A Bayesian framework is presented for finite element model-updating using experimental modal data. A novel likelihood formulation is proposed regarding the inclusion of the mode shapes, based on a probabilistic treatment of the MAC value between the model predicted and experimental mode shapes. The framework is demonstrated by performing model-updating for the Metsovo bridge using a reduced high-fidelity finite element model. Experimental modal identification methods are used in order to extract the modal characteristics of the bridge from ambient acceleration time histories obtained from field measurements exploiting a network of reference and roving sensors. The Transitional Markov Chain Monte Carlo algorithm is used to perform the model updating by drawing samples from the posterior distribution of the model parameters. The proposed framework yields reasonable uncertainty bounds for the model parameters, insensitive to the redundant information contained in the measured data due to closely spaced sensors. In contrast, conventional Bayesian formulations which use probabilistic models to characterize the components of the discrepancy vector between the measured and model-predicted mode shapes result in unrealistically thin uncertainty bounds for the model parameters for a large number of sensors.

The wave propagation in and the vibration of sandwich plates with cellular core are analyzed and controlled. Negative Poisson's ratio (auxetic) core materials of different geometry placed periodically in the plate introduce the proper impedance mismatch necessary to obstruct the propagation of waves over specified frequency bands (stop bands) and in particular directions. The location and the extension of the stop bands and the directions of wave propagation can be modified by proper selection of the periodicity and of the geometrical and physical properties of the core. A Finite Element model is developed to predict the dynamic response of three-layered sandwich panels with honeycomb core. The Finite Element model along with the theory of periodic structures is used to evaluate the influence of core materials of different geometry placed periodically along the two dimensions of the structure. This combined analysis yields the phase constant surfaces for the considered sandwich plates, which define location and extension of the stop bands, as well as the directions of wave propagation at assigned frequency values. The analysis of the phase constant surfaces and the evaluation of the harmonic response at specified frequencies indicate that the plates are characterized by dynamic behaviors with directional properties, with spatial patterns strongly dependent on the configuration of the periodic core and on the excitation frequency. Auxetic honeycombs are considered as core materials in order to obtain maximum design flexibility. The elastic and inertial characteristics of auxetic honeycombs in fact vary substantially with their internal geometry and for given configurations outcast up to five times the corresponding properties of traditional hexagonal honeycombs. The presented numerical results demonstrate the unique characteristics of this class of two-dimensional periodic structures, which behave as directional mechanical filters. The findings of this study suggest that optimal configurations for the periodic cellular core can be identified in order to design passive composite panels, which are stable and quiet over desired frequency bands and which fit desired transmissibility levels in particular directions. Such unique filtering capabilities are achieved without requiring additional passive or active control devices and therefore without compromising the size and the weight of the layered structure.

This paper examines the static and dynamic responses of strain gradient planar trusses. Classical elasticity (CE) theory lacks a material microstructural length parameter in its governing equations, making it insufficient to capture size-dependent effects. To address this limitation, higher-order continuum theories—such as micropolar, couple-stress, and strain gradient elasticity (SGE) theories—are essential. In this study, gradient elasticity theory is extended to describe the behavior of planar trusses by incorporating explicit internal length scales as additional material parameters. A key finding of this research is that the inclusion of the microstructural parameter results in a stiffening effect in both static and dynamic analyses.