Axiological approach to strengthening of timber load bearing floor structures

Timber load bearing floor structures of Italian historical constructions are complex systems made of girders, joists, subfloor, and completing components (lath to cover planking joints, small boards to cover the link between joists and girders, etc.). These floors are placed in and connected with the load bearing walls, thus constituting a more complex structural system. The need of strengthening of timber load bearing floors could issue from: timber decay (due to insects, fungi, fire, or creep), increase in loads, changes in safety and serviceability standards. Actual cases show countless states with regard to: building techniques; material state of preservation; size of the gap between required and provided performances; aesthetical, historical and material interest of ceiling and flooring. In the light of contemporary architectural preservation theories, several values must be considered while choosing from among the conceivable systems for the strengthening of timber floors: aesthetical quality; signs of usage; technological features; material characteristics. Other needs must also be evaluated along with those values: the requirement to assure physical and aesthetical fruition of the building; the need to respect the original technological conception of the structure; the compatibility of the strengthening solutions with the existing structure, the possibility to remove it, and maintain it in efficiency; moreover the added elements should be clearly recognisable as contemporary. This paper aims to single out the primary values to be considered, and to assess the most common strengthening solutions with regard to these aspects and to the actual state of the floor structure.