Simplified Finite-Element Analysis Method for Axial Compression Behavior of Rectangular Concrete Columns with Interlocking Multispiral Reinforcements

Abstract

This paper proposes a simplified finite-element analysis (FEA) method to analyze the axial compression behavior of rectangular concrete columns confined by interlocking multispiral reinforcements. The proposed method uses an elastic finite-element analysis to approximate the distribution and ultimate state of confining stress in each core concrete element, which is substituted into the Mander confined concrete model to obtain the integrated compressive curve of a column. Verification of the proposed method against the test results of four four-spiral and four five-spiral reinforcement columns showed good agreement. Parametric studies of the five-spiral reinforcement showed that for the same amount of transverse reinforcement, a column with a larger confined area, which closely depends on the radius ratio of the small to the large spirals (rs/rb), has better axial load-carrying capacity and confinement efficiency. To achieve economic confinement design, the volumetric ratio of large spirals to small spirals (ρs/ρb) to have the concurrent yielding of both large and small spirals was found to be around 1.0, 0.8, and 0.7 for rs/rb=1/2, 1/3, and 1/4, respectively.