Long-term behaviour of pre-stressed timber-CFRP composites

Richter, Klaus; Lehmann, Martin; Properzi, Milena (2004). Long-term behaviour of pre-stressed timber-CFRP composites In: Enhancing bondline performance : proceedings of the final conference in COSTE 34 "Bonding of timber" (pp. 80-88). Lövér-Print Nyomdaipari

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The application of pre-stressed CFRP-Iamella to timber beams is difficult because the concentrated shear stresses at the beam ends often lead to delamination of the lamella or to timber failure due to tension perpendicular to the grain. An alternative method involving decreased pre-tension force towards the beam ends shows promising results, but requires large and heavy equipment and is therefore not suitable for on-site applications. In order to post-strengthen historic wooden beams with CFRF-Iamella, a different approach of prestressing was developed where the timber beam is cambered prior to the bonding of the CFRP-Iamella with an epoxy resin. In short-term bending tests the potential efficiency of the method was confirmed by increased bending stiffness (+14%) and bending strength (approx. + 30%). In order to assess the long-term behaviour of timber after pre-stressing and CFRP reinforcement, six loaded and three unloaded spruce battens were exposed to seven climate regimes of one week duration each. Although the exposure time of each cycle was too short to reach moisture equilibrium, the cycling of temperatures between 19° and 49°C and relative humidities between 36% and 70% induced average wood moisture changes of up to 3.3%. Creep deflection of the beams showed a progressive trend in the first three cycles, where the timber is supposed to undergo plastic deformation, the deflection gradient reduces in the second part of the exposure time. The comparison of the creep factor of the loaded and unloaded specimens and the unchanged MOE of the battens after loading in cycling climate provided evidence that the reinforcing system, especially the applied epoxy resin, is able to withstand cyclic changes in climate class 2 without relevant stress relaxation.

Item Type:	Conference or Workshop Item (Paper)
Division/Institute:	School of Architecture, Wood and Civil Engineering School of Architecture, Wood and Civil Engineering > Institute for Materials and Wood Technology BFH Centres and strategic thematic fields > BFH Centre for Wood - Resource and Material School of Architecture, Wood and Civil Engineering > Institut for Building Materials and Biobased Products IBBM
Name:	Richter, Klaus; Lehmann, Martin0000-0002-0813-7023 and Properzi, Milena
Subjects:	Q Science > Q Science (General) T Technology > T Technology (General) T Technology > TA Engineering (General). Civil engineering (General) T Technology > TH Building construction
ISBN:	978-963-9364-97-4
Publisher:	Lövér-Print Nyomdaipari
Language:	English
Submitter:	Sally Haddad
Date Deposited:	12 May 2020 13:22
Last Modified:	14 Oct 2021 02:18
Uncontrolled Keywords:	cfrp climate cycling creep-deflection long-term behaviour pre-stressing
ARBOR DOI:	10.24451/arbor.11620
URI:	https://arbor.bfh.ch/id/eprint/11620