Report No.: CCEER-95-3

Authors: Nadim Wehbe, M. Saiid Saiidi, David Sanders, and Bruce Douglas

Date: July 1995

Sponsoring Agency: National Center for Earthquake Engineering Research

Performing Organization:

Department of Civil Engineering/258

University of Nevada, Reno

Reno, NV 89557

Abstract:

This study is part of a project to develop detailing guidelines for reinforced concrete bridge columns and walls in areas of moderate seismicity. The research examined the ductility and behavior of rectangular reinforced concrete bridge columns with moderate confinement. The research comprised experimental and analytical investigation of the response of such columns when subjected to lateral loading.

Four half-scaled rectangular bridge columns were built and tested. The geometrical dimensions and the amount of longitudinal reinforcement were kept the same for all specimens. Each specimen was tested under constant axial load while subjected to lateral load reversals with increasing drift levels. The lateral loading was quasi-static and uniaxial in the column strong direction.

Two parameters were varied: the transverse steel reinforcement amount and the axial load level. Based on the amount of lateral steel, the specimens were divided into two groups. The transverse reinforcement ratios, A_s /(s.h), in the long direction for the two groups corresponded to 42 percent and 54 percent of the minimum lateral reinforcement required by AASHTO for seismic detailing. The applied axial loads were approximately 0.1 f_c'.A_g and 0.25 f_c'.A_g. The specimens exhibited moderate displacement ductilities ranging between 4 and 7.

In the analytical study, several existing models pertaining to the concrete stress-strain relationship and the plastic hinge length were utilized and compared. For unconfined concrete, the Kent and Park model was used. On the other hand, the modified Kent and Park model and the model by Mander et al. (as modified by Paulay and Priestley) were utilized to represent the constitutive relationship of confined concrete. The equivalent plastic hinge length was calculated using two different models, the Baker's model and the model by Paulay and Priestley. The analytical study revealed that for rectangular bridge columns with relatively low axial loads and moderate confinement, it is possible to predict with reasonable accuracy the response of the columns to lateral cyclic loading (Abstract by authors).