Development Length and Lateral Spacing Requirements of Prestressing Strand for Prestressed Concrete Bridge Girders

Time-dependent evolution of strand transfer length in pretensioned prestressed concrete members

“…Then the friction mechanism and the mechanical action are activated and frictional bond stresses are developed, which are caused by radial compressive stresses around the prestressing strand. Several effects contribute to radial compressive stresses (den Uijl 1998, FIB 2000, including long-term effects such as shrinkage of concrete (William et al 2008) and creep of concrete (Balevicius 2010). Shrinkage of the concrete surrounding the prestressing strand enhances additional radial compressive strength and bond resistance over time, while creep of concrete and prestressing strand relaxation diminish high local stresses and strains and bond stresses (Weerasekera 1991;Barnes et al 2003;FIB 2010).…”

“…The ACI transfer length equation was derived from and based on an average transfer bond stress of 2.76 MPa (Tabatabai and Dickson 1993). In addition, several authors (Zia and Mostafa 1977;Shahawy et al 1992;Mitchell et al 1993;Deatherage et al 1994;Buckner 1995;Tadros and Baishya 1996;Mahmoud et al 1999) consider that using term f si (the initial effective stress in a prestressing strand just after the prestress transfer, accounting for losses only by the elastic shortening of concrete) in Eq. (1) is more rational for design purposes than f se by considering that transfer length is established at the release of prestress and that it does not significantly change over time.…”

“…(1) is more rational for design purposes than f se by considering that transfer length is established at the release of prestress and that it does not significantly change over time. However, U t = 2.76 MPa is retained in (Shahawy et al 1992;Deatherage et al 1994;Buckner 1995;Tadros and Baishya 1996), resulting in longer transfer lengths when f si is used. …”

Transfer Length of Strands in Prestressed Concrete Piles

“…10,11 Measurements of prestressed strand end slip consistently show higher end slip in the top of a cross section, regardless of cross-sectional shape or strand arrangement. [10][11][12][13][14] In reinforced concrete design, the importance of top bar effects has been accounted for in the ACI 318 Code since 1951. The development length of top cast bars in reinforced concrete is increased by a factor of 1.3 (ACI 318-99 9 ) or 1.4 (AASHTO 6 ).…”

Top Bar Effects in Prestressed Concrete Piles

“…Measurements of prestressed strand end slip, a measure of the resulting development length, consistently show higher end slip in the top of a cross section regardless of cross-sectional shape or strand arrangement. [10][11][12] In the most recent study, 12 strand end slip measurements were taken at five prestressing plants in the southeastern U.S. Strand end slip measurements were collected for 23 piles. Excessive strand end slip, at times exceeding 0.75 in.…”