FRP bar properties - Reinforced Concrete with FRP Bars: Mechanics and Design - page 41

of the anchor is such that the grout forms a cylindrical shell around
the specimen. After curing, the expansive grout exerts a pressure on
the specimen and decreases the likelihood of precipitating failure in the
grip region. The clamping pressure exerted on the specimen is dependent
upon the confinement provided by the steel pipe and the properties of the
grout layer, including the thickness, modulus of elasticity, Poisson's ratio,
and coefficient of linear expansion. One advantage of the expansive grout-
based grip is that one can adjust the grout layer thickness, level of con-
finement, and specimen embedment length (gripping length) to achieve
the desired gripping behavior. To achieve such a versatile design, accurate
assessment of the gripping pressure as a function of steel pipe dimensions
and grout thickness (volume) is needed.
A study by Schesser et al. [60] developed a method to determine the
grout material properties, including modulus of elasticity and the coeffi-
cient of linear expansion using the ASTM-recommended configuration for
actual bar testing. Based on these parameters and an analytical solution, a
design procedure was derived to dimension the anchor for any type of bar
commercially available as demonstrated by successfully testing more than
100 specimens (Figure 3.4). The measured strength values were remarkably
consistent with a coefficient of variance (CV) less than 5%. The design of
expansive grout-based grips includes determination of the minimum grip-
ping length, optimum confinement pipe dimensions, and minimum grout
material volume.
ASTM D7617/D7617M, Standard Test Method for Transverse Shear
Strength of Fiber Reinforced Polymer Matrix Composite Bars. The shear
strength is measured by forcing the FRP bar specimen to fail due to trans-
verse shear. Typical transverse shear test setup is shown in Figure 3.5. At
least five specimens are required.
ASTM D7337/D7337M, Standard Test Method for Tensile Creep
Rupture of Fiber Reinforced Polymer Matrix Composite Bars. The
load-induced, time-dependent tensile strains of the FRP bar correspond-
ing to at least five levels of load (ranging between 20% and 80% of the
tensile capacity) are measured at certain ages (such as after 1, 10, 100,
and 1000 hours) and in correspondence of at least five selected levels of
load. The empirical strain values are plotted with respect to time (that
is expressed on a logarithmic scale) and an approximation line from the
graph data is extrapolated by means of the least-square method. The load
ratio at 1 million hours, as determined from the calculated approxima-
tion line, is the creep-rupture load ratio. The load corresponding to this
creep-rupture load ratio is the million-hour creep-rupture capacity. The
million-hour creep-rupture strength is calculated by dividing this load
capacity by the cross-sectional area. At least five specimens at each level
of load are required.