Characterisation of an urban bridge portfolio and multi-risk prioritisation accounting for deterioration and seismic vulnerability

This contribution proposes a procedure to prioritise retrofit interventions on stocks of bridges according to their seismic vulnerability. The procedure also combines a previously presented approach to evaluate deterioration effects on bridges at a territorial scale. Thereby, the combi-nation of the two approaches provides a multi-risk classification method for bridge stocks. This method also allows refined prioritisation within each class, based on the proposed quantitative indices and on multicriteria decision-making methods. The method was applied to the bridge stock managed by the municipality of Padova, in North-East Italy. First, an extensive charac-terisation of the analysed stock is provided, according to typological, geometric, and structural parameters. Then, the application of the combined approach is presented, highlighting which bridge types resulted more vulnerable to either seismic actions or deterioration effects

Telecentric F-theta fisheye lens for space applications

A very wide angle lens with a field of view of 360°x180° - a fisheye lens - has been designed to be used in a space environment. As a case study, the lens is assumed to be mounted on a spinning probe passing through a comet’s tail. The lens, rotating with the probe passing through the comet coma, may map the entire sky as viewed from the interior tail, providing unprecedented data on the spatial distribution of plasma and dust. Considering the foreseen space applications for the lens, radiation hardened glass has been taken into account for the design. A key feature of the lens is the “angular scale” uniformity (F-theta) of the sky distribution map projected on the focal plane allowing to obtain a reliable whole sky reconstruction. Care has also been taken to obtain an almost telecentric design, in order to permit filters placed on the focal plane to work properly. A telecentric fisheye operating with a pixel-limited resolution in the waveband from 500 nm up to 770 nm and with an F-theta distortion is presented in this paper

The fisheye of the comet interceptor's EnVisS camera

Entire Visible Sky (EnVisS) camera is one of the payload proposed for the ESA selected F-Class mission Comet Interceptor. The main aim of the mission is the study of a dynamic new comet, or an interstellar object, entering the inner solar system for the first time. The Comet Interceptor mission is conceived to be composed of three spacecraft: a parent spacecraft A and two, spacecraft B1 and B2, dedicated to a close and risky fly-by. EnVisS will be mounted on spacecraft B2, which is foreseen to be spin-stabilized. The EnVisS camera is designed to capture the entire sky in some visible wavelength bands while the spacecraft pass through the comet's coma. EnVisS optical head is composed of a fisheye lens with a field of view of 180° x 40° coupled with an imaging detector equipped with both band-pass and polarimetric filters. The design of fisheye lenses requires to take into account some issues typical of very wide-angle lenses. The fundamental origin of the optical problems resides on the entrance pupil shift at large angle, where the paraxial approximation is no more valid: chief rays angles on the object side are not preserved passing through the optics preceding the aperture stop (fore-optics). This effect produces an anamorphic deformation of the image on the focal plane, i.e. the focal length is changing along the elevation angles. Tracing the rays appropriately requires some effort by the designer. It has to be considered that distortion, including anamorphism, is an aberration that does not affect the quality of a point source image, thus it can be present also in well corrected lenses. In this paper the optical design of the fisheye lens, that will be mounted on the EnVisS camera for the ESA F-class "Comet Interceptor" mission, will be presented together with the initial optical requirements and the final expected optical performances

The optical head of the EnVisS camera for the Comet Interceptor ESA mission: Phase 0 study

EnVisS (Entire Visible Sky) is an all-sky camera specifically designed to fly on the space mission Comet Interceptor. This mission has been selected in June 2019 as the first European Space Agency (ESA) Fast mission, a modest size mission with fast implementation. Comet Interceptor aims to study a dynamically new comet, or interstellar object, and its launch is scheduled in 2029 as a companion to the ARIEL mission. The mission study phase, called Phase 0, has been completed in December 2019, and then the Phase A study had started. Phase A will last for about two years until mission adoption expected in June 2022. The Comet Interceptor mission is conceived to be composed of three spacecraft: spacecraft A devoted to remote sensing science, and the other two, spacecraft B1 and B2, dedicated to a fly-by with the comet. EnVisS will be mounted on spacecraft B2, which is foreseen to be spin-stabilized. The camera is developed with the scientific task to image, in push-frame mode, the full comet coma in different colors. A set of ad-hoc selected broadband filters and polarizers in the visible range will be used to study the full scale distribution of the coma gas and dust species. The camera configuration is a fish-eye lens system with a FoV of about 180°x45°. This paper will describe the preliminary EnVisS optical head design and analysis carried out during the Phase 0 study of the mission

Synthesis and Characterization of Co-Doped ZnO Nanocompound

Zn1-xCoxO (x = 5%) nanopowders were prepared by using the autocombustion technique, and the structural, optical and magnetic properties were investigated. X-ray diffraction measurements show that the synthesized samples have a wurtzite structure. The formation of the wurtzite structure in Co doped ZnO nanoparticles was further confirmed by Fourier transform infra-red spectrometry. Optical absorption spectra show that the band energy of Zn0.95Co0.05O powders is about 2.42 eV at room temperature. Magnetic data obtained from as grown powders indicate the presence of antiferromagnetic interactions between particles

RC tied-arch bridges: Typological analysis for the definition of retrofit interventions

The Italian bridge asset is characterized by aged structures, most of which made of reinforced concrete, needing retrofit interventions to improve both their seismic performance and load-bearing capacity towards the increased traffic volume. In order to provide a series of guidelines for retrofit, a research project, carried out by the ReLUIS consortium supported by the Italian Department of Civil Protection, aims to identifying typological deficiencies and vulnerability of the main type of bridges widespread on the Italian territory, defining typological interventions. This paper presents the outcomes of the ongoing research focusing on RC tied-arch bridges, frequently built in the period between the two world wars. A typological study was carried out to define the main design deficiencies and construction details, and how degradation acts on this type of bridge, besides the main structural vulnerability to both gravitational and seismic loads. Numerical and parametrical analyses were carried out on a representative prototype tied-arch bridge with RC hangers, dating back to 1930s. The structural behavior was assessed by means of numerical analysis on FEM models, allowing the evaluation of the static and seismic capacity, the definition of the most vulnerable elements, and thus, the identification of the most suitable type of retrofit interventions

Application to an urban bridge stock of a prioritization procedure based on seismic assessment compared with the novel Italian guidelines

The challenge of large-stock maintenance with limited budget is faced by administrations in charge which need tools for management and intervention prioritization. This need is especially perceived for bridges which are strategic structures and represent crucial elements in roadway networks. Since 2016, a combined prioritization procedure has been applied to the bridge stock of the Municipality of Padova (Italy) to assess both the condition state, accounting for degradation, and the seismic vulnerability. The proposed methodology evaluates the level of degradation through visual inspections and type-specific forms for the defect survey, while the seismic vulnerability is assessed by means of fragility curves previously obtained by the authors for typical Italian bridges. This contribution focuses on the application of the seismic-based prioritization. The identification of the bridge typologies which appeared to be more seismically fragile is presented, comparing this aspect with results from the recently issued novel Italian Guidelines for the management of existing bridges

Dynamic Identification and Calibration of an Arch Steel Bridge Model for the Evaluation of Corrosion Effects

Bridges play a crucial role as they are critical elements in several road networks. Recent trends in condition state assessment require to evaluate not only the seismic vulnerability and the load carrying capacity for increased traffic loads, but also the damage state due to decay and environmental effects. in order to evaluate the structural reliability of the bridge and define priority lists for interventions on the network. In the framework of a series of inspections carried out at a municipality level for the above mentioned aims, a numerical and experimental analysis was carried out on a historical steel deck arch bridge, called Paleocapa bridge, located in the historic city centre of Padova (Italy). Paleocapa bridge is composed by six arches and is highly vulnerable to traffic load, due to a widespread and advanced corrosion state. In order to study the effects of both internal and external boundaries and the loss of mass and stiffness due to steel corrosion a parametric modal analysis was implemented. The steel material was characterized through uniaxial tensile test and metallographic and chemical analysis, while a dynamic identification test of the bridge was performed in order to extract modal parameters, i.e. natural frequencies, damping ratios and mode shapes. Modal analysis pointed out a decoupled behaviour of arches and deck, and among the same arches, with a consequent significant decrease in load-bearing capacity. The calibrated FE model of the bridge was used to assess the seismic and static capacity of the structure. In particular, the latter was very critical; therefore, it was necessary to limit the transitable load on the deck, in agreement with the public authority

Magnetic ordering of Mn2GeS4 single crystals with olivine structure

Single crystals of Mn2GeS4 were grown by chemical vapor transport. X-ray powder diffraction data show a single phase. Rietveld refinement results indicated that Mn2GeS4 crystalize in an olivine-type structure. The magnetic properties of the compound have been studied by means of DC magnetometry and AC susceptibility measurements. The system shows two different phase transitions on decreasing temperature, a first one at about 90 K, leading the system from the paramagnetic to an antiferromagnetic state and a second at about 25 K, corresponding to the onset of a weak ferromagnetic behavior superimposed to the underlying antiferromagnetic order. No evidence of a possible spin-glass behavior in the intermediate temperature region has been found