Report No.: CCEER-86-1

Title: A Simple Hysteretic Element For Biaxial Bending of R/C Columns and Implementation in NEABS-86

Authors: George E. Ghusn and Mehdi Saiidi

Date: July 1986

Sponsoring Agency: National Science Foundation

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557


A new nonlinear biaxial bending element for reinforced concrete columns was developed. The new element represents the column as a group of five translational springs, each representing the properties of the concrete and reinforcement. The element was implemented in a nonlinear static analysis program. Results using the five-spring element compared favorably with experimental results producing a better match than either the bilinear biaxial yield surface model or the trilinear degrading yield surface model.

The new element was added to an existing nonlinear dynamic analysis program (program NEABS). Three bridge structures, the Rose Creek Interchange, the Meloland Overpass, and the Flamingo Road Overpass, were modeled for dynamic analysis. Each bridge structure was modeled using both the elasto-plastic yield surface element and the five-spring element. Comparisons of the dynamic responses showed that the new element provided a more realistic stiffness degradation, a higher amplitude acceleration response, and a lower amplitude displacement response than the elasto-plastic yield surface element. The analyses using the elasto-plastic yield surface element generally required much longer execution times to produce stable results.

Nonlinear dynamic analyses using the five-spring element execute faster, do not become unstable, and provide for a more realistic response for reinforced concrete columns subjected to biaxial bending (Abstract by authors).