Date of Award

1-2012

Document Type

Thesis

Degree Name

Master of Civil Engineering (MCE)

Department

Civil Engineering

First Advisor

Dr. Mark F. Green

Second Advisor

Dr. Saud Aldajab

Third Advisor

Dr. Tamer El Maaddaw)'

Abstract

Repair and strengthening of existing reinforced concrete (RC) structures has increased drastically in recent years. Shear reinforcement in RC beams is typically of a small bar diameter, and hence any shear-damage would result in a severe safety hazard and a catastrophic mode of failure especially under extreme loading events. The present work was initiated to the effectiveness of different composite strengthening systems; namely externally bonded carbon fiber reinforced polymer (EB-CFRP), and near surface mounted glass fiber reinforced polymer (NSM-GFRP) to prolong the functional service life of RC beams pre-damaged in shear. It comprised experimental testing and analytical investigation.

The experimental work was conducted over two phases. Phase I comprised testing of 12 concrete T-beams with corroded stirrups strengthened in shear with EB-CFRP and NSM-GFRP systems. Test parameters included level of corrosion damage in stirrups and external shear reinforcement ratio used for strengthening. The reduction in shear capacity attributable to corrosion of stirrups was found proportional to the reduction in the stirrups cross section area. At stirrups corrosion of 8% cross section loss, both shear strengthening systems compensated the reduction in shear capacity and also provided an additional increase over the capacity of a control undamaged beam. At stirrups corrosion of 15% cross section loss, only the higher amounts of external composite shear reinforcement in both systems could restore the shear capacity of the corroded beams.

The effectiveness of using EB-CFRP system with mechanical end anchorage to retrofit severely shear-damaged RC beams with low compressive strength was examined in phase II. A total of 14 tests were performed on eight RC beams with a T-shaped section. To represent a severe damage condition, five beams were tested to failure, repaired and strengthened, then retested to failure for a second time. Test parameters included the presence of damage, number of EB-CFRP layers, and type of end anchorage system. Test results demonstrated that retrofitting of severely shear-damaged RC beams with EB-CFRP composites and proper mechanical end anchorage can fully restore the original shear capacity of the damaged beams. The use of a sandwich composite panel anchorage system in combination with a threaded anchor rod inserted through the entire web width (thru-bolt) as end anchorage system was more effective than using the panel with side powder-actuated fasteners. Increasing the number of EB-CFRP layers did not result in additional gain in shear capacity.

In the analytical study, the accuracy of four different international guidelines/standards namely; the American ACI 440.2R (2008), European fib TG 9.3 (2001), Italian CNR-DT200 (2004), and Australian HB 305 (2008), were demonstrated by comparing their predictions to the experimental results. The validity of other analytical models published in the literature to predict the contribution of external composite reinforcement to shear resistance was also examined. General conclusions of the work along with recommendations for future studies and developments on structural performance of RC beams strengthened in shear were documented.

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