Finite Element Investigation of Pre-Damaged RC Columns Retrofitted with FRCM

Abstract

Reinforced concrete (RC) structures in the UAE and globally face adverse deterioration during their lifetime. A novel retrofitting system using poly-paraphenylene-benzobisoxazole (PBO) Fiber Reinforced Cementitious Matrix (FRCM) is investigated in this thesis. FRCM is a noncorrosive two-dimensional high strength FRP mesh saturated with inorganic cement mortar which is compatible with concrete substrates. A three-dimensional (3D) nonlinear finite element (FE) model is developed using ABAQUS to study the behaviour of corrosion damaged RC columns retrofitted with PBO-FRCM systems. A total 180 cases of FE models are developed using a concrete compressive strength of 30 MPa and a longitudinal reinforcement ratio of 2% typical to columns. A comprehensive parametric study is conducted considering the effects of five parameters: (a) cross section type (square vs circular), (b) FRCM layers (1 vs 2 vs 3 vs 4 layers), (c) damage level (mild vs moderate vs severe damage), (d) eccentricity ratio (e/h= 0.0, 0.3, 0.5, 0.75, 1.0, 1.25 and 1.5) (e) column type/length (short/800mm vs slender/1200mm). Displacement controlled loading condition is used and material nonlinearities in concrete, cement mortar and composite are incorporated in the FE model. The FE models are validated against published literature. Results indicated a positive correlation between the number of FRCM layers, axial capacity, and ductility enhancement which is more pronounced in circular columns. Enhancement in axial capacity of 20% was observed in square columns and 35% in circular columns while axial ductility enhancement of 42% was observed in square columns and 164% in circular columns. All strengthened specimens failed by matrix damage indicating effectiveness of the strengthening system irrespective of the cross-section type. Retrofitting corrosion damaged RC columns with PBO-FRCM restored and enhanced the axial capacity and ductility at all damage levels. Increasing the number of FRCM layers increased the axial capacity of eccentrically loaded columns irrespective of damage level and eccentricity ratio. Comparison of column axial capacity, which was computed based on ACI 549.4R-13 provisions, against FEA revealed that the code provisions underestimate the axial capacity of short RC columns retrofitted with PBOFRCM by 20%.