Experimental cyclic studies on a three-girder steel bridge subassembly model

  • PI: Ahmad Itani
  • Co-PI: Ian Buckle
  • Research assistants: Hamid Bahrami, Kevin Friskel
  • Sponsor: California Department of Transportation
  • Caltrans project manager: Allaoua Kartoum
  • Project date: June 2009

Project summary

One promising technique for the seismic design of highway bridges with steel superstructures is to dissipate energy through the inelastic deformation of the end cross frames. These so-called ductile end cross frames reduce the shear demand on the substructure below the cross frames. However, this reduction in base shear is inversely proportional to the lateral drift in the end cross frames, i.e. the smaller the base shear, the larger the superstructure drift. Large drifts place large deformation demands on other bridge components, such as shear studs and steel girders. Damage to these components may lead to permanent deformations in the superstructure, which, in turn, may lead to reduced capacity for live load until repairs are completed.

The subassembly specimens are 50% scaled models of a three-girder bridge prototype. The prototype bridge dimensions are based on the bridge superstructure outlined in the Caltrans Steel Girder Bridge Design Example.

The specimens are three feet wide subassemblies of a three-girder bridge model with various shear studs and diagonal bracing configurations. The concrete slab is 4.5 in. thick with a haunch of 1.06 in. the deck overhangs are 2.5 ft. The girders are spaced at 6 ft on centers. The plate girders are made up of 1 in. thick by 9 in. wide flanges and webs of 5/16 in. thick by 39 in. deep. The bearing stiffener plates are 7/8 in. thick.

The general objectives of the experiments are to:

  • Investigate lateral response of steel plate girder subassembly with various cross frames
  • Determine the cyclic behavior of shear studs
  • Determine lateral response of various cross frames

The objectives of this experiment are to find the strength, stiffness and failure modes due to transverse cyclic displacement in end cross frames.

In this specimen, the buckling of compression braces is expected to be followed by formation of plastic hinges at the ends of top and bottom chords and yielding in diagonal bracing members.