Punching Shear Strengthening of Reinforced Concrete Slabs Using Fiber Reinforced Polymers

Reinforced concrete flat plates are widely used structural systems. The absence of beams makes these systems attractive due to advantages such as easier formwork, shorter construction time, less total building height with more clear space, and architectural flexibility. Changes in the force or displacement demands imposed by gravity loads, wind, and earthquakes necessitate the upgrade of slab-column connections that are not provided with shear reinforcement and those that do not comply with integrity steel requirements. This research introduces an upgrading scheme for slab-column connections using externally installed CFRP stirrups. Behavior of 15 slab specimens subjected to shear and combined shear and moment transfer was studied experimentally. Various configurations of strengthening, amounts and details of CFRP installation were investigated. The effectiveness of proposed details of external CFRP reinforcement was evaluated. Simple mechanical models were used to predict punching shear strength, post punching resistance and anchorage strength of CFRPs bonded to concrete. Finite element analyses were conducted to provide further insight to the mechanics of load transfer, cracking and local stress conditions. Proposed upgrade method proved to be successful in strengthening the slab-column connections. Based on the results of the experimental and analytical studies, a procedure, which makes use of punching shear strength provisions of ACI 318-02, was proposed for upgrade design of slab-column connections.