Steel exoskeleton systems for seismic retrofit: Connection design and performance

Steel exoskeletons are widely investigated in literature since they can strengthen the as-built structure without interrupting the activity within the existing structure. However, only few studies investigate the influence and the design procedure to define the connection between the existing structure and this strengthening solution. The main aim of the present work is to introduce a general design procedure for these connection systems as well as evaluate their influence on the global reinforced structural behaviour. Therefore, a real case-study steel school building was selected, and both the orthogonal exoskeleton and the connection system were properly designed. The local connection system performance in terms of capacity, stiffness and ductility was investigated by means of refined numerical analyses. A non-linear spring was then calibrated on the connection system response, and its performance was accounted for in the global analyses. The results showed that the design procedure introduced allows for obtaining a good connection system able to resist in the elastic range up to the design demand and to exhibit a ductile behaviour for larger values of imposed displacements. From a global perspective, it was underlined that only if the connection system capacity results in being stiff and resistant, its presence could be disregarded within the global analyses.