Stress relaxation behavior of prestressing strands under low temperatures

This paper presents the results of experimental and analytical studies on the stress relaxation behavior of steel strand under combined prestressing forces and low temperatures. An 18-specimen test program was conducted to investigate the stress relaxation behavior of steel strand under prestressing forces of 0.5 to 0.75 times the ultimate tension capacity and at temperatures ranging from 20 degrees C (68 degrees F) to -165 degrees C (-265 degrees F). The test results show the relaxation behavior of the steel strands as the time increased from 0 to 100 hours after prestressing and the effects of low temperatures and prestressing levels on the relaxation behavior. Based on the test results and using the best subset regression method, a mathematical model was developed to predict the relationship between the relaxation rate and different influencing parameters, including time, prestressing levels, and low temperature. The accuracy of the regression model was checked through validation against 134 test data points. Finally, a design equation is proposed based on these extensive validations.