Development Length for Large High Strength Reinforcing Bars


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Title: Development Length for Large High Strength Reinforcing Bars

Author(s): Phil M. Ferguson and J. Neils Thompson

Publication: Journal Proceedings

Volume: 62

Issue: 1

Appears on pages(s): 71-94

Keywords: beam, bond strength, crack width, cracking, development length, high strength steel, reinforced concrete, research.

Date: 1/1/1965

Supplementing an earlier report on # 3, # 7, and a few # 11 bar beams, this investigation reports on 33 # 11 bar beams and seven # 18s bar beams, all of ASTM A431 steel having fY above the 75 kips per sq in. minimum. Bar cover, beam width, stirrup ratio, development length, and depth of concrete cast below the bar were the primary variables. Diagonal tension limitations, at much lower stresses than expected, complicated these tests and possibly lowered the recorded bond values. The previously reported decrease in bond resistance with increasing development length showed to be less significant for lengths greater than 50 in. and possibly the resistance even levels off. Crack width at service load seemed significant for these Large high strength bars when development lengths were above 40 in., but crack width seemed little worse for a 101- in. length with a # 18s bar than for a 50-in. length with a # 11 bar. was not helpful in reducing surface crack width. Ordinary stirrups offset the reduction of bond strength brought about by placing two bars in a beam (equivalent to a narrower beam per bar) but otherwise generally added little to bond Extra cover over the bar increased bond resistance but strength or crack width control.