• Title/Summary/Keyword: moment connections

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A Balanced Panel Zone Strength Criterion for Reduced Beam Section Steel Moment Connections (보 플랜지 절취형 (RBS) 철골 모멘트 접합부의 균형패널존 강도)

  • Lee, Cheol Ho;Kim, Jae Hoon;Jeon, Sang Woo;Kim, Jin Ho
    • Journal of Korean Society of Steel Construction
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    • v.18 no.1
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    • pp.59-69
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    • 2006
  • This paper presents test results on reduced beam section (RBS)program addressed panel zone (PZ) strength as the key variables. PZ strength has been much debated issue for several decades. A desirable range of PZ strength has not yet been proposed despite the fact that a significant amount of RBS test data is available. Test results from this study and by others showed that panel zones could easily develop a plastic rotation of 0.01 radian without causing distress to the beam flange groove welds. At this deformation level, the amount of beam distortion (i.e., buckling) was about one half that developed in strong PZ specimens. A criterion for a balanced PZ strength that improves the plastic rotation capacity while reducing the amount of beam buckling is proposed.

Strengthening of concrete structures with buckling braces and buckling restrained braces

  • Mazloom, Moosa;Pourhaji, Pardis;Farash, Abbas Moosa;Sanati, Amir Hossein
    • Structural Monitoring and Maintenance
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    • v.5 no.3
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    • pp.391-416
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    • 2018
  • The purpose of this article is to strengthen concrete structures using buckling and non-buckling braces. Connection plates are modeled in three shapes including the effect of 1.5t hinge zone length, 2t one and without the zone (1.5t-CP, 2t-CP and WCP). According to the verification performed with ABAQUS software, the connection plates which are superior in ductility and strengthening are found. The results show adding steel braces in concrete moment frames increase the strength and stiffness of the structures up to about 12 and 3 times, respectively. The frame strength increased about 21 and 25 percent with considering the effect of 2t hinge length in connection plates compared to 1.5t-CPs and WCPs. Also the ductility of retrofitted frames with 2t-CP improved 2.06 times more than WCP ones. Thus, 2t-CP sample is the best choice for connecting steel braces to concrete moment frames for retrofitting them. Afterwards, optimum conditions for elemental coating in braces with no buckling are assessed. The length of concrete coatings could be reduced about 30 percent, and buckling did not occur. Therefore, the weight of restraining coating decreased, and its performance improved. It is worth noting that BRBs could be constructed with only steel materials, which have outer steel tubes too. In fact, only the square cross sections of the tube profiles are appropriate for removing the filler concrete, and the rectangular ones are prone to buckle around their weak axis.

The Structural Economical Efficiency Evaluation of Partially Restrained Composite CFT Column-to-Beam Connection (합성반강접 CFT기둥-보 접합부 구조의 경제성 평가)

  • Kim, Sun-Hee;Bang, Jung-Seok;Park, Young-Wook;Choi, Sung-Mo
    • Journal of Korean Society of Steel Construction
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    • v.24 no.1
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    • pp.109-117
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    • 2012
  • This study seeks to devise a design application for a beam structure with partially restrained composite connection to a CFT column. A cost-efficient and stable component is applied by adjusting the stiffness ratio of the column connection through partially restrained composite connection. Based on a review of the structure's stability, it was confirmed that in the case of a low-rise building as a moment frame, resistance without bracing is feasible because stiffness increased by virtue of the partial restrained composite connection by composite action. In the case of a high-rise building, lateral resistance load of moment frame was approximately 10% when proper partial restrained rate was at around 60%. With considerations related to economic efficiency, the partial restriction effect of the beam component was significantly activated by the uniform load, but that of the beam activated by concentrated load was not significantly indicative. The analysis indicated that 60% partial restrained girder at the connection was the most economical in the case of uniform load. It also showed that end moments can be reduced by approximately 25%.

A Study on the Structural Behavior of Profiled Composite Beams (박판 냉간성형강 합성보의 구조적 거동에 관한 연구)

  • Yang, Gu Rok;Hwang, Young Seo;Song, Jun Yeup;Kwon, Young Bong
    • Journal of Korean Society of Steel Construction
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    • v.11 no.2 s.39
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    • pp.143-151
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    • 1999
  • An analytical study on the behavior of composite beams, which are composed of cold-formed profiled steel sheeting and normal strength concrete, is described. An analytical method to trace the nonlinear behavior of a composite beam is developed to include the nonlinear material properties of steel sheeting, reinforcing steel bar and concrete. A simple Power Model has also been proposed for the nonlinear moment-curvature relation of the composite beam. The model, which has been originally used to predict the flexural capacity of the beam to column connections, is adapted to the composite beams. The load-deflection behavior of the beams has been simulated by the step-by-step numerical integration using the moment-curvature relation obtained by the Power Model. The results have been compared with test results.

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Cyclic behavior of steel I-beams modified by a welded haunch and reinforced with GFRP

  • Egilmez, O. Ozgur;Alkan, Deniz;Ozdemir, Timur
    • Steel and Composite Structures
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    • v.9 no.5
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    • pp.419-444
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    • 2009
  • Flange and web local buckling in beam plastic hinge regions of steel moment frames can prevent beam-column connections from achieving adequate plastic rotations under earthquake-induced forces. Reducing the flange-web slenderness ratios (FSR/WSR) of beams is the most effective way in mitigating local member buckling as stipulated in the latest seismic design specifications. However, existing steel moment frame buildings with beams that lack the adequate slenderness ratios set forth for new buildings are vulnerable to local member buckling and thereby system-wise instability prior to reaching the required plastic rotation capacities specified for new buildings. This paper presents results from a research study investigating the cyclic behavior of steel I-beams modified by a welded haunch at the bottom flange and reinforced with glass fiber reinforced polymers at the plastic hinge region. Cantilever I-sections with a triangular haunch at the bottom flange and flange slenderness ratios higher then those stipulated in current design specifications were analyzed under reversed cyclic loading. Beam sections with different depth/width and flange/web slenderness ratios (FSR/WSR) were considered. The effect of GFRP thickness, width, and length on stabilizing plastic local buckling was investigated. The FEA results revealed that the contribution of GFRP strips to mitigation of local buckling increases with increasing depth/width ratio and decreasing FSR and WSR. Provided that the interfacial shear strength of the steel/GFRP bond surface is at least 15 MPa, GFRP reinforcement can enable deep beams with FSR of 8-9 and WSR below 55 to maintain plastic rotations in the order of 0.02 radians without experiencing any local buckling.

Seismic risk assessment of concrete-filled double-skin steel tube/moment-resisting frames

  • Hu, Yi;Zhao, Junhai;Zhang, Dongfang;Zhang, Yufen
    • Earthquakes and Structures
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    • v.14 no.3
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    • pp.249-259
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    • 2018
  • This paper aims to assess the seismic risk of a plane moment-resisting frames (MRFs) consisting of concrete-filled double skin steel tube (CFDST) columns and I-section steel beams. Firstly, three typical limit performance levels of CFDST structures are determined in accordance with the cyclic tests of seven CFDST joint specimens with 1/2-scaled and the limits stipulated in FEMA 356. Then, finite element (FE) models of the test specimens are built by considering with material degradation, nonlinear behavior of beam-column connections and panel zones. The mechanical behavior of the concrete material are modeled in compression stressed condition in trip-direction based on unified strength theory, and such numerical model were verified by tests. Besides, numerical models on 3, 6 and 9-story CFDST frames are established. Furthermore, the seismic responses of these models to earthquake excitations are investigated using nonlinear time-history analyses (NTHA), and the limits capacities are determined from incremental dynamic analyses (IDA). In addition, fragility curves are developed for these models associated with 10%/50yr and 2%/50yr events as defined in SAC project for the region on Los Angeles in the Unite State. Lastly, the annual probabilities of each limits and the collapse probabilities in 50 years for these models are calculated and compared. Such results provide risk information for the CFDST-MRFs based on the probabilistic risk assessment method.

Seismic Evaluation of Welded-formed square Column-Beam Connection for External Diaphragm Stress path (외다이아프램 응력경로에 따른 용접조립 각형기둥-보 접합부의 내진성능 평가)

  • Kim, Sun Hee;Yom, Kyong Soo;Choi, Sung Mo
    • Journal of Korean Society of Steel Construction
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    • v.26 no.4
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    • pp.311-322
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    • 2014
  • Concrete filled tubular structure should be installed diaphragms for moment connection. However internal and through diaphragm should be special welded when connected to column tube. The other hand, that has become increase of stress concentration and extend of construction error. Therefore, In this study the seismic performance of beam to column connections with External Diaphragms and implement cycle loading experiment. we had evaluated seismic performance with mentioned experiment which is concrete filled or not, variable shapes, to be welded or not of diaphragm. Also, formula of strength of external diaphragm was analyzed and looked into adequacy with regard to formula of tension strength.

Lateral Resisting Capacity for CFT Column to RC Flat Plate Slab Connections (CFT 기둥 - RC 무량판 슬래브 접합부의 횡저항 성능)

  • Song, Jin-Kyu;Song, Ho-Beom;Oh, Sang-Won;Lee, Cheol-Ho
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.04a
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    • pp.65-68
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    • 2008
  • This paper verified the lateral resisting capacity of CFT column-RC flat plate connection in comparison with general RC column-flat plate connection and detected moment capacity and ductility capacity of connection according to lateral force-displacement ratio. We made and tested specimens which have different variables respectively and as a result derive a following conclusion. In CFT specimen a critical section was extended and initial stiffness and moment increased 35%, 25$^{\sim}$35% respectively in comparison to general RC column specimen. In all specimens generally shear governed behaviors and in CFT specimen complemented with seismic band, flexure behavior region of slab was extended and also ductility ratio and energy absorptance increased.

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Seismic Performance of Composite Beam-to-Column Joints Using Wedges (쐐기의 원리를 이용한 합성 보-기둥 접합부의 내진성능에 관한 연구)

  • Park, Jong-Won
    • Journal of the Earthquake Engineering Society of Korea
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    • v.11 no.6
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    • pp.63-68
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    • 2007
  • The purpose of this study was to develop a new connection method between steel beams and PC columns known as SL connectors. Composite moment frames consisting of PC columns (or composite columns) and steel beams make the best use of advantages of both concrete and steel materials. However, the connection between two members of different materials can be complex and/or increase the fabrication costs significantly. The concept of SL connectors is based on using wedges and the emphasis is on a self-locking (SL) feature. SL connectors are easy to install and provide better seismic performance compared to conventional connections. To evaluate the seismic performance of the steel beam-to-PC column joints with SL connectors, cyclic load tests were conducted. Test result showed that steel beam-to-concrete column joint with SL connectors was able to provide sufficient performance for use in seismic resistant moment frames.

Direct analysis of steel frames with asymmetrical semi-rigid joints

  • Chan, Jake L.Y.;Lo, S.H.
    • Steel and Composite Structures
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    • v.31 no.1
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    • pp.99-112
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    • 2019
  • Semi-rigid joints have been widely studied in literature in recent decades because they affect greatly the structural response of frames. In literature, the behavior of semi-rigid joints is commonly assumed to be identical under positive and negative moments which are obviously incorrect in many cases where joint details such as bolt arrangement or placement of haunch are vertically asymmetrical. This paper evaluates two common types of steel frames with asymmetrical beam-to-column joints by Direct Analysis allowing for plasticity. A refined design method of steel frames using a proposed simple forth order curved-quartic element with an integrated joint model allowing for asymmetrical geometric joint properties is presented. Furthermore, the ultimate behavior of six types of asymmetrical end-plate connections under positive and negative moment is examined by the Finite Element Method (FEM). The FEM results are further applied to the proposed design method with the curved-quartic element for Direct Analysis of two types of steel frames under dominant gravity or wind load. The ultimate frame behavior under the two different scenarios are examined with respect to their failure modes and considerably different structural performances of the frames were observed when compared with the identical frames designed with the traditional method where symmetrical joints characteristics were assumed. The finding of this research contributes to the design of steel frames as their asymmetrical beam-to-column joints lead to different frame behavior when under positive and negative moment and this aspect should be incorporated in the design and analysis of steel frames. This consideration of asymmetrical joint behavior is recommended to be highlighted in future design codes.