Correct Prediction of Transfer Lengths in Pretensioned Prestressed ConcreteStructures

摘要

The current ACI design code considers only the prestress intensity and the diameter of prestressing steels to calculatethe transfer length of steels. Other important parameters, however, including concrete strength and concrete cover may affectthe transfer length significantly. To this end, a comprehensive experimental program has been set up. The principal testvariables considered were strand diameter, concrete strength, concrete cover size and strand spacing. The results of presentstudy indicate that the current code equation for transfer length overestimates the actual measured transfer length. Thisoverestimation is particularly significant for high strength concrete with larger concrete cover, which are not covered by theACI code. The present study shows that the transfer length decreases with an increase of concrete strength and also decreaseswith an increase of concrete cover. These important parameters must be, therefore, included reasonably in the current designcodes. The strand spacing also affects the transfer length and the increase of strand spacing results in a decrease of transferlength. The present study also shows that the end slip values can be efficiently used to determine the transfer length ofpretensioned concrete members. The theoretical determination of transfer length based on slip agrees very well with test data.The present study provides valuable test data for the realistic and accurate determination of transfer length, which can beefficiently used for improving the design equation of transfer length in pretensioned prestressed concrete members.