Plate girders, usually characterized by having very deep sections, have been widely used for long-span structures and bridges. US design provisions (AASHTO Specifications for bridge design and AISC Specifications for building design) allow the designer to include the contribution of tension-field action after web buckling in calculating the ultimate shear strength of interior panels, but not exterior panels, because no effective anchor mechanism exists to resist the horizontal component of the tension-field force. This has had a negative impact on the evaluation and load rating of existing bridges; this conservatism often may requires unnecessary rehabilitation of steel girder bridges which have provided satisfactory service in the past half-century. Testing of two steel plate girders and two steel-concrete composite plate girders was carried out to investigate the shear resistance of end panels. Test results demonstrated a much higher shear resistance than that predicted by code provisions in the steel girders. The concrete slab in the composite specimens also contributed to the shear resistance, although to a lesser extent. Nonlinear finite element analyses were conducted to correlate the test results. Results from a parametric study strongly supported the behaviors observed from testing and confirmed the existence of partial tension-field action in the end panels. Based on the failure mode observed from both testing and finite element simulation, an analytical model was developed to simulate the collapse mechanism. Plastic analysis was used to derive a predictive shear resistance equation. This equation is similar in format to that used in AASHTO Specifications for interior panels but includes a parameter [alpha] to account for the contribution of partial tension-field action. Based on a strut-and-tie model, the contribution from the concrete slab was also presented. Rehabilitation of end panels by using a common scheme, first proposed by Basler and has been adopted in Eurocode 3, was found unconservative. A novel scheme was proposed and its effectiveness was verified by finite element simulation.