Analytical and computational modeling of the mechanical interlocking between steel/FRP reinforcing bars and concrete.

摘要

Mechanical interaction (commonly called bond) between concrete and reinforcing bars significantly affects the structural response of reinforced concrete. This study addresses modeling issues for the bond of steel and fiber-reinforced polymer—FRP bars. Two analysis scales are examined: the rib-scale (where the surface structure of the bar is often explicitly modeled) and the bar-scale (where the surface is idealized as smooth and an interface idealization is adopted). The study's main objective is to better understand how contact between concrete and a bar with a fabricated surface structure affects the radial elastic response and how these effects can be incorporated into bar-scale models. A limited modeling study on the local crushing near the ribs of a bar is also presented.; Experimental or analytical justifications for the radial elastic modulus (Dˆe) of a barscale model do not exist, yet Dˆ e is important toward predicting bond behavior and splitting failures. A proposed analytical framework defines Dˆe as characterizing the local elastic deformation resulting from mechanical interlocking. The approach enforces static and strain energy equivalencies of riband bar-scale idealizations. Assuming axisymmetric elastic behavior, homogeneous materials, and periodicity, closed-form analytical solutions are obtained for Dˆ e. Dˆe's dependence on interface traction distribution, material constants and bar geometry is studied for steel and FRP bars. Dˆ e increases with the contact area but remains finite for full contact (assuming a nonuniform traction). For FRP bars, Dˆe reproduces the radial snap-back behavior that occurs with longitudinal cracking, which helps explain the splitting behavior of some test specimens and the convergence problems in some numerical studies. For a steel bar Dˆe is incorporated into a bar-scale bond model via a local contact model which leads to improved prediction of the radial response.; Elastoplastic constitutive relations are adopted and implemented in a rib-scale analysis to simulate the local crushing behavior near the surface structure of a bar. Numerical examples show how the crushing is concentrated near the surface structure. For a given axial load, crushing is predicted to decrease with an increase in the level of specimen confinement stress due to frictional response along the remainder of the interface.