Abstract
The paper presents the comparison of the results of nonlinear static analyses carried out using six software packages (SWs) available at professional level and operating in the field of the equivalent frame (EF) approach on a model representative of a complex masonry building. The structure is inspired by the school “P. Capuzi” in Visso (MC, Italy), proposed as one of the benchmark structures in the “URM nonlinear modelling—Benchmark project” funded by the Italian Department of Civil Protection within the context of the ReLUIS projects. The 2-stories building is characterized by an irregular T-shaped plan and load-bearing walls consisting of two-leaf stone masonry with a rather regular bond scheme. The school was severely damaged by the seismic sequence that hit Central Italy in 2016/2017 and essentially exhibited a global in-plane box-type response, with a clear evidence of cracks concentrated in piers and spandrels. The availability of an accurate survey of the crack extension represents a precious and rare reference to firstly address in the paper the rules to be adopted in the EF models for the definition of the structural elements geometry. Then, the comparison of results is made with a twofold aim: firstly, by setting the models adopting shared and consistent modelling assumptions across the SWs; secondly, by investigating the sensitivity of the seismic response to some common epistemic and modelling uncertainties (namely: the adoption of various EF idealization rules for walls, the out-of-plane contribution of piers, the flange effect). In both cases, results are post-processed to define reference values of the achievable dispersion. The comparison is carried out in relation to a wide set of parameters, namely: global parameters (e.g. dynamic properties, pushover curves and equivalent bilinear curves); synthetic parameters of the structural safety (i.e. the maximum acceleration compatible with the ultimate limit state); the damage pattern simulated by SWs.
Highlights
The comparative studies, available in literature and addressed to the modelling of unreinforced (URM) buildings, document a large scattering of achievable results, especially when used to finalize the seismic assessment through nonlinear analyses
The sensitivity analysis adopted to calibrate the equivalent beams, which can be monitored through the variations of the results on the pushover curves and on the dynamic properties estimated by the modal analysis, is effective to define a plausible range of variation of stiffness to be assigned to the beams and can be replicated for all structures under examination to address the relevance of this epistemic uncertainty
The paper presents the results obtained within the research activity carried out by several research teams involved in the “URM nonlinear modelling—Benchmark project” on the benchmark structure BS5, inspired by the “P. Capuzi” school in Visso (MC, Italy)
Summary
The comparative studies, available in literature and addressed to the modelling of unreinforced (URM) buildings, document a large scattering of achievable results, especially when used to finalize the seismic assessment through nonlinear analyses. In the BS5/A case, among the different options (see Beyer and Manalaghu 2013; Betti et al 2008), the same criterion adopted for piers has been assumed that, on the safe side, presupposes to neglect any possible contribution of an equivalent tensile strength of spandrel generated at the end section by the interlocking effects with the adjacent masonry portions Such an assumption produces in the BS5/A case an almost negligible flexural strength of spandrel, that has been directly considered null by the RT that used SW7, by modelling the spandrels as axially rigid rod elements, coupling piers only for the horizontal displacements.
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