A NUMERICAL STUDY ON A TIMBER-BASED SEISMIC RETROFIT INTERVENTION FOR MASONRY INFILLED CONCRETE FRAMES

The paper focuses on a retrofit strategy applicable to existing reinforced concrete (RC) frame structures to reduce their seismic vulnerability.The intervention strategy, for the sake of brevity named RC-TP (Reinforced Concrete-Timber Panels), consists in the removal of the existing masonry infills and in their replacements with Cross Laminated Timber (CLT) panels fixed to the concrete elements by means of a timber subframe and a dissipative connection comprised of metal dowel-type fasteners.The analyses were performed via finite element modelling by adopting numerical strategies with different levels of refinement.In particular, refined 3-dimensional models (created using the software Abaqus) and simpler 2-dimensional models (created using the software SAP2000) were used.At first, the refined modelling approach was validated on experimental evidence on timber and concrete connectors available from the literature.Then, such 3-dimensional models were used to investigate the connection system of the proposed retrofit strategy paying particular attention to possible out-of-plane effects that cannot be directly observed with 2-dimensional models.The obtained results were used to calibrate the 2-dimensional models so that these "secondary" effects could be accounted for even in the simplified modelling.Subsequently, both modelling approaches were used to analyse an isolated one-storey one-bay frame via nonlinear static analyses that addressed the a) bare, b) original masonry infilled, and c) retrofitted configurations.The two alternative numerical strategies showed consistent results, both suggesting that the proposed intervention can significantly improve the seismic behaviour of existing RC frames.