Analysis and Design of High-Strength Concrete Bridge Girders and Seismically Isolated Bridges

Abstract

The research presented in this thesis is focused on the analysis and design of high-performance bridges, with consideration of both superstructure and substructure elements. Existing design methods for the shear strength of concrete beams are based on a combination of theoretical models for concrete shear behaviour and empirically-developed relationships. Of particular interest to bridge designers is the treatment of high-strength concrete beams for the design of bridge superstructures, and the limits imposed on shear stresses in high-strength concrete beams. An examination of the concrete shear design procedures in international design standards revealed an inconsistency in the methods used by designers worldwide, and an inconsistency in the limits imposed on high-strength concrete beams. This inconsistency was confirmed by a combination of a parametric analysis of databases consisting of all previous testing of concrete beams failing in shear and a series of experimental testing. It was concluded that the shear stress limit of 8 MPa imposed in NZS 3101 is overly conservative, leading to significant under-estimation of the shear capacity of high-strength concrete beams. The combined results of the database analysis and experimental investigation were used to develop improved shear stress limits which were proposed to both improve the accuracy of the shear design provisions of NZS 3101 and allow for more efficient design of concrete bridge beams than allowed by the 8 MPa limit currently imposed by the design standard. The analysis and design of seismically isolated bridges was examined through a parametric analysis to determine the influence of several common design parameters on bridge response and on the economics of seismic isolation. Parameters studied included soil condition, level of seismicity, pier regularity, and bridge skew. Subsequently, a Bi-Modal Simplified Method (BMSM) was proposed for the simplified analysis of seismically isolated bridges to replace the existing simplified method currently outlined in AASHTO Guide Specifications for Seismic Isolation Design. The Bi-Modal method was found to predict the response of seismically isolated bridge with considerably greater accuracy than the existing simplified method for almost all bridges, and was recommended for use for calculating the response of seismically isolated bridges with a combined structural-isolation ratio greater than 0.5 and no greater than 5.