Paolo Zanon

MANAGING THE HISTORICAL HERITAGE USING DISTRIBUTED TECHNOLOGIES

In this article we outline a research effort aiming to develop technological tools for real-time risk management of historic buildings. In detail, the project includes 1) the development of a prototype Historical Heritage Management System (HHMS), with 2) the technological and conceptual tools for integrating this HHMS with real-time monitoring, and 3) the demonstrative application of a pilot monitoring system, working within this framework, to a case study, the Aquila Gate in Trento. Motes network sensors are the basis of the monitoring system. We show that the risk-updating methodology proposed is able to deal with all the uncertainties involved (measurement noise, model uncertainty, inaccurate prior information) and to early-warn the manager of any possible future failure condition.

A Strain-Flexibility-Based Approach to Damage Location

The effectiveness of mode-shape-ba sed damage location methods is investigated, with specific regards to their application to the assessment of civil structures. Different location approaches proposed in the literature are compared and theoretically analysed. It is observed that, when damage is modelled as a loss in stiffness, the most direct way of exploiting mode-shapes information consists of estimating the flexibility matrix in a strain coordinate system. This matrix, referred to as strain-flexibility matrix, can be easily computed from the natural frequencies and the mode shapes expressed in terms of strain. Each diagonal element of the strain-flexibility matrix represents a local flexibility, thus changes in th ese quantities can be directly utilised as damage indexes. These findings have been validated through numerical and experimental examples. More specifically, the newly proposed damage indexes have been employed in the structural assessment of a 42.0 m long single-span steel bridge. The strain-flexibility indexes have been calculated comparing the experimental dynamic response, measured at 30 different locations, with that predicted through a simple FE model, representing the structure in the undamaged situation. Outcomes are consistent with the visual evidence of damage and with the outcomes of a static load test.

Direct Displacement-Based Design of Glulam Timber Frame Buildings

We introduce a direct Displacement-Based Design methodology for glued laminated timber portal frames with moment-resisting doweled joints. We propose practical expressions to estimate ultimate target displacement and equivalent viscous damping, and we demonstrate that these expressions provide prior values that are close to those obtained a posteriori using a more refined model. Applied to case studies, the method yields base-shear forces lower than those obtained using the force-based approach of Eurocode 8. This is due to the high dissipation capacity of the specific connection technology, which apparently is conservatively accounted for in the q-factor of Eurocode 8.

Vibration-based Condition Monitoring of Smart Prefabricated Concrete Elements

The University of Trento is promoting a research effort aimed at developing an innovative distributed construction system based on smart prefabricated concrete elements that can allow real-time assessment of the condition of bridge structures. So far, two reduced-scale prototypes have been produced, each consisting of a 0.2×0.3×5.6m RC beam specifically designed for permanent instrumentation with 8 long-gauge Fiber Optics Sensors (FOS) at the lower edge. The sensors employed are FBG-based and can measure finite displacements both in statics and dynamics. The acquisition module uses a single commercial interrogation unit and a softwarecontrolled optical switch, allowing acquisition of dynamic multi-channel signals from FBG-FOS, with a sample frequency of 625 Hz per channel. The performance of the system is undergoing validation in the laboratory. The scope of the experiment is to correlate changes in the dynamic response of the beams with different damage scenarios, using a direct modal strain approach. Each specimen is dynamically characterized in the undamaged state and in different condition states, simulating different cracking levels. The location and the extent of damage are evaluated through the calculation of damage indices which take into account changes in frequency and in strain-modeshapes. This paper presents in detail the results of the experiment as conducted on one of these prototypes and demonstrates how the damage distribution detected by the system is fully compatible with the damage extent appraised by inspection.

Historic Buildings: Long Term Stability Evaluation Using Wireless Sensor Networks

An automatic diagnostic monitoring system can guarantee the safety and integrity of a historic building. In this paper, we describe the long term application of a wireless sensor network (WSN) for permanent health monitoring in the Torre Aquila, a historic tower in Trento, Italy. The system consists of accelerometers, thermometers and fiber optic sensors (FOS) with customized wireless modules and dedicated software designed for wireless communication. The whole system was completed and started operation in September 2008, and data from the various sensor nodes are collected continuously, save during periods of system maintenance and update. Based on the first 1.5 years of operation in assessing the stability of the tower, the WSN is seen to be an effective tool. Modal analysis indicates that the tower has two independent structural parts. A comparison between the acquired long term deformation measurements and simulated numerical results shows good agreement. Monitoring of ambient vibration suggests that such vibration is not now a source of concern for the stability of the tower.

Bayesian Approach to Condition Monitoring of PRC Bridges

This paper presents a damage detection procedure based on Bayesian analysis of data recorded by permanent monitoring systems as applied to condition assessment of Precast Reinforced Concrete (PRC) bridges. The concept is to assume a set of possible condition states of the structure, including an intact condition and various combinations of damage, such as failure of strands, cover spalling and cracking. Based on these states, a set of potential time response scenarios is evaluated first, each described by a vector of random parameters and by a theoretical model. Given the prior distribution of this vector, the method assigns posterior probability to each scenario as well as updated probability distributions to each parameter. The effectiveness of this method is illustrated as applied to a short span PRC bridge, which is currently in the design phase and will be instrumented with a number of fiber-optic long gauge-length strain sensors. A Finite Element Model is used to simulate the instantaneous and time-dependent behavior of the structure, while Monte Carlo simulations are performed to numerically evaluate the evidence functions necessary for implementation of the method. The ability of the method to recognize damage is discussed.