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Effect of Adhesive Stiffness and CFRP Geometry on the Behavior of Externally Bonded CFRP Retrofit Measures Subject to Monotonic Loads

Reeve, Benjamin Zachary (2006) Effect of Adhesive Stiffness and CFRP Geometry on the Behavior of Externally Bonded CFRP Retrofit Measures Subject to Monotonic Loads. Master's Thesis, University of Pittsburgh. (Unpublished)

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Nine 10" (254 mm) deep, 6" (152 mm) wide and 186" (4730 mm) long concrete beams having three #4 longitudinal steel reinforcing bars as primary flexural reinforcement, were tested monotonically to failure under mid-point bending. Eight beams were strengthened with various arrangements of soffit-mounted externally bonded carbon fiber reinforced polymer (CFRP) and one beam was left as an unretrofit control specimen. A commercially available 4" (102 mm) wide, 0.055" (1.4 mm) thick preformed unidirectional high strength carbon fiber (CFRP) strip system was used in this study. Additionally, two commercially available adhesives, with significantly different moduli, were used to apply the CFRP strips to the concrete substrate. In order to investigate the effect of the CFRP strip width-to-soffit width ratio (bf/b), four different strip arrangements were used. All specimens tested in this program exhibited intermediate crack induced debonding behavior. The observed failures were generally bond-induced although concrete crushing was also observed in all cases. Increased flexural capacity and decreased flexural ductility was observed with increasing CFRP retrofit material area. Observations indicate retrofit geometry has an influence on the overall retrofit performance. The FRP width-to-substrate width ratio (bf/b) is shown to affect intermediate crack induced debonding behavior - an increase in strain at debonding is seen for specimens having a smaller bf/b ratio. Additionally, superior performance in the form of higher general yield and maximum loads, and higher deflections at these loads, was observed for the specimens having the lower modulus of elasticity adhesive. The current American Concrete Institute (ACI) recommendation intended to mitigate debonding failure by limiting the allowable strain in the FRP (the limiting strain is referred to as åfub) is shown to be non-conservative, overestimating the strain where debonding becomes likely by two fold for the high modulus adhesive and less so for the low modulus adhesive. The equation for estimating åfub recommended by Teng et al. (2001), including the modifying kb term, appears to provide appropriately conservative estimates of debonding for the specimens having low modulus adhesive although remains unconservative for the high modulus adhesive. This indicates that the nature of the adhesive should be included in the calculation of limiting strain. Proposed values for the coefficient kb which accounts for the bf/b ratio were found to generally underestimate the effect of the width ratio for the test specimens. Therefore, not only is the ratio bf/b (as represented by kb) a contributing factor to bond behavior, its contribution may be underestimated. Cover delamination (end peel debonding) was effectively mitigated in all specimens by extending the CFRP close to the support along the relatively long shear span.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Reeve, Benjamin Zacharybzrst@pitt.eduBZRST
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairHarries, Kent
Committee MemberKoubaa,
Committee MemberEarls,
Date: 31 January 2006
Date Type: Completion
Defense Date: 21 November 2005
Approval Date: 31 January 2006
Submission Date: 2 December 2005
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Civil and Environmental Engineering
Degree: MSCE - Master of Science in Civil Engineering
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Adhesive Stiffness; CFRP; CFRP Geometry; Externally Bonded CFRP; FRP; FRP Geometry; Retrofit
Other ID:, etd-12022005-115829
Date Deposited: 10 Nov 2011 20:07
Last Modified: 15 Nov 2016 13:52


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