designated performance level of a reinforced concrete (r.c.) irregular framed building to be retrofitted. To this end, a computer code for the nonlinear static analysis of spatial frames is developed to obtain the pushover curve for an assigned in-plan direction of the seismic loads. The town hall of Spilinga (Italy), a two-storey r.c. framed structure with an L-shaped plan built at the beginning of the 1960s, has been considered as case study. Four alternative structural solutions are examined, derived from the first one by the insertion of hysteretic damped braces, considering: the extended N2 and the extended pushover methods combined with a proportional and an inversely proportional in-plan stiffness distributions of hysteretic damped braces. To check the effectiveness and reliability of the design procedure, the nonlinear static response of the unbraced and damped braced frames is compared for different in-plan directions of the seismic loads. Frame members are simulated with a lumped plasticity model, including a flat surface modeling of the axial load-biaxial bending moment elastic domain, while the behavior of a hysteretic damped brace is idealized through the use of a bilinear law. Vulnerability index domains are adopted to estimate the directions of least seismic capacity at the ultimate (i.e. life-safety and collapse prevention) limit states prescribed by Italian and European seismic codes.  相似文献   

17.
In this paper, the effectiveness of different design solutions for tuned mass dampers (TMD) applied to high‐rise cross‐laminated (X‐Lam) timber buildings as a means to reduce the seismic accelerations was investigated. A seven‐storey full‐scale structure previously tested on shaking table was used as a reference. The optimal design parameters of the TMDs, i.e. damping and frequency ratios, were determined by using a genetic algorithm on a simplified model of the reference structure, composed by seven masses each representing one storey. The optimal solutions for the TMDs were then applied to a detailed finite element model of the seven‐storey building, where the timber panels were modelled with shell elements and the steel connectors with linear spring. By comparing the numerical results of the building with and without multiple TMDs, the improvement in seismic response was assessed. Dynamic time‐history analyses were carried out for a set of seven natural records, selected in accordance with Eurocode 8, on the simplified model, and for Kobe earthquake ground motion on the detailed model. Results in terms of acceleration reduction for different TMD configurations show that the behaviour of the seven‐storey timber building can be significantly improved, especially at the upper storeys. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

18.
新型形状记忆合金阻尼器的试验研究   总被引：23，自引：5，他引：23  
本文在对形状记忆合金(SMA)的力学性能研究的基础上，设计和制造出一种性能良好的SMA阻尼器，介绍了其工作原理及有关试验结果，将该阻尼器安装在斜拉桥模型上，进行了斜拉桥模型振动试验。试验结果表明该阻尼器的耗能效果明显，在工程结构振动控制方面具有比较好的应用前景。  相似文献   

19.
The potential of post‐tensioned self‐centering moment‐resisting frames (SC‐MRFs) and viscous dampers to reduce the economic seismic losses in steel buildings is evaluated. The evaluation is based on a prototype steel building designed using four different seismic‐resistant frames: (i) conventional moment resisting frames (MRFs); (ii) MRFs with viscous dampers; (iii) SC‐MRFs; or (iv) SC‐MRFs with viscous dampers. All frames are designed according to Eurocode 8 and have the same column/beam cross sections and similar periods of vibration. Viscous dampers are designed to reduce the peak story drift under the design basis earthquake (DBE) from 1.8% to 1.2%. Losses are estimated by developing vulnerability functions according to the FEMA P‐58 methodology, which considers uncertainties in earthquake ground motion, structural response, and repair costs. Both the probability of collapse and the probability of demolition because of excessive residual story drifts are taken into account. Incremental dynamic analyses are conducted using models capable to simulate all limit states up to collapse. A parametric study on the effect of the residual story drift threshold beyond which is less expensive to rebuild a structure than to repair is also conducted. It is shown that viscous dampers are more effective than post‐tensioning for seismic intensities equal or lower than the maximum considered earthquake (MCE). Post‐tensioning is effective in reducing repair costs only for seismic intensities higher than the DBE. The paper also highlights the effectiveness of combining post‐tensioning and supplemental viscous damping by showing that the SC‐MRF with viscous dampers achieves significant repair cost reductions compared to the conventional MRF. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

20.
The paper deals with the proposal and the experimental validation of a novel dissipative bracing system for the seismic protection of structures; compared with other similar systems, it is characterized by smaller size and weight, which makes it easier to move and to install, as well as particularly suitable to be inserted in light‐framed structures (e.g. steel structures of industrial plants). The proposed system consists of an articulated quadrilateral with steel dissipaters inserted, to be connected by tendons to frame joints; the prototypes have been designed and realized for the seismic protection of a two‐storey, large‐scale, steel frame, specially designed for shaking‐table tests. The paper, after an illustration of the system, and of its design and behaviour, presents the shaking‐table tests carried out. The experimental results have fully validated the proposed system, showing its good performance in controlling the seismic response of framed structures. A numerical non‐linear model, set up and validated on the basis of the physical tests, has been used to help interpreting the experimental results, but also to perform parametrical studies for investigating the influence of the design parameters on the performance of the control system. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

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