Creep in Prestressed Concrete Beams Under Time-Varying Sustained Loading

Abstract

In the design of prestressed concrete fl exural members it is necessary to allow for the longterm effects of creep and shrinkage, particularly in regard to defl ections and prestress loss. Various analytic methods can be used to evaluate these long-term effects, but the calculations for creep become extended and complex if, as is usually the case, the sustained load on the member varies over time. In this study a simplifi ed, approximate method is proposed for dealing with creep under a varying load history. The time-varying moment history in the cross-section of a member is replaced by a constant, sustained, “equivalent” moment, Meq, which has the same long-term effect as the time-varying moment. This equivalent moment can be used together with any appropriate constant-moment creep analysis, but is here combined with previously-derived, closed-form expressions for loss of prestress and creep curvature. The result is a simple procedure for dealing with creep in prestressed members under time-varying sustained loads.