Experimental Verification of Load-Bearing Capacity of FRP Bars under Combined Tensile and Shear Forces
Publication: Journal of Composites for Construction
Volume 27, Issue 2
Abstract
In recent decades, the number of applications of fiber-reinforced polymer (FRP) reinforcement for concrete has significantly expanded. This fact is mainly due to the FRP reinforcement cost competitiveness, the increasing availability of design provisions, and due to the advantageous physical-mechanical and chemical properties of this composite material, which open up new possibilities for the design and implementation of extremely durable elements. Currently, the most commonly used types of reinforcement bars are those containing glass FRP (GFRP) or basalt FRP fibers, which is mainly the result of their favorable price and high resistance to aggressive environments. The use of composites in construction is wide-ranging: it is possible to apply FRP bars not only in the design and strengthening of concrete structures but also in the installation of shear dowels in concrete pavement, as rock bolts or as anchors for overhanging facade components. In the case of the design of load-bearing elements subjected to a combination of tensile and shear force, it is necessary to quantify their shear resistance and concisely describe the effect of the interaction of the tensile and shear force on the load-bearing capacity of the reinforcing element. This is a broadly addressed area as regards composite laminates and fabrics, but when it comes to FRP bars, there are very few available experimental results. For that reason, this research deals with the experimental testing and quantification of the influence of the interaction of normal and shear force. The behavior of GFRP bars from two different manufacturers, with three different diameters, different surface treatments, and mechanical characteristics, was experimentally verified. The findings are presented, a material failure curve is compiled, and the results are compared with those predicted according to the available relationship for composite laminates and von Mises theory.
Practical Applications
The presented research was driven foremost by industry demand concerning prestressed fiber-reinforced polymer (FRP) rock bolts. In situations where such bolts are used, the slippage and displacement of parts of rocks can be expected, and consequently, the creation of a shear plane in the prestressed anchor occurs. However, there are no existing methods for determining the load-bearing capacity of such loaded FRP bars. This paper aims to determine the short-term behavior of specimens under the combined action of tensile and shear forces (failure envelope) and to compare their load-bearing capacity with available relationships for steel and composite laminates.
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Acknowledgments
The authors thank PREFA KOMPOZITY, a.s. and Schöck Bauteile GmbH for the provided composite bars. The presented results were obtained with the financial support of project FW01010520 “Development of bent composite reinforcement for environmentally exposed concrete constructions” and FAST-S-21-7503 “Use of indirect FRP reinforcement in the design of a selected detail of a locally-supported slab structure.”
Notation
The following symbols are used in this paper:
The code of specimens in Tables 2–4 was appended with the test type (Va—shear test with slightly distant shear planes (0.2 mm), Vb—shear test with joints with chamfered edges, NV – N + V test, T – tensile test) and specimen number at the end.
- c
- cos θ;
- cFRP
- proposed factor for the FRP bar;
- F
- acting force;
- fLt
- tensile strength in the longitudinal direction;
- fLts
- shear strength in a direction rotated 45° from the direction of the fibers;
- fN + S(θ)
- vector sum of the ultimate shear and normal stress;
- fTt
- shear strength in the transverse direction;
- fx(θ)t
- load-bearing capacity in the general direction;
- l
- longitudinal axis (parallel to the bar axis);
- M
- bending moment;
- max V
- ultimate shear force;
- N
- normal force;
- N_fail
- normal force at the ultimate shear force;
- r
- transverse axis (perpendicular to the bar axis);
- S
- shear strength;
- s
- sin θ;
- T
- tensile strength;
- V
- shear force;
- θ
- theta—angle of deviation of the resultant from the longitudinal axis;
- σ0
- ultimate short-term tensile strength;
- σL
- applied stress in the longitudinal direction;
- σT
- applied stress in the transverse direction;
- σθ
- ultimate normal stress at a given angle θ;
- τ0
- ultimate short-term shear strength;
- τLT
- applied shear stress; and
- τθ
- ultimate shear stress at a given angle θ.
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Published In
Journal of Composites for Construction
Volume 27 • Issue 2 • April 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: May 2, 2022
Accepted: Nov 15, 2022
Published online: Jan 18, 2023
Published in print: Apr 1, 2023
Discussion open until: Jun 18, 2023
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