The Influence of Shear Crack Angle on FRP Wall Strengthening

The paper presents an analysis of the influence of the shear crack angle on the shear strengthening of the reinforced concrete wall. Walls that are strengthened using fiber reinforced polymers (FRP) in the form of lamella, fabrics, or near-surface mounted are analyzed. The need to increase the shear capacity of reinforced concrete walls occurs in older reinforced concrete buildings in seismically active regions that were designed before the adoption of modern anti-seismic regulations. Shear strengthening is important because the shear failure is fragile (i.e., not ductile) and should be avoided. It is important that the building has a certain ductility, and that seismic energy is dissipated when the earthquake occurs. The calculation of shear capacity in reinforced concrete depends on the assumed angle of the compression struts in the reinforced concrete element because the angle of the shear crack determines the amount of material needed to achieve a certain shear capacity due to the anchoring of the FRP at the top and the bottom of strengthened wall. An additional problem arises with walls with openings (windows, doors) in which cracks appear depending on the location of the openings and crack angle depends on it. FRP strengthening can be used on both sides of the wall, but also only on one side (e.g., due to the inability to intervene on the façade of the building, etc.). In the case of single sided strengthening, depending on the type of strengthening, there is a problem with the effectiveness of anchoring at the edges of the walls and openings. This significantly reduces the effectiveness of strengthening.