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RISS 인기검색어
- 검색키워드
- 저자 : Mehmet Tevfik Bayer (검색결과 2 건)
- 무료
- 기관 내 무료
- 유료
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New Elastoplastic Analysis of Two-Dimensional Frames When Some Plastic Hinges Unload Elastically
Fethullah Uslu,Mehmet Tevfik Bayer,Mustafa Haluk Saraçoğlu 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.2
Two-dimensional frames are made of elastic and perfectly plastic materials. Frames are analized by using the step by step elastoplastic analysis method where the applied loads are gradually increased at each step until a plastic hinge is developed. Then an equivalent frame model is generated by placing a mechanical hinge at the location of the plastic hinge and the increased external loads and the reduced plastic moments acting at the plastic hinge sections are applied to this model and elastoplastic analysis is performed. This elastoplastic analysis is repeated by incrementally increasing the external loads and applying the new reduced plastic moments, until the next plastic hinge is developed. Then a new equivalent frame model is generated to search for the following plastic hinge. This step by step elastoplastic analysis continues until the frame partially or totally collapses. When a plastic hinge is developed, it means that the section is at a fully plastic stress state. In the following small load increment: if this fully plastic stress state moves to another fully plastic stress state then this movement is called plastic fl ow. But if this fully plastic stress state moves to an elastic–plastic stress state then this movement is called elastic unloading. During the search of the next plastic hinge if one of the plastic hinges begins to unload elastically then the current equivalent frame model must be revised. For this the frame member which contains the elastically unloading plastic hinge is replaced by the equivalent frame member carrying balancing loads.
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True Collapse Mechanisms of Two Dimensional Frames Determined from True Nonlinear Yield Surfaces
Fethullah Uslu,Mehmet Tevfik Bayer,Mustafa Haluk Saraçoğlu 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.1
In this work, collapse mechanisms and collapse load factors of two-dimensional frames which are subject to point loads and uniformly distributed loads are determined by employing new elastoplastic analysis method. In this new iterative method as the applied loads on frames are gradually increased, plastic hinges begin to develop at frame member sections and this continues until the partial or total collapse occurrence. If a plastic hinge develops at a section of a frame member, then a mechanical hinge is defined at this location and at each iteration reduced plastic moments are also applied as external loads. This is a new approach to search for the next plastic hinge where a series of linear elastoplastic analyses are executed. For each analysis the revised reduced plastic moments are used in the calculations. For elastoplastic calculations of two-dimensional frames, yield surface definitions of frame member sections are needed, and for I sections, yield surfaces are defined by two curves. In order to simplify collapse load factor calculations these yield surfaces are generally approximated by two lines. In this work the influences of the approximations on the elastoplastic behaviour of two-dimensional frames are examined by comparing the solutions of four example frames. When their solutions are compared, it is observed that almost equal collapse load factors are determined when true and approximate yield surfaces are used in the elastoplastic calculations but true collapse mechanisms are obtained only when true nonlinear yield surfaces are used.
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