Lightweight Concrete for High Strength - Expanded Shale & Clay

findings were comments that the AASHTO LRFD provisions for shear were very conservative
and required modification to improve their reliability.
A.10.4 Barnes, Burns and Kreger, 1999
Barnes, Burns and Kreger conducted an extensive research program at the University of
Texas at Austin using 0.6-inch diameter prestressing strand in I-shaped prestressed girders made
with normal weight HPC having strengths from 5,000 to 11,000 psi. The authors recommended
limiting the principal tensile stress in the region from the composite section centroid to the
extreme tensile fiber to 4(f c ’) 1/2 . This recommendation corresponds with ACI 318-99 Section
11.4.2.2 but extends the applicable area to include the section from the composite centroid to the
extreme tension fiber.
A.10.5 Ma, Tadros and Baishya, 2000
Ma, Tadros, and Baishya examined shear behavior in pretensioned I-girders made with
8,000 psi normal weight HPC. They concluded that both the AASHTO Standard and LRFD
Specifications produced conservative predictions of girder shear capacity. When considering the
results of their study, it must be recognized that prestressing strands were anchored in end
diaphragms thus eliminating the possibility of slip and possibly increasing shear capacity at the
girder ends.
A.10.6 Ramirez, Olek, Rolle, and Malone, 2000
Ramirez, Olek, Rolle, and Malone conducted research on HSLC pretensioned girders
made with ½-inch, and 0.6-inch diameter prestressing strands. The HSLC was made using
expanded shale aggregate; the resulting concrete strengths ranged from 6,500 to 10,000 psi. The
research at Purdue is thought to be the only other research conducted using 0.6-inch diameter
prestressing strand in HSLC. As with Ma, Tadros and Baishya (2000), an additional 1-meter
anchorage was provided for the prestressing strand behind the center of bearing. Their
conclusions related to shear were that the current AASHTO Standard and LRFD procedures
were conservative for shear. Additionally they reported that the minimum amount of shear
reinforcement for HSLC pretensioned girders must be further investigated based on a lower ratio
of measured/calculated shear capacity with increased concrete strength.
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