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1.
This paper is Part II of a two‐part paper describing a full‐scale 3‐story 3‐bay concrete‐filled tube (CFT)/buckling‐restrained braced frame (BRBF) specimen tested using psuedo‐dynamic testing procedures. The first paper described the specimen design, experiment, and simulation, whereas this paper focuses on the experimental responses of BRBs and BRB‐to‐gusset connections. This paper first evaluates the design of the gusset connections and the effects of the added edge stiffeners in improving the seismic performance of gusset connections. Test results suggest that an effective length factor of 2.0 should be considered for the design of the gusset plate without edge stiffeners. Tests also confirm that the cumulative plastic deformation (CPD) capacity of the BRBs adopted in the CFT/BRBF was lower than that found in typical component tests. The tests performed suggest that the reduction in the BRB CPD capacities observed in this full‐scale frame specimen could be due to the significant rotational demands imposed on the BRB‐to‐gusset joints. A simple method of computing such rotational demands from the frame inter‐story drift response demand is proposed. This paper also discusses other key experimental responses of the BRBs, such as effective stiffness, energy dissipation, and ductility demands. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

2.
Moment connections in an existing steel building located in Kaohsiung, Taiwan were rehabilitated to satisfy seismic requirements based on the 2005 AISC seismic provisions. Construction of the building was ceased in 1996 due to financial difficulties and was recommenced in 2007 with enhanced connection performance. Steel moment connections in the existing building were constructed by groove welding the beam flanges and bolting the beam web to the column. Four moment connections, two from the existing steel building, were cyclically tested. A non‐rehabilitated moment connection with bolted web‐welded flanges was tested as a benchmark. Three moment connections rehabilitated by welding full‐depth side plates between the column face and beam flange inner side were tested to validate the rehabilitation performance. Test results revealed that (1) the non‐rehabilitated existing moment connection made by in situ welding process prior to 1996 had similar deformation capacity as contemporary connection specimens made by laboratory welding process, (2) all rehabilitated moment connections exhibited excellent performance, exceeding a 4% drift without fractures of beam flange groove‐welded joints, and (3) presence of the full‐depth side plates effectively reduced beam flange tensile strain near the column face by almost half compared with the non‐rehabilitated moment connection. The connection specimens were also modeled using the non‐linear finite element computer program ABAQUS to further confirm the effectiveness of the side plate in transferring beam moments to the column and to investigate potential sources of connection failure. A design procedure was made based on experimental and analytical studies. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

3.
A welded end‐slot buckling‐restrained brace (WES‐BRB) has been developed at the Taiwan National Center for Research on Earthquake Engineering (NCREE). A steel frame equipped with a WES‐BRB can offer a cost‐effective solution to meet interstory drift and earthquake‐resistant design requirements for seismic steel buildings. According to the WES‐BRB and connection design procedure proposed by NCREE, there are seven key elements of a buckling‐restrained braced frame (BRBF) design that require design checking. In order to assist an engineer with the design of the WES‐BRB members and connections, an innovative cloud service named Brace on Demand has been constructed at NCREE. In this study, using 581 BRBF design examples, the effectiveness of the proposed design procedures to meet all design checks is demonstrated. It is found that the most critical limit states for an initial design are joint region buckling, gusset plate buckling, and gusset‐to‐beam and gusset‐to‐column interface strength. Accordingly, the causes of improper designs and associated strategies for improving the initial designs are discussed in this paper. Recommendations on initial selections including the BRB joint size and gusset plate thickness are given. The paper provides the detailed road map for engineers to develop the spreadsheet for BRB and connection designs. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

4.
This paper investigates the implications of designing for uniform hazard versus uniform risk for light‐frame wood residential construction subjected to earthquakes in the United States. Using simple structural models of one‐story residences with typical lateral force‐resisting systems (shear walls) found in buildings in western, eastern and central regions of the United States as illustrations, the seismic demands are determined using nonlinear dynamic time‐history analyses, whereas the collapse capacities are determined using incremental dynamic analyses. The probabilities of collapse, conditioned on the occurrence of the maximum considered earthquakes and design earthquakes stipulated in ASCE Standard 7‐05, and the collapse margins of these typical residential structures are compared for typical construction practices in different regions in the United States. The calculated collapse inter‐story drifts are compared with the limits stipulated in FEMA 356/ASCE Standard 41‐06 and observed in the recent experimental testing. The results of this study provide insights into residential building risk assessment and the relation between building seismic performance implied by the current earthquake‐resistant design and construction practices and performance levels in performance‐based engineering of light‐frame wood construction being considered by the SEI/ASCE committee on reliability‐based design of wood structures. Further code developments are necessary to achieve the goal of uniform risk in earthquake‐resistant residential construction. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

5.
This paper presents the results of a probabilistic evaluation of the seismic performance of 3D steel moment‐frame structures. Two types of framing system are considered: one‐way frames typical of construction in the United States and two‐way frames typical of construction in Japan. For each framing system, four types of beam–column connections are considered: pre‐Northridge welded‐flange bolted‐web, post‐Northridge welded‐flange welded‐web, reduced‐beam‐section, and bolted‐flange‐plate connections. A suite of earthquake ground motions is used to compute the annual probability of exceedence (APE) for a series of drift demand levels and for member plastic‐rotation capacity. Results are compared for the different framing systems and connection details. It is found that the two‐way frames, which have a larger initial stiffness and strength than the one‐way frames for the same beam and column volumes, have a smaller APE for small drift demands for which members exhibit no or minimal yielding, but have a larger APE for large drift demands for which members exhibit large plastic rotations. However, the one‐way frames, which typically comprise a few seismic frames with large‐sized members that have relatively small rotation capacities, may have a larger APE for member failure. The probabilistic approach presented in this study may be used to determine the most appropriate frame configuration to meet an owner's performance objectives. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

6.
Post‐tensioned (PT) self‐centering moment‐resisting frames (MRFs) have recently been developed as an alternative to welded moment frames. The first generation of these systems incorporated yielding energy dissipation mechanisms, whereas more recently, PT self‐centering friction damped (SCFR) moment‐resistant connections have been proposed and experimentally validated. Although all of these systems exhibited good stiffness, strength and ductility properties and stable dissipation of energy under cyclic loading, questions concerning their ultimate response still remained and a complete design methodology to allow engineers to conceive structures using these systems was also needed. In this paper, the mechanics of SCFR frames are first described and a comprehensive design procedure that accounts for the frame behavior and the nonlinear dynamics of self‐centering frames is then elaborated. A strategy for the response of these systems at ultimate deformation stages is then proposed and detailing requirements on the beams in order to achieve this response are outlined. The proposed procedure aims to achieve designs where the interstory drifts for SCFR frames are similar to those of special steel welded moment‐resisting frames (WMRFs). Furthermore, this procedure is adapted from current seismic design practices and can be extended to any other PT self‐centering steel frame system. A six‐story building incorporating WMRFs was designed and a similar building incorporating SCFR frames were re‐designed by the proposed seismic design procedure. Time‐history analyses showed that the maximum interstory drifts and maximum floor accelerations of the SCFR frame were similar to those of the WMRF but that almost zero residual drifts were observed for the SCFR frame. The results obtained from the analyses confirmed the validity of the proposed seismic design procedure, since the peak drift values were similar to those prescribed by the seismic design codes and the SCFR frames achieved the intended performance level under both design and maximum considerable levels of seismic loading. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

7.
This paper presents a rehabilitation technique developed under a design and construction scheme, termed minimal‐disturbance seismic rehabilitation. This scheme pursues enhancing the seismic performance of buildings with the intention of improving the continuity of business while minimizing obstruction of the visual and physical space of building users and the use of heavy construction equipment and hot work (welding/cutting). The developed rehabilitation technique consists of light‐weight steel elements and aims to decrease demands to beam‐ends of steel moment‐resisting frames. The behavior of the baseline model was verified through numerical analysis and proof‐of‐concept testing. Furthermore, the effectiveness of rehabilitation is studied through retrofitting a four‐story steel moment‐resisting frame originally designed with Japanese design guidelines. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

8.
The selection of representative input ground motions (IGMs) is important for a proper nonlinear response time history analysis (NLRHA) of modern structures. The prevailing IGM selection procedure requires that the response spectra of selected ground motions are matched with the code-specified design spectra, while the effect of the frequency contents combination in the time domain on the multimode interactions is not considered. Ignoring the effect of the frequency contents combination in the time domain of IGMs may cause significant variations in the analysis results for selected IGMs, although they are matched to the same design spectrum. In this paper, a modal-based ground motion selection (MGMS) procedure is proposed as a supplement to spectrum matching-based IGM selection procedures for selecting proper IGMs that can sufficiently induce the multimode interactions. In the proposed procedure, three equivalent single-degree-of-freedom (ESDOF) systems are developed by pushover analysis. NLRHA is then conducted for these ESDOF systems with a set of 20 seed IGMs chosen by the spectrum-matching–based selection procedure. Finally, seven IGMs are selected from the seed IGMs for NLRHA in the full structural model. To verify MGMS, seismic demands of high-rise buildings were computed by NLRHA with seven MGMS-selected IGMs, seven IGMs with closest spectrum matching, and groups of seven randomly selected IGMs derived from three different sets of 20 seed IGMs. The computed seismic demands with MGMS-IGMs show very good agreement with the mean demands determined using the whole set of seed IGMs, while the deviation is much lesser compared with those groups of randomly selected IGMs.  相似文献   

9.
This paper presents the development, experimental testing, and numerical modelling of a new hybrid timber‐steel moment‐resisting connection that is designed to improve the seismic performance of mid‐rise heavy timber moment‐resisting frames (MRF). The connection detail incorporates specially designed replaceable steel links fastened to timber beams and columns using self‐tapping screws. Performance of the connection is verified through experimental testing of four 2/3 scale beam‐column connections. All 4 connection specimens met the acceptance criteria specified in the AISC 341‐10 provisions for steel moment frames and exhibit high strength, ductility, and energy dissipation capacity up to storey drifts exceeding 4%. All of the timber members and self‐tapping screw connections achieved their design objective, remaining entirely elastic throughout all tests and avoiding brittle modes of failure. To assess the global seismic performance of the newly developed connection in a mid‐rise building, a hybrid timber‐steel building using the proposed moment‐resisting connection is designed and modelled in OpenSees. To compare the seismic performance of the hybrid MRF with a conventional steel MRF, a prototype steel‐only building is also designed and modelled in OpenSees. The building models are subject to a suite of ground motions at design basis earthquake and maximum credible earthquake hazard levels using non‐linear time history analysis. Analytical results show that drifts and accelerations of the hybrid building are similar to a conventional steel building while the foundation forces are significantly reduced for the hybrid structure because of its lower seismic weight. The results of the experimental program and numerical analysis demonstrate the seismic performance of the proposed connection and the ability of the hybrid building to achieve comparable seismic performance to a conventional steel MRF.  相似文献   

10.
An assessment of seismic demands and capacities of welded column splice (WCS) connections in steel moment frames is presented. For demand assessment, nonlinear dynamic analyses are conducted for two case‐study buildings, that is, a 4‐story and a 20‐story moment frame. Results from the nonlinear dynamic analyses are assessed through a probabilistic seismic demand analysis (PSDA) framework to characterize recurrence rates of longitudinal flange stress in these connections. The PSDA is applied in two contexts. First, in the context of WCS connections constructed prior to the M 6.7 1994 Northridge earthquake, the PSDA is combined with sophisticated finite element‐based fracture mechanics analysis to compute the mean annual frequencies of fracture in these connections. The pre‐Northridge WCS are especially critical because they feature partial joint penetration and brittle materials that compromise their resistance to fracture. The analysis indicates that the mean annual frequencies of fracture in these connections may be unacceptably high for both the 4‐story and the 20‐story frames. This warrants a serious and urgent consideration of retrofit strategies. These findings are attributed to the brittleness of the pre‐Northridge splices (as indicated by the fracture mechanics simulations), as well as the force‐controlled nature of these components, wherein low‐intensity ground motions contribute disproportionately to fracture risk, as evidenced by fracture risk disaggregation. Second, in the context of new construction, the PSDA provides meaningful stress magnitudes for design. Currently, WCS connections employ complete joint penetration welds with the intent to develop the smaller column flange in yielding. The PSDA conducted in this study suggests that this requirement may be too stringent because stress demands in the splices corresponding even to high return periods (e.g., 2475 years) are significantly lower (~40 ksi), as compared with the stress required to yield the column (~55 ksi). Limitations of the study are outlined. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

11.
The task of selecting and scaling an appropriate set of ground motion records is one of the most important challenges facing practitioners in conducting dynamic response history analyses for seismic design and risk assessment. This paper describes an integrated experimental and analytical evaluation of selected ground motion scaling methods for linear‐elastic building frame structures. The experimental study is based on the shake table testing of small‐scale frame models with four different fundamental periods under ground motion sets that have been scaled using different methods. The test results are then analytically extended to a wider range of structural properties to assess the effectiveness of the scaling methods in reducing the dispersion and increasing the accuracy in the seismic displacement demands of linear‐elastic structures, also considering biased selection of ground motion subsets. For scaling methods that are based on a design estimate of the fundamental period of the structure, effects of possible errors in the estimated period are investigated. The results show that a significant reduction in the effectiveness of these scaling methods can occur if the fundamental period is not estimated with reasonable certainty. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

12.
A new type of energy‐dissipated structural system for existing buildings with story‐increased frames is presented and investigated in this paper. In this system the sliding‐friction layer between the lowest increased floor of the outer frame structure and the roof of the original building is applied, and energy‐dissipated dampers are used for the connections between the columns of the outer frame and each floor of the original building. A shaking table test is performed on the model of the system and the simplified structural model of this system is given. The theory of the non‐classical damping approach is introduced to the calculation analyses and compared with test results. The results show that friction and energy‐dissipated devices are very effective in reducing the seismic response and dissipating the input energy of the model structure. Finally, the design scheme and dynamic time‐history analyses of an existing engineering project are investigated to illustrate the application and advantages of the given method. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

13.
In‐plane buckling‐restrained brace (BRB) end rotation induced by frame action is a commonly observed phenomenon in buckling‐restrained braced frames (BRBFs). However, its effect on BRB end connection behavior has not yet been clear. In this study, four BRB end deformation modes for quick determination of end rotational demand are proposed for non‐moment BRBF considering different BRB arrangements, installing story of BRBs, and boundary condition of corner gussets connected with column base. Key factors affecting BRB end rotation and flexural moments are examined theoretically by parametric analysis. Subassemblage tests of seven BRB specimens under horizontal cyclic loading were conducted by adopting two loading frames to impose the expected BRB end deformations. It shows that BRB end rotation subjected BRB ends to significant flexural moments, leading to premature yielding of BRB ends or even tendency of end zone buckling. The deformation modes, the flexural rigidity of BRB ends, and the initial geometric imperfections of BRBs were found to have significant influence on BRB end connection behavior. The triggering moment induced by BRB end rotation was the main contributor to end flexural moment. However, the moment amplification effect induced by flexure of BRB end zones became prominent especially for small flexural rigidity of BRB ends. Implications and future research needs for design of BRB end connections are provided finally based on the theoretical and experimental results. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

14.
The concept of the hybrid passive control system is studied analytically by investigating the seismic response of steel frame structures. Hybrid control systems consist of two different passive elements combined into a single device or system. The hybrid systems investigated in this research consist of a rate‐dependent damping device paired with a rate‐independent energy dissipation element. The innovative configurations exploit individual element strengths and offset their weaknesses through multiphased behavior. A nine‐story, five‐bay steel moment‐frame was used for the analysis. Six different seismic resisting systems were analyzed and compared. The conventional systems included a special moment‐resisting frame (SMRF) and a dual SMRF–buckling‐restrained brace (BRB) system. The final four configurations are hybrid passive systems. The different hybrid configurations utilize a BRB and either a high‐damping rubber damper or viscous fluid damper. The analyses were run in the form of an incremental dynamic analysis. Several damage measures were calculated, including maximum roof drift, base shear, and total roof acceleration. The results demonstrate the capability of hybrid passive control systems to improve structural response compared with conventional lateral systems and to be effective for performance‐based seismic design. Each hybrid configuration improved some aspect of structural response with some providing benefits for multiple damage measures. The multiphased nature provides improved response for frequent and severe seismic events. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
This paper presents experimental and numerical studies of a full‐scale deformable connection used to connect the floor system of the flexible gravity load resisting system to the stiff lateral force resisting system (LFRS) of an earthquake‐resistant building. The purpose of the deformable connection is to limit the earthquake‐induced horizontal inertia force transferred from the floor system to the LFRS and, thereby, to reduce the horizontal floor accelerations and the forces in the LFRS. The deformable connection that was studied consists of a buckling‐restrained brace (BRB) and steel‐reinforced laminated low‐damping rubber bearings (RB). The test results show that the force–deformation responses of the connection are stable, and the dynamic force responses are larger than the quasi‐static force responses. The BRB+RB force–deformation response depends mainly on the BRB response. A detailed discussion of the BRB experimental force–deformation response is presented. The experimental results show that the maximum plastic deformation range controls the isotropic hardening of the BRB. The hardened BRB force–deformation responses are used to calculate the overstrength adjustment factors. Details and limitations of a validated, accurate model for the connection force–deformation response are presented. Numerical simulation results for a 12‐story reinforced concrete wall building with deformable connections show the effects of including the RB in the deformable connection and the effect of modeling the BRB isotropic hardening on the building seismic response. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

16.
Buckling‐restrained braces (BRBs) are widely used as ductile seismic‐resistant and energy‐dissipating structural members in seismic regions. Although BRBs are expected to exhibit stable hysteresis under cyclic axial loading, one of the key limit states is global flexural buckling, which can produce an undesirable response. Many prior studies have indicated the possibility of global buckling of a BRB before its core yields owing to connection failure. In this paper, BRB stability concepts are presented, including their bending‐moment transfer capacity at restrainer ends for various connection stiffness values with initial out‐of‐plane drifts, and a unified simple equation set for ensuring BRB stability is proposed. Moreover, a series of cyclic loading tests with initial out‐of‐plane drifts are conducted, and the results are compared with those of the proposed equations. © 2013 The Authors. Earthquake Engineering & Structural Dynamics published by John Wiley & Sons Ltd.  相似文献   

17.
The outrigger system is an effective means of controlling the seismic response of core‐tube type tall buildings by mobilizing the axial stiffness of the perimeter columns. This study investigates the damped‐outrigger, incorporating the buckling‐restrained brace (BRB) as energy dissipation device (BRB‐outrigger system). The building's seismic responses are expected to be effectively reduced because of the high BRB elastic stiffness during minor earthquakes and through the stable energy dissipation mechanism of the BRB during large earthquakes. The seismic behavior of the BRB‐outrigger system was investigated by performing a spectral analysis considering the equivalent damping to incorporate the effects of BRB inelastic deformation. Nonlinear response history analyses were performed to verify the spectral analysis results. The analytical models with building heights of 64, 128, and 256 m were utilized to investigate the optimal outrigger elevation and the relationships between the outrigger truss flexural stiffness, BRB axial stiffness, and perimeter column axial stiffness to achieve the minimum roof drift and acceleration responses. The method of determining the BRB yield deformation and its effect on overall seismic performance were also investigated. The study concludes with a design recommendation for the single BRB‐outrigger system.  相似文献   

18.
Non‐linear dynamic time‐history analyses conducted as part of a performance‐based seismic design approach often require that the ground motion records are scaled to a specified level of seismic intensity. Recent research has demonstrated that certain ground motion scaling methods can introduce a large scatter in the estimated seismic demands. The resulting demand estimates may be biased, leading to designs with significant uncertainty and unknown margins of safety, unless a relatively large ensemble of ground motion records is used. This paper investigates the effectiveness of seven ground motion scaling methods in reducing the scatter in estimated peak lateral displacement demands. Non‐linear single‐degree‐of‐freedom systems and non‐linear multi‐degree‐of‐freedom systems are considered with different site conditions (site soil profile and epicentral distance) and structural characteristics (yield strength, period, and hysteretic behavior). It is shown that scaling methods that work well for ground motions representative of stiff soil and far‐field conditions lose their effectiveness for soft soil and near‐field conditions for a wide range of structural characteristics. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

19.
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.  相似文献   

20.
A series of E‐Defense shaking table tests are conducted on a large‐scale test specimen that represents a high‐rise steel building. Two types of connections featuring the connection details commonly used in 1970s, in the early days of high‐rise construction in Japan, are adopted: the field‐welded connection consisting of welded unreinforced flanges and a bolted web type, and the shop‐welded connection in which the flanges and web are all‐welded to the column flange in the shop. To examine the seismic capacity of a total of 24 beam‐to‐column connections of the specimen, particularly when it is subjected to long‐period ground motion characterized not so much by large amplitude as by very many cycles of repeated loading, the test specimen is shaken repeatedly until the connections fractured. The test results indicate that a few of the field‐welded connections fractured from the bottom flange weld boundary in a relatively small cumulative rotation primarily due to the difficulties in ensuring the welding and inspection performance in the actual field welding. The shop‐welded connections are able to sustain many cycles of plastic rotation, with an averaged cumulative plastic rotation of 0.86 rad. Two shop‐welded connections exhibit ductile fractures but only after experiencing many cycles. The presence of RC floor slabs promotes the strain concentration at the toe of the weld access hole in the bottom flange by at least twice compared with the case without the slab, which had resulted in a decrease in the cumulative plastic rotation by about 50%. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

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