Development Length for Straight Deformed Bars in High-Strength Concrete


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Title: Development Length for Straight Deformed Bars in High-Strength Concrete

Author(s): F. A. Al-Jahdali, F. F. Wafa, and S. A. Shihata

Publication: Special Publication

Volume: 149


Appears on pages(s): 507-522

Keywords: compressive strength; deformed reinforcement; failure; high-strength concretes; pullout tests; reinforcing steels; Structural Research

Date: 10/1/1994

Experimental results on the bond behavior of high-strength concrete are presented. A total of 36 specimens was tested. The variables were the concrete compressive strength, the bar diameter, and the embedded length. The concrete compressive strength varied from 42 to 78 MPa (6000 to 11,000 psi). The bar diameters were 14, 16, 18, and 20 mm. The bond tests were conducted using a modified version of the Danish Standard DS 2082 pullout test in which the concrete surrounding the bar was in uniform tension. The test results indicate that the average bond stress at failure increases with the increase in the concrete compressive strength and decreases with the increase in the embedded length. The embedded length calculated using the ACI Building Code 318-89 equation caused a steel yielding failure. The predominant type of failure was the splitting of concrete; however, yielding of the embedded steel preceded the splitting failure in more than half of the specimens. It was observed that the ACI Building Code equation underestimates average bond stress for high-strength concrete. A model is developed to predict the bond strength of high-strength concrete in terms of the concrete cover, bar diameter, embedded length, and concrete compressive strength as variables. The proposed equation gave good prediction to the bond stress at failure of the pullout specimens tested in this investigation. 260-594