Application of Fragility Analysis to Timber-Framed Structures for Seismic and Robustness Assessments

In the past few years, the construction of multi-storey timber buildings has increased significantly in locations where high-intensity ground motions are likely to occur. On the other hand, the fast development of wood engineered products, as glued-laminated timber (GLT) and cross-laminated timber (CLT), has been challenging researchers to provide adequate guidelines for the design and assessment of structures built in seismic regions. Some guidelines and analysis methods considered in seismic design can improve robustness, commonly described as the ability of structures to sustain limited damage without disproportionate effects. This paper proposes a probabilistic methodology for seismic and robustness assessment of timber-framed structures. The seismic performance and the progressive collapse potential of a three-storey building are here exemplified through the proposed methodology, which accounts for uncertainties in mechanical properties of members and connections, as well as for external loads. The Latin Hypercube Sampling (LHS) was used in each assessment to generate a set of 1000 structural models. Each structural model corresponds to a realization of the random variables used to define the structural model. Incremental dynamic analyses were performed to develop seismic fragility curves for different damage levels. The fragility functions for robustness assessment were developed for distinct damage scenarios, exploiting the results of an alternate load path analysis (ALPA) that involved the performance of nonlinear static analyses (pushdown analyses). The methodology presented is suitable for risk-based assessments that consider the occurrence of different exposures, such as earthquakes, impacts, and explosions, while considering the direct and indirect consequences of failures. However, the methodology involves time-consuming analyses with distinct load scenarios, which can constitute a burdening task within a typical building design phase.