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-di-mensional models (created using the software Abaqus) and simpler 2-dimensional models (cre-ated 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 lit-erature. 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 can-not 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 iso-lated 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 strat-egies showed consistent results, both suggesting that the proposed intervention can signifi-cantly improve the seismic behaviour of existing RC frames.