Implementation of Direct Displacement-Based Design for Highway Bridges

Abstract

In the last decade, seismic design shifted towards Displacement-Based methods. Among the several methodologies that have been devolved, the Direct Displacement-Based Design Method (DDBD) has been shown to be effective for performance-based seismic design of bridges and other types of structures.

The main objective of this Dissertation is to bridge the gap between existing research on Direct Displacement-Based Design (DDBD) and its implementation for design of conventional highway bridges.

Real highway bridges have complexities that limit the application of DDBD. This research presents new models to account for: limits in the lateral displacement capacity of the superstructure, skewed configurations, P-Δ effects, expansion joints and different types of substructures and abutments. Special interest is given to the definition of predefined displacement patterns that can be used for direct application of DDBD to several types of bridges.

The results of the research show the effectiveness of the proposed models. One of the most relevant conclusions is that bridge frames of bridges with seat-type abutments, which comply with the balanced mass and stiffness requirements of AASHTO, can be designed with DDBD using rigid body translation patters, which greatly simplifies the application of DDBD.

Another objective of the research was to compare the execution and outcome of DDBD to the design method in the new AASHTO Guide Specifications for LRFD Seismic Bridge Design. This was accomplished by a comparative study of four real bridges designed with the two methods. Results of that study indicate that DDBD is compatible with the new AASHTO Guide Specification and furthermore, it has several advantages over the design method in that specification.

Important products of this research are the computer programs DDBD-Bridge and ITHA-Bridge for design and assessment of highway bridges.