Effectiveness of implanting prestressed threaded rods to strengthen shear-damaged full-scale prestressed hollow-core slabs

Due to the structural configuration of prestressed hollow-core slabs (PHCS), which are horizontally connected in sequence, there is no accessible working space for shear strengthening once shear cracks develop in the middle slabs. To address this limitation, a novel retrofitting method was developed by drilling vertical holes and implanting prestressed threaded rods across the shear cracks in the web. A series of shear tests were initially conducted on four full-scale PHCSs with 16-meter spans under monotonic and cyclic loading, followed by shear strengthening on the slabs subjected to cyclic loading to verify the effectiveness of this method. Results showed little changes in bearing capacity and failure modes between cyclic and monotonic loading. A significant negative correlation was found between stiffness and both residual deflection and crack width, and simple models were developed to predict stiffness degradation. Strengthening with prestressed threaded rods allowed shear-damaged PHCSs to recover and enhance certain initial stiffness and shear capacity, preventing brittle damage under sudden heavy loads. Strain at the top of the slabs decreased by 8–25 % during initial loading and up to 32 % in later stages. At the ultimate state, the width of principal shear cracks was reduced by 10–35 %.