Seismic fragility and risk assessment of existing long-span precast industrial buildings retrofitted with different techniques

Over the past decades, the progressive evolution of structural design standards in the national building codes has supported the conception and construction of precast frame buildings in Italy—a country with significant seismic hazard and an extensive industrial built heritage. In most industrialised Italian areas, subsequent reviews of the seismic design codes have upgraded both hazard levels and seismic resistance criteria. Currently, a substantial portion of industrial buildings designed in conformity with past codes may be deemed to be seismically inefficient according to current standards. This highlights potential deficiencies in the flexural capacity of frame columns and in the performance of support connections of horizontal members and non-structural elements, such as cladding panels. This paper collectively investigates structural retrofit design and seismic risk assessment of a benchmark long-span precast building representative of modern single-storey industrial facilities characterised by large structural grids and tall roofs. Rational retrofit solutions of increasing impact and efficiency are implemented to improve the seismic response of vulnerable connections both between structural members within the main resisting frames, and between structural members and peripheral cladding panels. This work also introduces a comprehensive from-code-to-performance framework to evaluate the effectiveness of the proposed retrofit strategies. The proposed methodology encompasses state-of-the-practice code-conforming seismic design of retrofit interventions with state-of-the-art non-linear numerical modelling and probabilistic seismic fragility and risk assessment methodologies. This framework leverages advanced numerical modelling and statistical fitting tools to calibrate fragility curves and to estimate annual failure rates with respect to different performance levels, namely Usability Preventing Damage (UPD) and Global Collapse (GC).