Diagnosi strutturale per l’aggiornamento delle valutazioni dello stato di danno post-sisma

Nella fase successiva a un sisma uno dei problemi da affrontare è l’individuazione di danni che non richiedono interventi di emergenza ma modificano la predisposizione delle strutture ad essere danneggiate da un evento sismico successivo. L’applicazione di tecniche basate sull’analisi della risposta strutturale a vibrazioni può costituire un ausilio per la rivalutazione dello stato di danno della struttura a valle di un evento sismico. In questo lavoro si propone a tale scopo l’utilizzo del metodo di analisi del danno mediante interpolazione (IDDM). Tale metodo è particolarmente adatto all’utilizzo per edifici dotati di strumentazione permanente poiché non richiede la stima dei parametri modali e quindi l’aggiornamento della diagnosi strutturale può essere compiuto in maniera automatica senza richiedere particolari interazioni con un operatore. Il metodo è stato applicato al caso del Factor Building situato nel campus dell’Università della California a Los Angeles (UCLA) dotato di una strumentazione permanente che registra la risposta dell’edificio anche a vibrazioni ambientali e a piccoli eventi sismici. Le risposte accelerometriche disponibili sono state utilizzate per tarare un modello numerico dell’edificio poi utilizzato per simulare scenari di danno caratterizzati da diversa intensità e posizione del danno e quindi per stimare la sensibilità del metodo di identificazione del danno a scenari caratterizzati da intensità e posizione del dann

Structural monitoring for post-earthquake damage

Accurate and quick location of seismic damage is critical to establish a hierarchy of both immediate rescue or evacuation operations and of future repairs, strengthening and rehabilitation interventions. The Interpolation Damage Detection Method (IDDM) has proved efficient in localized seismic damage detection. This method is based on the analysis of the significant variation of a properly defined error function occurring as a consequence of a local reduction of stiffness in the structure. In order to distinguish significant variations from random fluctuations of the error function a statistical approach based on a binary hypothesis test is applied. The design of the hypothesis test is based paper upon a probability of false alarm defined basing on data relevant to the undamaged configuration. In this paper the joint influence on the accuracy of the method of the noise in recorded data and of the value selected for the probability of false alarm is investigated

Vibration based damage localization using MEMS on a suspension bridge model

In this paper the application of the Interpolation Damage Detection Method to the numerical model of a suspension bridge instrumented with a network of Micro-Electro-Mechanical System sensors is presented. The method, which, in its present formulation, belongs to Level II damage identification method, can identify the presence and the location of damage from responses recorded on the structure before and after a seismic damaging event. The application of the method does not require knowledge of the modal properties of the structure nor a numerical model of it. Emphasis is placed herein on the influence of recorded signals noise on the reliability of the results given by the Interpolation Damage Detection Method. The response of a suspension bridge to seismic excitation is computed from a numerical model and artificially corrupted with random noise characteristic of two families of Micro-Electro-Mechanical System accelerometers. The reliability of the results is checked for different damage scenarios. Copyright © 2013 Techno-Press, Ltd

Damage detection in a suspension bridge model using the Interpolation Damage Detection Method

Herein the feasibility of a damage detection and localization method (the Interpolation Damage Detection Method) is investigated for damage detection of long span suspension bridges. Based on the re- sponse induced by wind loading, a ‘signature’ of the structure in the intact state is obtained in terms of the power spectral densities of responses along the bridge deck and is compared with that in the potentially damaged conditions, considering measurement and process noise. A finite element model of the Shimotsui-Seto suspension bridge, in Japan, is adopted for this study. Wind loading descends from a spatially correlated model for the wind action. Several damage scenarios are considered; these are obtained by reducing the stiffness of a number of elements along the bridge deck. Results show that the IDDM is able to provide, with a good level of accuracy, the correct location of the damage for the damage scenarios herein considered

Wind-driven damage localization on a suspension bridge

The paper focuses on extending a recently proposed damage localization method, previously devised for structures subjected to a known input, to ambient vibrations induced by an unknown wind excitation. Wind induced vibrations in long-span bridges can be recorded without closing the infrastructure to traffic, providing useful data for health monitoring purposes. One major problem in damage identification of large civil structures is the scarce data recorded on damaged real structures. A detailed finite element model, able to correctly and reliably reproduce the real structure behavior under ambient excitation can be an invaluable tool, enabling the simulation of several different damage scenarios to test the performance of any monitoring system. In this work a calibrated finite element model of an existing long-span suspension bridge is used to simulate the structural response to wind actions. Several damage scenarios are simulated with different location and severity of damage to check the sensitivity of the adopted identification method. The sensitivity to the length and noise disturbances of recorded data are also investigated. © 2016 Vilnius Gediminas Technical University (VGTU) Press Technika

Interpolation damage detection method on a suspension bridge model: Influence of sensors disturbances

In this paper the influence of noise due to sensors disturbances on the results of a recently proposed damage detection and localization method is investigated with reference to a numerical model of a cable suspension bridge excited by wind. Noise is modeled as a white-noise and used to corrupt numerical simulations of measured responses. The relationship between the level of noise, the intensity of damage and the length of the recorded signals required to reduce the effect of noise is investigated with reference to various damage scenarios. The bridge model is derived from the ANSYS model of the Shimotsui-Seto Bridge in Japan (940m length of the main span). The wind excitation is simulated as a spatially correlated process acting in the horizontal direction, transversal to the deck. The bridge is assumed to be monitored by sensors located along the girder longitudinal axis, recording the absolute acceleration of the bridge deck in the transversal direction. © (2013) Trans Tech Publications