A practical approach for modeling FRP wrapped concrete columns

Fiber reinforced polymers (FRP) have gained rapid popularity in recent years as one of the strengthening techniques of structural concrete elements. Particularly, increase in the use of FRP composite materials for strengthening and retrofitting of reinforced concrete columns has urged the development of several approaches to determine their compressive strength. Although substantial experimental and analytical researches have been conducted to model and simulate the response of concrete confined with FRP jackets under concentric loading. there is still an apparent need for the detail analyses and efficient numerical models to further understand the stress-strain behavior and failure mechanisms of the confined concrete. In order to predict the compressive behavior of concrete even under high confinement pressures, this paper introduces new relations for calculation of the cohesion parameter of Drucker-Prager criterion in terms of cylindrical compressive strength only. These relations are developed from a parametric study of a large number of nonlinear finite element analyses (NLFFEA) of FRP wrapped concrete columns to account for the axial load level and the shape of the stress-strain curve. Incorporating a realistic one-parameter failure criterion of concrete, the failure cone of Drucker-Prager model is enforced to approximate and coincide with the whole compressive meridian of the criterion up to the analytically predicted point of the ultimate hydrostatic pressure in the analyses. Based on this failure cone, mainly seven different relations corresponding to the various levels of lateral pressure are proposed for the compressive meridian and the cohesion while keeping the internal friction angle as a constant value of 33 degrees. The proposed approach is shown to fit quite well the experimental results of 42 specimens tested by eight different researchers, for various square and rectangular cross-sections under concentric loading. (C) 2008 Elsevier Ltd. All rights reserved.