An Approach to Determine the Prestress Loss in Unbonded Prestressed Composite Concrete Members

Based on the age-adjusted effective modulus method, this paper proposes a set of closed-form equations to estimate the prestress loss in prestressed composite concrete girders made up of a concrete girder and a cast-in-situ concrete deck slab with internal unbonded tendons. The composite girder can be prestressed with either steel or fiber-reinforced polymer tendons. The equations are valid for statically determinate beams with generic tendon profiles and take into account the effects of concrete creep, shrinkage, and relaxation of prestressing tendons. In order to validate the proposed equations, the numerical results are compared with previously published case studies.