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

Abstract

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.

The effect of helical pitch on the behaviour of helically confined HSC beams

“…The comparison between the effect of helix with rectangular confinement of over reinforced concrete beams using the experimental data of Mansur et al [9] and Ziara et al [10] The results of the tests in this study correlate very well with other tests done and reported, for example [3,[11][12][13].…”

Displacement Ductility of Helically Confined HSC Beams

“…Also the beams, which have longitudinal compression reinforcement, suffer from early failure because of the compression reinforcing buckling problem. Furthermore Mansur et al [7] and Ziara et al [8] found that the mid-span displacement ductility of beams enhanced significantly by using rectangular tie confinement. As a result of the experimental program conducted by Shah and Rangan [6], which proved that providing confinement in the compression zone of the beam is more efficient than providing steel fibres or compression longitudinal reinforcement.…”

Flexural Behavior of Over Reinforced HSC Beams Confined by Rectangular Ties

“…However, that is proved experimentally that the helix is more effective than the rectangular ties for NSC by [15]. The comparison between the effect of helix with rectangular confinement of over reinforced concrete beams using the experimental data of Mansur et al [17] and Ziara et al [12] was very difficult because of different variables such as size and span of the beam, tie spacing and longitudinal reinforcement ratio. The comparison between the effectiveness of helix and tie in the compression zone of HSC beams will be undertaken during the next stage of the extensive experimental program at the University of Wollongong [15].…”