BEHAVIOUR OF SLOTTED AND FLEXIBLE PERFOBOND RIB SHEAR CONNECTORS

The perfobond rib connector is a new type of shear connector, first used in the construction of the Third Caroni bridge in Venezuela. Except for a limited number of proprietary tests conducted in Germany, research on perfobond rib shear connectors has been carried out mainly in Canada. Results of earlier experimental investigations at the University of Saskatchewan showed that the perfobond rib connectors performed satisfactorily in both solid slabs and slabs with wide and narrow ribbed metal decks. The load carrying capacity and the overall ductility improved considerably when reinforcing bars were passed through the perfobond rib holes. The overall conclusion drawn from the investigations was that the perfobond rib connector is a viable alternative to the headed studs. This thesis presents the results of a current investigation which attempts to address some of the minor deficiencies of the perfobond rib connectors identified from earlier tests. Although previous investigation showed that the effect of passing reinforcing bars through the rib holes was an increase in the capacity of the connectors, the task associated with this exercise in an actual construction site may be cumbersome. The earlier test results also showed that the perfobond rib shear connector is not as flexible as headed studs. Lack of flexibility encourages unequal distribution of shear load between the connectors. These minor drawbacks may be rectified by replacing some of the holes with vertical slots. The vertical slots would increase the flexibility of the perfobond connector as well as greatly simplify the task of placing reinforcing bars through the rib holes. Two series of tests involving 24 pushout specimens were carried out to investigate the effectiveness of slotted perfobond rib connectors in comparison to normal perfobond rib connectors and headed studs. The flexibility of a perfobond rib connector can also be enhanced by reducing the thickness of the plate. Besides savings in the cost of material, thinner plates would allow punching of holes rather than drilling. Previous investigations at the University of Saskatchewan were limited to a plate thickness of 12 mm. In this research project, the effectiveness of 6 mm thick perfobond rib connectors was investigated by conducting two additional series of tests involving 32 push-out specimens. In addition to realizing the aforementioned objectives, the test program was designed to provide further information on a number of important issues such as the influence of concrete dowels, concrete strength, and additional transverse reinforcement through the rib openings. The experimental program also included two additional series involving 32 specimens which were tested to investigate the effects of welding a face plate in front of a perfobond rib connector and to study the influence of rectangular openings. Shank shear was the principal mode of failure in specimens with headed studs. In specimens with perfobond ribs, failure was triggered by the longitudinal splitting of the concrete slab along the line of the shear connector, followed by the crushing of concrete in the bearing zone immediately in front of the perfobond rib. A considerable deformation was observed in the perfobond rib connectors with thin and/or slotted ribs. The test results indicated that slotted perfobond rib connectors improve the overall ductility of the test specimens. However, the increased concrete dowel area provided by the slots in the perfobond rib connector tends to offset the increase in flexibility at low load levels. The addition of transverse reinforcement through the slots increases the ultimate load and the load retention capability. The specimens with 6 mm thick perfobond rib connectors exhibited more ductile behaviour than those with 12 mm thick perfobond rib connectors although their ultimate shear capacity was somewhat reduced. This test program confirmed the ability of perfobond rib connectors to retain a substantial portion of the ultimate load in the unloading stage of the load-displacement curve. As expected, the face plate greatly enhanced the performance of the perfobond rib connector. The increase in the ultimate load capacity was in excess of 30%. There was also a substantial increase in the ductility. However, for these specimens, failure was caused largely due to the crushing of concrete in front of the face plate. Once the concrete crushed, the load retention capability decreased rapidly. The load-slip behaviour of specimens featuring perfobond rib connectors with square and circular holes of equal area was almost identical. The sharp comers of the square hole did not produce any noticeable detrimental effects. Finally, the results presented in this thesis indicate that thin and slotted perfobond rib connectors can be effectively used in composite beams with solid slabs