Seismic assessment of existing precast structures with dry-friction beam-to-column joints

In seismic countries of Southern Europe, including Italy, a large stock of existing precast structures for industrial buildings is characterized by beam-to-column dry friction joints. Several failures of this type of structures occurred during recent seismic events, including the Emilia earthquakes in 2012, due to the loss of the friction restraint and shift of the beam out of the support at the top of the column under the combined effects of horizontal and vertical seismic shaking. The seismic behaviour of precast structures with dry-friction joints is investigated based on nonlinear dynamic analysis to support the vulnerability assessment and design of seismic retrofitting interventions of existing industrial buildings. A dry-friction modelling of beam-to-column joints is proposed and case studies are presented to identify the most critical factors affecting the seismic response of precast frame buildings. The results show that flexible systems are more prone to structural failure due to the loss of support of the beam, particularly when the frequency content of the main shock of the seismic excitation includes the natural frequency of the structure in the vertical direction.