Vibration versus Deflection Control for Bridges with High-Performance Steel Girders

The use of high-performance steel (HPS) in highway bridges has proved successful in structural performance and in the cost-efficiency of the constructed bridges. However, the use of optional deflection criteria as specified in a subsection of the AASHTO LRFD Bridge Design Specifications may impede the use of HPS in highway bridges. Besides the deflection criteria, the current AASHTO specifications provide a depth-to-span limitation table for steel superstructure designs. The values in that table are based primarily on the use of Grade 36 steel and were initially a carryover from railroad bridge construction. Therefore, both the deflection criteria and the depth-to-span limitation need to be evaluated for bridges constructed with HPS. This paper presents an investigation of the vibration control (e.g., acceleration and velocity) of HPS bridges using a three-dimensional (3-D) dynamic computer model. The 3-D dynamic model was validated with the use of field test data on various bridges, including a three-span continuous steel girder bridge. A suite of typical bridges designed with various slab thicknesses and span-to-depth ratios was selected for this study. In particular, the effects of the steel girder depth and concrete slab thickness on bridge vibration were identified. The analysis results indicated that bridge vibrations were better controlled with the choice of optimal concrete slab thicknesses (i.e., by adding to the mass and moment of inertia of a composite girder) rather than with specifications of the span-to-depth ratio limits, deflection limits, or first natural frequency.