Effect of Grouting Pressure in Posttensioned Bulbtee Girders

Abstract

Out-of-plane stresses due to the wedging effect of the strands caused high stress concentration at the end of the transition zone of Florida bulbtee girders. Adding the hydrostatic stresses due to grout pressure in the posttensioning ducts severed the tensile stresses in the web section and caused some crack initiation between the ducts and on the surface of the girders. Other related factors were found to contribute to these stresses. Among these factors were the shape of the posttensioning ducts, and the type of the duct material. Two fully instrumented 22.9-m-long Florida bulbtee end girders were prepared and tested under typical field conditions. Testing results indicated that stress accumulation due to the grout pressure was more severe in ducts with oval cross sections than in the round ones. Although steel ducts were used in the full-scale field testing, a comparative study using 3D nonlinear finite-element analyses showed that cracking was even more severe when using high-density polyethylene ducts.