Browsing by Author "Bozkurt, MB"

Now showing 1 - 13 of 13
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    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.
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    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.
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    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.
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    Numerical validation on novel replaceable reduced beam section connections for moment-resisting frames
    Özkiliç, YO; Bozkurt, MB
    This study presents replaceable reduced beam sections with connection detail for MRFs under residual drift. The proposed detail includes end-plated mid-spliced reduced beam sections. Pursuant to this goal, the proposed detail has been investigated under cyclic loading protocol required by AISC 341-16 by using ABAQUS finite element program. Seismic response of the proposed connection detail was compared from PEEQ and Rupture Index standpoint. The obtained findings indicate that the proposed mid-spliced replaceable reduced beam section satisfies all requirements indicated by AISC 341-16.
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    Excessive snow induced steel roof failures in Turkey
    Korkmaz, HH; Dere, Y; Ozkilic, YO; Bozkurt, MB; Ecemis, AS; Özdoner, N
    In January 2017, collapses of the numerous roofs were reported due to excessive snowfall in many provinces of Turkey. In this study, the reasons behind the collapses of the steel roofs of 19 factory buildings were investigated. The steel roofs supported by the precast reinforced concrete columns indicated a similar collapse pattern to each other under the unexpected heavy snow loading. The failure mechanisms of the roofs under the snow loading were simulated numerically. Nonlinear finite element models of a typical industrial building were developed and analyzed under an incremental vertical loading that is identical to snow loading. As a result of the analysis, the vertical load carrying capacity of the roof system and the snow load level causing the collapse of roof were determined. The resulting snow load was compared with the snow load values provided by the code specifications. In addition, the collapse mechanism of the steel roof system was analytically determined and compared with the collapse modes observed in the field and the causes of the failure were evaluated. The failure mechanism and the buckling modes obtained from analyses were found very similar to those observed during the site inspections. The main reasons of the roof failures may be attributed to excessive amount of snow caused by climate change and discrepancy of designed project and as-built project due to lack of building inspection control during the construction of the buildings.
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    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.
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    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.
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    Experimentally investigation of replaceable reduced beam section utilizing beam splice connection
    Özkiliç, YO; Bozkurt, MB
    This study presents a replaceable reduced beam section (R-RBS) located at the column end in moment resisting frames (MRFs). An end of the R-RBS is connected to column by using end-plate moment connection and the other end of that is connected to main beam with beam splice connection. Therefore, the RBS that is expected to yield under an earthquake can be easily replaceable. Geometry of the RBS and the thickness of the beam splice connection are the prime variables of this study. A total of eight experimental test was carried out to examine the seismic performance of the proposed R-RBS with the connection details. The results obtained from experimental studies demonstrated that plate sizes of the beam splice connection significantly affect the seismic performance of RBSs used in MRFs.
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    Comparison of Turkish Steel Building Specifications, TS 648 and SDCCSS 2018
    Bozkurt, MB; Ergüt, A; Özkiliç, YO
    This study presents similarities and differences between Turkish Building Code for Steel Structures, which are TS 648 and SDCCSS (Specification for Design, Calculation and Construction of Steel Structures) in terms of the design of the members. Hot-rolled I-shaped steel sections for symmetrical and U-shaped steel sections (i.e., channels) for monosymmetric sections were elaborated in detail. The design strength of tension members under tensile load, compression members under axial load and flexural members under flexure and shear were examined separately. Connection details for tension members, slenderness for compression members and distance between lateral supports for flexural members were considered as prime variables. Analysis results revealed the design strength of the tension members where at least one of the cross-sectional parts is not connected to the connection plates, I-shaped compression members where a slenderness ratio is below 39 (.<39), U-shaped compression members and flexural members where Lb is between Lp and Lr (Lp
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    Development of replaceable core all-steel buckling-restrained braces
    Serin, B; Bozkurt, MB
    This paper presents a replaceable core all-steel buckling-restrained brace (BRB). In this proposed BRB, as the encasing system composed of steel members alone without any filling material can be separated into two pieces by unfastening bolts, the damaged core plate inside the BRB can be easily replaced with the new one after an earthquake event. Two-directional slots at the end connections circumvent assembly and disassembly problems of the BRBs into the frames under residual drift. Pursuant the seismic performance of the proposed BRB, ten core plates, five encasement systems and one set of connection plates were produced and a total of ten full-scale subassemblage testing was performed. The connection set was used ten times and each encasing system was used two times. Based on the test results, all specimens exhibited stable behavior up to 4 % axial strain and the cumulative inelastic axial strain was computed as 744 for Specimen 1 and 643 for others. As a result of experimental and numerical studies, the seismic performance of the proposed BRBs, both in their first use and in the second use, satisfy AISC 341-22 requirements.
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    Comparison on Dynamic Performance of CBFs Designed as per TEC2007 and TEC2018
    Bozkurt, MB; Serin, B
    In this study, dynamic performance of six chevron and split-X braced concentrically braced frames (CBFs) having 3, 6 and 9 number of stories designed as per Turkish Seismic Code 2007 (TSC-2007) and Turkish Seismic Code for Buildings 2018 (TSCB- 2018) were compared. By using Opensees software, a total of 1056 nonlinear time history analyses was conducted under 44 far-field ground motions scaled based on TSC-2007 and TSCB-2018 by considering maximum considered earthquake having a 2% probability of being exceeded in 50 years. The results indicate that the archetypes designed as per TSCB-2018 are more reliable in CBFs employing both chevron and split-X brace configuration.
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    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.
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    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.