Abstract
With passage of time, strengthening techniques have become more and more refined. Carbon fiber reinforced polymer (CFRP) and steel plates have been adopted since years as few of the popular materials for strengthening of structural elements such as beams and columns. A series of studies have been carried out in the past for shear strengthening of reinforced concrete beams using various mechanisms of strengthening, and response of such strengthened structural elements is found to be quite satisfactory as compared to non-strengthened structural elements. De-lamination /debonding is a major issue faced while strengthening any structural member using fiber reinforced polymer (FRP). Debonding occurs at regions of high stress concentration, which are often associated with material discontinuities and with presence of cracks. However, this can be avoided, if strengthening is done after proper understanding and analysis of the problem. Adaptation of proper guideline to overcome debonding plays a vital role in the resolution of debonding problem, however these guidelines are also limited. The increasing use of FRP in structural strengthening although has revoked a need for framing of guidelines in this segment, but eventually fails to address the debonding aspect to a larger extent. Also, the debonding load after strengthening remains unknown. The magnitude of this load, if known, can contribute to a much greater extent as long as FRP strengthening is concerned. This paper aims at highlighting the method for strengthening of reinforced concrete beam in flexure and shear using CFRP strip mechanism and thereby overcoming CFRP debonding problem in order to achieve enhanced performance in flexure and shear along with prevention of strengthened member failure against debonding.
This is a preview of subscription content, log in via an institution to check access.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Abbreviations
- \( f_{ctm} \) :
-
Mean value of concrete tensile strength
- \( {\Gamma }_{Fd} \) :
-
Design value of specific fracture energy
- \( I_{cr} \) :
-
Moment of inertia of cracked section transformed to concrete
- \( L_{e} \) :
-
Active bond length of FRP laminate
- \( M_{DL} \) :
-
Moment due to dead load
- \( M_{n} \) :
-
Nominal flexural strength
- \( M_{nf} \) :
-
Contribution of FRP reinforcement to nominal flexural strength
- \( M_{ns} \) :
-
Contribution of steel reinforcement to nominal flexural strength
- \( S_{f} \) :
-
Spacing between FRP strips
- \( V_{f} \) :
-
Nominal shear strength provided by FRP stirrups
- \( f_{f,s} \) :
-
Stress level in FRP caused by a moment within elastic range of member
- \( f_{fdd} \) :
-
Design debonding strength of FRP
- \( f_{fe} \) :
-
Effective stress in FRP
- \( f_{s,s} \) :
-
Stress level in steel reinforcement at service loads
- \( f_{s} \) :
-
Stress in steel reinforcement
- \( k_{G} \) :
-
Corrective factor
- \( k_{b} \) :
-
Geometric corrective factor
- \( k_{v} \) :
-
Bond dependent coefficient for shear
- \( \alpha_{1} \) :
-
Multiplier on f′c to determine intensity of an equivalent rectangular stress distribution for concrete
- \( \beta_{1} \) :
-
Ratio of depth of equivalent rectangular stress block to depth of neutral axis
- \( \gamma_{f,d} \) :
-
Partial safety factor for FRP
- \( \varepsilon_{bi} \) :
-
Strain level in concrete substrate at the time of FRP installation
- \( \varepsilon_{c} \) :
-
Strain level in concrete
- \( \varepsilon_{cu} \) :
-
Ultimate axial strain of unconfined concrete
- \( \varepsilon_{fd} \) :
-
Debonding strain of externally bonded FRP reinforcement
- \( \varepsilon_{fe} \) :
-
Effective strain level in FRP reinforcement attained at failure
- \( \varepsilon_{s} \) :
-
Strain level in steel reinforcement
- \( \psi_{f} \) :
-
FRP strength reduction factor
- ∅ :
-
Diameter of reinforcement
- A f, A fv :
-
Area of externally bonded FRP
- A s :
-
Area of steel reinforcement
- b :
-
Width of beam
- b f :
-
Width of FRP sheet
- c :
-
Distance from extreme compressive fiber to neutral axis
- C E :
-
Environmental reduction factor
- \( d, d_{fv} \) :
-
Effective depth of beam
- d f :
-
Overall depth of beam
- E c :
-
Modulus of elasticity of concrete
- E f :
-
Modulus of elasticity of FRP
- E s :
-
Modulus of elasticity of steel
- \( {f^{*}}_{fu} \) :
-
Ultimate tensile strength of FRP
- \( {f^{\prime}}_{c}, f_{cm} \) :
-
Specified compressive strength of concrete
- FC :
-
Confidence factor
- f fu :
-
Design ultimate tensile strength of FRP
- f y :
-
Specified yield strength of steel reinforcement
- L :
-
Length of beam
- M s :
-
Moment due to dead load and live load
- M u :
-
Moment after 50 % increase in live load
- n :
-
Number of layers of FRP sheet
- P db :
-
Debonding load of CFRP strip
- P max :
-
Actual load on CFRP strip
- s sv :
-
Permissible tensile stress in shear reinforcement
- t f :
-
Thickness of FRP strip
- V :
-
Total shear capacity of beam
- V c :
-
Nominal shear strength provided by concrete with steel flexural reinforcement
- V f, required :
-
Shear force to be resisted by FRP strip
- V s :
-
Nominal shear strength provided by steel stirrups
- V u :
-
Maximum shear force on strengthened beam
- \( {\varepsilon^{*}}_{fu} \) :
-
Rapture strain of FRP
- ε fu :
-
Design rupture strain of FRP reinforcement
- \( k \) :
-
Ratio of neutral axis to reinforcement depth measure from extreme compressive fiber
- \( m \) :
-
Modular ratio
- \( \alpha \) :
-
Angle between FRP strip and longitudinal axis of beam measured anti-clockwise
- \( \phi \) :
-
Strength reduction factor
References
ACI 440 2R (2008) Guide for the design and construction of externally bonded FRP system for strengthening concrete structures. American Concrete Institute (ACI), Committee, 2008, Farmington Hills, Michigan, USA
ACI 318 (2005) Building code requirements for structural concrete (ACI 318-05) and commentary (318R-05). American Concrete Institute (ACI), Farmington Hills, Michigan, USA
CNR-DT 200 R1 (2013) Guide for the design and construction of externally bonded FRP systems for strengthening existing structures. National Research Council (NRC), May 2014
Faella C, Martinelli E, Nigro E, Billota A (2012) The influence of the load condition on the intermediate debonding failure of EBR-FRP strengthened. In: Proceedings of composites in civil engineering (CICE), Rome, Italy
Bibliography
Khalifa A, Gold WJ, Nanni A, MI AA (1998) Contribution of externally bonded FRP to shear capacity of RC flexural members. J Compos Constr 2(4)195–202
Billota A, Ludovico DM, Nigro E (2009) FRP debonding on concrete member. In: Fiber reinforced plastics for reinforced concrete structures (FRPRCS-9), Sydney, Australia
Jummat MZ, Rahman MA, Alam MA, Rahman MM (2011) Premature failure in plate bonded strengthened RC beam with an emphasis on premature shear. Int J Phys Sci 6(2):156–168
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2015 Springer India
About this paper
Cite this paper
Patel, M.R., Tank, T.G., Vasanwala, S.A., Modhera, C.D. (2015). Assessment of Debonding Load for RC Beam Strengthened with Pre-designed CFRP Strip Mechanism. In: Matsagar, V. (eds) Advances in Structural Engineering. Springer, New Delhi. https://doi.org/10.1007/978-81-322-2187-6_152
Download citation
DOI: https://doi.org/10.1007/978-81-322-2187-6_152
Publisher Name: Springer, New Delhi
Print ISBN: 978-81-322-2186-9
Online ISBN: 978-81-322-2187-6
eBook Packages: EngineeringEngineering (R0)