Industrial precast buildings are characterized by multiple vulnerabilities. In particular, in the case of an earthquake, this type of building highlights the development of a plastic hinge at the base of the column, the loss of the roof elements-beam support, and the loss of the beam-to-column support. The problem of the loss of beam-column support mainly concerns buildings built within the 1970s as they were not designed to withstand seismic loads; for this reason, the beam-to-column connections on these buildings are simple friction. To date, the retrofit of pre-fabricated industrial buildings involves the introduction of mechanical devices at the connec-tions between the structural elements to solve the problem of inadequacy of friction connec-tions in the event of an earthquake. However, it is interesting to evaluate the level of safety guaranteed by simple friction connections to establish priorities of interventions. This paper aims to evaluate the influence of infill panels on the loss of simple friction support in existing precast structures. The behavior of the friction connection is evaluated through a simplified model that describes the behavior of a portal frame composed of two columns, one beam and an infill panel between the two columns. The equations of motion are derived, and parametric analyses are performed to investigate the influence of the geometry of the structural elements, the non-linear behavior of the columns, and the friction coefficient used in the col-umn-beam connections for varying horizontal and vertical seismic acceleration.