Stability of Short-span Bridges Subject to Overtopping during Floods: Case Studies from UK and the USA

As a consequence of increased levels of flooding, largely attributable to urbanization of watersheds (and perhaps climate change, more frequent extreme rainfall events are occurring and threatening existing critical infrastructure. Many of which are short-span bridges over relatively small waterways (e.g., small rivers, streams and canals). Whilst these short-span bridges were designed, often many years ago, to pass relatively minor the then standard return-period floods, in recenttimes the failure incidence of such short-span bridges has been noticeably increasing. This is suggestive of insufficient hydraulic capacity or alternative failure mechanism not envisaged at the time of design e.g. foundation scour or undermining. This paper presen ts, and draws lessons, from bridge failures in Ireland and the USA. For example, in November 2009, the UK and Ireland were subjected to extraordinarily severe weather conditions for several days. The resulting flooding led to the collapse of three UK bridges that were generally 19th century masonry arch bridges, withrelatively shallow foundations. Parallel failure events have been observed in the USA. To date, knowledge of the combined effect of waterway erosion, bridge submergence, and geotechnical collapse has not been adequately studied. Recent research carried out considered the hydraulic analysis of short span bridges under flood conditions, but no consideration was given towards the likely damage to these structures due to erosive coupling of hydraulic and geotechnical factors. Some work has been done to predict the discharge downstream of an inundated arch, focusing onpredicting afflux, as opposed to bridge scour, under both pressurized and free-surface flows, but no ! predictive equation for scour under pressurized conditions was ever considered. The case studies this paper presents will be augmented by the initial findings from the laboratory experiments investigating the effects of surcharged flow and subsequent scour within the vicinity of single span arch bridges. Velocities profiles will be shown within the vicinity of the arch, in addition to the depth of consequent scour, for a series of flows and model spans. The data will be presented and correlated to the most recent predictive equations for submerged contraction and abutment scour. The accuracy of these equations is examined, and the findings used as a basis for developing further studies in relation to short span bridges.

Serviceability of bridge deck slabs with arching action

The deterioration of infrastructure, such as bridges, has been one of the major challenges facing both the designers and the owners of such utilities. Sustainable development and a climate of increasing commercialism has led to a requirement for more accurate means of structural analysis. Bridge assessment is one area where this is particularly relevant. It has been known for some time that bridge deck slabs have inherent enhanced strength due to the presence of arching or compressive membrane action (CMA) but only in recent years has there been some acceptance of a rational treatment of this phenomenon for design and assessment purposes. To use the benefits of arching action, this paper presents the results of tests carried out on a reinforced-concrete beam and slab bridge in Northern Ireland that incorporated novel reinforcement type and position. The research was aimed at extending previous laboratory tests on 1/3scale bridge deck edge panels. The measured crack widths and deflections have been compared with the current code requirements.

Observations of the interstellar medium in the Magellanic Bridge.

We present ultraviolet and optical spectra of DI 1388, a young star in the Magellanic Bridge, a region of gas between the Small and Large Magellanic Clouds. The data have signal-to-noise ratios of 20-45 and a spectral resolution of 6.5 km s-1. Interstellar absorption by the Magellanic Bridge at vLSR~200 km s-1 is visible in the lines of C I, C II, C II*, C IV, N I, O I, Al II, Si II, Si III, Si IV, S II, Ca II, Fe II, and Ni II. The relative gas-phase abundances of C II, N I, O I, Al II, Si II, Fe II, and Ni II with respect to S II are similar to those found in Galactic halo clouds, despite a significantly lower metallicity in the Magellanic Bridge. The higher ionization species in the cloud have a column density ratio N(C+3)/N(Si+3)~1.9, similar to that inferred for collisionally ionized Galactic cloud interfaces at temperatures ~105 K. We identify substructure in the stronger interstellar lines, with a broad component (FWHM~20 km s-1) at ~179 km s-1 and a sharp component (FWHM~11 km s-1) at 198 km s-1. The abundance analysis for these clouds indicates that the feature at 198 km s-1 consists of a low electron density, mainly neutral gas that may be associated with an interface responsible for the highly ionized gas. The 179 km s-1 cloud consists of warmer, lower density gas that is partially ionized.

CO and optical observations of the Magellanic Bridge

We present (CO)-C-12(1-0) molecular line and BV CCD observations towards 0311-7651: a region in the Magellanic Bridge where cold atomic Hydrogen has previously been detected by Kobulnicky & Dickey: Additionally, BV images of a comparison held 1 degrees to the South were taken. No CO was detected to a limit of similar to 0.06 Kelvin, and the colour-magnitude diagrams show no evidence for a stellar association in either field.

Ca II K observations of QSOs in the line-of-sight to the Magellanic Bridge

We describe medium-resolution spectroscopic observations taken with the ESO Multi-Mode Instrument (EMMI) in the CaII K line (lambda air = 3933.661 angstrom) towards 7 QSOs located in the line-of-sight to the Magellanic Bridge. At a spectral resolution R =lambda/Delta lambda = 6000, five of the sightlines have a signal-to-noise ( S/N) ratio of similar to 20 or higher. Definite Ca absorption due to Bridge material is detected towards 3 objects, with probable detection towards two other sightlines. Gas-phase CaII K Bridge and Milky Way abundances or lower limits for the all sightlines are estimated by the use of Parkes 21-cm H. emission line data. These data only have a spatial resolution of 14 arcmin compared with the optical observations which have milli-arcsecond resolution. With this caveat, for the three objects with sound CaII K detections, we find that the ionic abundance of CaII K relative to HI, A = log( N( CaK)/ N( HI)) for low- velocity Galactic gas ranges from - 8.3 to - 8.8 dex, with HI column densities varying from 3- 6 x 10(20) cm(-2). For Magellanic Bridge gas, the values of A are similar to 0.5 dex higher, ranging from similar to- 7.8 to - 8.2 dex, with N( HI) = 1- 5 x 1020 cm(-2). Higher values of A correspond to lower values of N( HI), although numbers are small. For the sightline towards B 0251 - 675, the Bridge gas has two different velocities, and in only one of these is CaII tentatively detected, perhaps indicating gas of a different origin or present-day characteristics ( such as dust content), although this conclusion is uncertain and there is the possibility that one of the components could be related to the Magellanic Stream. Higher signal-to-noise CaII K data and higher resolution H. data are required to determine whether A changes with N( HI) over the Bridge and if the implied difference in the metalicity of the two Bridge components towards B 0251-675 is real.

A method to bridge the gap between breadth and depth in IS narrative analysis

A method extending narrative analysis with grounded theory analysis is proposed to bridge the gap between breadth and depth in IS narrative research. The purpose of the method is not to develop a theory but to make narrative analysis more accessible, transparent and accountable; and the resultant narrative more contextually grounded. The method is aimed particularly at inexperienced narrative researchers who currently lack guidance through the complexity of narrative analysis, but may also benefit experienced narrative researchers who may not be familiar with the applicability of grounded theory tools and techniques in this area.

Role of conformational constraints of position 7 of the disulphide bridge of h-alpha-CGRP derivatives in their agonist versus antagonist properties

Previous structure-activity studies have shown that the disulphide bridge of calcitonin gene-related peptide (CGRP) is important for the highly potent, CGRP receptor-mediated effects of this peptide. In this study penicillamine (Pen) was substituted for one or both of the cysteinyl residues to determine conformational and topographical properties of the disulphide bridge favourable for binding to CGRP receptors and/or receptor activation. Pen constrains the conformational flexibility of disulphide bridges in other peptides. Binding affinities were measured using a radioligand binding assay with membranes prepared from pig coronary arteries and I-125-h-alpha-CGRP. Functional effects were characterized using a previously reported pig coronary artery relaxation bioassay. The binding affinity of [Pen(2)]h-alpha-CGRP was not significantly different from that of h-alpha-CGRP. All other analogues showed reduced affinity for CGRP receptors. [Pen(2)]h-alpha-CGRP also caused relaxation of coronary arteries. The remaining analogues either caused relaxation with significantly reduced potency or failed to relax the arteries at concentrations up to 1 x 10(-5) M. All analogues that did not relax coronary arteries contained a D-Pen in position 7 and inhibited CGRP-induced relaxation. [D-Pen(2,7)]h-alpha- CGRP was the most potent antagonist with a K-B value of 630 nM. This affinity is similar to that of the classical CGRP receptor antagonist, h-alpha-CGRP(8-37), on these arteries (K-B, 212 nM). These studies show that modifying the topography of the disulphide bridge can cause large and variable effects on ligand binding and activation of CGRP receptors. The contribution of position 7 to the conformation and topography of the disulphide bridge of h-alpha-CGRP is crucial to the future design of agonists of CGRP receptors. Furthermore, position 7 is important for the development of new CGRP receptor antagonists with structures based on the whole sequence of h-alpha-CGRP.

The iron abundance of the Magellanic Bridge

High-resolution Hubble Space Telescope ultraviolet spectra for five B-type stars in the Magellanic Bridge and in the Large (LMC) and Small (SMC) Magellanic Clouds have been analysed to estimate their iron abundances. Those for the Clouds are lower than estimates obtained from late-type stars or the optical lines in B-type stars by approximately 0.5 dex. This may be due to systematic errors possibly arising from non-local thermodynamic equilibrium (non-LTE) effects or from errors in the atomic data, as similar low Fe abundances have previously been reported from the analysis of the ultraviolet spectra of Galactic early-type stars. The iron abundance estimates for all three Bridge targets appear to be significantly lower than those found for the SMC and LMC by approximately -0.5 and -0.8 dex, respectively, and these differential results should not be affected by any systematic errors present in the absolute abundance estimates. These differential iron abundance estimates are consistent with the underabundances for C, N, O, Mg and Si of approximately -1.1 dex relative to our Galaxy previously found in our Bridge targets. The implications of these very low metal abundances for the Magellanic Bridge are discussed in terms of metal deficient material being stripped from the SMC.