NUMERICAL ANALYSIS OF THE TWO BASIC COLLAPSE MECHANISM OF A TYPICAL COLONIAL FACADE

The paper presents the computational modelling and the seismic damage assessment of a typology of facade that is recurring among the churches built during the colonial period in México, between 16th and 18th century. This typology is symmetric, with two relatively stubby bell towers on either side of the main facade itself, while the openings are usually aligned along the vertical axis of symmetry, including a portal that is much wider than the window underneath the tympanum. Even if these churches were built differently, according to the regional seismicity, this notwithstanding we considered This is an “archetype model” whose characteristics can be considered as a good basis to be representative of this typology in general, even if there is some local variability, mainly related to the regional level of seismicity. The main seismic collapse mechanisms of this typology tend to involve both the towers and the central part of the facade with damages that can be related both to in-plane shear actions and to the out-of-plane actions. The central part of the facade often presents damages and cracks along the symmetry axis and along the sides connecting the towers. These towers present very often a localized damage in the belfry due to flexural actions and also can present a damage mechanism related with the torsion in their middle part. In order to study the complex nature of these damage mechanisms, we adopted two specific Rigid Body and Spring Models (RBSM) to analyse separately the in-plane and the out-of-plane dynamical behaviours. Great attention has been posed into selecting a set realistic constitutive rules to describe the main meso-scale material-damage mechanisms. The main characteristics are: i) orthotropy of the flexural and membranal response; ii) material response is strongly influenced by average vertical axial compression; iii) modelling the hysteretic energy dissipated by repeated cyclic loading. Given a suitable discretization, these RBSM allowed us to describe realistic damage patterns and also the effects of the higher modes of vibration with a reasonable computational effort and using real accelerograms.