NSBA Issues Guidance on Fit of Skewed and Curved Steel Girder Bridges

The Weaver Road Bridge in Douglas County, Ore. Photo: Courtesy of OBEC Consulting Engineers 

A free new document titled “Skewed and Curved Steel I-Girder Bridge Fit,” developed by the NSBA Technical Subcommittee, provides designers with guidance on determining the appropriate fit for skewed and curved steel I-girder bridges.

"Fit decisions are made on every steel bridge, and sometimes this decision has a significant impact on constructability or loads,” said Ronnie Medlock, P.E., vice president of technical services at High Steel Structures in Lancaster, Penn. (an AISC/NSBA member and AISC certified fabricator), and head of the NSBA Technical Subcommittee. “The summary raises awareness about the importance of fit, describes how fit comes to play in I-girder bridge construction and provides guidance on how to handle fit, especially for skewed and curved I-girder bridges."

As roadway alignments and interchanges become more complex, steel girders are the preferred solution for skewed and curved bridges required to accommodate the roadway. However, the design and detailing of these bridges must recognize and allow for change of shape of the steel girders, as dead load is incrementally applied during the process of construction.

This document discusses the issue and offers recommendations to ensure a trouble-free project. It includes information on effects of twisting girders as well as detailing of cross bracing and diaphragms when differential deflection is present in the I-girders.

The document is available for free downloading at