Type of Document Master's Thesis Author Axson, Daniel Peter URN etd-06232008-215305 Title Ultimate Bearing Strength of Post-tensioned Local Anchorage Zones in Lightweight Concrete Degree Master of Science Department Civil Engineering Advisory Committee
Advisor Name Title Roberts-Wollmann, Carin L. Committee Chair Charney, Finley A. Committee Member Cousins, Thomas E. Committee Member Keywords
- Lightweight Concrete
- Modulus of Elasticity
- Tensile Strength
Date of Defense 2008-05-21 Availability unrestricted AbstractCurrently, NCHRP Report 356 has published an equation to estimate the ultimate strength of the
local zone in normal weight concrete. The local zone is the area of concrete directly ahead of the
bearing plate. The equation can be broken into two distinct parts: unconfined bearing strength of
concrete enhanced by the A/Ab ratio and the enhancement of strength due to the presence of
confining. Research has shown that the strength enhancement of the A/Ab ratio and confining
reinforcing is less in lightweight concrete than in normal weight concrete.
To determine the strength of the local zone in lightweight concrete 30 reinforced prisms, 2
unreinforced prisms, and concrete cylinders were tested. The dimensions of the prisms were 8
in. x 8 in. x 16 in. and the cylinders were 4 in. x 8 in. cylinders. The simulated reinforcing in the
prisms extended only through the top 8 in. of the prism and consisted of either ties or spirals with
different spacing or pitch, respectively. To determine the effect of the A/Ab ratio for each
spacing or pitch arrangement of the reinforcing, one of two different size bearing plates were
From the testing performed in this research and other research, it is apparent that the NCHRP
equation is unconservative when estimating the ultimate strength of the local zone in lightweight
concrete. By modifying both parts of the NCHRP equation it is possible to conservatively
predict the ultimate strength of the local zone in lightweight concrete.
Also investigated in this thesis are equations to predict the splitting cylinder strength and
modulus of elasticity of lightweight concrete. For a sand-lightweight concrete, as defined by
ACI 318-05 Building code and Commentary, the splitting tensile strength can be accurately
predicted by multiplying the square root of the compressive strength by 5.7.
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