Cracking Down on Cracked Concrete

A concrete bridge can crack under the pressure of the daily grind, but this team of civil engineers are working to keep our bridges safe, long-lived and crack-free. 

Kent Harries, FASCE, FACI, FIIFC, P.Eng., professor of civil and environmental engineering at the University of Pittsburgh’s Swanson School of Engineering, shared the Robert J. Lyman Award from the Precast/Prestressed Concrete Institute (PCI) for the paper, “Experimental background behind new AASHTO LRFD specifications for partially debonded strands,” which looks to improve the design of partially debonded strands in prestressed concrete highway bridge girders. 

“Using partially debonded strands is a simple technique for reducing potential cracking in prestressed concrete members and increasing the girder’s durability - extending its useful life” says Harries. “Debonded strands are necessary for longer and more economical bridge spans to be achieved.”

Partially debonded strands result when the ends of embedded prestressing strands are wrapped in a split plastic tube. Stress is not transferred between the strand and surrounding concrete over the debonded region, reducing local stresses in the bridge girder. 

After testing both full-scale I- and U-shaped girders, Harries and his team, led by Bahram Shahrooz at the University of Cincinnati, found that partially debonding strands are effective at reducing local stresses and do not otherwise impact the structural behavior of the girder. 

“We examined amounts of partial debonding, distribution of partially debonded strands within the cross section, debonded lengths, locations and staggering of termination of debonded strands, confinement of debonded regions and their termination points, and the impact of adding non prestressed reinforcement in the region of partial debonding to help reach our conclusion,” Harries said. Recommendations from the study have been adopted by AASHTO into the National Bridge Design Specifications.

The paper (DOI: 10.15554/pcij68.2-01) was published by the Precast/Prestressed Concrete Institute Journal. Joining Harries in this research were: 

• Matthew W. Bolduc, Ph.D., former graduate student, University of Cincinnati 
• Bahram M. Shahrooz, Ph.D., Professor at the University of Cincinnati
• Richard A Miller, Ph.D. Professor at the University of Cincinnati
• Henry G. Russell, engineering consultant, Henry G. Russell, Inc. 
• Avdhesh Gaur, former graduate student, University of Cincinnati 

According to the PCI website, the Robert J. Lyman Award is a prestigious honor that recognizes authors who offer “the greatest contribution to the advancement of plant production, site erection, or general construction of precast concrete structures.”