Papers by Author: Alberto Carpinteri

Abstract: Historical churches, masonry towers and bell towers are structures subjected to high risk, due to their age, elevation and low base area on height ratio. In this work, an innovative monitoring technique for structural integrity assessment of historical buildings is reported. At the same time, the emblematic case study of the Turin Cathedral Bell tower is presented. The damage evolution in the tall masonry structure is described by the evaluation of the cumulative number of AE and by different parameters able to predict the time dependence of damage. In particular, since environmental disturbances have been minimized, and instrumental noises have been filtered out. The b-value analysis shows a downward trend to values compatible with the growth of localized macro-cracks at the base of the tower. These results seem to be in good agreement with the numerical analysis. Extension to longer monitoring periods and, later, investigation of different segments are strongly recommended to assess the stability of the monument.

Abstract: Non-destructive tests were performed to assess cracking evolution in two medieval masonry buildings, Sineo and Asinelli towers rising respectively in the Cities of Alba and Bologna, in Italy. As regards the case study of Alba, in situ compressive flat-jack tests on small-sized elements of the tower were conducted in conjunction with acoustic emission (AE) monitoring. At the same time, crack patterns taking place in large volumes of the tower were likewise monitored through the AE technique.As for the case study of Bologna, a masonry wall of the Asinelli tower was monitored during a period of intense seismic activity. The observed correlation between the AE activity in the monitored structural element and local earthquakes points out a significant dependence of deterioration processes in the tower on the action of nearby earthquakes.In both cases, the trends of two evolutionary parameters, the b-value and the natural time (NT) variance κ₁, were derived from the AE time series to identify the approach of the monitored structures to a critical state in relation to the earthquake occurrence.

Abstract: The coupled Finite Fracture Mechanics (FFM) criterion is applied to investigate brittle fracture in rounded V-notched samples under mode I loading. The approach is based on the contemporaneous fulfilment of a stress requirement and the energy balance, the latter being implemented on the basis of a recently proposed analytical expression for the stress intensity factor. Results are presented in terms of the critical crack advance and the apparent generalized fracture toughness, i.e. the unknowns related to the system of two equations describing the FFM criterion. A validation of the theory is performed by employing varying root radius notched, as-quenched, AISI 4340 steel specimens fracture results.

Abstract: In the present paper, a project for integrated investigation is described, using noninvasive methods, specially designed for dealing with the highly diversified historic heritage of Piedmont (Italy). The stability of the decorated surfaces will be investigated by innovative Acoustic Emission (AE) and ultrasonic methods already experimentally tested in the field of artistic and monumental cultural heritage in Italy. The ultrasonic investigation techniques allow assessing separations, defects and damage phenomena that can regard the decorated surfaces and the masonry supports. Innovative acoustic methods will allow distinguishing a well-preserved artwork in comparison to a damaged one providing a quantitative criterion for the definition of intervention priority.

Abstract: A scaled model of a two-span masonry arch bridge has been built in order to investigate the effect of the central pile settlement due to riverbank erosion. The bridge model has been equipped with different Non Destructive Testing (NDT) instruments and subjected to incremental settlement of the pier. The evolution of the pier scour has been investigated experimentally by means of a hydraulic model and reproduced accordingly. The numerical interpretation of damage, carried out by finite element analyses, has been compared with the results of the Acoustic Emissions (AE) monitoring. Several ultrasonic emissions have been detected and main damage source areas have been localized.

Abstract: An experimental analysis on a set of strengthened masonry walls has been carried out by means of cyclic loading tests in order to simulate the creep effects. The damage evolution of specimens reinforced by traditional or innovative methods is evaluated by the Acoustic Emission (AE) technique. The AE time dependence during fracture propagation is analysed through a power law. In addition, the AE frequency analysis is used to obtain information on the criticality of the ongoing process.

Abstract: Many biological materials exhibit a hierarchical structure over more than one length scale. Understanding how hierarchy affects their mechanical properties emerges as a primary concern, since it can guide the synthesis of new materials to be tailored for specific applications. In this paper the strength and stiffness of hierarchical materials are investigated by means of a fractal approach. A new model is proposed, based both on geometric and material considerations and involving simple recursive formulas.

Abstract: Acoustic emissions (AE) are ultrasonic waves generated by the rapid release of energy from discontinuities or cracks spreading in materials subject to a stress and strain field. By identifying the complete shape of the signals and taking into account a larger quantity of data, it becomes possible to ascertain the three-dimensional location of damage sources from AE sensor records. In this connection, the authors have fine-tuned an original procedure that uses seismic analysis techniques, such as the moment-tensor solution. The experimental program consisted of tests conducted in situ on masonry walls of historical buildings.

Abstract: In this contribution some characteristics and predictive capabilities are discussed of a recently introduced model for damage progression and energy release, in view of modelling Acoustic Emission. The specimen is discretized in a network of connected springs, similar to a Fibre Bundle Model approach, with the spring intrinsic strengths statistically distributed according to a Weibull distribution. Rigorous energy balance considerations allow the determination of the dissipated energy due to crack surface formation and kinetic energy propagation. Based on results of simulations, the macroscopic behaviour emerging from different choices at “mesoscopic” level is discussed, in particular the relevance of model parameters such as the distribution of spring cross sections, Weibull modulus values, and discretization parameters in determining results like stressstrain curves and energy scaling versus time or specimen size.

Abstract: Extensive research and studies on concrete fracture and failure have shown that concrete should be viewed as a quasi-brittle material having a size-dependent behaviour. Numerous experimental techniques have been employed to evaluate fracture processes, and a number of modelling approaches have been developed to predict fracture behaviour. The non-destructive method based on the Acoustic Emission (AE) technique has proved highly effective, especially to check and measure the damage phenomena that take place inside a structure subjected to mechanical loading. In this paper an experimental investigation conducted on concrete and RC structures by means of the AE technique is described. The AE signals reflecting the release of energy taking place during the damage process were recorded and micro-cracking sources were localised by measuring time delays by means of spatially distributed AE sensors.