Elastic Buckling Assessment of Doubly Symmetric I-Beams with Singly Stepped Section at Midspan

J. Korean Soc. Hazard Mitig. Vol. 17, No. 6 (Dec. 2017), pp.301~312 https://doi.org/10.9798/KOSHAM.2017.17.6.301 ISSN 1738-2424(Print) ISSN 2287-6723(Online) www.kosham.or.kr 시설물방재 Elastic Buckling Assessment of Doubly Symmetric I-Beams with Singly Stepped Section at Midspan Santos, Ralph Raymond V. * , Kang, Jun Suk ** , and Park, Jong Sup *** Abstract Over the years, several studies have been made for the improvement of the design criteria of stepped beams. However, studies on lateral-torsional buckling of stepped beams located at the midspan have been very limited. Hence, this study aims to evaluate the elastic lateral-torsional buckling strength of doubly symmetric singly stepped I-beam at midspan considering the load-height effect and various loading conditions. To model and perform the analysis for the I-beams, a universal finite element analysis program, ABAQUS, will be used. In addition, S4R elements will be used to model the simply supported beams where loads are applied at shear center and at top flange, and to check the accuracy of the models guide design specifications are used. The results from the finite element analysis will be shown using tables and illustrative figures. Based from the obtained results, conclusions and new design guidelines are proposed. Key words : Lateral-Torsional Buckling, Stepped Beam, FEM, Elastic Buckling 요 지 최근 스텝보의 설계기준 활용성을 향상시키기 위한 여러 연구가 진행된바 있다. 그러나 지간 중앙에 스텝단면이 보강된 I형보의 횡-비틀림 좌굴에 대한 연구는 제한적이었다. 본 연구는 지간 중앙에 스텝보가 적용된 I형보에 하중고 효과와 다양한 하중을 고려한 횡-비틀림 탄성좌굴강도를 평가하고자 한다. 범용유한요소해석 프로그램 ABAQUS가 사용되었으며, 쉘 요소인 S4R요소를 모델링에 적용되었고 해석결과는 기존 설계기준 및 기 발표된 제안식과도 비교분석 되었다. 본 논문은 다양한 표와 그림을 활용하여 해석결과를 나타내고 있으며, 해석연구 비교분석을 통하여 새로운 설계식 제안되었다. 핵심용어 : 횡-비틀림 좌굴, 스텝보, FEM 해석, 탄성 좌굴 *Member, Master Student, Department of Civil Engineering, Sangmyung University(E-mail: [email protected]) **Member, Assistant Professor, Department of Landscape Architecture and Rural Systems Engineering, Seoul National University(E-mail: [email protected]) ***Corresponding Author, Member, Professor, Department of Civil Engineering, Sangmyung University (Tel: +82-41-550-5314, Fax: +82-41-550-5313, E-mail: [email protected]) 1. Introduction The cross section of continuous multi-span beams are sometimes suddenly increased, or stepped, at interior supports of continuous beams to resist high negative moment. However, sometimes in interior spans, the flanges are stepped at both the center of the span near maximum positive moment area and the supports at the negative moment areas which can be conservatively considered doubly stepped beam (Park and Kang, 2004). In fabrication of built-up weld beams, it is a common practice to use a constant web depth as well as flange width with increase in flange thickness to provide increased in moment of inertia. Stepped beams are either constructed by increasing the flange thickness of a welded beam or by welding additional flange plates to a hot-rolled I-section. This paper presents an evaluation on the elastic lateral- torsional buckling (LTB) strength of doubly symmetric singly stepped I-beam at midspan considering the load-height effect. The loadings considered include cases with negative bending moments at both ends, a concentrated load, uniformly distributed load, and 2-point loading applied at shear center or at top flange. This research also presents new design equations that are similar to current lateral torsional buckling - 301 -

Elastic Buckling Assessment of Doubly Symmetric I-Beams with Singly Stepped Section at Midspan

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