ANALYTICAL MOMENT-CURVATURE RELATIONS FOR TIED CONCRETE COLUMNS

The research reported here is a follow-up on experimental work in which 16 12 in. (305 mm) square and 9 ft (2.74 m) long columns were tested under flexure to large inelastic deformations while simultaneously subjected to axial load that remained constant throughout the test. The main variables included the distribution of longitudinal and lateral steel, amount of lateral steel, tie spacing, and axial load level. In this paper, the predictions for the behavior of these specimens from the available stress-strain models for confined concrete are compared with the test results. After a critical examination of the analytical models and the variables that affect the behavior of the specimens, a model originally proposed for concentric compression was modified to include the effects of strain gradient and the level of axial load. As a result of strain gradient, the concrete is able to sustain additional deformation at and beyond the peak stress. The effect of increased axial load is incorporated with reduced concrete strength. A numerical example is presented in which the use of a rectangular stress block representing the actual stress-strain curve of concrete obtained from the confinement model is demonstrated.