Secondary structures and attachments under seismic actions: modeling and analysis

The chapter deals with the methodologies focused on the seismic analyses of the so-called secondary (sometimes attachments) elements that are part of a construction whose seismic resistance is delegated to a primary resistant structure. Although secondary elements can be decontextualized from the primary resistant structures, they will be subjected to seismic action as well and, having their own structures, need to be modeled and analyzed by means of methods included in the general methodologies proper of seismic branch. Among the methodologies usually adopted for secondary element analyses, the Floor Response Spectra (FRS)-based analyses become popular due to their recognized simplicity. FRSs provide acceleration (consequently velocity and displacement) to which the secondary element (with a given period and damping) will be subjected to when attached (from which the alternative name attachments derives) to a given part of the structures such as a building floor (from which the name Floor Response Spectra derives). Given that FRS generation could require onerous numerical analyses, simplified expressions are proposed in literature and discussed in the following together with the general methodologies tailored to secondary element modeling and seismic analyses.