Retrofitting and Repairing of Heavily Cracked Unbonded Post-Tensioned Structural Systems with Composite Materials

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Title: Retrofitting and Repairing of Heavily Cracked Unbonded Post-Tensioned Structural Systems with Composite Materials

Author(s): P. R. Chakrabarti, PhD, PE, SE

Publication: Special Publication

Volume: 225

Issue:

Appears on pages(s): 147-162

Keywords: composite; FRP (CFRP & GFRP); post-tensioned; repair & retrofit

Date: 3/1/2005

Abstract:
Composite materials and high strength adhesives are becoming popular for various structural repair jobs. These materials provide good solutions for repairing, and retrofitting concrete structures. In this system repair work can be done within a short time, without using much labor, and the repair materials generally do not alter the geometric shapes of the original structural member. However, the interactive behavior (both short and long term) of un-bonded post-tensioned structural components, when repaired and retrofitted with composite materials is not yet properly understood. The current research was conducted to understand this. Eleven 12’-0" long beams B1 thru B11, were loaded close to their ultimate values. The tests were stopped based on three criteria: excessive cracking, or pre-stressing load reaching over 80%-85% fpu, or deflection reaching twice the allowable deflection. The cracked beams were repaired with varying amount of composite materials adhesives, and tested again. The beams were named B1CR, B2CR, B3EgR and so on, where CR represents repair with carbon FRP and EgR represents repair with e-glass FRP. The tests were stopped again based on the above three criteria. Using Carbon and E-glass FRP and adhesives, a very effective repairing and retrofitting system has been developed. The load carrying capacities and deflections of these beams and that of the original un-cracked beams were compared. Various repairing schemes were adopted. Attempts were made to find the minimum usage of the composite materials, prevent diagonal shear cracking, and prevent sudden compression failures. The changes in post-tensioning forces, the effect of having mild steel in the tension zone, and crack propagation at ultimate stage were recorded and discussed here.