Problem and its Significance.

Recently, the issue of limiting interference with existing buildings and their use is particularly important in the field of seismic retrofit. In fact, the use of punctual techniques and interventions on the structural elements considered critical is often incompatible with the use of the building. In many cases, the interruption of existing activities such as strategic or public interest activities is not permitted. On other occasions, the limitation of interference is due to the fact of preserving the architectural asset by avoiding interventions with a high aesthetic impact. Further limitations are also attributable to urban planning and administrative aspects that do not allow modifications to the building envelope.

Approach.

In the field of seismic retrofit, the use of additional structural systems coupled to existing buildings has spread in recent years. These systems are typically seismic-resistant steel frames equipped with an independent foundation and capable of absorbing almost all of the seismic action. The present paper deals with these systems and in particular with the use of steel exoskeletons and endoskeletons suitably coupled to the existing seismic-resistant elements. The objective of this technology is to transfer most of the seismic action to the additional structure avoiding to intervene directly on the existing structure. The latter will be required to bear only a reduced rate of the design seismic action limited to the capacitive levels of the existing structure. In order to obtain this result, the additional systems must be equipped with high stiffness or subtract the main mass rates from the existing structure. The coupling system is therefore fundamental, which is calibrated according to the structure on which to intervene (RC, masonry), to the type of interference to be resolved, to the type of additional system used (endoskeleton, exoskeleton).

Results/Applications.

The paper illustrates the study of innovative solutions for the coupling of additional structural systems for the seismic improvement project of real buildings. The most significant aspects of interventions carried out on both reinforced concrete structures and masonry.