Lightweight Concrete for High Strength - Expanded Shale & Clay

A.10.7 ACI Committee 213, 2001
In a draft copy of Chapter 5, ACI 213, shear and diagonal tension strength is covered in
Section 5.8. Committee 213 reports that lightweight concrete members behave in fundamentally
the same manner as normal weight concrete members. They recommend that the permissible
shear capacity may be determined by substituting the splitting tensile strength, f ct /6.7 for (f c ’) 1/2
in the shear provisions of Chapter 11, ACI 318.
A.11 Development Length
Development length of prestressing strands is the sum of the transfer length and the
flexural bond length. Development length can be defined as the minimum distance from the end
of the member beyond which the application of a point load will result in a flexural failure. As
in transfer length, many factors are thought to affect development length. Many experimental
programs have addressed development length resulting in suggested equations for its prediction.
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 development length. The
following is a summary of current code provisions and other proposed equations as determined
for NWC. The summary closely mirrors the development of transfer length equations. There are
no known equations specifically addressing development length for HSLC.
A.11.1 Janney, 1954
Initial development length testing by Janney in 1954 was based on the use of 5/16-inch
wire having two different surface conditions prestressed to 0, 60, 120 and 165 ksi in beams made
with NWC having strengths from 4,500 to 4,800 psi. Janney reported a “wave of flexural bond
stress concentration” and noted that once general bond slip occurred, the beam failed shortly
thereafter. Janney contributed bond in the transfer region predominantly to the Hoyer effect,
which was the confining pressure applied to the wire by the concrete. Janney also reported
improved bond characteristics for slightly rusted wire.
A.11.2 Hanson and Kaar, 1959
Hanson and Kaar conducted a study involving 47 small-scale concrete beams reinforced
with various sizes of Grade 250 stress-relieved strand. The tests focused on five factors
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