The effect of reinforcement strength on the overstrength factor for reinforced concrete beams

Abstract

The design of earthquake resistant structures in New Zealand is based around the philosophy known as capacity design. In order for this philosophy to be successfully applied, it is essential that the flexural overstrength factor is appropriately defined. Overstrength factors for reinforced concrete structures are defined in the New Zealand Concrete Structures Standard, NZS 3101:2006, which currently prescribes the flexural overstrength factor for beams as 1.25 if the beam contains Grade 300E longitudinal reinforcement and as 1.35 if the beam contains Grade 500E longitudinal reinforcement. However, review of existing literature and consideration of structural behaviour does not support the use of different overstrength factors for different types of reinforcement. Analysis of a database of approximately one hundred beam-column joint tests indicates that the same overstrength factor should be used for reinforced concrete beams irrespective of whether they contain Grade 300E or Grade 500E longitudinal reinforcement.