Shear resistance of pinned connections of precast members to monotonic and cyclic loading

One of the major issues in the design of precast structures against earthquakes is the proper design of their connections, mainly the beam-to-column joints. Many different types of such connections are used worldwide, as monolithic, emulative and dry pinned ones. The latter case is the most common solution in southern Europe and elsewhere for single-storey or low-rise precast buildings, and is the subject of the experimental research reported in this paper. The experiments were performed at the Laboratory for Earthquake Engineering of the National Technical University of Athens, Greece in the framework of the European FP7 project, SAFECAST. Precast beam and column elements connected with dowels were tested under monotonic and cyclic, pure shear loading and the research was focused on several design aspects, as the shear ductility capacity of the connections and the effect of various parameters on their strength. The parameters examined include the diameter D of the dowels, their number, their distances d and dn from the edges in the longitudinal and the transverse direction of the beam respectively, and the strength of the grout of their ducts. Improvements in the design were also proposed and tested experimentally. The results show that, for small values of the ratio d/D, the strength of the connection is lower in the pull direction than that in the push direction for both monotonic and cyclic loading, due to the early spalling of the cover concrete that occurs. Compared to the strength for monotonic loading, the cyclic response shows significantly lower resistance, less than half the monotonic one. The results for cyclic loading also show that significant values of shear ductility can be achieved by dry pinned joints, provided that the concrete cover of the dowels has sufficient thickness. Comparisons between the experimental results obtained for various design parameters show that secondary effects related to the number of the dowels can occur for large forces during monotonic loading, but are less important for cyclic response. A formula is proposed for the calculation of the shear strength of pinned connections, which can be used in seismic design.

► The shear resistance of pinned connections is investigated experimentally.
► The thickness of the cover concrete of the dowels is important to the response.
► The resistance for cyclic response is less than one half the monotonic one.
► Significant values of shear ductility can be achieved by dry pinned connections.
► A new formula is proposed that can be used in the seismic design.