Epoxied rebar pullout

[mr5890]

According to the label on the epoxy that the contractor is using, a #6 rebar dowel epoxied 6" into 2500psi concrete has a bonding strength of approx. 39,000lbs. Here is my question. If you embedded this bar 6" into a 7'x7'x2.5' pier of 3000 psi concrete which has a steel mat at the bottom of the pad, even though the boding strength is more than the dead weight of that pier (approx. 20,000 lbs) I assume that the bar would remain bonded to the surrounding concrete, but a failure cone would break out. Is this correct, and if so, approx. how much force would it withstand before a cone failure? Thanks.

Matt Roberts

 

[boo1]

Allowable load is the lesser of the load based on bond strength (adjusted for edge, spacing and elevated temperature effects) or steel strength. ASTM A615, Grade 60 Rebar allowable load is 10,560 lb uplift. Typical allowable loads concrete loads are reduced by a safety factor of 4.

Allowable loading would be ~9750 lb, assuming proper fire protection and no reduction for corrosion, over sized hole size, field errors, prying, shear loading and temperture effects.

 

[Ron]

Epoxy bonded rebar does not fail in the same manner as an expansion anchor. The pullout resistance is much more dependent on the shear strength of the epoxy/concrete interface and a tension cone does not usually develop.

Pullout strength depends on two primary factors: Depth of embedment and bar strength. If the depth of embedment is great, the pullout will develop the entire bar strength to failure. If less than required for the full development, will depend on the shear interface with the concrete.

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[boo1]

U/V degradation of the epoxy causes chaulking at the surface. This reduces the bond strength.