Timber framed with masonry infill: a historical anti-seismic device. The Portuguese Pombaline gaiola.

Post-seismic reconstruction and seismic prevention have always been a major concern worldwide. This work analyses the Pombaline gaiola (meaning cage), a structural system of masonry reinforcement used in the reconstruction of Lisbon following the earthquake of 1755. A gaiola consists in the insertion of a three-dimensional timber frame embedded in stone masonry in order to bind together the various structural parts, and contribute to the overall seismic resistance. Timber framed reinforcement is an old anti-seismic device that may be globally observed in the history of the constructive technology. From the Roman times, this system spread in the Mediterranean area during the XVIII century but a large quantity of examples can be observed almost worldwide. The Pombaline gaiola is analysed from an architectural, constructive, and structural point of view to show how that traditional system made a robust (re)construction possible. Beyond the suboptimal rules of the art and tacit historical instances, and by means of philological criterion and detailed analysis of seismic improvement, contemporary preservation works should ensure the structural safety of the historical construction. In such a perspective, this study examines aspects of diffused timber frameworks with masonry infill that go beyond the anti-seismic technology and develops guidelines for preservation.

La ricostruzione postsismica e la prevenzione sismica sono stati da sempre un fondamento costruttivo.Questo studio analizza la tipologia costruttiva della gaiola pombalina, un sitema costruttivo e strutturale molto diffuso in Portogallo ma non solo, adottato a Lisbona a seguito del terremoto del 1755. Si analizzano i materiali e le tecniche costruttive, gli elementi utili al rinforzo e consolidamento della struttura muraria, ampiamente diffuso in area mediterranea a partire dal XVIII secolo.Questo sistema costruttivo può e deve anche oggi essere considerato un utile presidio antisismico da riconoscere e preservare da interventi incolti, se non addirittura da incongrue demolizioni.