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Bridges & Special Structures Design

Underbridge inspection units (UBIUs) that reach from above deck to below.
Department of Transportation

Bridges & Special Structures Design

Development of Guidelines for the use of Intermediate Diaphragms on Precast Concrete Beam Superstructures

Project Number: SPR-1702

Contract Number: 2019-0314 Z1

Status: Complete

Start Date: 10/01/2019

End Date 07/31/2021


This study examines the need for intermediate diaphragms (IDs) and lateral support on low skew, low curvature prestressed concrete (PC) bridges while in-service and under construction. AASHTO beam, bulb tee, and spread box beam sections across a variety of span lengths and girder spacings were considered. To examine the in-service effect of IDs on vehicular live load distribution, validated finite element analysis (FEA) models were used to determine the change in distribution factor (DF) on a set of hypothetical PC girder bridges. During construction, the need for beam lateral bracing upon girder seating until deck cure was analyzed, considering the failure modes of girder rollover and lateral torsional buckling (LTB). Girder rollover was modeled with an analytical approach calibrated to numerical (FEA) results, while LTB was modeled with a validated, material and geometrically nonlinear FEA procedure. It was found that IDs provide little change in DF for typical structures, while elastomeric bearing pad properties and beam length significantly affected beam stability during bridge construction. Lateral bracing guidelines were developed as a function of section type, span, girder position, overhang length, and bearing pad width to provide stability during construction. 




Research Manager Project Manager Performing Organization
 Staff photo of Michael Townley    Wayne State University logo
 Michael Townley John Nadjarian   Wayne State University