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Behavior and Design of Hybrid Composite Beams with High-Strength Steel : 고강도 강재를 적용한 하이브리드 합성보의 거동 및 설계

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Authors

소현준

Advisor
이철호
Major
공과대학 건축학과
Issue Date
2015-02
Publisher
서울대학교 대학원
Keywords
high-strength steelhybrid composite beamsstrain compatibility methodplastic stress distribution methodplastic neutral axisplastic neutral axis limit
Description
학위논문 (석사)-- 서울대학교 대학원 : 건축학과, 2015. 2. 이철호.
Abstract
Composite beams are developed for better structural performance than rolled I-shape steel beams. The use of high-strength steel in bottom flange of composite beams provides higher load-carrying capacity without increasing size compared to beams of ordinary strength steel. Composite beams which have different steel types in the same section are often called as hybrid composite beams. But high-strength steel may cause greater chance that the concrete will crush before achieving ductile behavior. It should be considered in designing hybrid composite beams with high strength steel.

The nominal flexural strength of composite beams can be determined according to either the plastic stress distribution method or the strain compatibility method in currents codes. Usually, the plastic stress distribution method is used in most of design practice because it is more convenient and simple than the strain compatibility method. But the assumption used for the plastic stress distribution method may not be conservative and not be applicable to hybrid composite beams will be discussed in this paper. In this regard, KBC 2009 and AISC 360-10 do not provide any design provisions or limitations. But Eurocode 4 and AASHTO LRFD 2012 consider the strength reduction concept in their nominal flexural strength calculations according to the depth of the plastic neutral axis (D_p).

Previous researchers indicated that the depth of the plastic neutral axis (D_p) is the key factor for ductile behavior of composite beams and tried to define the neutral axis limit for achieving plastic moment and assuring ductile behavior. And their efforts were reflected in the AASHTO LRFD specifications as the plastic neutral axis limit (D_limit ) in their equations of nominal flexural strength of composite beams. But current equations to calculate the plastic moment and D_limit in the codes were proposed based on traditional composite beams with ordinary strength steel (F_y ≤ 485 MPa). However, the behavior of hybrid composite beams with high-strength steel flange are not well-known and the design equations for assuring strength and ductility have get to be developed.

In order to investigate whether current equations of the plastic moment is applicable to hybrid composite beams with high-strength steel, relevant equations were modified considering high-strength steel. Tests of hybrid composite beams with high strength steel were also conducted. From the test results, it was shown that the modified equations of the plastic moment is applicable to hybrid composite beams. Then, analysis program was developed to investigate the plastic neutral axis limit (D_limit) of hybrid composite beams. The analysis program accurately predicted the test results well.

In establishing the plastic neutral axis limit (D_limit) of hybrid composite beams, both strength and ductility were considered. From strength perspecitve, parametric study of Yakel and Azizinamini (2005) was adopted. For ductility, rotation capacity of R=3 in section level by Yura et al. (1978) was adopted. Based on extensive test-based numerical studies, D_limit was suggested for both achieving plastic moment and ductile behavior of hybrid composite beams.
Language
English
URI
https://hdl.handle.net/10371/124083
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