Accounting for P-Delta Effects in Structures when using Direct Displacement-Based Design

Student: Didier Pettinga
Supervisor: Prof. M.J.N. Priestley

Abstract

An outline of how P-Delta influences single-degree-of-freedom response is presented, from which the explicit inclusion of this second-order effect in the Direct Displacement-Based Design method is developed. The differences in sensitivity to P-Delta of both elasto-plastic (approximating steel response) and stiffness degrading (reinforced concrete) hysteresis are discussed, from which a proposed multiplicative factor is derived to account for the enhanced performance of reinforced concrete structures.

Parametric investigations, using a suite of seven spectrum-compatible "massaged" real records, are carried out to assess the influence of differing levels of P-Delta significance, ductility demand and post-yield stiffness ratio. It is found that for most systems considered the proposed design approach is very effective. Where necessary limits in application and effect are presented based on these results. To further demonstrate the effect of the design approach, a four-storey frame designed for both reinforced concrete and steel response is tested. It is found that the proposed account for P-Delta satisfactorily reduces the storey drift amplifications, such that the design performance targets are maintained at the original level when second-order effects are not included in the analyses.

This work has been, or is about to be, published as a ROSE Research Report, for which reason a copy of it is not available for download, but can rather be obtained from IUSS Press.