Mechanical Response of Timber Beams Strengthened with Variable Amounts of CFRP and Bamboo Scrimber Layers
Publication: Journal of Composites for Construction
Volume 26, Issue 4
Abstract
This paper proposes a novel method for strengthening existing timber beams that can effectively improve the deformability of beams. As high-performance engineered bamboo, bamboo scrimber was attached to the bottom tensile area of a timber beam together with carbon fiber–reinforced polymer (CFRP) layers. The CFRP was used to improve flexural strength, and the bamboo scrimber was used to enhance the flexural stiffness and strength of the original timber beams. Fourteen timber beams were tested to study the flexural behavior of the reinforced timber beams. The main test parameters included the bamboo scrimber thickness and the number of CFRP layers. The results showed that the stiffness and bending strength of the beam increased with the increasing thickness of the bamboo scrimber, but no noticeable effect was observed with the addition of the CFRP layers. The cross-sectional stiffness at the serviceability limit state and ultimate bending strength increased by approximately 70%–130% and 50%–90%, respectively. A stable and durable platform segment was observed for most reinforced beams, which displayed excellent deformability. The large deformable behavior was mainly due to the fact that the addition of bamboo scrimber delayed the tensile failure of the wood, and timber under compression parallel to the grain showed plastic behavior. By considering the simplified stress–strain relationship for the constituent materials and force equilibrium in the cross section, an analytical strength model was developed for predicting the flexural capacity of timber beams reinforced with bamboo scrimber.
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Acknowledgments
The project received financial support from the National Natural Science Foundation of China (Grant Nos. 51208262 and 51778300), the Natural Science Foundation of Jiangsu Province (Grant No. BK20191390), the Six Talent Peaks Project in Jiangsu Province (Grant No. JZ-017), the Key Research and Development Project of Jiangsu Province (Grant No. BE2020703), and the Qinglan Project of Jiangsu Province.
Notation
The following symbols are used in this paper:
- Ai
- section area of material i;
- a
- thickness of the bamboo scrimber;
- b
- width of the beam;
- bb
- width of the bamboo scrimber;
- bf
- width of CFRP;
- bw
- width of the timber;
- db
- distance between the center of the bamboo scrimber and the neutral axis of the beam;
- df
- distance between the center of the CFRP and the neutral axis of the beam;
- dw
- distance between the center of timber and the neutral axis of the beam;
- Eb
- modulus of elasticity parallel to the grain of the bamboo scrimber;
- Ef
- modulus of elasticity (MOE) of CFRP;
- Ei
- MOE of material i;
- Ew
- MOE parallel to the grain of the timber;
- Fb
- tensile force of the bamboo scrimber;
- Fc
- compressive forces related to the preyield part of the compression area of the timber beam;
- Fcp
- compressive forces related to the plastic part of the compression area of the timber beam;
- Ff
- tensile force of CFRP;
- Ft
- tensile force of the timber;
- hb
- depth of the bamboo scrimber;
- hc
- height of the elastic compression area of the timber beam;
- hcp
- height of the plastic compression area of the timber beam;
- hf
- depth of CFRP;
- ht
- height of the tensile region;
- hw
- depth of the timber;
- L
- clear span of the beam;
- l
- distance from a support to the nearest load point;
- Mest
- calculated value of the ultimate flexural moment;
- Mexp
- experimental value of the ultimate flexural moment;
- P
- ultimate load of the beam;
- tf
- thickness of the CFRP;
- yi
- distance between the center of layer i and the bottom;
- ΔP
- increment of the applied load;
- Δδ
- given range of displacement for the load range (mm);
- ɛb
- strain of the bamboo scrimber;
- ɛb,ce
- elastic limit compressive strain of the bamboo scrimber;
- ɛb,cu
- plastic ultimate compressive strain of the bamboo scrimber;
- ɛb,tu
- ultimate tensile strain of the bamboo scrimber;
- ɛf
- tensile strain of CFRP;
- ɛfu
- ultimate tensile strain of CFRP;
- ɛtu
- ultimate tensile strain at the bottom;
- ɛw
- strain of the timber;
- ɛw,ce
- elastic limit compressive strain of the timber;
- ɛw,cu
- plastic ultimate compressive strain of the timber;
- ɛw,tu
- ultimate tensile strain of the timber;
- σb
- stress of the bamboo scrimber;
- σb,ce
- elastic limit compressive stress of the bamboo scrimber;
- σb,cu
- plastic ultimate compressive stress of the bamboo scrimber;
- σb,tu
- ultimate tensile stress of the bamboo scrimber;
- σf
- tensile stress of CFRP;
- σw
- stress of the timber;
- σw,ce
- elastic limit compressive stress of the timber;
- σw,cu
- plastic ultimate compressive stress of the timber; and
- σw,tu
- ultimate tensile stress of the timber.
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Published In
Journal of Composites for Construction
Volume 26 • Issue 4 • August 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Nov 14, 2021
Accepted: Mar 31, 2022
Published online: Jun 14, 2022
Published in print: Aug 1, 2022
Discussion open until: Nov 14, 2022
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