History of the Prestressing Strand Development Length Equation

摘要

A research study was conducted to determine the history of the AmericanAssociation of State Highway and Transportation Officials (AASHTO) prestressing strand development length equation and to evaluate the significance, with respect to development length, of changes in the AASHTO provisions for the determination of steel stress at ultimate flexural strength. The accuracy of the AASHTO provisions in determining steel stress at ultimate flexural strength was also evaluated for a number of typical cross sections used in bridge construction. The strand development length equation was first introduced in the 1963 ACI Building Code and was adopted by AASHTO in 1973. The original research that formed the basis for the equation was conducted at the Portland Cement Association (PCA) in the late 1950's and early 1960's. ACI Committee 423 derived and proposed the development length equation based on a reappraisal of the PCA results. A comparison of calculated steel stress at ultimate flexural strength using AASHTO Equation 9-17 and compatibility analyses using the RESPONSE computer program indicated that for AASHTO I-beams, bulb-tees, and box sections with deck slabs, the results were within 5 percent. The differences were higher (up to 8 percent) in the cases of box beams without deck slabs (high reinforcement ratios) and prestressed concrete piles.