Transfer and Development Length of 0.6-inch Strand in High Strength Lightweight Concrete

摘要

This paper presents the findings of a research project conducted at Georgia Tech that tested six pretensioned AASHTO Type Ⅱ girders constructed using expanded slate lightweight concrete with design strengths of 8,000 and 10,000 psi (55.2 and 68.9 MPa). Actual strengths ranged from 8,790 to 11,010psi(60.6 to 75.9 MPa). Each was prestressed using 0.6-inch (15.2-mm) diameter low relaxation strands tensioned to 75% of strand ultimate stress. External strain measurements showed transfer lengths of 21.9 inches (556 mm) and 15.6 inches (396 mm) for the 8,000 and 10,000 psi (55.2 and 68.9 MPa) concretes; these were 73 percent and 52 percent of the design values given by AASHTO 16th Edition. Three-point bending tests were conducted on each beam to determine development length characteristics. The distance from the beam end to the load point was varied from between 70 and 100 percent of the AASHTO specified development length. Strand slip was measured for each test. Results indicated that the development lengths were91 inches (2.31 m) and 67 inches (1.70 m) for the 8,000 and 10,000 psi (55.2 and 68.9 MPa) concretes; these were 95 percent and 70 percent of the design development lengths given by AASHTO 16th Edition.