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The National Academies

NCHRP IDEA 20-30/IDEA 227 [Completed (IDEA)]

Adjustable Cross-frames for the Erection of Steel Girder Bridges

  Project Data
Funds: $135000
Staff Responsibility: Inam Jawed
Research Agency: University of Notre Dame
Principal Investigator: Ashley Thrall
Effective Date: 7/1/2021
Completion Date: 12/31/2024
Fiscal Year: 2020

This project developed, numerically investigated, and experimentally demonstrated a novel, cost-effective deployable tool to facilitate the installation of cross-frames in highly skewed and curved steel girder bridges. The design, fabrication, and installation of cross-frames for curved and highly skewed steel girder bridges can be difficult and time-consuming. In these bridges, the girders twist and deflect, creating differential vertical displacements and rotations such that cross-frame fit can result in the following challenges: 1) un-planned force-fitting and hole reaming may be required in the field, 2) girder webs do not meet plumbness requirements, potentially resulting in high locked-in stresses both in the cross-frames and girders, 3) excessive bearing rotations, and 4)  poor joint alignment. To address these challenges, this project developed a deployable tool that can provide the necessary geometry adjustments to adjacent girders for the fit-up and installation of cross-frames. This tool consists of two cables and one hydraulic jack that can be deployed near where a cross-frame needs to be installed. The jack can be extended or contracted to rotate the girders such that they are approximately parallel to one another to achieve the desired geometry for the installation of the cross-frame without requiring force-fitting. After the cross-frame is installed, the deployable tool can be released and re-used elsewhere. 
In the first phase of the project, the concept was developed and the efficacy of the tool to facilitate the installation of cross-frames in a highly skewed and a curved steel girder prototype bridge was numerically demonstrated. Three-dimensional finite element (FE) analyses of the two prototype bridges under steel dead load at the construction increment just before the cross-frames would be installed were performed to first understand the challenges in cross-frame fit-up. The deployable tool was then incorporated into the developed FE model to determine the forces in the system throughout its deployment and the installation of the cross-frames. A control sequence for the deployment was developed and evaluated. For the prototype bridges considered in this research, the peak force in the hydraulic jack was 26.6 kN (5.97 k), meaning that off-the-shelf technologies could be used. The peak von Mises stress in the installed cross-frame was 22.4 MPa (3.25 ksi), indicating that the procedure is not over-stressing the system. 
In the second phase, a prototype demonstration was carried out and recommendations for use of the tool were developed. The prototype demonstration was performed using a one-quarter scale experimental test setup that represents a portion of a built bridge during one stage of erection where cross-frames would be installed. The girders were shifted vertically and rotated relative to one another to represent the differential vertical deflection and differential rotation that can result during erection. The behavior of the girders and the deployable tool was monitored as the tool was deployed (i.e., the hydraulic jack is extended in displacement control) to achieve the desired geometry adjustment between the girders. Measured behavior was compared with numerical predictions. Findings indicate the deployable tool is able to provide the necessary geometry adjustment to enable cross-frame installation. 

The Final Report is available.

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