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–concretefriction. 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–concretefriction 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–concretefriction coefficient is proposed.