Avaliação do comportamento mecânico ao cisalhamento de conectores de barras de aço com ganchos em vigas mistas de madeira laminada colada e concreto

Abstract

The main objective of this work was to propose a reference specimen for the push-out test of rod-type fasteners in timber-concrete connections. The following experimental tests have been performed in order to achieve the goals of this research: pull-out tests of bonded-in steel rods in wood specimens, pull-out tests of bonded-in steel rods in concrete specimens, push-out tests and bending tests in timber-concrete compositebeams. The pull-out tests were executed with the following objectives: to define what adhesive would be adopted for the glue-in rods, to evaluate influence of the hole diameter in the pull-out strength, and to compare the pull-out strength of bonded-in steel rods in concrete and wood. The push-out tests were performed to evaluate the influence of the form and dimensions of the test specimens (concrete-wood-concrete CWC orwood-concrete-wood WCW) on the results of the connection strength and on the connection slip modulus. The main purpose of the bending tests was to evaluate the behaviour of the bonded-in steel rods in mixed beams and to compare it to the rod behavior in the push-out tests through the slip modulus. Furthermore, the experimental values obtained for the connection strength and slip modulus were compared withanalytical results, calculated using the formulae suggested by technical standards and by some researchers. The connection system was constructed using 8,0, 10,0 and 12,5 mm diameter corrugated bars made of steel CA50 and Eucalyptus Grandis glulam. The types of adopted adhesive were based on epoxy resin denominated: Scuna 5100, Scunamass for filleting with microfibre plant (MFM), epoxy mass of two components (ME) and epoxy adhesive of two components A313. The concrete mix was dosed to present a compressive characteristic resistance (fck) of 25 MPa, at 28 days of age, and had a steelreiforcement mesh composed of 6,0 mm diameter corrugated bars made out of steel CA50. In the pull-ou tests the results indicated that the adhesive Scuna 5100 showed the best performance and that the variations adopted for the diameter of the hole showed nosignificant influence on the value of the pull-out strength. In addition, the bonded-in steel rods in wood, using the adhesive Scuna 5100, MFM and ME showed greater pullout strength than the bar anchored in concrete. In the push-out tests, the form and dimensions of test specimens (WCW or CWC) had influence on the joints strength and on the slip modulus of joints. In bending tests, the values of the connections slip modulus were quite different from those determined in push-out tests. A reasonableapproximation, between the experimental an analytical results for the connection resistance, was obtained by adopting the theoretical models for steel-to-timber connections proposed through the formulae suggested by EUROCODE 5. For the connection slip modulus, a good approximation between experimental an analytical results was also obtained. The specimen that best represented the connection strengthand the connection slip modulus, experimental and theoretical, was the CWC. However, the geometric features that CP respected the minimum provisions, prescribed in the standards of design, to enable it to be assessed the performance of the connector, without premature rupture of the concrete or wood.