Analytical Evaluation of Capacity of Steel Fiber Reinforced Polymer Strengthen Circular Column

Abstract

The capacity of existing columns needs to be enhanced by retrofitting when there is an increase in loading due to changes in usage or change in design specifications. Steel and concrete jacketing have been used since long for retrofitting of columns. Fiber Reinforced Polymer (FRP) wrapping is emerging as new method for strengthening of columns. Common type of fibers used for wrapping are Carbon Fiber Reinforced Polymer (CFRP), Glass Fiber Reinforced Polymer (GFRP), and Aramid Fiber Rein- forced Polymer (AFRP). Recently, Steel Fiber Reinforced Polymer (SFRP) has been introduced as a new class of composites for strengthening applications. The steel cords that make up SFRP have some inherent ductility. SFRP has advantage of be- ing relatively lightweight in comparison to steel plates, making it relatively easy to install. It is also economical as compared to GFRP or CFRP. Experimental methods for wrapping of columns are costly, time consuming and dificult. Because of this, numerical methods have became the choice to study the behavior of SFRP wrapped column. The performance of the structure can be predicted and analyzed with greater precision by Finite Element Analysis (FEA) compared to ex- perimental approach. For concrete structure, FEA is widely used numerical method. The objective of the present study is to explore the application of nonlinear FE model- ing and to evaluate axial load carrying capacity of Plain Cement Concrete (PCC), Re- inforced Cement Concrete (RCC) columns and strengthened PCC and RCC columns with diferent numbers of layers of SFRP. Numerical investigation using FEA is car- ried out on PCC and RCC circular columns of 200 mm diameter in cross-section having length 400 mm, 800 mm and 1200 mm. Nonlinear material properties for con- crete, steel and SFRP are considered. SFRP properties are evaluated at laboratory and used for nonlinear FE analysis. Concrete is modeled with 4-node linear tetra- hedron element, steel reinforcement is modeled with 2-node linear 3-D truss type of elements and SFRP is modeled as 4-node doubly curved thin or thick shell, reduced integration, hourglass control, finite membrane strains. Perfect bond is considered between steel and concrete element, concrete and SFRP element and two di erent layers of SFRP element. The analytical results in terms of load-displacement behavior, ultimate load are pre- sented. The results of PCC column and RCC column with and without wrapping of SFRP element are compared to understand the improvement in axial load carrying capacity. Further the efect of diferent layer of SFRP wrapping on increase in axial load carrying capacity and the efect of confining pressure on the diferent height of the column wrapped with SFRP are studied. Increase in axial load carrying capacity of retrofitted column with increase in num- ber of layer of SFRP is evaluated. Analytical models specified by various guidelines namely ACI 440.2R-08, ISIS Educational module-4 and CNR-DT 200/2004 for calcu- lating axial load carrying capacity of column wrapped with SFRP are also presented. Comparison of results obtained from numerical as well as analytical methods are presented.