Lightweight Concrete for High Strength - Expanded Shale & Clay

A.10 Shear Behavior
Similar to flexural behavior, only a limited amount of research has been conducted on
prestressed HSLC. Comments are provided for both HSLC and normal weight HPC as well as
for LWC as applicable to this research.
A.10.1 Hanson, 1961
The origination of the lambda factor for use with LWC was based on work done by
Hanson. Using the results of testing performed at PCA and at the University of Texas, Hanson
determined a good correlation between diagonal tensile strength in beams with the splitting
tension test. Hanson then determined that the ratio of splitting tension strength in lightweight
concrete to that for normal weight concrete of the same compression strength was in general
about 0.85 for concrete strengths below 5,000 psi. This relation was first reported in the 1963
ACI 318 Code. In the early 1970’s, the reduction factor was formalized as lambda, λ, as 0.85 for
sand LWC and 0.75 for all LWC. Based on the high degree of variability of LWA, concerns
exist today that the lambda factors may become unconservative for concrete strengths over 5,000
psi (Holm, 2002).
A.10.2 Johnson and Ramirez, 1989
Johnson and Ramirez conducted research on non-prestressed beams, but made some
observations that may be applicable for prestressed HSLC and normal weight HPC. One
conclusion reached in their research was that in higher strength beams, shear reinforcement
spacing was greater creating a deficiency in reserve shear strength. Once the upper limit of
concrete shear capacity was exceeded, the shear force transferred to shear reinforcement would
cause it to yield and rupture. They suggested applying either an upper limit to the term (f c ’) 1/2 to
limit the increase in V c due to increasing f c ’ or increasing the minimum shear reinforcement
requirement as concrete strength increases. The 1989 ACI 318 code has included a specification
reflecting this recommendation.
A.10.3 Shahawy and Batchelor, 1996
Shahawy and Batchelor conducted a research program examining the shear behavior of
full-scale prestressed concrete girders made from 6,000 psi NWC. Of particular interest in their
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