• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05a
• /
• pp.331-334
• /
• 2005

The nature of bond of untensioned prestressed strand in concrete differs from that of plain or deformed reinforcing bar as well as tensioned prestressed strand. There is a very limited amount of published research information regarding bonding of this type reinforcing. In order to use and design untensioned strand as reinforcing, relationships defining the load transfer characteristics of the strand are necessary. A program based upon pullout tests was designed to develop data relating the critical parameters for determining load transfer behavior of the untensioned strand. The purpose of this study is to investigate the characteristics of bond and development length between untensioned strand and concrete. The test variables include diameter of strands (9.3mm, 12.7mm) and development lengths. The maximum bond stress at the 9.3mm and 12.7mm strands decreases with the increase of the rate of development length. The untensioned prestressed strands displayed bond performance when secure development length more than 80$\%$ according to the development of deformed bars equation.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.5
• /
• pp.101-108
• /
• 2008

The primary objective of this research is a study on the pullout bond characteristics of untensioned prestressing strand in concrete. The bond characteristics of untensioned prestressing strand in concrete differs from that of deformed reinforcing bar. In order to use and design untensioned prestressing strand as deformed reinforcing bar, a study for bond characteristics of the untensioned prestressing strand was progressed. Major test variables are embedment length ($10d_b{\sim}60d_b$), concrete cover (45mm, 70mm, 100m) and diameter of strands. (12.7mm : SWPC7, 9.3mm : SWPC7A) As a results, these showed that average bond stress was decreased as a growing the embedment length, and then showed that the bond performance of untensioned prestressing strand was improved if embedment length was above 60$60d_b$.

• Structural Engineering and Mechanics
• /
• v.76 no.1
• /
• pp.67-81
• /
• 2020

Pretensioned concrete (PC) is widely used in contemporary construction. Bond of prestressing strand is significant for composite-action between the strand and concrete in the transfer and flexural-bond zones of PC members. This study develops a new methodology for quantifying the bond of 18-mm prestressing strand in PC members based on results of a pullout test, the Standard Test for Strand Bond (STSB). The experimental program includes: (a) twenty-four pretensioned concrete beams, using a wide range of concrete compressive strength; and (b) twelve untensioned pullout specimens. By testing beams, the transfer length, flexural-bond length, and development length were all measured. In the STSB, the pullout forces for the strands were measured. Experimental results indicate a significant relationship between the bond of prestressing strand to the code-established design parameters, such as transfer length and development length. However, the code-predictions can be unconservative for the prestressing strands having a low STSB pullout force. Three simplified bond equations are proposed for the design applications of PC members.