Title:
Experimental Investigation on Stress Distribution in Florida Bulb-Tee Concrete Girders
Author(s):
Kamal Tawfiq and Moussa Issa
Publication:
Structural Journal
Volume:
95
Issue:
6
Appears on pages(s):
758-767
Keywords:
girders; grouting; post-tensioning; prestressed concrete
DOI:
10.14359/589
Date:
11/1/1998
Abstract:
The appearance of longitudinal cracking and spalling in the web section near the end block of Florida bulb-tee concrete girders have raised some concerns regarding possible problems which may be inherent in the design and construction procedures of the girders. Several factors believed to cause the stress buildup and the cracking were investigated in this study. Among these factors were the shapes of the post-tensioning ducts, the duct material, in-plane/out-of-plane stresses, and grouting pressure. Additionally, the estimation of the friction losses in designing the bulb-tee girders was considered to verify the adequacy of the existing specifications in predicting these losses. Two fully instrumented girders were prepared and tested under field conditions. Instrumenting the beams was based on an extensive finite element study that was performed before beam construction. An additional three-dimensional nonlinear finite element analysis was conducted after field testing. Results from the study showed that stress accumulation started at the end of the transition section where the web width gradually reduced to 178 mm (7 in.). A wedging effect due to out-of- plane stresses was the most critical factor causing stress buildups in the transition zone. The effect of grout pressure was more severe in ducts with oval cross sections than in round ones. Regardless, the durability and lower friction coefficient of the plastic ducts (high density polyethylene) were not as efficient as the metallic counterparts. Comparisons between friction losses obtained from the code and those determined in the field are presented in this study.