Minimally Invasive FRP Strengthening of External Beam–Column Joints
Publication: Journal of Composites for Construction
Volume 28, Issue 4
Abstract
Premature shear failure in reinforced concrete (RC) beam–column joints (BCJs) or at the top of columns can significantly compromise a building’s seismic response, leading to major damage or global collapse, as observed in the aftermath of recent seismic events. Local strengthening solutions based on the employment of fiber-reinforced polymers (FRPs) are effective at increasing shear strength and preventing the failure of BCJs, and are also quick and easy to apply. This has led to their increased use in recent postearthquake reconstruction processes. However, large-scale plans to mitigate seismic risk require strengthening solutions that produce a minimum level of disruption and do not prevent the use of buildings. This can be achieved only by conducting work from a structure’s exterior. This paper, therefore, proposes a novel FRP strengthening layout for exterior RC BCJs that combines the use of quadriaxial fabric and mechanical FRP spike anchors. In order to validate the proposed solution and quantify the effects of the number of layers and anchors, four full-scale BCJs are tested under a constant axial load and reversed cyclic displacement. The results are presented and discussed in relation to: global subassembly and local joint-panel response, energy dissipation, and the strain demand on the FRP fibers. A comparison with current available design formulations for anchored-FRP fabrics is made to produce preliminary design criteria.
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Data Availability Statement
All the data, models, and codes generated or used during the study are contained in the published article.
Acknowledgments
This study was performed within the framework of the PE 2022–2024 joint program DPC ReLUIS, WP5 Fast and Integrated Retrofit Interventions. The materials used to strengthen the specimens were provided by Mapei SpA, Milan.
Notation
The following symbols are used in this paper:
- Af,eq
- equivalent FRP area on the joint panel;
- Ajh
- joint horizontal area;
- b
- width of the concrete support;
- bb
- beam width;
- bc
- column width;
- bf
- width of the FRP fabric;
- CI.D.
- numerical coefficient accounting for the initial damage in the concrete substrate;
- CM.A.
- numerical coefficient accounting for the presence of mechanical anchors;
- Ef
- elastic modulus of the FRP system;
- Etot
- total energy dissipation;
- Fmax,th,m
- contribution of the direct bond to the total tensile force;
- fa
- N/Ajh = axial stress in the joint panel;
- fc
- concrete cylindrical compressive strength;
- fcm
- mean concrete cylindrical compressive strength;
- fctm
- mean concrete tensile strength;
- fy
- yielding stress of steel reinforcement;
- hb
- beam height;
- hc
- column height;
- kb
- geometrical corrective factor;
- kG
- corrective factor calibrated on experimental results;
- kpp
- peak-to-peak secant stiffness;
- Myb
- yielding moment of the beam;
- N
- axial load on the column;
- nl
- number of CFRP layers on the joint panel;
- ns
- is the number of joint sides strengthened in shear;
- Pd
- total tensile action in the quadriaxial fabric;
- Pu
- ultimate load;
- Pu,anch
- ultimate capacity of anchors;
- tf
- thickness of dry fibers;
- Vb
- beam shear;
- Vb,flex
- beam shear at the maximum flexural strength;
- Vb,max
- maximum recorded shear strength on the beam;
- γjoint
- joint shear strain;
- ΔEtot
- percentage relative differences with respect to the energy dissipation of the reference specimens;
- ΔVb
- percentage relative differences with respect to the shear strength of the reference specimens;
- ɛf,e
- equivalent strain predicted using the design approach suggested by Del Vecchio et al. (2015);
- ɛf,mean
- mean of the maximum recorded strains on the quadriaxial CFRP fabric in all directions;
- ɛfu
- ultimate fracture strain of the FRP system;
- ν = N/(bc × hc)
- normalized axial load;
- σ
- standard deviation; and
- θ = arctan(hb/hc)
- inclination of concrete compressive strut with respect to the beam axis.
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Information & Authors
Information
Published In
Journal of Composites for Construction
Volume 28 • Issue 4 • August 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Aug 23, 2023
Accepted: Mar 26, 2024
Published online: May 23, 2024
Published in print: Aug 1, 2024
Discussion open until: Oct 23, 2024
ASCE Technical Topics:
- Concrete
- Earthquake engineering
- Engineering fundamentals
- Engineering materials (by type)
- Failure modes
- Fiber reinforced polymer
- Forensic engineering
- Geotechnical engineering
- Material failures
- Materials characterization
- Materials engineering
- Polymer
- Reinforced concrete
- Seismic effects
- Seismic tests
- Shear failures
- Structural engineering
- Synthetic materials
- Tests (by type)
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