Lightweight Concrete for High Strength - Expanded Shale & Clay

Second, in some cases, the length over which the largest amount of prestressing force was
transferred appeared to be a distance somewhat less than the original transfer length discussed in
Chapter 5. Figure C.26 shows test G1A-East as an example of the strand stress increase in the
transfer length region as well as the apparent reduction in transfer length. The embedment length
on this test was only 67 inches. The “lone” triangle plots the maximum stress in the strand at the
point of loading at the girder’s ultimate load. This actual plot of strand stress differs
significantly from the theoretical diagram which would go linearly from “0” to the triangle.
300
Stress in Strands (ksi)
250
200
150
100
50
0
0 10 20 30 40 50 60 70 80
Distance From Girder End (Inches)
Strand Yield Stress at Load Point
Strand Maximum Stress at Load Point
Strand Maximum Stress
Effective Prestress
Crack Locations
Figure C.26 G1A-East Strand Stress vs. Distance from Girder End
Figure C.27 shows typical CSS data corresponding with applied shear levels, the location
of shear cracks crossing the bottom strands, and the transfer length region. CSS data was plotted
because it provided a measure of crack growth and allowed identification of the cracks that were
increasing most significantly in size. Comparing crack locations with the resulting end slip
allowed determination of the region where shear cracking most significantly impacted strand
slip. Based on crack location, a comparison was made between strand slip in girders with single
and double density shear reinforcement.
C-17