Diana Faiella

In seismically isolated structures for buildings, bridges, etc., nonlinear viscous dampers (NVDs) are often deployed within the isolation layer to supply supplemental damping aimed at limiting displacement demands. Post-earthquake reconnaissance has frequently documented visible damage to NVDs attributed to excessive axial force demands. However, internal damage due to large force demand under earthquakes, evidenced by large-amplitude dynamic tests but undetectable through standard visual inspection, remains hidden in practice, complicating the condition assessment of NVDs. This study proposes an approach for estimating the peak force sustained by NVDs placed in parallel with seismic isolators, thereby establishing a rational basis for post-earthquake condition evaluation, particularly regarding the occurrence of concealed internal damage. The proposed method leverages the peak drift of the isolation layer, a readily visible and measurable response quantity, as the primary input for inferring the peak NVD force, which is directly correlated with the damper’s damage state. An equivalent linearization technique for NVDs is integrated with a structural linearization procedure that accounts for the elastoplastic behavior of the isolators. An iterative algorithm developed for single-degree-of-freedom (SDOF) isolation systems demonstrates that the peak NVD forces can be estimated with errors below 6%. The algorithm is subsequently extended to multi-degree-of-freedom (MDOF) isolation systems. Validation against a base-isolated structure (BIS) and an inter-story isolated structure (IIS) indicates that the discrepancies between the proposed estimates and nonlinear time-history analysis (NTHA) results remain within 4%. These findings confirm the accuracy of the proposed approach for estimating the peak NVD forces experienced during earthquakes, thereby offering a rational tool for post-earthquake condition assessment and directly informing damper’s replacement decisions.

The paper focuses on tall timber buildings. The major aim of this paper is to identify the most sustainable and efficient structural system to increase the height of timber buildings, also considering steel–timber hybrid structures. First of all, a brief review of tall buildings’ evolution is presented to understand why tall timber buildings are considered nowadays and which are the most adopted structural solutions. Then, the case study of the tallest timber building in the world is selected and utilized as an archetype. Once the model has been validated, seven alternative structural systems are considered by varying the horizontal load resisting system and preserving the same member cross-sections as the reference building. The variants are tested and compared in terms of material consumption, vibration characteristics and lateral load response. Using the best structural system, the height of the building is increased, pushing the structures beyond the current limits and identifying the most efficient option. The idea is to preserve the column cross-sections and balance the increase in gravity loads due to the additional floors by replacing the concrete floors with timber counterparts. With the same structural system, equivalent steel–timber hybrid solutions are finally tested and compared in terms of sustainability to timber-only counterparts and to the original project. The results of analyses show that the use of steel elements combined with timber can lead to optimized and sustainable structural solutions.