Abstract
Experimental procedures used for the study of reinforcement to concrete bond have been hampered for a long time by inconsistencies and large differences in the obtained behavior, such as bond strength and mode of failure, depending on the specimen form and setup used in the test. Bond is controlled by the mechanics of the interface between reinforcement and concrete, and is sensitive to the influences of extraneous factors, several of which underlie, but are not accounted for, in conventional pullout test setups. To understand and illustrate the importance of specimen form and testing arrangement, a series of computational simulations are used in the present work on eight distinct variants of conventional bar pullout test setups that are used routinely in experimental literature for the characterization of bond-slip laws. The resulting bond strength increase generated by unaccounted confining stress fields that arise around the bar because of the boundary conditions of the test setup is used to classify the tests with respect to their relevance with the intended use of the results. Of the pullout setups examined, the direct tension pullout test produced the most conservative bond strength results, completely eliminating the contributions from eccentricity and passive confinement.
Highlights
Bond tests are used to support the development of design provisions for reinforcement anchorage in concrete structures for several different applications including: (a) Prooftesting and characterization of new reinforcing products in construction; (b) quantifying a dependable level of characteristic bond strength to be used in design and detailing; and (c) extracting pertinent constitutive bond slip relationships that could be used in either practical design or in numerical simulations of concrete structural members
Bond, measured through the tests, is a function of the test arrangement and is not an intrinsic property of the interface. It is one of the primary outcomes of this study to demonstrate the interdependency of the experimental bond setups and the resulting bond strength, through analytical simulation of the mechanics of the problem
To illustrate the effects of confinement and lateral stresses resulting from the unaccounted for boundary condition effects acting on the bar, it is imperative for the interface element on the bar surface to have the necessary pressure sensitivity so as to be able to capture the interaction between normal and tangential stresses
Summary
Bond tests are used to support the development of design provisions for reinforcement anchorage in concrete structures for several different applications including: (a) Prooftesting and characterization of new reinforcing products in construction; (b) quantifying a dependable level of characteristic bond strength to be used in design and detailing; and (c) extracting pertinent constitutive bond slip relationships that could be used in either practical design or in numerical simulations of concrete structural members. In the SPT, a bar embedded in the center of a concrete prism is pulled out while the concrete block is restricted through bearing on a stationary steel plate (Figure 1a) [2,3]. This type of test is still preferred today due to its simplicity by the steel industry for proof testing and quality control, whereas many researchers use it as a benchmark for the experimental assessment of bond.
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