Lightweight Concrete for High Strength - Expanded Shale & Clay

steel and concrete consolidation in the transfer length region. Many experimental programs have
focused on the above factors in determining a relation to predict transfer length.
The Master’s Thesis by Chris Reutlinger, “Direct Pull-Out Capacity and Transfer Length
of 0.6-Inch Diameter Prestressing Strand in High Performance Concrete” provides very thorough
coverage of the history and development of equations to predict transfer length. The following is
a summary of current code provisions and other proposed equations as determined for NWC.
There are no known proposed equations specifically addressing transfer length for HSLC.
A.8.1 Janney, 1954
Initial transfer length testing by Janney in 1954 concluded that transfer length and the
general shape of the stress transfer distribution were attributable to diameter and surface
condition of the prestressing wire and concrete strength. Janney did not suggest a relation for
predicting transfer length.
A.8.2 Hanson and Kaar, 1959
Although the focus of Hanson and Kaar’s work was on flexural bond, an appendix
included comments on an assumed average transfer bond stress of 400 psi. Equation A.3 was
proposed as a way to determine the transfer bond stress.
u
t
=
A
ps
Σ
f
l
0 t
se
( A.3)
A ps is the area of prestressing strand, f se is the effective prestressing stress at transfer, Σ o is the
actual perimeter of the prestressing strand, l t is the transfer length and u t is the transfer bond
stress.
A.8.3 Kaar, LaFraugh and Mass, 1963
Kaar et al. concluded that transfer length varied directly based on strand diameter for ¼-
inch and ½-inch strands but did not follow this same direct proportion for 0.6-inch strand. Kaar
et al. found concrete strength did not impact transfer length, but affected the shape of the stress
distribution. Higher concrete strength allowed the concrete to pick up stress more quickly when
A-10