Proposed changes to flexural design in BS 8110 to allow over-reinforced sections to fail in a ductile manner

The provisions for flexural design contained in BS 8110 have been reviewed in the context of introducing improvements in the level of ductility that can be achieved in structural concrete sections. Increased ductility will lead to corresponding enhancements in the flexural behaviour of members. Accordingly, changes to the present approach to flexural design in this code have been put forward. Design equations have been developed and compared to those present in the code. The proposed approach permits a section to be designed regardless of its longitudinal reinforcement ratio and also allows the amount of stirrups required to achieve the increased level of ductility to be determined. A test programme comprising 21 beams has been carried out to investigate the validity of the proposed design approach. The test results have confirmed the validity of the proposed approach. All of the beams exhibited enhanced flexural behaviour even though their longitudinal reinforcement ratios were significantly in excess of the maximum limit allowed in the code.