PSI - Issue 44

Giacomo Iovane et al. / Procedia Structural Integrity 44 (2023) 1870–1876 Giacomo Iovane et al. / Structural Integrity Procedia 00 (2022) 000 – 000 5

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particular, as a function of the available useful space along the perimeter, the actions can be transferred by a bi dimensional (2D) or a tri-dimensional (3D) timber systems. As for the 2D-systems, they are placed in parallel (2D// exo ; Fig. 2) or orthogonal (2D ⊥ exo ; Fig. 2) to the masonry walls or RC frames. They can be made with timber walls (CLT, LVL or light timber frames panels) or timber braced frames (X, V concentric braces and eccentric braces), as a function of the seismic resistant system chosen (Fig. 2). In some configurations, exoskeletons require own foundations, joined or linked to the existing ones, to ensure a correct load transmission from top to bottom of the structure. The connection to existing buildings can be done through links able to withstand forces due to earthquakes or, to increase the dissipation capacity with purposely additional devices. Concerning the 3D-systems, it is possible to distinguish partial (P) systems located at selected part of the building (3D P,exo ; Fig. 2) and spatial (S) systems wrapping all around the building (3D S,exo ; Fig. 2). In both cases, the system 3.3. Local interventions Generally in masonry buildings, but in many cases also in RC buildings, floors and roofs are made with timber structures. Recently all timber buildings are also common. The resisting cross sections of timber structural elements and the mechanical properties of timber can be reduced, becoming sometimes insufficient, due to mechanical degradation and/or biological attacks. Therefore damaged timber elements can be repaired with local interventions. These are beneficial, especially in case of historic buildings, they allowing to preserve ancient material and architectural features. The interventions can be distinguished according to the function, as it follows: re construction/repair of existing timber elements and joints, strengthening of the element cross-sections and reinforcement of timber floors (Table 1). Timber degradation can occur due to water infiltration and consequent biotic or abiotic attacks, but also failures can be due to creep or to overload due to change of service loads. When timber members are affected by significant deterioration and damage, reducing the structural safety and inducing a limitation of the use, it is possible to strengthen the transversal cross-section to restore acceptable level of bearing capability. This can be generally done by adding to the existing structural element new boards made of laminated structural timber of the same wooden species, adequately connected through metal fasteners (Fig. 3). More massive interventions for repairing existing solid timber members consist in using new timber prostheses to be connected with the damaged element using smooth or ribbed rods, connectors or bars. Holes are drilled, or groove cut, in the undamaged existing timber to accommodate the reinforcement. The prosthesis is usually made with new laminated structural timber or solid wood of the same species of the element to be repaired. Typically, rods are made of fiberglass, carbon FRP or stainless steel. Pouring or injection resins are used to fix the rods into the prostheses and the existing beam (Fig. 3). Likewise, concerning degraded joints, strengthening of cross sections of converging members, as well as prosthesis for reconstruction can be applied. Reinforcement solutions can be also simply based on the substitution of connectors or addition of new ones, by using timber pegs, specially for carpentry joints, as for example scarf-joints (Ceraldi et al., 2022), or metal devices. The rehabilitation of historic buildings for new use and occupancy often requires the reinforcement of timber floors for improving the bearing capabilities in bending. In seismic areas, floors play also the fundamental roles to transfer seismic loads to the resisting vertical walls or frames, as well as to prevent the out-of-plane mechanism of walls, if suitably connected to them. To this purposes, respectively, an increment of the in-plane stiffness of timber floors, as well as the opportune connection to the walls, are often necessary. An effective strengthening technique consists in the application of horizontal CLT panels over the floor, efficiently connected to the existing timber joists or beams by means of metal connectors (Riccadonna et al. 2020, Piazza et al. 2000, Bedon et al. 2020), obtaining a composite cross-section behavior of the system (Fig. 3). Therefore also the seismic response is significantly enhanced. A further solution, valuable in case of excessive degradation of existing floors, is the replacement with new timber floors, which can be realized with timber beams and CLT panels adequately connected, or even entirely with CLT panels. can be made with timber walls, timber braced frames and timber reticular structures. The most convenient option depends on the structural and architectural requirements.