Time-Dependent Behavior of Concrete Beams Externally Prestressed with Carbon Fiber-Reinforced Polymer Tendons for 1000 Days

摘要

This paper presents an experimental program designed to examine the time-dependent behavior of concrete beams externally prestressed with carbon fiber-reinforced polymer (CFRP) tendons under sustained load for 1000 days. The experimental parameters included the type of prestressed tendon (CFRP or steel), type of nonprestressed reinforcement (glass fiber-reinforced polymer [GFRP] or steel), and the cracking situation (cracked or uncracked). The general trend was a high rate of increase in deflections for the early period (~100 days) after applying the sustained load, followed by a more gradual rate of increase in deflections. The ratios of terminal deflection on the 1000th day to initial deflection at the midspan for the externally prestressed concrete (PC) beams with cracked sections ranged from 1.31 to 1.34, whereas the ratio for the uncracked beam was 4.45. The results revealed that the long-term deflection of uncracked PC beams increased more rapidly than those of cracked PC beams, owing to relatively high compressive stress throughout the cross section. Furthermore, a validated step-by-step finite element analysis program was developed. The values calculated by the program corresponded well with the test results. Based on parametric analysis results of 46 beams in conjunction with regression analysis, a revised calculation method for predicting the midspan deflections of externally PC beams was suggested. It was found that the values calculated by the proposed method were in good agreement with the experimental results.