Title page for ETD etd-06232008-215305

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
  • Lightweight Concrete
  • Post-tensioning
  • Modulus of Elasticity
  • Tensile Strength
Date of Defense 2008-05-21
Availability unrestricted
Currently, 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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