Effect of Embedment Length on Bond of 18 mm (0.7 in.) Strand by Pullout Test

摘要

A series of experimental tests were conducted to investigate the bond performance of untensioned 18 mm (0.7 in.) diameter strand in high-strength concrete. Eight pullout tests were conducted on prismatic specimens with four different strand embedment lengths. The relationship between strand slip and pullout force, along with the concrete surface strain distribution along the strand and its development with force, was investigated. Observed failure modes of the pullout tests varied, but seemed to be dependent on strand embedment length. Also, transfer length L_t and development length L_d were examined. The measured transfer length was 610 mm (24 in.) and the observed development length was from 910 to 1220 mm (36 to 48 in.) for the 18 mm (0.7 in.) diameter strand. A correlation is demonstrated between transfer and development lengths and strand embedment length in pullout tests in terms of strand stress development and strand slip in the end. Crack effect in flexural beam test was discussed. Pullout testing of specimens with different strand embedment lengths can determine transfer length and development length, and serve as a basis in predicting bond performance in prestressed concrete members.