PSI - Issue 64

Alba Hyseni et al. / Procedia Structural Integrity 64 (2024) 246–253 Alba Hyseni / Structural Integrity Procedia 00 (2019) 000 – 000

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Introduction The preservation of the historical masonry-based building Heritage has the scope of making a memory of the human culture. This mainly includes structures primarily attributed of supporting own weight, Heyman (1998). Moreover, seismic analyses are run by practitioners to define the potential failure in the eventuality that earthquake induced stresses, according to the probability related to a certain time behind whose it can manifest, exceed the strength of the masonry. At this aim, the mechanical properties in the state-of-play are investigated by means of destructive or minor-destructive in-situ tests to make them act as inputs of the analysis. The historical masonry structures are intended to be long-term preserved; Iscarsah Recommendations (2003). Nonetheless, the decay influence on the seismic vulnerability evaluation is not generally considered. A critical aspect of this challenge is the creep phenomenon: a time-dependent deformation observed in materials subjected to prolonged axial stress. Basically, creep behavior is not negligible in masonry especially for high and slender structures, like towers. In fact, creep generates both the axial shortening (deformation) and the lateral softening (stiffness) which may be very severe depending on the total weight of the structure and age. Currently, the retrofitting technology is poorly able to contrast creep when already manifest; so, foreseeing it is the most effective option since the retrofitting may be provided before creep itself became relevant. In this perspective, the seismic analysis should be run in-series according to the significant creep stages (better described in the next sections) aiming to a more realistic long-term preservation. Hence, a Creep-Affected Seismic Analysis (herein CASA) should take advantage by the state-of-knowledge concerning the cases-study in which the creep behavior of masonry towers was manifest (e.g. in Anzani et al. (2010); Tomor & Verstrynge (2013); Brotóns et al. (2013); Valente & Milani (2016). One of the most emulative examples is reported in Binda et al. (1992) where the time-dependent mechanical behavior was realized after the medieval Tower of Pavia ’ s collapse. The failure was apparently without premonition, but a series of thin vertical cracks opened at the base of the tower due to the excessive deformation in the mortar joints corresponding to the highest level of compression stress. The present paper aims to propose the beforementioned CASA-method by means of a real-case application concerning a masonry tank-tower. It was already focused on a previous study by the authors Hyseni et al. (2022) throughout a Finite Element Model (FEM) assuming the Verstrynge et al. (2011) proposed constitutive law. 1. Creep-Affected Seismic Analysis (CASA) The CASA-method simply consists of a coupled decay and structural analysis having one aspect affecting the other in relation with a certain age of the building to be evaluated with. To provide a more comprehensive and understanding sight of the proposal, a flow-chart is illustrated in Fig. 1.

Fig. 1. flow-chart of the proposed CASA-method.