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Grout Bonded Concrete Anchors

Grout Bond
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Williams grouted concrete anchors are post-installed bars utilizing a high strength grout for the bonding material. The advantage of using a grout versus an epoxy is cement grout does not break down in high heat areas and can be pumped into deep embedded holes easier than epoxy. The disadvantages are longer set times than epoxy and the bond stress may also be lower. Williams offers US Spec RA Grout for cement grout bonded anchors. This product manufactured by US Spec has excellent grout bond characteristics and quick set-up times. See page 47 for the US Spec RA Grout properties. Shown on the following pages are the various steels and corresponding hex nuts that are used for Williams Grout Bonded Concrete Anchors.
Grouted Concrete AnchorHex NutHex NutHex NutSteel PlateSteel Plate150 KSI All-Thread-Bar150 KSI All-Thread-BarWil-X Cement GroutWil-X Cement Grout
Grouted concrete anchors typically use a hex nut at the bottom of the anchor rod. This helps to assure that a failure will not occur at the grout to bar interface. The modes of failure that can be evaluated for a single grouted concrete anchor include, ductile steel failure, concrete breakout failure and bond failure. By setting the bar’s ultimate steel strength equal to the concrete breakout strength, the designer can estimate a recommended embedment depth using industry design models. In addition bond failure can be checked by using a Uniform Bond Stress Model. Presently the anchor industry is absent of a formal design code for grouted anchors, however the designer can consider the following equations for assistance.
Uniform Bond Stress Model
The Uniform Bond Stress Model has been used in some testing to demonstrate the bond behavior of adhesive and grouted anchor systems by assuming a bond stress that is uniform throughout the anchor systems embedment length. This model is used to calculate the overall tensile strength of the bond at the grout/concrete interface. The equation shown below only gives an estimate as bond stress values and concrete compressive strengths do not always give consistent anchor test pull results. Please call Williams Concrete Anchor Division for more information on bond stress.
N
= Bond Strength (lbs.)
= Bond Stress for fully cured Grout
= 3.14
d
= Drill Hole Diameter (in.) Note: Minimum 1.5 x bar diameter
hef = Anchor Embedment Depth (in.)

Concrete Breakout Strength

A designer can estimate the concrete capacity using methods such as ACI 349-97 Appendix B or ACI 318-02 Appendix D. Example:
P
= Concrete Capacity (lbs.)
fc'
= Concrete Compressive Strength (psi)
Ac
= (hef)2 = Projected Cone Area (in2)
hef
= Anchor Embedment Depth (in.)
Williams Form Engineering Corp.
Grout Bond
Information
Parts &
Accessories
Installation
Equipment
Case
Histories
Corrosion
Protection
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