Sliding channel cladding connections for precast structures subjected to earthquake action

The traditional seismic design of precast frame buildings concerns the calculation of the frame, considering the cladding panels as non-structural added masses without stiffness, assuming they are connected so to not interact with the frame. Under seismic excitation, the cladding connections are subjected to complex multi-directional actions, depending on the panel static scheme, all of which involve relative motion between cladding and structure. The correct kinematics of these connections in decoupling the panels from the structure has rarely been demonstrated, and accidental coupling may result in dangerous sudden increase of forces and subsequent failure of the connections. This is also confirmed by post-earthquake field observations on precast structures, which are characterised by pronounced deformation under seismic loading due to their flexibility. An innovative panel-to-structure sliding connection conceived to allow for an effective cladding-structure decoupling has been tested to check its correct kinematics within a uniaxial test apparatus, imposing displacement histories with application of constant normal force. The experimental results of cyclic tests with a tailored test protocol are presented, and static and dynamic friction coefficients are experimentally evaluated. A cyclic test on a full-scale precast prototype equipped with sliding panel connections has been carried out, checking the global behaviour of such systems and their installation peculiarities. Design rules for the evaluation of seismic actions arising within the proposed panel arrangements are finally provided, accounting for the experimentally evaluated friction coefficients.