Modelling of traffic loading on long span bridges

Existing long span load models have typically been developed using a number of conservative assumptions, and as such are more applicable to the design of new bridges rather than the assessment of existing structures. Excessive conservatism in such assumptions can lead to expensive and unnecessary interventions in existing bridges. Furthermore, existing load models do not always allow for correlations in traffic weights and vehicle positions on the bridge. This thesis proposes a method of simulating load effects on long span bridges termed ‘Long Span Scenario Modelling’ (LSSM). The ‘scenarios’ are blocks of vehicles extracted from a stream which contain the inherent correlations between vehicle weights and positions. The correlation in load intensity between successive scenarios is explicitly modelled. The scenarios can be used to simulate congested conditions for the required number of congestion events. A large Weigh-in-Motion (WIM) dataset from a site in the USA is used to demonstrate the process. Free-flowing WIM data is converted into a congested traffic stream using lane changing and gap distribution models. Recurring rush hour type congestion is simulated. The load intensities for 500, 1000 and 1500 m loaded lengths are determined for 1000-year return periods. An efficient computer algorithm to allow simulation of long span bridge load events for long return periods is also developed. Such long run simulations can avoid the uncertainties with extrapolation techniques where data recorded over relatively short periods of time is extrapolated to large return periods. To ensure a diversity of load events, the measured scenario library is extended through the generation of new scenarios. The LSSM is shown to better represent the long span load intensities when compared to measured traffic, particularly when the correlation between successive scenarios is accounted for. For the studied cases it is also shown that a Gumbel (linear) extrapolation from one year of WIM data overestimates the long run simulation value by approximately 12%. The developed algorithm therefore allows the long run simulations for the LSSM method to be carried out on a desktop computer and therefore greatly reduce the variability of results and limit potential issues regarding extrapolation techniques and choice of suitable statistical distributions

Simulation of traffic loading on long span bridges

Existing long span load models have typically been developed using a number of conservative assumptions, and as such are more applicable to the design of new bridges rather than the assessment of existing structures. Excessive conservatism in such assumptions can lead to expensive and unnecessary interventions in existing bridges. Furthermore, existing load models do not always allow for correlations in traffic weights and vehicle positions on the bridge. This paper introduces a method of simulating the load effect on long-span bridges, termed 'Long Span Scenario Modelling' (LSSM). The scenarios are blocks of vehicles extracted from a congested traffic stream that contain the inherent correlations between vehicle weights and positions. For long-span bridges, the combination of vehicles, such as platoons of Heavy Goods Vehicles (HGVs), has a greater influence on bridge loading than individual heavy vehicles. The scenario modelling approach allows for these critical vehicle combinations. Weigh-in-Motion (WIM) data from a site in the USA is used to demonstrate the process. The LSSM is shown to better represent the long span load effect when compared to measured traffic, particularly when the correlation between successive scenarios is accounted for

Selenium-π-Acid Catalyzed Oxidative Functionalization of Alkynes: Facile Access to Ynones and Multisubstituted Oxazoles

Unprecedented selenium-catalyzed propargylic oxidation of alkynes is disclosed. Various propargylphosphonates and 3-alkynoates were efficiently converted to valuable ynones via unusual C–C triple bond migration and deselenenylation at a vinyl carbon. By the strategies of tautomerization of enamine intermediate and S_N2 displacement, similar conditions were effective for the oxidative difunctionalization of ynamides to afford multisubstituted oxazoles with high regioselectivity. Mechanistic studies revealed these detailed processes

Molecular Dynamics Investigation of Nanoscale Hydrophobicity of Polymer Surfaces: What Makes Water Wet?

The wettability of a polymer surfacerelated to its hydrophobicity or tendency to repel watercan be crucial for determining its utility, such as for a coating or a purification membrane. While wettability is commonly associated with the macroscopic measurement of a contact angle between surface, water, and air, the molecular physics that underlie these macroscopic observations are not fully known, and anticipating the relative behavior of different polymers is challenging. To address this gap in molecular-level understanding, we use molecular dynamics simulations to investigate and contrast interactions of water with six chemically distinct polymers: polytetrafluoroethylene, polyethylene, polyvinyl chloride, poly(methyl methacrylate), Nylon-66, and poly(vinyl alcohol). We show that several prospective quantitative metrics for hydrophobicity agree well with experimental contact angles. Moreover, the behavior of water in proximity to these polymer surfaces can be distinguished with analysis of interfacial water dynamics, extent of hydrogen bonding, and molecular orientationeven when macroscopic measures of hydrophobicity are similar. The predominant factor dictating wettability is found to be the extent of hydrogen bonding between polymer and water, but the precise manifestation of hydrogen bonding and its impact on surface water structure varies. In the absence of hydrogen bonding, other molecular interactions and polymer mechanics control hydrophobic ordering. These results provide new insights into how polymer chemistry specifically impacts water–polymer interactions and translates to surface hydrophobicity. Such factors may facilitate the design or processing of polymer surfaces to achieve targeted wetting behavior, and presented analyses can be useful in studying the interfacial physics of other systems

Design, Synthesis, and Analysis of Thermophysical Properties for Imidazolium-Based Geminal Dicationic Ionic Liquids

To enhance the thermal stability of ionic liquids (ILs) and increase the latent heat, the effect of amount of hydrogen bonds for geminal dicationic ionic liquids (DILs) was investigated and compared to that of monocationic analogues. A series of geminal dicationic ionic liquids with alkyl chain or electronegativity functional groups in the imidazolium were synthesized. Thermal stability was determined by TGA; melting point, heat of fusion, and heat capacity were investigated by DSC for synthetic DILs. The effect of molecular structure on the heat of fusion was examined by changes alkyl side-chain, linkage chain, C2–H of imidazole ring, and functional groups. Hydrogen bonding in DILs was studied, in the case of C₂(eim)₂(Br)₂, by single-crystal X-ray diffraction. The thermal analysis results indicate that functionalized geminal dicationic ionic liquids show excellent thermal stability. The decomposition temperatures of geminal dicationic ionic liquids can be up to 603.74 K, and the latent heat can reach 159.35 J g^–1. It is increased on average by 64.5% and 212.5%, respectively, as compared to alkyl chain ionic liquid (C₄mim)­Br. It can be expected that these geminal dicationic ionic liquids are suitable for thermal storage applications

A performance comparison of various algorithms based on the client-side prefetching mode.

<p>A performance comparison of various algorithms based on the client-side prefetching mode.</p

Comparative CHRs obtained from GUDC based on different data sizes.

<p>Comparative CHRs obtained from GUDC based on different data sizes.</p

Rh(II)-Catalyzed [2,3]-Sigmatropic Rearrangement of Sulfur Ylides Derived from Cyclopropenes and Sulfides

A new type of Rh₂(OAc)₄-catalyzed [2,3]-sigmatropic rearrangement of sulfur ylides is reported. A series of cyclopropenes were successfully employed for [2,3]-sigmatropic rearrangement by a reaction with either allylic or propargylic sulfides. Under the optimized conditions, the reaction afforded the products in moderate to excellent yields. In these transformations, the vinyl metal carbenes generated in situ from the cyclopropenes were effectively trapped by sulfides, resulting in the formation of corresponding products upon [2,3]-sigmatropic rearrangements

Comparative CHRs obtained from different prefetching algorithms based on multi-user mode.

<p>Comparative CHRs obtained from different prefetching algorithms based on multi-user mode.</p

Comparative disk access performance obtained from different algorithms.

<p>Comparative disk access performance obtained from different algorithms.</p