The construction of reliable numerical models is a key aspect within the seismic assessment of existing unreinforced masonry buildings. However, it is also a complex process due to the many uncertainties involved that can affect the structural response. In situ tests allow for the acquisition of data at a local scale. Nonetheless, supplementary information representing the global response is necessary to overcome other uncertainties (i.e., wall-to-wall connections or floor stiffness). To this end, data from ambient vibration tests (AVT) are useful to support seismic assessments. In fact, they allow for the identification of dynamic structural properties, which are useful in refining the calibration of numerical models. In addition, they address solutions for the aforementioned uncertainties. In this context, the paper presents how to efficiently exploit AVT data by using the case study of the former Courthouse of Fabriano (Ancona, Marche). This structure has been monitored since 2010 by the Italian Department of Civil Protection with a network of 28 seismic accelerometers. As a result, the equivalent frame (EF) model was calibrated in the linear field thanks to the dynamic identification provided under operational conditions. Subsequently, nonlinear dynamic analyses were performed using the recordings acquired during the Central Italy earthquake in 2016/2017. Even if the building experienced only a slight nonlinear behaviour, this comparison between the simulated and actual seismic response made it possible to validate the EF model, especially with reference to the capability in reproducing the amplification phenomena, which is extremely important for the assessment of structural and non-structural components. K E Y W O R D Sdynamic identification, equivalent frame models, masonry structures, permanent monitoring, recordings from seismic eventsThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
This paper focuses on the so-called “flange effect” in unreinforced masonry buildings when the connection among walls is good, thus forming a 3D assembly of intersecting piers (with L-, C-, T-, or I-shaped cross-sections). Given the direction of the horizontal seismic action, the presence of such flanges (the piers loaded out-of-plane) can influence the response of the in-plane loaded pier (the web) in terms of failure modes, maximum strength, and displacement capacity. Specific rules are proposed in codes to evaluate the effective width of the flange, for the in-plane verification of a single masonry wall. However, in the case of 3D equivalent frame (EF) modeling of the whole building, all the intersecting piers should be considered entirely, to model the response in both the orthogonal directions as well as the torsional behavior, but this may lead to overestimating the flange effect if a perfect connection is assumed. This paper investigates the capability of simulating the actual behavior in EF models by introducing an elastic shear connection at the intersection between two piers using an “equivalent beam”, coupling the nodes at the top of piers. A practice-oriented analytical formulation is proposed to calibrate such a flange effect on the basis of the geometric features and material properties of the web and the flange. Its reliability is tested at the scale of simple 3D assemblies and entire buildings as well. Finite element parametric analyses on masonry panels with symmetrical I- and T-shaped cross-sections have been performed to investigate the axial load redistribution between the flanges and the web and the consequent repercussion on the overall performance of the web. The results have proven that, after a calibration of the shear connection, the variation of axial force between the web and the flanges is correctly reproduced and the strength criteria for 2D panels provide reliable results. Finally, in the conclusions, some practical hints for simulating an imperfect wall-to-wall connection are also provided, since this case is relevant in historic masonry buildings, which are characterized by different masonry types, transformations over time, and already-cracked conditions.
Historical masonry structures constitute a fundamental part of the built cultural heritage but are characterized by an intrinsic vulnerability to ageing and natural hazards, in particular to earthquakes. The related need to assess their current health condition and to ensure their future conservation is giving rise to increasing efforts in scientific research. The combined employment of health monitoring systems and structural modelling is widely adopted in this field, either to better interpret the effects of age-related degradation or to reliably predict the structural response to earthquakes. Both scenarios can leverage experimental measurements for the model calibration, thus reducing epistemic and aleatory uncertainties in the assessment phase. Among the available modelling strategies, refined Finite Element (FE) models represent the most common choice in the SHM perspective for monumental URM structures. Nonetheless, the computational effort required by the assessments in the nonlinear fieldunavoidable in seismic evaluationsis often unfeasible, especially in practice engineering. In the case of palaces, an alternative is the employment of more computationally efficient formulations such as Equivalent Frame (EF) models. Within this framework, the paper firstly deals with the equivalent-frame modelling and model updating of the Consoli Palace, a historic masonry building in Gubbio (Italy) investigated through ambient vibration tests. The peculiar aspects of the buildinge.g. the unusually high inter-storey height, the presence of vaulted floors, the irregular distribution of the openingsmake the equivalent-frame idealization a challenging task. The comparison with a detailed finite element model developed in previous research points out the differences and limits of the two approaches, providing some suggestions to benefit from their integrated use.
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