Construction Effects on Bracing on Curved I‐Girders

Abstract

The placement of the concrete deck and the attachment of adjacent girders and diaphragms is generally not considered in the design of horizontally curved bridges unless the entire bare steel structure has been completely constructed and is an integral unit. The supporting of the individual girders prior to attachment of diaphragms is an important control within the construction phase in that shoring may be necessary for stability. Contained herein are general guidelines, that apply to various popular erection schemes, to prevent overstress during construction. The guidelines are determined via a parametric study that quantifies the effect that the top and bottom lateral bracing has upon the stress levels within the main girder elements. The study examines the response of a single‐span, twogirder, curved I‐girder system subjected to its own self‐weight. Multigirder bridges are also examined to determine the effect that the placement of a concrete deck slab has upon the response of the curved girder with the top and bottom lateral bracing system for a representative range of span lengths and radii. Two‐ and threespan, continuous, curved braced bridges are also examined to determine the effect of lateral bracing on the stress levels on main girder elements. The final results are in the form of equations that define the dead load distributions throughout the superstructure system. These equations can be used in conjunction with the results given by the two‐dimensional grid analysis method, which is often used to analyze and design curved bridges.