Early Loading Effects on Bond Strength


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Title: Early Loading Effects on Bond Strength

Author(s): Craig R. Clark and David W. Johnston

Publication: Journal Proceedings

Volume: 80

Issue: 6

Appears on pages(s): 532-539

Keywords: anchorage (structural); bond (concrete to reinforcement); bond stress; concrete construction; cracking (fracturing); creep properties; embed-ment;loads (forces); reinforced concrete; reinforcing steels; slippage.

Date: 11/1/1983

An investigation was conducted to determine the effects of early loading on concrete bond with deformed steel reinforcement. Bond tests were conducted on identical beam end specimens with a 4000 psi concrete mix using 60 ksi reinforcement. The 28 day ultimate bond strength and the concrete bond load-slip characteristics were compared for specimens loaded at one day and maintained for 27 days to specimens only loaded at 28 days and to specimens loaded to ultimate at one day. Three different embedment lengths were tested. The results indicated no detrimental effects on the day ultimate bond strength as a result of the early working stress level of load that was applied at one day. The tests also indicate that such early loading will result in larger permanent deformations due to the increase in slip that takes place during early loading. But the total slip and thus probable deflections that took place at the ultimate loading were very similar to the 28 day loading results without early loading.