MS18.14 - System Identification and Damage Detection

Masonry vaults represent one of the most recurrent types of horizontal structural elements in architecture in European countries, even in areas characterized by a high level of seismic risk. Therefore, the evaluation of their structural safety and their mechanical behaviour remains of primary importance, and they are topics widely treated in the literature. This paper proposes to apply already consolidated structural analysis methodologies – on traditional vaults of historic buildings – on traditional vaults of historic buildings on a contemporary vaulted space and, in particular, the use of scaled vault model made of 3D printed for the experimental analysis. The aim, therefore, is to investigate the material characterization and the dynamic behavior of a newly concept vault generated starting from the “Flat vault of Abeille” patented in 1699. The reinterpretation of this vault and its use would allow both to enhance the existing Architectural Heritage and to characterize the realization of new buildings according to the guidelines of architectural restoration. It follows that the identification of this “new type” of vault is essential to design it correctly and to optimize the geometry for structural purposes. The scale of the vault model in 3D printing is 1:8. The material used for blocks is Polylactic Acid (PLA). All the blocks have an infill of 70% and are assembled with dry joints. The dynamic behavior of the vault was studied. The paper describes the results of the material characterization and the experimental tests analyzed in terms of crack pattern, damage/collapse mechanisms and ultimate displacements.

Identification and extraction of damage sensitive features is a crucial task for the health, serviceability, and lifetime assessment of civil and industrial structures. Within this framework, the vibration-based structural damage detection of nonlinear beams is herein accomplished using a convolutional deep autoencoder. First, numerical simulations are performed in which the auto-encoder is trained by exploiting the time history of the response obtained from the nonlinear normal modes of a simply supported nonlinear undamaged beam modelled in COMSOL Multiphysics. Subsequently, the trained autoencoder is used to reconstruct the time history of the response obtained from the nonlinear beam in case of damage. The reconstruction error is examined in order to identify the existence and severity of the damage. These numerical results are also corroborated by laboratory experiments. The experimental setup consists of beam specimens excited by an electrodynamic shaker whereas the dynamic response is acquired on a grid of points using a PSV-3D laser scanning vibrometer. The damage is introduced as a localized reduction of the cross-section of the nonlinear beam.

Space truss structures are a type of versatile lightweight systems that are applied in different fields such as civil and aerospace engineering. For some of these systems that were built decades ago, for example as roof structures for relatively large spans, not all proofs regarding the load-bearing capacity and serviceability can be satisfied according to current codes of practice as the requirements may have changed since the initial design phase of these systems. In such cases, it may become necessary to obtain the actual stress status of the structural skeleton based on experimental investigations. From the identification of forces in many members, a general stress status can be derived, which leads to an estimation current status and possible reserves in the load-bearing capacity of space truss structures. One option for the identification of element forces is their identification from modal parameters of the structure. In literature, the main focus has been put so far on the identification of longitudinal forces and boundary conditions inside a single tension member/cable utilising vibration-based methods. Very good results were also reported for the identification of longitudinal forces in elements of two-dimensional truss structures of moderate complexity. Fewer studies documented in the literature concentrate on space truss structures. For these modular systems consisting of standardized elements, not only the identification of element forces based on identified modal parameters is very challenging, but also the modal identification itself. The latter is often caused by the situation that space truss structures often have numerous modes characterised by both local and global vibrations at close natural frequencies. The study presented in this contribution focuses on the identification of mode shapes and natural frequencies required as a prerequisite for a model-based approach to estimate the stress state of the complete considered space truss structure. Apart from aspects with respect to the instrumentation for modal testing, specific issues within a parametric modal analysis such as the choice of model order are discussed. It is explained by means of a case study, why the minimal model order to be taken into account in the modal identification of space truss structures can become considerably higher than those commonly applied in the analysis of, for example, bridge structures, towers or floor systems. These descriptions are illustrated by the results of both numerical and experimental analyses.