Numerical simulation of post-tensioned concrete girders with defective grouting including local stress-strain tendons response

In internally post-tensioned (PT) prestressed concrete (PC) structures, the prestressing system is usually made of high-strength steel tendons embedded within concrete through either metallic or plastic ducts filled with cement grout or grease. Construction defects or degradation phenomena may lead to insufficient covering, exposing the prestressing steel to a harmful environment, potentially compromising the durability and load-bearing capacity of the structure. Based on experimental tests on six 1:5 scaled PT specimens, this study presents accurate numerical simulations of four-point bending tests on girders with unbonded and partially bonded tendons having different levels of initial prestress. Nonlinear finite element analyses (FEAs) were developed to reflect the friction-type interaction mechanism between unbonded tendons and external ducts under increasing external load up to failure. Both global and local response parameters of the girders were studied validating numerical results against experimental findings. The numerical simulations provide insights on the stress pattern of unbonded and partially bonded strands, shedding light on the lower bearing capacity of defective girders compared to those with bonded tendons. Such findings contribute to a multi-scale assessment and decision-making framework for existing PT girders with defective grouting and low residual prestress levels, enhancing the understanding of their structural behavior and informing maintenance or retrofitting decisions.