Guide for Widening Highway Bridges
|Publication Date:||1 July 2013|
This document provides design professionals and constructors with general guidelines for bridge widening. The widening of highway bridges is commonly conducted to improve the functionality of existing structural systems. Several factors contribute to this demand:
a) Increased traffic volumes requiring additional lanes
b) Safety hazards of narrow bridges requiring wider shoulders
c) Provision for bikeways and pedestrian walkways
Government-funded programs are enabling public agencies to widen many functionally obsolete bridges as needed to improve safety. If a bridge was designed for current live loads and has not deteriorated appreciably, widening is likely more cost-effective than complete replacement.
It is imperative to perform in-depth nondestructive testing (NDT) and invasive testing to quantify the level of existing concrete deterioration and section losses in existing sections, and design protection methods to prevent future deterioration prior to investing in widening a structure.
Many problems unique to bridge widening are not encountered in new bridge work. Failures or serious maintenance problems can be created by misunderstanding these problems. Each bridge widening is unique.
This guide emphasizes construction practices, but because construction sequence, structure type, framing details, and other decisions critical to the success of the work are determined during the design phase, some discussion of design concepts must be included. Structural analysis and design for widening bridges are not addressed. Much of the discussion that follows also applies to new bridges constructed in stages, part width at a time.