Book excerpt: The shear provisions of the AASHTO LRFD Bridge Design Specifications (2008), as well as the simplified AASHTO procedure for prestressed and non-prestressed reinforced concrete members were investigated and compared to their equivalent ACI 318-08 provisions. Response-2000 is an analytical tool developed for shear force-bending moment interaction based on the Modified Compression Field Theory (MCFT). This tool was first validated against the existing experimental data and then used to generate results for cases where no experimental data was available. Several reinforced and prestressed concrete beams, either simply supported or continuous were examined to evaluate the AASHTO and ACI shear design provisions for shear-critical beams. In addition, the AASHTO LRFD provisions for combined shear and torsion were investigated and their accuracy was validated against the available experimental data. These provisions were also compared to their equivalent ACI code requirements. The latest design procedures in both codes can be extended to derive exact shear-torsion interaction equations that can directly be compared to the experimental results by considering all factors as one. In this comprehensive study, different over-reinforced, moderately-reinforced, and under-reinforced sections with highstrength and normal-strength concrete for both solid and hollow sections were analyzed. The main objectives of this study were to evaluate the shear and the shear-torsion procedures proposed by AASHTO LRFD (2008) and ACI 318-08, validate the code procedures against the experimental results by mapping the experimental limit points on the code-based exact ultimate interaction diagrams, and also develop a MathCAD program as a design tool for sections subjected to shear or combined shear and torsion effects.