Abstract
Although the author is well aware that it is nothing special, presented here is the method that he uses to design the columns of a seismic resistant reinforced concrete structure, in hopes that this could be of use to someone. The method, which is directed at satisfying the capacity design requirements without excessively large sections, consists of proportioning the column so that the seismic action effects shall be resisted by the maximum of the bending moment–axial force interaction curve. That design condition is defined by two equations whose solution provides the optimal aspect ratio (or, alternatively, the optimal section side length) and the maximum feasible reinforcement ratio. The method can be used directly to determine the optimal column for given beam spans and vertical loads, or indirectly to determine the optimal beam spans and vertical loads for given cross-sectional dimensions. The paper presents the method, including its proof, and some applications together with the analysis on the optimality of the obtained solutions. The method is intended especially for the practicing structural engineer, though it may also be useful for educators, students, and building officials.
Highlights
Framing the Subject Matter and Review of LiteratureWhen reinforced concrete (RC) frames are used as part of a seismic-resisting system in buildings that are designed to resist earthquakes, special requirements must be satisfied
This paper focuses on special RC frames, but the method that is presented can be applied to intermediate frames
The application to real cases has proven that the method furnishes the optimal design solution in compliance with the capacity design principles, where optimal is meant in the sense that the column consists of the minimum cross-sectional size with the maximum reasonable amount of steel reinforcement
Summary
Framing the Subject Matter and Review of LiteratureWhen reinforced concrete (RC) frames are used as part of a seismic-resisting system in buildings that are designed to resist earthquakes, special requirements must be satisfied. Special proportioning and detailing requirements result in a frame capable of resisting extreme earthquake shaking without global collapse, and of resisting the design seismic action for local failure prevention (life safety), retaining its vertical load-carrying capacity as well as a residual seismic load-carrying capacity after the seismic event. Those frames can be called “special frames” or “intermediate frames” (the difference is explained below), because of those additional requirements, which improve the seismic resistance in comparison with less stringently detailed frames, called “ordinary frames”. The proportioning and detailing requirements for special moment frames are intended to ensure that the inelastic response is ductile (capacity design)
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