Key words
(English)
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Timber-concrete-composite; adhesive connection; failure of the bonding line; load-bearing behaviour; long- term behaviour
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Research programs
(English)
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COST-Action C12 - Enveloppe and structure: interactive facades
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Short description
(German)
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Holz-Beton-Konstruktionen werden geklebt statt mit mechanischen Verbindungen miteinander verbunden. Die Gefahr eines vorzeitigen, spröden Verbundversagens wird mit Berechnungsmodellen und Versuchen sorgfältig abgeklärt. Neben Plattenelementen werden auch Plattenbalken aus Holz und Beton im Klebverbund untersucht. Die Langzeit-Deformationen werden geprüft.
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Further information
(English)
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Full name of research-institution/enterprise: Haute école spécialisée bernoise Haute école de l'architecture, du génie civil et du bois
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Partners and International Organizations
(English)
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AT, BE, CZ, DK, FI, MK, FR, DE, EL, IE, IT, LV, LT, NL, PL, PT, RO, SI, ES, CH, UK
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Abstract
(English)
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In timber-concrete-composite structures, the bonding between the timber and concrete members has traditionally been achieved with mechanical connectors such as screws, bolts or indentations in the timber. The transmission of the shear forces between the two layers can also be achieved with the help of adhesives. The main advantages include the increased stiffness due to the stiff joint with no slippage, as well as the favourable distribution of the shear forces, avoiding the stress concentrations when bolts or screws are used. At the University of Applied Science, Department of Architecture, Civil and Wood Engineering HSB in Biel, a feasibility study was carried out between 1998 and 2000. The so-called 'wet-on-wet' process was used: the concrete was poured onto the still wet adhesive on the surface of the timber layer. Most of the specimens performed very well in bending tests. However, a small but not insignificant number of specimens failed prematurely on the bonding line. The current follow-up project was launched in 2003 with the main aim of improving the reliability of the bonding line. Possible applications were to be proposed and tested. The first project phase was concerned with the applied gluing technology. Concrete layers of different thickness were cast on a timber three-ply layer of constant thickness. A number of factors were varied in order to study their effects. Visual analysis backed up by shear tests revealed the main problem as being a displacement of the wet adhesive during the pouring of the concrete. The most important parameters for the control of the displacement appeared to be the type of concrete used (normal concrete performed better that self-compacting concrete) as well as the time interval between the mixing of the two-component adhesive and the pouring of the concrete (90 minutes was preferable to 15 minutes). During the second project phase, the possible application as a composite slab was investigated. Thanks to be optimized gluing technology, all the test specimens performed as expected in bending tests: there was no case of premature bonding failure. In the third project phase, the suitability of the adhesive bonding for cases of reduced gluing surface was investigated. Possiblities include flanged beams for bridges (concrete slab on timber beam) or composite slabs for houses where many cable conduits may be fixed directly on the timber surface. The tests performed demonstrated that even when the bonding surface was reduced to less than a third of the surface of the solid composite slab, the bonding line still held and failure occured elsewhere in either the concrete or the timber. The failure mode and the ultimate load agreed well with the calculated results. The investigations have yielded very good results. The gluing technology has been optimized for the 'wet-on-wet' process and the danger of a premature bonding failure has been greatly reduced. The favourable load-bearing behaviour with no slippage between the concrete and the timber layers was clearly verified with respect to ultimate load, failure mode and bending stiffness. The process seems to be particularly suitable for the prefabrication of single elements under factory conditions where the production conditions are constant and quality control can be readily carried out. The production of the test specimens has shown, however, that the economy must be improved upon, particularly with a more rationalised and mechanized adhesive application. Finally, the long-term deflections were investigated. The results were written up in a separate report because of the duration required: the tests continued to be monitored for a year after the official end of the COST-Action C12 in February 2005. Two beams, each 5m long and 0.49m wide, were loaded with 2 constant loads concentrated at a third of the span. Both beams were 200mm thick: 80mm concrete layer glued on top of 120mm glulam. One beam had two hemispherical pipes running longitudinally, the other beam had four transversally placed hemispherical pipes at each of the two ends. The results corresponded well to the expectations: the measured long-termdeflections deviated from the calculated values by less than 7%.
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References in databases
(English)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C02.0090
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