Behavior of internally stiffened webs for bridge girders using high performance steel

The research described in this thesis is part of a research program on innovative bridge designs using high performance steel (HPS). The objective of the program is to investigate the use of high performance steel in the design-of highway bridge girders. The first phase of the program demonstrated that the weight of steel I-shaped bridge girders designed according to current highway bridge design practice can be reduced ,significantly by using HPS. However, the effectiveness of using steels with nominal yield strengths of . 70 ksi (483 MPa) or greater is restricted by factors such as web stability, deflection, and fatigue design limits. This thesis describes new and innovative bridge design concepts developed to take advantage of the enhanced properties ofHPS. The main focus of the thesis is a design innovation that utilizes I-girders with double web plates. The web is composed of two steel face plates connected internally by continuous longitudinal stiffening elements. The voids between the face plates may be grouted or ungrouted. The stiffeners permit thin webs to be used, while still allowing the material to reach stresses as high as the yield strength without buckling. This arrangement reduces or eliminates the reliance on bond between the face· plates and the grout core in increasing web stability. However, it is shown that even in a debonded state, the presence of grout enhances the buckling capacity of the face plates significantly. . Using classical plate buckling theory, design criteria are proposed for bend buckling, shear buckling and vertical buckling of the web face plates. Both grouted and