Interaction diagrams of FRP Wrapped Hollow Core Reinforced Concrete Columns

Hollow core reinforced concrete columns are usually used to decrease the cost and weight/stiffness ratio of members. These columns usually carry axial forces together with bending moment.
Fiber- reinforced polymer FRP wrapping provides a confinement to the concrete.In this study,concrete columns were analyzed with and without external confinement; and interaction diagramswere compared with those obtained from experimental results. Based on the results it was realized that external confinement with FRP composite could increase the strength of concrete column.However, the influence of the number of layers of FRP on the specimens after five Layers under loading is not so pronounced. Wrapping three layers of FRP increases columns axial strength about 30% to 40%, while it can reach up to 50% for pure bending. Strength increase with seven and nine layers is about 5% more than retrofitting with five layers. Also, increasing hole dimensions reduces columns ultimate strength. Comparing columns with circular and square hole shows that columns with circular hole have better function.