Buchanan County IBRD Bridge Project: Evaluation of a Folded Plate Girder Bridge System

Project Details



13-458 FHWA IBRD Program






FHWA Innovative Bridge Research and Deployment (IBRD) Program
Iowa Department of Transportation

Principal Investigator
Brent Phares

Bridge Research Engineer, BEC

About the research

With the assistance of the Iowa Department of Transportation (DOT) and the Institute for Transportation (InTrans) at Iowa State University, Buchanan County, Iowa was awarded a Federal Highway Administration (FHWA) Innovative Bridge Research and Deployment (IBRD) Program grant to help construct and evaluate an innovative short-span bridge (i.e., the Amish Sawmill Bridge). The bridge was designed and constructed using folded plate tub girders.

This bridge utilizes a folded plate girder superstructure supported on geosynthetic-reinforced soil (GRS) abutments. To evaluate the structural behavior of the bridge, the researchers conducted laboratory and field testing with the goal of validating the adequacy of the folded plate girder for short-span bridge construction.

The research team conducted three laboratory tests on a folded plate girder specimen similar to the girders that were used on the completed bridge to study the girder’s construction-stage behavior, flexural behavior, and shear behavior. The researchers conducted live load field tests immediately after completion of the bridge with the girders and one year after bridge construction to evaluate the behavior of the bridge and its components. Full-scale finite element models of the bridge were established to interpret the test results. The researchers drew the following conclusions from experimental and numerical evaluation results:

  • No noticeable, unwanted deformations or strain levels were found during laboratory tests, and the strains and displacements were well predicted by the design calculations.
  • The girder has two webs with large associated shear capacity; thus, the shear strength of the folded plate girder when placed is not a point of concern for design considerations.
  • Due to the shear lag effects, the strain near the bottom corners of the bottom flanges is larger; due to the biaxial bending effects, strains in the bottom flanges vary from one side to the other.
  • The GRS-integrated bridge system (GRS-IBS) and abutments provide significant restraint to the girder ends. And, the end supports have restraint characteristics of an intermediate support condition, between the pinned and fixed support conditions.
  • American Association of State Highway and Transportation Officials (AASHTO) equations were reasonably accurate at estimating the load distribution factors (LDFs) for interior and exterior girders of the investigated folded plate girder bridge.
  • The folded plate girder is an effective alternative for construction of short-span bridges.