PSI - Issue 11

Siro Casolo et al. / Procedia Structural Integrity 11 (2018) 20–27 Siro Casolo & Giuseppina Uva / Structural Integrity Procedia 00 (2018) 000–000

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Figure 5. Damage patterns (NLD analysis) for the median events, Zones 1, 2. Thickness and intensity of the segments and crosses are proportional to the maximum curvature (flexural and torsional). Left: Church of Rosario; right: Church of Trasfigurazione (Casolo & Uva, 2013).

The computations, both in the static and in the dynamic field, have been performed applying the previously described RBSM approach. Comparisons are based on extensive numerical analyses, which focus on flexural and torsional mechanisms, while in-plane damage mechanisms and the possible detachment between the façade and lateral walls because of a poor connection are disregarded (Casolo & Uva, 2013). The objective, here, is a strict comparison between NLD analysis and NSP and not a technical verification, and in this framework, dynamic analyses have been made by considering a single earthquake’s component perpendicular to the main façade. In-plane seismic actions have also been neglected, whereas the effects of self-weight on flexural strength are incorporated into the definition of the moment–curvature relationship. For each case study and for four reference seismic zones, 12 design-consistent accelerograms have been generated according to EC8 Standards, to match the elastic response spectra corresponding to the ultimate limit state of life safety. In Figure 6, a graphical comparison in the AD plane between dynamic and pushover analyses is presented, in order to allow an immediate comparison in terms of performance level and obtain further indications about the role played by the different bond-textures. The target displacements corresponding to each seismic zone are also shown (grey dashed lines - Z1, Z2, Z3, Z4). For the NLD analyses, 4 points are marked on the diagram, respectively representing the results of the group of accelerograms generated for each seismic zone. The abscissa of each point is the median value of the maximum displacement attained during the time histories. The ordinate is the spectral acceleration Sae(T*) of the reference design spectrum. The standard deviation of the displacements is also reported. The violet symbol represents the collapse of the façade in NLDs. With regard to the identification of the failure condition of the two façades in the case of texture (I), the diagrams show that non-linear dynamic and the non-linear static analyses are in a good agreement: the collapse is predicted in zones 1 and 2 for both churches. When considering the texture (II), the situation changes. The pushover analyses show very high available displacements, well beyond the target of all the zones. For the Church of Rosario, the displacement capacity (mode 1) is 38% higher than the target required in zone 1. For the Church of Trasfigurazione, the capacity is 55% higher than the zone 1 target (mode 1). Dynamic analyses, instead, show that the Church of Rosario suffers a significant damage in the tympanum in zone 1, with maximum displacements that are about the half of the pushover capacity. For the Church of Trasfigurazione, the partial collapse of the tympanum (related to higher vibration modes) is attained, and the corresponding displacements are again less than half the capacity provided by the pushover. It can be said that the nonlinear static analysis has provided a good appraisal of the failure of out-of-plane façades in the presence of damage modes governed by the first vibration mode.