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Non destructive testing and system identification to evaluate diagnostics methods and reinforcement techniques applied to historical buildings

Objective

Development of a methodology, based upon non-destructive techniques, for diagnostics, recovery and final evaluation of restoration techniques related to the rehabilitation of historical buildings.

Nondestructive testing methods have been assessed for diagnostics, recovery and final check of restoring techniques related to the rehabilitation of historical buildings. A promising method is a ground prospecting radar (GPR) system which transmits electromagnetic energy to the medium to be investigated and receives the energy reflected back by any internal nonuniformity. Two different GPR methodologies used were transparency measurements and reflection measurements which detected variations ascribable to physical changes in the historic structures. The method proved successful not only for the investigation of homogeneous marbles and massive rock bodies, but also for the detection of thin fractures and humidity variations. The methodology appears suitable for modern buildings.

Mathematical methods have been developed within the context of system identification to estimate stiffness characteristics and, possibly, detect areas where reinforcement is needed. Parameter estimation methods can be used a nondestructive inspection technique and can be interpreted as a complement to other techniques (GPR, ultrasonic investigation, seismic tomography). The parameter estimation technique is being applied to masonry walls subjected to quasistatic load conditions. To this end, a test rig has been developed for the application of quasistatic loads to masonry walls. In this case displacements are the measured quantities and several investigations related to reinforcement methods are possible at low cost.

The experimental program also included pseudodynamic tests in order to evaluate the effect of seismic actions on different kinds of injections. In addition, they allowed checking of numerical models for dynamic analysis.
The research programme is to be developed through the application of non-destructive testing methods, numerical models of structural systems, parameter estimation techniques and reinforcement procedures. The survey will be carried out by electromagnetic methods, microseismics, flat actuators and dynamic excitation.

Electromagnetic methods will be based on GPR (Ground Prospecting Radar) investigation in the range of 500-1000 MHz. Ultrasonic measurements will also be performed in areas where high definition of mechanical parameters is required. Dynamic excitation will be needed to apply system identification methods, which can be used to estimate parameters related to the stiffness of a structure. The purpose is to obtain the indirect measure of unknown parameters by minimising the discrepancy between the response predicted by a numerical model and the measured response (for instance in terms of frequencies and vibration modes).

The above tests are expected to take place in sites of historical interest in France and Italy. Appropriate boundary walls of Middle Age towns are being selected, together with a Venetian building, due to the outstanding interest of the location and to the difficulties involved in that particular environment.
The non-destructive testing methods will be utilised in two phases, before and after applying convenient reinforcement techniques. Laboratory tests will also be performed on small specimens in order to calibrate the equipment and to evaluate different injection methods on simple structural components. The experimental programme will also include pseudodynamic tests in order to check the effect of seismic actions on different kinds of injections.

This technique of system identification (supplied by GRP investigation) should be recognised as a new, competitive methodology for diagnostics and repair appraisal, with particular reference to historical monuments.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Università degli Studi di Trieste
Address
Via Valerio 6
34127 Trieste
Italy

Participants (2)

Idrogeo Srl
Italy
Address
Via Mercato Vecchio 1
34124 Trieste
LABORATOIRE CENTRAL DES PONTS ET CHAUSSEES
France
Address
Boulevard Lefebvre 58
75732 Paris