Date of Graduation


Document Type


Degree Type



Statler College of Engineering and Mineral Resources


Civil and Environmental Engineering

Committee Chair

Karl E. Barth.


High performance steel (HPS), specifically HPS 70W, was introduced to the bridge market in the United States in the late 1990s. With its added strength, greater durability, and improved weldability, HPS allows engineers to design longer and shallower spans, which may increase the live-load deflections. The AASHTO Standard Specification limits live-load deflections to L/800 for ordinary bridges and L/1000 for bridges in urban areas subjected to pedestrian use. Bridges designed by the AASHTO LRFD Specification have an optional deflection limit. Previous research focused on evaluating AASHTO live-load deflection limits showed that the justification for existing deflection limits was not clearly defined and the best available information indicated that they were initiated to control undesirable bridge vibrations and assure user comfort. Significant design costs may be saved if more rational live-load serviceability criteria can be adopted. Bridge design specifications from other countries do not commonly employ direct live-load deflection limits. Vibration control is often achieved through a relationship between the first flexural natural frequency of the bridge and live-load deflection. However no direction is provided to how to calculate the flexural natural frequency.;This research establishes the rationale behind existing design provisions and compares AASHTO provisions to design methods used in other countries. The effect of AASHTO and other existing live-load deflection limits on steel bridge design and performance are evaluated through a parametric design study and analysis of existing typical highway bridges. In this work, 3D FEA tools have been developed to investigate the natural frequency of continuous span bridges and have been employed in a comprehensive parametric study. From these results, practical and simplified equations are proposed to predict the natural frequencies of continuous span bridges to be used in conjunction with frequency based serviceability limit states.