Donato Sabia

Influence of Foundation Scour on the Dynamic Response of an Existing Bridge

Foundation scour is a major issue affecting the structural safety of existing bridges, hence its monitoring is of paramount importance. This paper reports a case history of assessment and monitoring with dynamic tests for a bridge affected by scouring and subjected to retrofitting. Two different approaches measuring traffic-induced vibrations are applied as potential tools for monitoring foundation scour. The modal identification of bridge spans is one approach, and the observation of the dynamic response of pier foundations is the other approach. A finite-element model is used to choose the parameters for scour monitoring. Both approaches are applied to the experimental data collected about the structure prior to and after retrofitting to show their effectiveness.

Hierarchical use of neural techniques in structural damage recognition

This study explores the possibility of using neural techniques to detect the presence of structural faults from dynamic response data in simple structures of practical interest for structural engineering. Some techniques of structural response signal processing and analysis devised for the purpose of improving the diagnostic capabilities of connectivistic methods are proposed through numerical experiments. To this end, cross-correlations between dynamic response signals are used as inputs for hierarchically organized networks which are able to assess and locate structural damage in numerical models. The satisfactory results obtained are discussed and explained with the aid of projections of the multi-dimensional decision space through the use of simple `grow and learn` neural models.

Seismic Vulnerability Assessment of Chemical Plants through Probabilistic Neural Networks

Abstract A chemical industrial plant represents a sensitive presence in a region and, in case of severe damage due to earthquake actions, its impact on social life and environment can be devastating. From the structural point of view, chemical plants count a number of recurrent elements, which are classifiable in a discrete set of typological families (towers, chimneys, cylindrical or spherical or prismatic tanks, pipes etc.). The final aim of this work is to outline a general procedure to be followed in order to assign a seismic vulnerability estimate to each element of the various typological families. In this paper, F.E. simulations allowed to create a training set, which has been used to train a probabilistic neural system. A sample application has concerned the seismic vulnerability of simple spherical tanks.

Influence of experimental data and FE model on updating results of a brick chimney

The present study deals with dynamic identification and model updating of the Howa brick chimney to preserve brick chimneys. From the results of dynamic tests, the fundamental frequencies of the Howa brick chimney are estimated to be about 3.06Hz and 2.69Hz in north-south and east-west directions, respectively. The natural modes and damping factors are identified by ARMAV (auto-regressive moving average vectors) model. The numerical model updating based on IEM (inverse eigensensitivity method) is applied to two models with two updating procedures; using only frequencies and both frequencies and mode shapes. The updating results show the mode shapes are very important to obtain the good results for the numerical model updating. From the results of the numerical model updating, the damaged areas are identified; these are found to correspond well to the position of the cracks of the static collapse test.

Identification Technique for Soil-Structure Analysis of the Ghirlandina Tower

Historical towers, in particular medieval towers, are an important part of cultural heritage, and their preservation mandates monitoring and detailed analyses of vulnerability under seismic actions as well as of their long-term performance. Certain aspects of structural nature are linked to the masonry behavior as a unilateral material, and other are aspects related to the interaction with soft soil conditions. This study aims to contribute to the aspects of preservation by exploring the role of the soil-structure interaction in predicting the behavior of the structures, with specific reference to the well-documented case history of the medieval Ghirlandina Tower (Modena, Italy). A significant contribution comes from an experimental identification analysis, performed in the presence of ambient vibration. A novel finding is that the soil structure interaction cannot be neglected, in contrast to most published identification analyses that usually assume the structure to have rigid constraint at base.

Structural Characterization of a Stone Arch Bridge by Experimental Tests and Numerical Model Updating

The Rakanji stone arch bridge has three spans of approximately 26 m, and the total length of the bridge is approximately 89.3 m. The rise:span ratio is approximately 0.19; hence, the arches are very shallow. To clarify the structural characterization of the Rakanji stone arch bridge, a series of dynamic, non-destructive and destructive tests are conducted. From material tests, the Youngs modulus and compressive strength of the stone are estimated to be 17.2 kN/mm2 and 28.5 N/mm2, respectively, whereas those of the mortar are estimated as 5.5–7.8 kN/mm2 and 3.9–9.1 N/mm2, respectively. From the results of dynamic tests, the fundamental frequencies, modes, and damping factors of the Rakanji stone arch bridge are identified by eigensystem realization algorithm (ERA) model. From the results of numerical model updating based on inverse eigensensitivity method (IEM), the damaged areas including the effect of boundary condition and bridge-soil interaction are identified and these areas correspond well to those through the in situ tests and visual inspection.

Model Updating to Forecast the Dynamic Behavior of the Ghirlandina Tower in Modena, Italy

Historical masonry towers survive at an alarming angle of inclination and may be in danger of leaning instability due to the lack of stiffness of the supporting soil. Therefore, careful investigation is required to estimate the seismic vulnerability as well as its long-term behavior. These problems require a multidisciplinary approach to properly model the behavior of the structure and its interaction with the supporting soil. This article is intended to contribute to these aspects, by showing how identification analyses can highlight the role of soil–structure interaction, and focuses on the model-updating techniques to forecast its behavior under seismic events.

Experimental identification of beams with localized nonlinearities

The idea underlying time-frequency identification techniques is that, for certain classes of structural response signals, the availability of a limited number of experimental data can be partially mitigated by taking into account the localization in time of the frequency components of the signals. This paper aims to assess the efficacy of time-frequency and time-scale estimators in the identification of weakly nonlinear systems. The example described refers to a beam characterized by a concentrated nonlinearity, whose first mode and related super-harmonics were seen to simulate a Duffing oscillator. A parametric time-frequency identification was conducted under the assumption that the beam’s input/output relationship could be approximated by a certain number of terms of the Volterra series representation, this resulting in a set of diagrams of instantaneous estimators. Though a substantial stability over time was observed only for the estimates associated with linear parameters, the identified model showed a good predictive capacity. Experimental data used in this research come from tests performed on a steel beam tested within the framework of the European research project COST Action F3 on Structural Dynamics.

Advances in Identification and Fault Detection in Bridge Structures

The paper presents some results obtained via the eigen-sensitivity up-dating procedure applied to two different kind of bridges, the former being the well known Z24 bridge, the latter consisting of a railway masonry arch bridge crossing the Tanaro river, in the Northern of Italy. More than a simple exercise to test the features of the well established output-only identification routines (ARMAV and CVA on this occasion), as well as the up-dating eigen-sensitivity techniques, the papers deals with the typical problems encountered during real size bridge tests and emphasizes the differences with other previous analyses performed by the same authors on other bridge structures

Safety assessment of the Sanctuary of Vicoforte, Italy

In order to evaluate safety assessment of the Sanctuary of Vicoforte, Italy, a series of non-destructive tests were carried out for diagnostic inspection of its deterioration. Delamination of stone finishing and fresco painting were detected. Dynamic ambient vibration test was carried out and the relevant modes of vibration were identified resorting to the stochastic subspace identification method. The first two natural frequencies of the Sanctuary of Vicoforte were estimated to be about 1.93 Hz and 2.07 Hz in East-West and North-South directions, respectively. Therefore, the dome seems to be vulnerable to severe earthquakes characteristic of the local seismicity such as we experienced in recent years.