Neoprene-concrete friction relationships for seismic assessment of existing precast buildings

In Italy many precast industrial buildings built between 1950s and 1970s present beam-column connections with strength coming from neoprene-concrete friction. Numerical studies recently performed by the authors confirm that, in order to determine the seismic vulnerability of such structures, a reliable value of the neoprene-concrete friction coefficient has to be known. Technical bibliography provides many and different values for this coefficient; consequently, in order to define reliable values, a specific experimental campaign is carried out. Three types of experimental tests are performed: tests on neoprene hardness, tilting tests and pulling tests; in the last case, the specimen is also axially loaded.Tilting tests provide a value of the mean friction coefficient equal to about 0.5, with very low C.O.V.. Pulling tests underline a friction strength dependence on axial load and, in particular, a decrease in the friction coefficient as the axial load increases; a relationship for compressive stress-neoprene-concrete friction coefficient is proposed.