General Analytical Model for the Bond Capacity of NSM FRP-Concrete Joints
Publication: Journal of Composites for Construction
Volume 24, Issue 6
Abstract
Fiber-reinforced polymer (FRP) near-surface mounted (NSM) reinforcement represents an effective solution for strengthening and retrofitting existing concrete structures. As it is embedded into concrete, NSM reinforcement is protected from accidental impact, high temperature, and vandalism and it is less prone to debonding than externally bonded reinforcement. However, debonding of the NSM reinforcement remains the main issue associated with this strengthening technique. Numerous studies have focused on the bond behavior of NSM-concrete joints and in some of them analytical models for the prediction of NSM-concrete joint bond capacity were proposed. However, these models are often based on a few experimental results of a specific strengthening configuration. In this paper, a new analytical model to estimate the effective bond length and the bond capacity of NSM-concrete joints that fail due to cohesive debonding within concrete is proposed. The model is based on a pure fracture mechanics Mode-II loading condition and can be applied to either NSM strips, round bars, or rectangular bars. The accuracy of the model proposed and of existing analytical models was assessed by comparing analytical and experimental results of 117 NSM-concrete joints collated from the literature. The assessment showed that the model proposed provided accurate estimations of the NSM-concrete bond capacity for all types of reinforcement considered.
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Data Availability Statement
All data, models, and code generated or used during the study appear in the published article.
Notation
The following symbols are used in this paper:
- A
- cross-sectional area of the reinforcement;
- C
- constant to be determined by regression analysis of experimental results;
- Cper
- length of the fracture path, equal to the sum of the lengths of the groove’s three sides;
- c
- reinforcement cover;
- dF
- length of the fracture path;
- df
- depth of the reinforcing strip;
- dg
- depth of the groove;
- E
- elastic modulus of the reinforcement;
- fc
- concrete (mean) compressive strength;
- fct
- concrete (mean) tensile strength;
- ff
- reinforcement tensile strength;
- GF
- fracture energy;
- Lb
- bonded length;
- Lper
- length of the fracture path;
- leff
- effective bond length;
- m
- constant to be determined by regression analysis of experimental results;
- N
- number of specimens considered in the assessment;
- n
- constant to be determined by regression analysis of experimental results;
- P
- load applied to the reinforcement;
- Pdeb
- NSM-concrete load-carrying capacity;
- Pexp
- experimental maximum applied load;
- s
- reinforcement-concrete relative displacement (slip);
- smax
- slip associated to the complete separation of the interface;
- wf
- thickness of the reinforcing strip;
- wF
- width of the fracture path;
- wg
- width of the groove;
- y
- coordinate along the reinforcement bonded length;
- α
- constant that expresses the relationship between fct and GF;
- βc
- cover factor;
- βe
- edge factor;
- βL
- length factor;
- Δk
- discrepancy from the average of the ratio between P and the corresponding Pexp;
- ɛfd
- maximum strain that can be borne by an NSM composite applied to an RC beam;
- ɛfu
- composite ultimate strain;
- γ
- constant of the model that describes the relationship between fc and GF;
- η
- constant of the model that describes the relationship between fc and GF;
- φF
- interface failure plane aspect ratio;
- φg
- groove ratio;
- τ
- interfacial shear stress; and
- τmax
- interfacial shear strength.
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Published In
Journal of Composites for Construction
Volume 24 • Issue 6 • December 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Aug 30, 2019
Accepted: Jun 24, 2020
Published online: Aug 26, 2020
Published in print: Dec 1, 2020
Discussion open until: Jan 26, 2021
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