Estudio experimental de la influencia de la ejecución en la resistencia a rasante de piezas en flexión

Experimental study on the influence of execution on the resistance to shear at the interface in composite concrete flexural members

Investigations into composite members made up partly of prefabricated concrete and partly of concrete in-situ, began some thirty years ago due to the interest that it aroused, being semi-industrialized elements of a wide range of usage. There have been few systematic investigations into members with interfaces without connection reinfiorcement that analyze the parameters conditioned by its execution and this when such types of members are widely used in this country as building slabs. For the experimental investigation we used a beam model, the suitability of which have been previously confirmed by pilot testson the effects of load distribution. As basic variables of the investigation we adopted two states of superficial saturation when wet (H) and flooded (E), two methods of consolidation, rod tamped (P) and internal vibration (V); finally we used two types of joint, natural (N) and brushed (C). In addition we selected two new variables of states pf surface treatment to the interface, combed (P) and tamped (T) and a further state of surface humidity by artificially drying the surface (A D). The selected variables made up 11 combinations which lead to the fabrication and testing of 22 beams, using two identical models for each group of variables. The tests were carried out in the Laboratory of the "Instituto Técnico de Materiales y Construcciones" and results were obtained on the resistance of shear at the intertface under stress and relative sliding between the two parts of the composite members and deflection in the centre of of the beam span, throughout the loading process. Prior to the testing, the components of the concrete, the concrete itself and the steel for reinforcing were sampled and tested. The results of the tests have been analysed in order to evaluate the influence of the parameters investigated both, under service limit states, cracking and deformation, and under ultimate limit states for the investigations that were shear at the interface. The basic conclusions of the investigation show the complete lack of dependence of resistance to shear at the interface with the procedures of consolidation for the type of member tested, the null influence of roughness, the inappreciable influence of joint treatment be it combed or tamped. On the other hand the investigations show the positive efffect of flooding as oposed to the states of wet joints including artificially drying interface. The extraordinary rigidity of the joint was confirmed likewise in all cases as was the inappreciable influence of the parameters investigates in the performance of ther members tested against characteristics that condition its deformability and cracking scheme.