Experimental and analytical study of an innovative strengthening system for deep corrugated structural plates (15-in. pitch by 5.5-in.) is described. A typical 5/16-in.-thick deep corrugated structural plate can typically span up to 65-ft for typical bridge design loads. In order to achieve longer spans, it is necessary to increase the flexural stiffness of the plate. The new strengthening system consists of a wide flange beam connected to the corrugated structural plate using a rigid bracket. Several tests were conducted at the University of Cincinnati Large Scale Testing Facility to evaluate the behavior and stiffness of the beam-plate system. Tests were carried out using a number of reinforcing beams and different bracket spacing. Equations for determining the cross-sectional properties and capacity of the stiffened system were developed. Design case studies were conducted using a special finite element program called CANDE (Culvert Analysis and Design). Different plate gauges in combination with a number of wide flange beams were used in the finite element analyses. The efficiency of the strengthened system was evaluated. In this paper, recommendations are made for design and analysis of strengthened long-span buried bridges. This study has found that it is possible to design lighter, longer, and cost effective structures through the use of stiffened plates.