Final Scope

There is lack of uniformity of information available to state departments of transportation (DOTs) about current steel bridge fabrication and erection tolerance practices both in the shops and in the field. The majority of the information available is for precast concrete bridges. The AASHTO National Steel Bridge Alliance Steel Bridge Collaboration group has noted that the use of oversize holes can lead to loss of overall structure geometry and fit-up problems during erection. Tolerances in steel fabrication require special processes such as shop blocking beams to drill field splice holes to ensure proper fit-up. Significant variability exists in state DOT fabrication and erection practices around the country and even from project to project. For example, some DOTs require full shop erection and fit-up to resolve tolerance issues in connections while others allow progressive assembly or digital fit-up.

The objective of this synthesis is to document current state DOT practices related to tolerance management for steel bridges. The synthesis will focus only on steel bridge components.

Information to be gathered regarding state DOT fabrication, assembly, and erection tolerances includes (but is not limited to):
• Current specifications (e.g., value of tolerance range, plate cutting, drilled holes, camber management, applicable conditions when tolerances are applied, extent of assembly);
• In practice adherence to DOTs current steel bridge fabrication tolerances (e.g., percentage of RFIs related to out of tolerance occurrences, quantity of field modifications, cumulative tolerances, commonality of out of tolerance components);
• Impact of component tolerances on field connections, including innovative or high-tech erection methods (e.g., required field modifications, re-fabrication)
• Quality assurance plan for tolerance management in the shop and in the field; and
• Recent DOT specification changes for improving tolerance management.

Information will be gathered through a literature review, a survey of state DOTs, and follow-up interviews with selected DOTs for the development of case examples. Information gaps and suggestions for research to address those gaps will be identified.

Information Sources (Partial):
• NCHRP Web-Only Document 243 “Recommended Guidelines for Prefabricated Bridge Elements and Systems Tolerances and Dynamic Effects of Bridge Moves” (https://www.trb.org/Main/Blurbs/177187.aspx
• AASHTO/NSBA Steel Bridge Collaboration G12.1-2020 "Guidelines to Design for Constructability and Fabrication" (https://www.aisc.org/globalassets/nsba/aashto-nsba-collab-docs/nsbagdc-4.pdf
• State DOT Specifications. (https://highways.dot.gov/federal-lands/specs/state-specifications)