Strengths of RC beams with a fibre-reinforced polymer (FRP)-strengthened web opening

For the passage of utility ducts and/or pipes, openings often need to be created in the web of a reinforced concrete (RC) beam. Such a web opening can lead to a significant decrease in the ultimate load (i.e., strength) of the beam due to the reduced cross-sectional area and/or the severing of some of the existing steel reinforcement (particularly stirrups). In such cases, an externally-bonded fibre-reinforced polymer (FRP) strengthening system may be installed around the web opening to ensure the safety of the weakened beam. While existing experimental and numerical studies have provided useful information on the structural behaviour of RC beams with an FRP-strengthened web opening, this paper presents a theoretical study on the strength of such beams. First, a relatively simple, iterative numerical procedure (referred to as the iterative method) based on the static method of plastic limit analysis for predicting the plastic limit load (i.e., strength) of RC beams with an FRP-strengthened web opening is proposed, and then a closed-form, algebraic strength equation (referred to as the strength model) for such beams is established as a simplified approach of the iterative method. The accuracy of the proposed iterative method and strength model is verified with test results.