Sources of Crack Growth in Pretensioned Concrete-Bridge Girder Anchorage Zones after Detensioning

Abstract

As a result of heavy prestressing, anchorage zones of bridge girders frequently crack in consistent patterns at prestress transfer and cause durability concerns. These cracks, which appear during prestress release, continue to grow in width and length in the months following detensioning. This study investigated reasons behind crack growth after detensioning. Load effects created by differential cooling, creep, and shrinkage of bulb-tee cross sections were studied as potential reasons for crack growth. Fully coupled thermal-mechanical analyses included nonlinear concrete material properties. The analyses were verified and validated by analytical calculations and test data. A parametric study was conducted to understand the sensitivity of results to concrete thermal properties and ambient temperatures. Temperature changes resulting from curing and creep had a favorable and negligible effect on concrete strains, respectively. Shrinkage strains, although not sufficient to initiate cracking without prestressing, were determined to be a cause for increase in crack width and length after detensioning. Reinforcing bar stresses increased up to 20% in low ambient temperatures and for low-thermal-expansion concrete under curing temperatures and exceed the AASHTO limits.