COURSE WORK

Structure of Bridge



Structure of Bridge

Introduction

This paper discusses the structures of a new bridge constructed over a canal situated at Old Church Road. This paper specifically discusses the 2 viable options structures of new bridge i.e. one concrete and the other one is steel. Finally recommendations are made regarding the the chosen scheme.

Concrete Bridge Design

Concrete is the most-used construction material for bridges in the United States, and indeed in the world. For many years the design of precast prestressed concrete girders was based on concrete compressive strengths of 34 to 41 MPa (5,000 to 6,000 psi). For the future, the industry needs to seek ways to effectively utilize even higher concrete compressive strengths.

High-performance concrete (HPC) can be specified as high compressive strength (e.g., in prestressed girders) or as conventional compressive strength with improved durability (e.g., in cast-in-place bridge decks and substructures). (Jackson, 2010: 146)

Concrete design specifications have in the past focused primarily on the compressive

strength. Concrete is slowly moving toward an engineered material whose direct performance can be altered by the designer. Material properties such as permeability, ductility, freeze-thaw resistance, durability, abrasion resistance, reactivity, and strength will be specified. New materials will also find increasing demand in repair and retrofitting. As the bridge

inventory continues to get older, increasing the usable life of structures will become critical.

Some innovative materials, although not economical for complete bridges, will find their

niche in retrofit and repair.

The scheme chosen for the design example was a two span integral bridge, with equal spans each having a length of 20.0m. The bridge carries a 7.3m wide carriageway with a 2.0m wide footway on either side. The superstructure consists of eight standard precast, pretensioned concrete Y beams with a 160 mm deep in-situ reinforced concrete deck slab cast on ribbed permanent GRC formwork. There are in-situ diaphragms at the abutments and pier. (Patteeuw, 2010: 235)

The superstructure is made integral with the substructure. The foundations for the bridge consist of precast concrete piles with in-situ pile-caps. The pile-caps at the abutments are integral with the end diaphragms, while the pier wall is rigidly fixed to both its pile cap and the central diaphragm, avoiding the need for bearings altogether and simplifying the construction. The integral abutments are small and the piles relatively flexible in order to avoid excessive reactions resulting from thermal expansion of the deck. However, there is still sufficient fill behind the abutment diaphragms to resist longitudinal acceleration and braking forces.

The global analysis of the deck was carried out using a grillage model with eight longitudinal members at 1.5m centres representing the precast beams and associated sections of deck slab, and transverse members at 1.85m centres. The restraint provided by the pier and abutments were represented by rotational springs. The superstructure and sub-structure could have been modelled together in a single 3D model, but the practicalities of the design process mean that they may often be considered separately - in this case, the PD6694-1, which was particularly relevant to the substructure design, was not available ...