Shear Strength Computation of Reinforced Concrete Beams Strengthened With Composite Materials

Remodeling buildings often implies a modification of the mechanical behavior of the structural system, which may include the application of concentrated loads to beams that before have only been subjected to distributed loads. In the case of reinforced concrete beams, the new condition causes the beam to support a concentrated load in the cracked condition determined by the distributed loads that had been acting in the past. If the concentrated load is applied at or near the midspan of the beam, consequently, the shear demand reaches its maximum where the shear capacity is low. At and near the midspan, in fact, the cracks in the tension zone are vertical, as the stirrups are. Therefore, the truss mechanism provides the shear capacity with a nil contribution, since both the struts and ties are vertical. Fiber-reinforced polymer composites allow these beams to increase their shear strength, up to guaranteeing adequate safety. This paper presents a method for analyzing the mechanical behavior of beams with vertical cracks, strengthened with FRP reinforcement, subjected to concentrated loads. The method defines the direction of the fibers that the reinforcement has to be composed of and computes the shear strength of the beam.