Title:
Effect of Confinement on Bond Strength between Steel Bars and Concrete
Author(s):
Mohamed H. Harajli, Bilal S. Hamad, and Ahmad A. Rteil
Publication:
Structural Journal
Volume:
101
Issue:
5
Appears on pages(s):
595-603
Keywords:
bond stress; confined concrete; development length; fiber-reinforced concrete; fiber-reinforced polymer; splice; tensile splitting strength
DOI:
10.14359/13381
Date:
9/1/2004
Abstract:
The local bond aspect between steel bars and concrete confined with ordinary transverse steel is experimentally investigated. The test parameters included diameter of reinforcing bar, ratio of concrete cover to bar diameter db , and area of transverse reinforcement. The results were compared with the results of similar specimens for concrete confined either internally using steel fiber reinforcement or externally using fiber-reinforced polymer (FRP) sheets. Based on these comparisons, a unified expression for the local bond strength of confined concrete is derived, and a general model for the local bond stress-slip response is proposed and used to conduct an analytical evaluation of the effect of confinement on development/splice strength. Results predicted by the analysis were in good agreement with experimental results. For small development/splice lengths corresponding to local bond conditions, confining the concrete only slightly increases the local bond resistance but leads to considerable improvement in the ductility of bond failure. The corresponding ductility at the local level allows, for the practical range of development/splice lengths, more bar lugs to participate in resisting the applied bar force resulting in a more uniform bond stress distribution along the development/splice length and, consequently, a sizable increase in the average bond strength at bond failure as compared with plain unconfined concrete. The bond strength due to FRP confinement increases in proportion to the modulus of elasticity of the FRP material. For the same area of transverse reinforcement per unit length along the splice, taking into account the relative modulus of elasticity of the confining materials, external confinement of concrete using FRP sheets is more effective in increasing the development/splice strength than internal confinement with ordinary transverse steel. A general design expression is proposed to estimate the development/splice length of steel bars embedded in concrete confined with ordinary transverse steel, FRP, or steel-fiber reinforcement.