Performance of T-shaped concrete beams with a web opening under repeated loads using different strengthening methods

In long-span constructions, T-shaped beams are frequently used. In addition to providing a high compressive force, the steel reinforcement resists tension, permitting the design of smaller and lighter elements in the tension region. Many ducts and pipes are installed during the construction of contemporary structures to ensure the delivery of essential services, including water, sewerage, and the internet. A crack is more likely to occur where an opening occurs because it interferes with the usual flow of stresses. The goal of the study was to determine the performance of T-section reinforced concrete beams that are internally or externally strengthened in the presence of an opening with a rectangular shape of (100x250mm) in mid-span in the stem at mid-span during two-point repeated loads. The T-section beams have a length of 2000mm, a thickness of 100mm on their flanges, and a width of 300mm, while their webs have heights of 200mm and widths of 120mm. The design of the beams ensured flexure failure. The central load will be applied in two-point bending repeatedly until failure occurs. The repeated load is based on cycles in the positive phase consisting of 20 ascending cycles with a magnitude equal to 70% of the ultimate load in counterpart beams at a static load. A total of six T-shaped beams were constructed and incrementally tested by load. Control beams for the other four specimens are the first two specimens. One of the control beams has an opening in the web at mid-span, while the other one is solid without any openings. This study employs four strengthening strategies to estimate each method’s capacity. The web strengthening was done by means of CFRP sheets, CFRP bars as near-surface mounting (NSM), steel bars around openings, and concrete with steel fiber with a volumetric ratio of 1%. There were reductions in first cracking load and deflection, moreover to a decline in load capacity, ductility, initial stiffness, and energy dissipation by about (57%, 44.3%, 19.4%,35.1%,9.3%, and 42%), respectively. T-shaped beams are strengthened by steel bars around the web opening, and CFRP sheets have the best results regarding load capacity by 51.7% in both methods. For ultimate deflection, strengthening using steel bars around an opening is the most effective. The gains in ductility are between (11.4%- 131.9%). A moderate decline in stiffness was achieved by strengthening the beam with steel bars around the web opening. The beams perform significantly better than 61.5% in terms of energy dissipation capacity, except with CFRP sheet strengthening. In all beams, flexural failure dominates. FPR material de-ponds almost exclusively on the bottom side of T-shaped beams reinforced with CFRP bars or CFRP sheets.