EVALUATION OF A MODIFIED TRUSS-MODEL APPROACH FOR BEAMS IN SHEAR

A modified truss model design approach with variable angle of inclination diagonals and a concrete contribution for beams with web reinforcement is proposed as a viable and economic design tool. Computed values were compared with a wide range of test results of reinforced and prestressed concrete beams failing in shear. The modified truss model approach was shown to be conservative and in good agreement with test results. A diminishing concrete contribution is proposed to supplement the strength of the variable angle truss model for reinforced concrete beams. For prestressed concrete beams the proposed modified truss model utilizes a constant concrete contribution. A maximum allowable compressive stress of 30 square-root f(c)' together with lower angle limits of 30 deg for reinforced concrete beams and 25 deg for prestressed beams, was shown to provide adequate safety against web crushing failures prior to yielding of the stirrup reinforcement.