Sara Casciati

Local damage detection from dynamic SOFO experimental data

Two goals are pursued in this paper. The first goal consists of comparing the performance of the innovative SOFO dynamic system, which uses long-gauge fiber-optic sensors, with the traditional monitoring method based on accelerometers. For this purpose, a dynamic laboratory test was carried out, and measurements were taken from a single-storey three-dimensional steel frame model excited at the base by a shaking table. The SOFO dynamic system was installed on one column of the frame structure, while two accelerometers were mounted on the base and on the frame storey, respectively, for comparison. The use of fiber-optic sensors allows to overcome the difficulties associated with the traditional dynamic measurement methods, such as the limitations in the number and in the locations of the monitoring devices. Furthermore, the long-gauge fiber-optic strain sensors show a very high sensitivity and extend the frequency range (1mHz-1KHz). The second goal is to investigate the sensitivity to local damage of a recently proposed method for damage detection and localization. Indeed, the use of better performing long-gauge strain sensors allows the detection of local damage that is hardly visible in the global response of the structure. Damages of increasing intensities are therefore gradually introduced in the structure, and the measurements acquisition is repeated for each of the damaged cases. The SHM-RSM method, which is based on the idea of using a response surface model to approximate the relationship between the measurements collected by different sensors during the same test, is finally applied to the collected data to detect and locate the damages of different intensities.

Dynamic Behavior of Shape Memory Alloy Structural Devices: Numerical and Experimental Investigation

The first author was recently engaged in an editorial effort [1] having the modeling and applications of shape memory alloys (SMA) as subject. This activity followed a wide band cooperation period with specialty teams, working in Russia, France and Spain, and their associates [2]. The second author is taking care of an attempt to implement SMA devices in the seismic retrofitting of an ancient monument: the Luxor Memnon Colossi, in Egypt [3][4].

PGA and structural dynamics input motion at a given site

The computation of the representative ground motions, to be used as input for the dynamic analyses of a structure at a particular site, can be approached by several methods. The choice of the approach depends on two factors : the data available and the type of problem to be solved. This paper reports the experience of the authors in approaching a specific case study: the Southern Memnon Colossus, located in Luxor, Egypt. The results are of interest when the hazard analysis estimation in developing countries and the safeguard of cultural heritage are concerned. Monuments have to be treated as important structures, due to their historical and economical value. Hence, standard procedures of probabilistic seismic hazard analysis for the seismic classification of common buildings have to be disregarded. On the other hand, the consequences of the collapse of a monument are not comparable to those related to structures such as nuclear power plants and large dams, for which the deterministic seismic hazard analysis provides a straightforward framework for evaluation of the worst case ground motions. An “intermediate” approach, which requires a lower amount of input data with respect to the deterministic one, is adopted. Its stochastic component can capture significant characteristics of earthquakes, primarily the frequency contents which depend on the magnitude (often referred to as the earthquake scaling law).

HUMAN INDUCED VIBRATIONS IN A PEDESTRIAN TIMBER BRIDGE

The mountain landscape fits well with slender timber structures. Among them tim- ber bridges are becoming very popular, and the designers are extending the span toward the hundred meters threshold. For a long pedestrian timber bridge in the Italian Alps, the authors had the chance to acquire measurements of the structural response which were collected for periods of few days and repeated in different seasonal weather conditions. A previously de- veloped elaboration of the collected data leads to the validation of a numerical model. In this paper, the numerical model is used to investigate the dynamic response of the structural sys- tem which, according to the current structural code, can be ignored along the design process.

Conceiving semi-active control devices for large-size monolithic monuments

CHIME is a research project, funded by the European Union, which investigates the adoption of innovative structural control techniques in view of the seismic rehabilitation of the wide monumental cultural heritage in Mediterranean countries as Egypt, Tunisia and Cyprus. The structural control devices are mainly of the semi-active type. In this particular paper one reports the first results achieved within a case study. It considers an Egyptian large size monolithic monument. Alternative solutions for its seismic rehabilitation are eventually conceived and discussed.

Pedestrian bridges monitoring data for stochastic modelling of human-induced loads

A model of the human-induced actions, where the consequences of humans unpredictability, together with their response to social and psychological stimuli, are regarded as stochasticity, is developed. After defining a moving grid of nodes in the direction of the crossing, an average action per node is assigned. This value is modified by the following two contributions. A fluctuation, which involves two spatial variables and the time variable, is introduced by stochastic simulation, with a cross-spectral density function which accounts for the spatial dispersion of the single trajectories. A geometric shape function is formulated to account for a non-homogeneous spatial distribution of the pedestrians across the bridge deck. The procedure of assessing the vibrations serviceability of new footbridges requires to be thoroughly revised in light of the increased slenderness and spans achieved by using innovative construction materials of high strength (Zivanovic et al., 2005; van Nimmen et al., 2014). Particular attention must be paid to avoid the lock-in phenomenon induced by the crossing of a group of pedestrians. Nowadays, increasing efforts are made to quantify the vibrations due to crowds using the basis of wind engineering theory. Indeed, the correlation between pedestrians at different locations on a structure suggests an approach similar to estimating the dynamic response of structures to turbulent buffeting by wind (Carassale and Solari, 2006). It is worth noting that the simulation of the time history of a wind field affects at different time instants the same impact surface. Adopting a similar model for pedestrians crossing a bridge also requires that instant after instant the surface of impact moves along the bridge. Furthermore, whereas most studies found in the literature are focused on modelling the crowd load as homogeneous across the bridge deck, there is a lack of investigations concerning the possibility that the synchronization phenomenon occurs among a group of pedestrians which does not fully occupy the spatial domain. Based on these considerations, a model of the human-induced actions, where the consequences of humans unpredictability, together with their response to social and psychological stimuli, are regarded as stochasticity, has been developed. After defining a moving grid of nodes in the direction of the crossing, an average action per node is assigned. This value is modified by the following two contributions. A fluctuation which involves two spatial variables and the time variable is introduced by stochastic simulation, with a cross-spectral density function which accounts for the spatial dispersion of the single trajectories. A geometric shape function is formulated to account for a non-homogeneous spatial distribution of the pedestrians across the bridge deck. 12 International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP12 Vancouver, Canada, July 12-15, 2015 2 The deterministic shape function can only be applied on the result of the fluctuation simulation, since this requires a matrix Cholesky decomposition and the matrix properties are influenced by the shape function. In other words, the supposed nature of the eigenvalues of the simulation matrix could go lost if the order of the operations is changed. The obtained loading realizations are applied to the finite element model of a cable-stayed timber footbridge for which experimental data were collected. It is shown how the availability of experimental data is fundamental to support the selected approach, and to identify the refinements which have still to be implemented. 1. GOVERNING RELATIONS Pioneering studies on Human Induced Loading (HIL) were developed in (Eriksson, 1994). The basic result of this PhD thesis was the plot in Figure 1, which is also incorporated in the review paper (Zivanovic et al., 2005). Mainly the figure represents a synthesis of experimental results achieved in tests carried out in Sweden. Figure 1: Figure 3-8 of the PhD Thesis by Eriksson (1994). “Spectral densities of the force from a male person (mass 75 kg) walking at different frequencies: A) 1.4 Hz; B) 1.7 Hz; C) 2.0

Reducing Energy Performance Gap in Buildings—Built2Spec Project Solution

Built to Specifications (B2S) is a Horizon 2020 EU-funded project involving 20 European partners that seeks to reduce the gap between a building designed and as-built energy performance. To do this, the project will put a new set of breakthrough technological advances for self-inspection checks and quality assurance measures into the hands of construction professionals. This collection of smart tools will help building stakeholders at all levels in meeting EU energy efficiency targets.

HIL Excitation in the Damage Assessment of a Timber Footbridge

During experimental tests in situ, footbridge identification is usually pursued by exploiting the response to environmental actions. The aim of this manuscript is to replace the environment excitation with “Human Induced Loading” (HIL), when carrying out the periodical assessment of timber footbridges. Due to the stochastic component of the model, the tests should be repeated several times along the experimental campaign. The statistical analysis of the collected structural responses will then allow one to detect discrepancies, if any, from the expected spectral response. The proposal runs with the support of data collected on an existing timber footbridge located in North-Eastern Italy. doi: 10.12783/SHM2015/48