Browsing by Author "Topkaya, C"

Now showing 1 - 7 of 7
  • No Thumbnail Available
    Item
    Replaceable links with gusseted brace joints for eccentrically braced frames
    Bozkurt, MB; Topkaya, C
    Various replaceable link details were developed for use in steel eccentrically braced frames (EBFs) during the past decade. These details include but are not limited to bolted flush end-plated links, bolted extended end-plated links, web connected replaceable links, and bolted flange- and web-spliced links. Another detail which is based on splicing the beam outside the link and braces was recently proposed by the authors. The performance of this detail when used with directly connected braces was studied through experimental testing and acceptable performance was demonstrated. In practice gusseted attachments are widely used for connecting the braces to the beams in EBF systems. In this paper, the proposed detail by the authors is extended to replaceable links with gusseted brace attachments. The use of gusset plates enables to tailor the geometry of the replaceable link and allows different details to be developed. Three replaceable link details are proposed herein. The first detail employs standard gusset plated detail where splicing the beam is performed outside the connection region. The second detail develops a more compact replaceable link by connecting the beam to the link within the brace connection panel. The third detail is a pin connected detail where minimal amounts of bending moments are transferred to the brace member. The proposed details are studied by conducting nine nearly full-scale EBF tests under quasi static loading. The type of replaceable link, link length ratio, connection type, gap size of splice connections, demand-to-capacity ratio of members are considered as the prime variables. The inelastic rotation capacity provided by the replaceable links satisfied the requirements of the AISC Seismic Provisions for Structural Steel Buildings (AISC341-16). The links failed mainly due to fracture of the link web or flange. No failures were observed in the gusseted joints demonstrating the potential of the proposed details.
  • No Thumbnail Available
    Item
    Replaceable links with direct brace attachments for eccentrically braced frames
    Bozkurt, MB; Topkaya, C
    This paper reports findings of an experimental study conducted on replaceable links for steel eccentrically braced frames (EBFs). A replaceable link detail which is based on splicing the directly connected braces and the beam outside the link is proposed. This detail eliminates the need to use hydraulic jacks and flame cutting operations for replacement purposes. Performance of this proposed replaceable link was studied by conducting eight nearly full-scale EBF tests under quasi-static cyclic loading. The link length ratio, stiffening of the link, loading protocol, connection type, bolt pretension, gap size of splice connections, and demand-to-capacity ratios of members were considered as the prime variables. The specimens primarily showed two types of failure modes: link web fracture and fracture of the flange at the link-to-brace connection. No failures were observed at the splice connections indicating that the proposed replaceable link detail provides an excellent response. The inelastic rotation capacity provided by the replaceable links satisfied the requirements of the AISC Seismic Provisions for Structural Steel Buildings (AISC341-10). The overstrength factor of the links exceeded 2.0, which is larger than the value assumed for EBF links by design provisions. The high level of overstrength resulted in brace buckling in one of the specimens demonstrating the importance of overstrength factor used for EBF links. Copyright (C) 2017 John Wiley & Sons, Ltd.
  • No Thumbnail Available
    Item
    Low-Cycle Fatigue Testing of Shear Links and Calibration of a Damage Law
    Bozkurt, MB; Kazemzadeh Azad, S; Topkaya, C
    This paper experimentally studies the low-cycle fatigue (LCF) behavior of shear links in eccentrically braced frames (EBFs) with the aim of calibrating a convenient damage law for estimating the exhausted as well as remaining life of these members under any loading history. A total of 14 specimens are tested using a nearly full-scale EBF setup under constant-amplitude cycles as well as proportional and arbitrary loading histories. A generalized damage law is subsequently calibrated using results of the present study as well as a comprehensive data compilation of previous experiments for predicting the occurrence of link fracture under earthquake-induced loading histories. The approach forms a basis for the development of acceptance criteria based on cumulative measures which can be incorporated into the current performance-based design and evaluation procedures. For further validation, the procedure is applied to the case of EBF links fractured during the Christchurch earthquakes. Finally, the current standards for EBF shear links are discussed based on the findings of the LCF tests.
  • No Thumbnail Available
    Item
    Mid-spliced end-plated replaceable links for eccentrically braced frames
    Özkiliç, YO; Bozkurt, MB; Topkaya, C
    Eccentrically braced frames (EBFs) can be re-used after a major seismic event by replacing the link members. Recent years have witnessed the development of numerous replaceable links. Among various details developed for this purpose, extended end-plated replaceable links are found to be the most efficient. The use of these links enables the engineer to minimize the size and the weight of the part to be replaced. In addition, the performance of end-plated links is similar to that of conventional links. Research reported to date has shown that end-plated links have disadvantages in terms of removal and replacement. Large axial forces can develop within the link member. Removal and replacement operations may require the use of hydraulic jacks to push the ends of the collector beams and the flame cutting of the links to gradually release the residual stresses and deformations. More important are the difficulties associated with link replacement under residual frame drifts. A novel detachable, replaceable link is proposed in this study which employs a splice connection at the mid-length of the link. The splice connection consists of channel sections welded to both parts of the replaceable link. The detail employed provides an erection tolerance which facilitates easy removal and enables replacement under residual frame drifts. Proof-of-concept testing of the proposed links was performed on 3 specimens where the type of force transfer in the splice connection was considered as the prime variable. All specimens failed at link rotation angles that were significantly higher than the link rotation angle required by AISC341 and demonstrated the potential of the proposed link concept. Complementary finite element parametric studies were conducted to validate the design procedure developed for the proposed replaceable link concept.
  • No Thumbnail Available
    Item
    Evaluation of seismic response factors for BRBFs using FEMA P695 methodology
    Özkiliç, YO; Bozkurt, MB; Topkaya, C
    This paper reports the details of a numerical study undertaken to evaluate seismic response factors for steel buckling-restrained braced frames (BRBFs) using the FEMA P695 methodology. In the United States, BRBFs are designed according to Minimum Design Loads for Buildings and Other Structures (ASCE 7) and the Seismic Provisions for Structural Steel Buildings (AISC 341). Twenty-four archetypes were designed according to the U.S. specifications and their behavior was assessed by making use of non-simulated collapse models. The interstory drift, brace axial strain and cumulative brace axial strain demands under collapse level ground motions were determined. The results obtained indicate that the current seismic response factors are adequate in terms of interstory drift and cumulative axial strain demands. On the other hand, large differences between the design level and collapse level axial strains were reported, which can result in undesirable brace behavior. Modified approaches were developed to estimate the axial strains for collapse level ground motions. These indude a modification to the deflection amplification factor and a modification to the AISC 341 requirements for expected brace deformations. The archetypes were redesigned using the proposed modifications and reevaluated using the FEMA P695 methodology. The results indicate that the proposed modifications result in axial strain demands that are in close agreement with the calculated demands. (C) 2018 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Development of welded overlap core steel encased buckling-restrained braces
    Bozkurt, MB; Topkaya, C
    This paper reports development of a new type of buckling-restrained brace (BRB) named the welded overlap core steel encased BRB. A two phase experimental research program was undertaken where BRBs were investigated under subassemblage testing. The first phase of the program aimed at studying the performance of steel encased BRBs which utilize constant width core plates. Test results indicated that these braces develop unacceptably high compression and tension resistances and the behaviors of these BRBs under uniaxial testing and subassemblage testing are markedly different. In the second phase of the research program a new type of BRB which utilizes a welded overlap core was developed to improve the cyclic performance observed in the first phase. Experimental results showed that the braces sustain axial strains that vary between 2.0 and 2.5% and resistances in tension and compression were found to improve significantly when compared with the findings of the first phase. Welded overlap core steel encased BRBs were found to sustain cumulative axial strains that are 419 times the yield strain when properly detailed. (C) 2016 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Development of detachable replaceable links for eccentrically braced frames
    Bozkurt, MB; Kazemzadeh Azad, S; Topkaya, C
    Eccentrically braced frames (EBFs) can be repaired after a major earthquake by replacing the links. The link replacement is not a straightforward process and is influenced by the type of the link and the amount of residual frame deformations. The past decade has witnessed the development of different types of replaceable links such as end-plated links, web connected links, bolted flange and web spliced links, and collector beam and brace spliced links. All of the developed replaceable link details, except the web connected links, are not suitable for link replacement under residual frame drift. In this paper, a detachable replaceable link detail which is based on splicing the link at its mid-length is proposed. The detail is well suited for installation under residual frame drifts. In addition, the weight and size of the members to be transported and erected are reduced significantly, thereby facilitating the replacement procedure. Performance of this proposed replaceable link is studied by conducting six nearly full scale EBF tests under quasi-static cyclic loading. The link length ratio, type of end-plated mid-splice connection, and the amount of residual drift are considered as test variables. The test results revealed that the inelastic rotation capacity of the detachable replaceable links exceeds the requirements of the AISC Seismic Provisions for Structural Steel Buildings. No failures are observed in the end-plated mid-splice connections demonstrating the potential of the proposed details. The detachable replaceable links are investigated by numerical analysis as well to further validate their applicability and to develop design recommendations.