Predictions of Ultimate Behavior of Confined Columns Subjected to Large Deformations


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Title: Predictions of Ultimate Behavior of Confined Columns Subjected to Large Deformations

Author(s): Apostolos Fafitis and Surendra P. Shah

Publication: Journal Proceedings

Volume: 82

Issue: 4

Appears on pages(s): 423-433

Keywords: columns (supports); confined concrete; cyclic loads; deformation;,ductility; earthquake resistant structures; high-strength concretes; moment-curvature relationship; spiral reinforcement; stress-strain relationships; structural design

Date: 7/1/1985

A stress-strain relationship for unconfined and confined concrete is proposed. Based on this relationship, the behavior of reinforced concrete columns subject to axial and lateral loading is predicted and compared with experimental dataa on round and square columns. A good agreement between theoretical and experimental results is observed. A parametric study was conducted to assess the influence of the concrete strength, the degree of confinement, the level of axis load, and the shape of the section on the capcity of columns subjected to large deformations. It was found that (a) under constant axial load, the moment resistance of the column may exhibt a peak follwed by a drop (the predicted values according to the ACI procedure are close to this first peak); (b) the extent in drop in moments depends on compressive strength of concrete, axial load level, shape of the section, and confinement; © the square sections examined exhibit higher moment capcity than those of the circular section, espically at large deformations; (d) the contribution of the cover concrete becomes negliable beyond axial strains of 0.01; (e) the contribution of confined concrete to moment variation is substantial (about 30 percent); and (f) the ACI method for lateral reinforcement seems satisfactory for high-strength concrete; however, the design of a small square section may be more ductile than a larger one if both are designed according to ACI.