DISPLACEMENT BASED APPROACH FOR DESIGN OF HIGHWAY BRIDGES

Abstract

Current design codes use forced based design approach to design the sections of the bridges. Forced based design has limitations like stiffness which is unknown until design is not completed and inadequate representation of variation of hysteretic characteristic of bridges. To overcome these limitations direct displacement based design (DDBD) method is introduced which is based on displacement of the bridges. Hysteretic and stiffness characteristics are calculated based on yield and design displacement. The yield displacement and design displacement can be estimated by pushover curve and drift ratio limits. The aim of this article is to study the difference between forced based design and direct displacement design. A bridge pier is designed by both design methods for different pier heights and diameters. The designed piers are modeled in SAP2000 with fixed base and flexible base cases to take account of soil foundation structure interaction. Pushover analysis is performed for each modeled piers and from . pushover curves yield displacement uy and design displacement u„ is calculated. The pier section is designed by DDBD method for uy and u as calculated by pushover curve and drift ratio limits, percentage of longitudinal rebar is calculated for forced based design and DDBD method and compared. It is observed that different methods yield conservative nature at various heights for different diameters.