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.     

On-Line Characterization of Morphology and Water Adsorption on Fumed Silica Nanoparticles

The first wetting layer on solid nanoparticles has direct implications on the roles these particles play in industrial processes and technological applications as well as in the atmosphere. We present a technique for online measurements of the adsorption of the first few water layers onto insoluble aerosol nanoparticles. Atomized fumed silica nanoparticles were dispersed from aqueous suspension and their hygroscopic growth factors (HGF) and number of the adsorbed water layers at subsaturated conditions were measured using a nanometer hygroscopic tandem differential mobility analyzer (HTDMA). Particle morphology was characterized by electron microscopy and particle density was determined by mobility analysis. The HGFs of the size-selected particles at mobility diameters from 10 to 50 nm at 90% relative humidity (RH) varied from 1.05 to 1.24, corresponding to 2–6 layers of adsorbed water. The morphology of the generated fumed silica nanoparticles varied from spheres at 8–10 nm to agglomerates at larger diameters with effective density from 1.7 to 0.8 g/cm³ and fractal dimension of 2.6. The smallest spheres and agglomerates had the highest HGFs. The smallest particles with diameters of 8 and 10 nm adsorbed two to three water layers in subsaturated conditions, which agreed well with the Frenkel, Halsey, and Hill (FHH) isotherm fitting. In comparison to the small spheres or large agglomerates, the compact agglomerate structure containing a few primary particles increased the number of adsorbed water layers by a factor of ～1.5. This was probably caused by the capillary effect on the small cavities between the primary particles in the agglomerate.     

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.     

Boiling characteristics of ternary mixtures inside enhanced surface tubing

Two phase flow characteristics such as coefficient of heat transfer and pressure drop observed during boiling of ternary azeotropic refrigerant mixtures R-404A (R-125/RR--134a/R-143a:44/4/52), R-407B (R-32/R-125/R-134a: 10/70/20), R-407C (R-32/R-125/R-134a:23/25/52) and R-408A (R-22/R-125/R-143a:46/7/47) are presented and analyzed in this paper.Experiments showed that for Reynolds numbers higher than 4.5 E04, R-408A and R-404A appear to have greater heat transfer rates than the other blends under investigation. Furthermore, it is quite evident from this data that at higher Reynolds number R-404A and R-408A have the highest pressure drop while R-407 experiences the lowest pressure drop among the refrigerants under investigation.     

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.     

Investigation of the phase separation of PNIPAM using infrared spectroscopy together with multivariate data analysis

The use of vibrational spectroscopy to investigate complex structural changes in polymers yields chemically rich data, but interpretation can be challenging and subtle but meaningful spectral changes may be missed through visual inspection alone. Multivariate analysis is an efficient approach to gain an oversight of small but systematic spectral differences anywhere within the spectra, providing further insight into structural changes and associated transformation mechanisms. In this study, the novel analytical approach of infrared spectroscopy combined with principal component analysis and Gaussian peak fitting was used to investigate the structural changes in aqueous solutions of a polymer, using poly(N-isopropyl acrylamide) (PNIPAM) in the atactic form and with controlled tacticity as a model system. Subtle spectral changes associated with the dehydration and phase separation upon heating included peak shifts, an area ratio change of the amide I band to the amide II band and formation of a new peak in the amide I band were efficiently detected. Dehydration and phase separation of PNIPAM occurred in two temperature ranges, one for the atactic and one for isotactic rich part, both involving a complex re-organization of the hydrogen bonds and change of the hydration layer. The changes agreed with existing results from other techniques, and new insights were gained into the effect of controlled tacticity on phase transformation behaviour. The study demonstrates that infrared spectroscopy combined with the multivariate analytical method principal component analysis and Gaussian peak fitting is an efficient approach to probing structural change in polymers during heating. The simplicity of the presented approach could find excellent use in analysing and understanding the molecular environment of a range of stimuli-responsive polymers, for instance block or grafted types of polymers, as well as those with controlled tacticity.