Modal Identification Study of Vincent Thomas Bridge Using Simulated Wind-Induced Ambient Vibration Data

Abstract:   In this article, wind-induced vibration response of Vincent Thomas Bridge, a suspension bridge located in San Pedro near Los Angeles, California, is simulated using a detailed three-dimensional finite element model of the bridge and a state-of-the-art stochastic wind excitation model. Based on the simulated wind-induced vibration data, the modal parameters (natural frequencies, damping ratios, and mode shapes) of the bridge are identified using the data-driven stochastic subspace identification method. The identified modal parameters are verified by the computed eigenproperties of the bridge model. Finally, effects of measurement noise on the system identification results are studied by adding zero-mean Gaussian white noise processes to the simulated response data. Statistical properties of the identified modal parameters are investigated under an increasing level of measurement noise. The framework presented in this article will allow us to investigate the effects of various realistic damage scenarios in long-span cable-supported (suspension and cable-stayed) bridges on changes in modal identification results. Such studies are required to develop robust and reliable vibration-based structural health monitoring methods for this type of bridge, which is a long-term research objective of the authors.     

Laser Treatment of Sintered Silicon Carbide Surface for Enhanced Hydrophobicity

In this study, laser treatment of sintered SiC surfaces is carried out to enhance the surface hydrophobicity. Morphological and metallurgical changes of the treated surfaces are evaluated using optical and scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction (XRD). Microhardness and fracture toughness are measured using indentation tests. The residual stresses present are determined using the XRD technique. The wetting characteristics of the treated surfaces are assessed through contact angle measurements. It is found that the laser-treated surfaces consist of fine grooves and pillars and that the resulting surface roughness enhances the surface hydrophobicity. The fracture toughness of the treated surface is reduced possibly because of the microhardness increase at the surface. The residual stress formed in the surface region is on the order of 1.8 GPa, and it is compressive.     

Adhesion, spreading and osteogenic differentiation of mesenchymal stem cells cultured on micropatterned amorphous diamond, titanium, tantalum and chromium coatings on silicon

It was hypothesized that human mesenchymal stromal cell (hMSC) can be guided by patterned and plain amorphous diamond (AD), titanium (Ti), tantalum (Ta) and chromium (Cr) coatings, produced on silicon wafer using physical vapour deposition and photolithography. At 7.5 h hMSCs density was 3.0–3.5× higher (P < 0.0003, except Ti) and cells were smaller (68 vs. 102 μm, P 0.000006–0.02) on patterns than on silicon background. HMSC-covered surface of the background silicon was lower on Ti than AD patterns (P = 0.015), but at 5 days this had reversed (P = 0.006). At 7.5 h focal vinculin adhesions and actin cytoskeleton were outgoing from pattern edges so cells assumed geometric square shapes. Patterns allowed induced osteogenesis, but less effectively than plain surfaces, except for AD, which could be used to avoid osseointegration. All these biomaterial patterns exert direct early, intermediate and late guidance on hMSCs and osteogenic differentiation, but indirect interactions exist with cells on silicon background.     

Fundamental mechanisms of bonding of glass fiber reinforced polymer reinforcement to concrete

Fundamental mechanisms of bonding between glass fiber reinforced polymer (GFRP) bar and concrete are presented. Contributions from chemical bonding, bearing resistance, and frictional resistance to bond were delineated by measuring the following: the load corresponding to complete debonding of the bar, the load corresponding to onset of sliding and pullout of the bar along the entire embedment length, and the frictional load corresponding to frictional resistance to sliding. Research findings indicate that while chemical bonding was the main contributor to the interfacial bond strength, the other two mechanisms contributed to the pullout strength of the bar. Correlation between the bar’s surface geometry and the contributions from the three mechanisms are discussed.     

Evaluation du transport solide et de l’envasement dans le bassin versant de Siliana (Tunisie): cas des barrages Siliana et Lakhmess

The evaluation of the sediment transport and the silting in the artificial dam installed on the Siliana river (Tunisia) has been obtained using direct and indirect methods through the qualitative and quantitative study of the erosive phenomena existing in the subtended catchment area and the sedimentation entity accumulated on the dam’s reservoir. The study area, which extends approximately 1036 km², is mainly composed of quaternary alluvial deposits (clay, sandy clay, gravels, limestone). The relief is almost flat (600 meters of altitude), dominated by the presence of mountains of the Tunisian dorsal (the most elevated are: Jebel Bargou, Jebel Sardj). The dominant climate is the semi arid one. The study area is among the zones which are mainly concerned by several erosion phenomena in Tunisia. The indirect evaluation of the lands erodibility of the catchment area has been obtained through the application, with the aid of geo-informatics technologies, of two previsional models: the Quantitative Geomorphological Analysis and the PISA model. The obtained results, for the total Siliana catchment and for Lakhmess sub-catchment, allowed to estimate the entity and the variability of lands erodibility on the basis of some representative factors of the physico-climatic conditions that characterize the study area. The direct measurement of the sediment volumes present in the Siliana dam’s reservoir, has allowed to quantify the effective entity of silting of the same reservoir. The latter, obtained through a bathymetric relief has turned out equal to 14.66 10⁶ m³, to which corresponds a medium erodibility, pertinent to the entire catchment area, of 1322 t/km²/year. The comparison of such value with those obtained from the two indirect applied models has shown, at least for the studied area, the better suitability of the Quantitative Geomorphological Analysis as an instrument of indirect evaluation of the erosion entity in Lakhmess catchment and the PISA model as a good model for estimating the siltation on Siliana dam. The quantitative data obtained from this study, with the qualitative information shown in the numerous thematic charts realized, relative to the various physico-environmental characters of the catchment area, represent an adapted base, to which it will be possible to make reference to the manager responsible for the administration of the dam so as to realize the pertinent and necessary interventions of hydraulic management and soil conservation which are required for the protection of the water resource of the dam.     

Prediction of fabrics mechanical behaviour in uni-axial tension starting from their technical parameters

On the basis of a phenomenological study, which consists in determining the response of a fabric sample to the traction and the relaxation, we proposed a rheological model with 15 coefficients. This model of mechanical behaviour in uni-axial tension takes into account the elastic and the viscous components. To characterize the coefficients of this model, simple tension and relaxation tests were performed for 29 fabrics in the warp and the weft directions. An artificial neuronal network trained with a retro-propagation algorithm performs functional mapping between these mechanical coefficients and the technical parameters of fabric, which allowed us to predict the mechanical behaviour in tension and relaxation of fabrics starting only from their technical parameters.     

Application of cognitive robotics in disassembly of products

Disassembly is a critical step to increase the value of end-of-life (EOL) products and to reduce the environmental footprint. Despite worldwide efforts, disassembly is still performed manually due to the uncertainty associated with the quality and the quantity of the returned EOL products. In this paper, a cognitive robotics based system is proposed to address this problem. The system is equipped with four cognitive functions: reasoning, execution monitoring, learning and revision. The proposed system is tested using LCD screens. The results show that the system is flexible enough to deal with any product models without prior information.     

The effects of lead on the electrochemical and adhesion behavior of zinc electrodeposits

The presence of excessive lead in zinc sulfate electrolytes can lead to problems related to both processing efficiency and the properties of the metal produced. For example, poor adhesion can occur in electrogalvanized steel when it is heated in the temperature range of 215 °C to 280 °C if lead is present in the deposit. The duration of heating necessary to induce the peeling of the zinc was found to be dependent on the temperature, time, and concentration of lead in the electrolyte and the plating parameters. The presence of lead slowed the formation of the intermetallic, and the peeling occurred between the zinc and the iron-zinc intermetallic layer. In order to gain a better fundamental understanding of the role of lead, rotating disc electrodes were used to measure the diffusion coefficient of lead in the zinc sulfate electrolyte. The experimentally determined mass transport data on lead can be used as an aid to set an acceptable limit of lead allowable in the electrolyte or to evaluate the electrochemical characteristics of an electrolytic zinc system. By the addition of strontium carbonate to the plating solution followed by filtration, the lead concentration in the electrolyte could be reduced to an acceptable level, preventing the poor adhesion on heating.     

CORRELATIONS FOR ESTIMATING THE DIFFUSIVITIES OF NITROUS OXIDE IN AQUEOUS SOLUTIONS OF DIETHANOLAMINE AND N-METHYLDIETHANOLAMINE AND THE SOLUTION DENSITIES AND VISCOSITIES

Experimentally measured diffusion coefficients of nitrous oxide in water, aqueous solutions of diethanolamine, aqueous solutions of N-methyldiethanolamine, and aqueous blends of diethanolamine and N-methyldiethanolamine have been used to arrive at a modified Stokes-Einstein correlation by using nonlinear least-squares filling. The average deviation of this correlation from the experimentally measured diffusion coefficients is about 13%. Comparisons are also made to the estimated diffusivities of nitrous oxide in the amine solutions which are obtained from the Wilke-Chang and Hayduk-Minhas correlations. The average deviations of the Wilke-Chang and Hayduk-Minhas correlations from the measured values are about 13% and 19%, respectively. Correlations were also presented for estimating the solution densities and viscosities. Predicted values for the solution densities and viscosities from these correlations deviate from experimentally measured values on average by 1.2% and 4.8% respectively.