This paper researches rheological behaviour of a wood-concrete structure connected by dowels of a particular kind, i.e., behaviour under long-term constant load. In order to determine yielding of the joint, i.e. of slipping module, samples with two joint dowels were examined. Also, compounds with two diameter sizes of single dowels of particular types E48M12 and E75M16 were tested. Besides the impact of the dowel\u27s size on the joint deformability, we also monitored the impact of indoor physical conditions on the behaviour of the composite structure.U radu se opisuje istraživanje reološkog ponašanja kompozita drvo-beton spregnutog moždanicima naročite vrste, tj. ponašanje pri dugotrajnom konstantnom opterećenju. U cilju određivanja popustljivosti spoja, odnosno određivanja modula klizanja spajala, ispitivani su uzorci sa spojem pomoću dva moždanika. Ispitivani su spojevi s dvije vrijednosti promjera jednostranih moždanika naročite vrste E48M12 i E75M16. Osim utjecaja dimenzije moždanika na pomjerljivost spoja praćen je i utjecaj promjene okruženja u zatvorenom prostoru na ponašanje kompozita

Mirjana Bošnjak Klečina

Silva Lozančić

Stjepan Takač

English

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1IntroductionUvodComposing of various materials into a compositerenders their basic properties utilized and improved. Woodas a material has good elastomechanical characteristics,such as: durability, orthotropy, and environmentalfriendliness. A disadvantage of wood is its deformability,and this is improved by wood-concrete compositestructures. Such systems may be applied for ceilingstructures in housing and other facilities; they are applied inadaptation of old buildings and construction of bridgestructures.279S. Lozančić, S. Takač, M. Bošnjak KlečinaISSN 1330-3651UDC/UDK 539.4:[691.88:624.016RESEARCH OF THE RHEOLOGICAL SLIPPING MODULE ON THE COMPOSITEWOOD-CONCRETE STRUCTURE SAMPLESSilva Lozančić, Stjepan Takač, Mirjana Bošnjak KlečinaThis paper researches rheological behaviour of a wood-concrete structure connected by dowels of a particular kind, i.e., behaviour under long-term constantload. In order to determine yielding of the joint, i.e. of slipping module, samples with two joint dowels were examined. Also, compounds with two diametersizes of single dowels of particular types E48M12 and E75M16 were tested. Besides the impact of the dowel's size on the joint deformability, we also monitoredthe impact of indoor physical conditions on the behaviour of the composite structure.Keywords: concrete, composite structures, dowel, rheological behaviour, slipping, woodOriginal scientific paperU radu se opisuje istraživanje reološkog ponašanja kompozita drvo-beton spregnutog moždanicima naročite vrste, tj. ponašanje pri dugotrajnom konstantnomopterećenju. U cilju određivanja popustljivosti spoja, odnosno određivanja modula klizanja spajala, ispitivani su uzorci sa spojem pomoću dva moždanika.Ispitivani su spojevi s dvije vrijednosti promjera jednostranih moždanika naročite vrste E48M12 i E75M16. Osim utjecaja dimenzije moždanika napomjerljivost spoja praćen je i utjecaj promjene okruženja u zatvorenom prostoru na ponašanje kompozita.Ključne riječi: beton, drvo, klizanje, moždanici, reološko ponašanje, spregnute konstrukcijeIzvorni znanstveni članakIstraživanje reološkog modula klizanja uzoraka spregnute konstrukcije drvo-betonIstraživanje reološkog modula klizanja uzoraka spregnute konstrukcije drvo-betonTechnical Gazette 17, (2010),3 279-283describes the impact of yielding of connection on thedistribution of stressing and strains along the height of acomplex cross-section, which is significantly different incomparison with rigid connected cross-sections.A key factor of behaviour of composite systems is thetypes of connections and mode of composing of wood andconcrete. The mode of composing dictates the behaviour ofthe whole structure, its stress and strains.The paper examines the properties of composite wood-concrete structures of composite single dowels, in particularthe kinds of the C type (according to DIN 1052 T2). Thosedowels may carry substantial loads, are applied in wood-steel connections, they are produced serially, and are costes-Figure 1Slika 1.Schematic display of slipping elements in combinationShematski prikaz klizanja elemenata u spojuThe slipping module for the samples of wood-concretecomposite structures of C type dowels was determined byan experiment, by examining the shear on small samplesusing the following expression:uFKu (1)where:- static slipping module; - force; - (horizontal)displacement 1,5 mm.The objective of the research is defining the rheologicalslipping module = / . The slipping moduleK F uK F uu( ) ( )t tFigure 2Slika 2.Effect of connection method on the stress distributionof composite structuresUtjecaj načina sprezanja na raspodjelu naprezanja kompozita280Research of the rheological slipping module on the composite wood-concrete structure samplesTehni ki vjesnikč ,17, 3(2010)  279-283-costTesting wood-concrete composites were made inCroatia as part of the doctoral dissertation of V. RajčićŽefficient. In theoretical terms, the slipping module is avalue describing the stiffness of a joined system orconstructed joint.The examinations under the research covered the initialand rheological slipping modules, useable in the calculationof current and finite, i.e. long-term strains.[9],without studying the rheology of slip joints, in the use oflightweight concrete and with different way of coupling.Numerical models of such systems processed Z. agar [10]as well.S. Lozančić, S. Takač, M. Bošnjak KlečinaSample 1Sample 2The sample 1 is 42 cm long, it is made of a beam ofglued laminated wood made of class I fir-wood, MB 30concrete, and two 75-mm diameter dowels, with centrespacing of 14 cm. Two 16-mm diameter bolts were fitted aswell. Bolts provide for load transfer from concrete to thedowel, and from the dowel to the wood. The connection isconcrete-bolt-dowel-wood. Wire fabric reinforcement(Q503) is inserted into the concrete slab, with 8-mmdiameter rods due to possible take-up of the tension in thelower edge of concrete slab, as well as a foil between woodand concrete intended for reducing the impact of humidityon the wood-concrete joint.The sample 2 is 36 cm long. It is made of a beam ofglued laminated wood of class I fir-wood, MB 30 concreteand two 48-mm diameter dowels, with centre spacing of 12cm. Two 12 diameter bolts were fitted as well. Wire fabricreinforcement (Q503) is inserted, with 8-mm diameter rodsdue to possible take-up of the tension in the lower edge ofconcrete slab, as well as a foil between wood and concreteintended for reducing the impact of humidity on the wood-concrete joint. During mounting the dowels are firstimpressed by means of a press for purpose of evenimpression and correct fitting. The schematic of sampledimensions is illustrated in Fig. 4.Dowels were examined during application of force ofthe intensity of the allowable bearing capacity. Theallowable bearing capacity of sample 1 for 2 dowels is thevalue of bearing capacity of two dowels; for sample 1 it is19,2 kN, whereas for sample 2 it is 10,6 kN.3Sample research methodsProvedba ispitivanja uzorakaFigure 3Slika 3.Single dowel of the type C and the corresponding wood screwJednostrani moždanik tipa C i odgovarajući vijak za drvo2Research programProgram istraživanjaThe manner of composing wood and concrete and typesof connections impact the distribution of stress incomposite cross-section (Fig. 2). As indicated above, thispaper describes composing wood and concrete by dowels ofa particular kind of C type according to DIN 1052 T2.Examination was carried out on two models. Model 1 isa joint with E75M16 dowels, and model 2 with E48M12dowels. For each model five samples were examined.esFigure 4Slika 4.Dimensions of testing samplesDimenzije uzoraka za ispitivanje, in cm, u cm281Technical Gazette ,17, 3(2010)  279-283Istraživanje reološkog modula klizanja uzoraka spregnute konstrukcije drvo-betonS. Lozančić, S. Takač, M. Bošnjak Klečina1 and model 2.Diagrams of slipping of sample 2 with E75M16 for allthe 5 models are presented in Fig 7. Sample slipping is anaverage value read from two sides of the sample, asindicated above.Fig. 8 illustrates the diagrams of slipping for sample 1with constant load intensity. All slipping curves are similar;curves for samples with connections E48M12 are "quieter"than the ones measured with E75M16 connections.Sample 2 curves consist of several parabolic - withopposite parabolic directions.The forms of slipping curves for both samples aresimilar, with a certain difference in the slipping values.Initial slipping module for E48M12 dowels is 8 684 21N/mm. Rheological slipping module for long-term loads is6 726 0 N/mm, it is by 22 5 % lower than the initial one.The initial slipping module for dowels E75M16 is26 301 0 N/mm. Rheological slipping module at the end ofresearch is 16 410 0 N/mm, and it is lower by 37 5 % thanthe initial one.A comparison of the values of rheologic modules ofsamples with different dowel diameters indicates that theslipping module of connections of larger diameters issignificantly bigger.Slipping increment was the biggest during the first 7days after loading, and the slipping increment became stableafter 340 days for sample 2, whereas it became stable forsamples 1 after 200 days.The slipping module decreases faster in the initial timeof loading..,, ,,, ,f s....A device has been designed for applying loads whichsubjects samples to longitudinal force. The value of theforce is controlled by a force transducer on the measuringstation.The testing device and placing of the sample areillustrated in Fig. 5.Figure 5Slika 5.Device for testing samplesUređaj za ispitivanje uzorakaSlipping in joint is measured by strain gauges on bothsides of the model. Reading on 10 measuring points andrecording the data was carried out for the first 8-10 daysevery day on a daily basis, and then in regular 7-dayintervals. The testing was carried out in indoor heated spaceconditions with mostly even temperatures between 20 and24 C, with relatively constant 55 to 65 % air humidity.Sample 1 was loaded for 343 days, and sample 2 for 426days. The ruling slipping was obtained as an average valueof all measured data. In sample 2 asymptotic approximationof slipping to the final value occurred after 427 days,whereas in sample 1 it occurred after 343 days.Fig. 6 illustrates an average value of slipping from twosides of the sample. The Figure shows a clear difference ofdisplacement from two sides, although the starting pointwas the presumption of the same elastomechanicalcharacteristics of the samples. This was repeated for model°4Research resultsRezultati ispitivanjaFigure 6Slika 6.The average slipping sample 2 in the first 106 daysSrednja vrijednost klizanja uzoraka 2 u prvih 106 danaFigure 7Slika 7.Slipping curves of samples 2Krivulje klizanja uzoraka 2282 Tehni ki vjesnikč ,17, 3(2010)  279-283There is a graphic presentation of the behaviour of theslipping module of connections. It has been shown that theslipping module decreases with time, as the slippingincreases (Fig. 9).Research of the rheological slipping module on the composite wood-concrete structure samples S. Lozančić, S. Takač, M. Bošnjak KlečinaFigure 8Slika 8.Slipping curves of samples 1, and the relevant average valueKrivulje klizanja uzoraka 1, te mjerodavna prosječna vrijednost,,Furthermore, it is evident that even with smallvariations of humidity over time there are outliers fromstandard slipping values.Fig. 10 illustrates a comparison of the change ofslipping sample 1, with the change in the air humidity of theenvironment in one time segment.Reverse proportionality of measured values is evident:with the increase in humidity of the environment the valuesof the slipping module are reduced due to the change in themechanical properties of wood, which itself changes thehumidity, as already indicated.On samples 1 behaviour after unloading was alsomeasured. A graphic presentation of the results of thatmeasurement is presented in Fig. 11.Fig. 11 indicates that almost instantaneously afterunloading the slipping values drop to the level that becamestable almost immediately. The return slipping curve is aline with a small inclination angle – almost horizontal.It means that there are no viscose strains. A comparisonof the size of slipping after lifting load of 0 647 mm withcurrent slipping of 0 608 mm shows large plastic strains.The reason for that is that connections with prescribedvalues per DIN 1052 were taken as bearing capacity values.Figure 9Slika 9.Display of average displacement values and slipping module for E75M16Prikaz srednjih vrijednosti pomaka i modula klizanja za  E75M16Figure 10Slika 10.Comparison of humidity curves and slipping samplesat certain timeUsporedba krivulja vlage zraka i klizanja uzorkaza isječak vremena283Technical Gazette ,17, 3(2010)  279-283Istraživanje reološkog modula klizanja uzoraka spregnute konstrukcije drvo-betonS. Lozančić, S. Takač, M. Bošnjak Klečina, ..-., ., .a, , .Takač, S, .Rajčić, V. Karakteristike spregnutih nosača drvo-laganibeton, doktorska disertacija, Građevinski fakultetSveučilišta u Zagrebu, 2000.Žagar, Z. Drvene konstrukcije III, Prostornost i usloženost,Udžbenici Sveučilišta u Zagrebu, 1999.International Rilem Symposium on Timber Engineering,Proceedings, Stockholm, Sweden, 1999 747-756[3] Amadio, C.; Ceccoti, A.; Di Marco, R.; Fragiacomo, M.Long-term behaviour of a timber-concrete connectionsystem, International RILEM Symposium, Joints in timberStructures, Stuttgart, 12-14 September 2001[4] Blaß, H. J.; Van der Linden, M.; Schlager, M. Trag- undVerformungverhalten von Holz-Beton-Verbundkonstruktionen, Informationsdienst Holz, Holzbauwerke, Step 3,Düsseldorf, E14/1-E14/25; 1995[5] Capretti, S.; Ceccotti, A. Service Behaviour of Timber-Concrete Composite Beams: a 5-Year Monitoring and TestingExperience, International Wood Engineering Conference,New Orleans, October 28-31 1996, 3/443-449[6] Feldborg, T.; Johansen, M. Slip in joints under long-termloading, CIB-IUFRO Meeting, Florence 1986[7] Gressel, P. Prediction of long term deformation behaviourfrom short term creep experiments Holz ls Roh-undWerkstoff, 42 8(1984) 293-301[8] . Experimental contribution to the findings ofrheological wood properties, International timberengineering conference London, 1991[9][10],5Conclusion6ReferencesZaključakAn examination of small (shear) composite wood-concrete samples connected with single dowels of a specialtype established that there is a large increment in slippingover a certain period of time, that the connection diameterhas a large impact on stiffness of connections and change ofstiffness over a certain period of time.For examined samples with two sizes of connectionsE48 and E75 modules of slipping for short-term and long-term loads were established.Initial slipping module for E48 dowels is =8 684 21N/mm, whereas the rheological slipping module for loadslasting for 343 days is 6 726 0 N/mm. The biggest ratio ofrheological and initial slipping module is 1 33, read for day246, and later on this ratio became stable and wasapproximately 1 3 for E48M12 after 200 days of loading.The initial slipping module for dowels E75 is=26 301 0 N/mm, whereas the rheological slippingmodule for loads in the duration of 426 days is 16 410 0N/mm. The biggest ratio of rheological and initial slippingmodule for E75M16 is 1 63, which was read on day 396, theratio has become stable and is at the approximate level of 1 6after 340 days.The results are appropriate for serviceability variation 1of wood, with shift in variation of humidity intoserviceability variation 2. The biggest increment of slippingon small samples is in the initial seven-day period.A change in the conditions of a micro-climate has asignificant impact on slipping of small samples, as reflectedin varying of the loads-slipping diagram, due to thehy  roscopic property of wood, but also due to a big impactof changes on the characteristics of concrete and joint.KKserser,,,,,,,,gLiteratura[1]J.[2] Amadio, C.; Di Marco, R.; Fragiacomo, M. A linear finiteelement model to study creep and shrinkage effects in timber-concrete composite beam with deformable connections, 1stLozančić, S. Doprinos spoznajama spregnutih konstrukcijadrvo-beton, doktorska disertacija, Sveučilište J.Strossmayera u Osijeku, Građevinski fakultet, 2003.....Figure 11Slika 11.Return sample slipping with the built E48M12Povrat klizanja uzoraka sa ugrađenim E48M12Authors' addressesAdrese autoraSilva Lozančić, Ph.D.Stjepan Takač, Ph.D., ProfessorMirjana Bošnjak Klečina, Ph.D.J. J. UniversityUniversityUniversity,,,Strossmayer in OsijekFaculty of Civil Engineering Osijek16 a Drinska31000 Osijek  CroatiaJ. J. Strossmayer in OsijekFaculty of Civil Engineering Osijek16 a Drinska31000 Osijek  CroatiaJ. J. Strossmayer in OsijekFaculty of Civil Engineering Osijek16 a Drinska31000 Osijek  Croatia

Istraživanje reološkog modula klizanja uzoraka spregnute konstrukcije drvo-beton

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