Bridge Design

7Substructure: Analysis and Design

7.1 Introduction

The substructure of a bridge includes the piers, abutments and foundations as described in Chapters 1 and 4 of this book. The connections and force transfer of the superstructure to the piers and abutments is generally made by bridge bearings. The foundations of piers and abutments may be made by footings, piles or other special types of foundations, like caissons for very large bridges. The design of the various elements of the substructure requires the knowledge of the distribution between piers and abutments, whether due to applied forces or due to imposed displacements by the superstructure.

This chapter will address the basic aspects for the analysis and design of piers, foundations and abutments. Basic design concepts for structural bearings and seismic dampers are also discussed.

7.2 Distribution of Forces Between Piers and Abutments

7.2.1 Distribution of a Longitudinal Force

A longitudinal bridge model is shown in Figure 7.1. The deck is connected to an abutment E1 with a longitudinal stiffness K_E and it is simply supported at the other abutment E2. The connection to the piers is made by fixed bearings (P1 and P3), movable bearings (P4) or through a monolithic connection (P2). Assuming the deck to be rigid, the distribution of an horizontal force H is made according to the longitudinal stiffness of each substructure element, that is

(7.1)

Here, EI_i is the flexural rigidity of the pier i with length l_i admitted to ...