Dynamic assessment of bridges and large structures

Research focus

The Peer review has evaluated this group as Good

This research group focuses on the use of dynamic testing and dynamic monitoring to study the response and the health condition of both new and existing bridges and large structures under traffic, wind, or seismic loads. The excitation is assumed to be provided mainly by the environmental or "ambient" actions; hence two main topics were studied, the first related to the use of ambient excitation (micro-tremors, wind and traffic) to evaluate the modal characteristics of the structures while in the second, the prediction of the response to seismic excitation is specifically addressed. Research Focus A: Ambient vibration-based assessment Within the context of ambient vibration assessment of large structures, the research activity was focused on carrying out broad campaigns of dynamic testing on bridges, historic buildings and monuments; for each investigated system, the research generally included: (a) dynamic testing and experimental modal analysis; (b) development of F.E. models and dynamics-based model updating; (c) damage identification (model-based or not); (d) prediction of the dynamic response under service or exceptional loads. Paticularly, over the reporting period theoretical and experimental investigations were carried out on more than 20 full-scale bridges, including very important infrastructures like the Carpineto cable- stayed bridge, the twin curved cable-stayed bridges of the Milan-Malpensa airport, the Bordolano cable-stayed bridge, the new curved cable-stayed bridge of Porto Marghera, the historic Morca suspension footbridge (1928), the Victory bridge (1923). In addition, experimental investigations were carried out on several steel bridge decks characterised by different types of damage and on an historic masonry tower (the bell-tower of the Cathedral of Monza, XVII century). Among the main results of the above investigations, the following must be mentioned: (a) the evaluation of the accuracy of the modal parameters estimated from an ambient vibration survey; (b) the development of two different algorithms for the identification of the uncertain parameters of F.E. models (with the first method being based on an original formulation of the objective function while the second approach basically consists in the application of the simple Douglas-Reid method, preceded by an extensive sensitivity analysis); (c) the evaluation of damage from dynamic testing and theoretical modelling of the bell-tower of the Cathedral of Monza and the Morca footbridge. In the past months, the main efforts have been devoted to: (a) the discrete dynamic monitoring of the Victory bridge. The monitoring consists in the periodic repetition of ambient vibration tests and operational modal analysis over a 1 year period in order to assess the structural conditions of the investigated system and to evaluate the effects of temperature. Successively, a permanent monitoring system with MEMS sensors will be installed on the bridge; (b) the formulation of two methodologies for the damage evaluation: The first approach is directly based on a systematic analysis of the recorded signals by using techniques known in literature like time-frequency or polynomial decomposition. The second procedure arises from the possibility of expressing, in a discrete formulation, the relationship between the mass and stiffness distribution, the natural frequency and the modal shapes so that an over-determined system of linear equation is obtained, with the unknown being represented by the stiffness parameters. (c) the calibration of a novel microwave interferometer through dynamic testing of prototypes and full-scale large structures. Research Focus B: seismic response prediction A technique has been developed to estimate the seismic demand on multistory buildings in terms of appropriate performance parameters such as story absolute accelerations, velocity and displacements, interstory drifts, story and base shear, from a limited number of recorded signals. A reduced number of signals is assumed to be recorded by sensors placed according to an optimal distribution 115 defined by local minima of a function of the effective participation factors of the dominant modes of the structure. Unknown responses, in locations where sensors are not available, are calculated using a spline shape function to interpolate recorded responses along the height of the considered building. Recorded and interpolated signals are then used to estimate the seismic performance parameters. The method has been applied to a real instrumented multistory building using records from recent earthquakes characterized by different intensity and frequency content. Calculated performance parameters are compared to those obtained from recorded responses showing that the method leads to an excellent estimate of the seismic performance parameters even with a very limited number of recording sensors. Successively, the methodology has been applied to various real instrumented systems always providing very good results. Furthermore, this procedure might be extended to the monitoring of bridges and historic towers, also with the aim of damage identification.

Dipartimento di afferenza

Dipartimento di Ingegneria Strutturale (DIS)

Docenti afferenti

Associate Professors
Carmelo Gentile
Maria Giuseppina Limongelli
Antonio Capsoni