CCEER-89-2-B: A Simple Model to Predict the Ultimate Response of R/C Beams with Concrete Overlays

Abstract

This report describes a study in which a relatively simple computer model was developed to predict the ultimate response of R/C composite beams retrofitted with concrete overlays. This model follows another more accurate but very complex model developed previously in the University of Nevada-Reno. The present model uses idealized bilinear laws for steel and interface shear flow, as well as an elasto-plastic idealized law for concrete. The model was implemented in a microcomputer program called URCCO.

The model was tested against measured data provided by the University of Puerto Rico. For specimens in which flexure was the primary mode of failure, the calculated loads matched the measured ones within a reasonable accuracy. However, the calculated displacements were, on the average, lower than the measured ones.

A parametric study was conducted to identify possible beneficial effects of certain parameters associated with the ultimate strength, the interface shear, and the ductility of the composite specimens. The parameters were (1) ratio of compressive overlay thickness to beam effective depth, (2) compressive overlay concrete strength, (3) steel ratio in beams with tensile overlays and (4) ratio of tensile overlay effective depth to beam effective depth.

The results show that strength, interface shear, and ductility are strongly influenced by these parameters. The shear capacity of the interface shear connectors should be adequate to maintain composite action until concrete crushing in the retrofitted beam. It was concluded that heavily-reinforced beams with thick compressive overlays are bound to have high interface shear and should be avoided. The same was true in tensile overlays with large amounts of steel resulting in heavily-reinforced beams. In contrast, beams with tensile overlays which are moderately reinforced have a relatively low interface shear and, hence, exhibit desirable strength and ductility (Abstract by authors).