Structural health monitoring of the Traffic Bridge in Saskatoon using strain gauges

The steel through-truss Traffic Bridge, located in Saskatoon, Saskatchewan is over one hundred years old. The bridge has been subject to ongoing maintenance throughout its service life. However, inspection reports from 2005 and 2006 highlighted the severe deterioration experienced primarily by the steel members immediately above and below the deck surface. These reports prompted the City of Saskatoon (COS) to implement a rehabilitation project that involved the installation of a post-tensioning system to relieve the badly corroded bottom chord members of the axial loads due to the self-weight of the structure, in 2006. Due to the severe deterioration and the structural modifications that the Traffic Bridge has endured, a limited scope structural health monitoring (SHM) system, based on strain measurements, was implemented to reduce some of the uncertainty regarding the active load paths occurring at the deck level. The objectives of the SHM study were to obtain more information regarding the actual load paths and ascertain possible types of structural redundancy, to determine how to best model this type of structure, and to find ways to track ongoing deterioration using instrumentation. The SHM study involved controlled truck loading scenarios to permit measurement of the load paths and provide data to compare the measured results to a finite element (FE) model of the instrumented span. In addition, random loading scenarios were used to capture the vertical dynamic response of the structure in order to further refine the FE model. This study focused on the response of one-half of one interior span. A total of 72 strain gauges were installed. The downstream truss was highly instrumented at ten locations, three members of the upstream truss were instrumented to measure the distribution, and the floor joists in the downstream lane were instrumented to establish possible redundancy paths. Using an FE model in combination with the measured strain data, it was found that redundant load paths only existed at the level of the deck. The bottom chord members experienced non-zero strains once the control vehicle was past the span, possibly indicating some level of redundancy. The members believed to relieve a portion of the bottom chord tensile forces included the car joists, edge joists, and the timber deck. The amount of force transferred from the bottom chord to the deck members was found by FE analysis to be highly related to the lateral stiffness of the floor beams. The FE model was adjusted to match the measured results by modifying various modelling parameters. The most important features of the model were that all deck elements were modelled to be located at the elevation of the bottom chord, that the lateral stiffness of the floor beams was reduced by 50% to best represent the transfer of forces to deck elements, and that the stiffness of bottom chord members was reduced to 80% of their pristine values. In combination with calibrated modification factors applied to the measured values, this FE model is believed to be a useful tool to represent the behaviour of the structure to assist in detecting further damage by modelling the strain differential between members, and components of members

Structural health monitoring the Traffic Bridge in Saskatoon using strain gauges

The steel through-truss Traffic Bridge, located in Saskatoon, Saskatchewan is over one hundred years old. The bridge has been subject to ongoing maintenance throughout its service life. However, inspection reports from 2005 and 2006 highlighted the severe deterioration experienced primarily by the steel members immediately above and below the deck surface. These reports prompted the City of Saskatoon (COS) to implement a rehabilitation project that involved the installation of a post-tensioning system to relieve the badly corroded bottom chord members of the axial loads due to the self-weight of the structure, in 2006. Due to the severe deterioration and the structural modifications that the Traffic Bridge has endured, a limited scope structural health monitoring (SHM) system, based on strain measurements, was implemented to reduce some of the uncertainty regarding the active load paths occurring at the deck level. The objectives of the SHM study were to obtain more information regarding the actual load paths and ascertain possible types of structural redundancy, to determine how to best model this type of structure, and to find ways to track ongoing deterioration using instrumentation. The SHM study involved controlled truck loading scenarios to permit measurement of the load paths and provide data to compare the measured results to a finite element (FE) model of the instrumented span. In addition, random loading scenarios were used to capture the vertical dynamic response of the structure in order to further refine the FE model. This study focused on the response of one-half of one interior span. A total of 72 strain gauges were installed. The downstream truss was highly instrumented at ten locations, three members of the upstream truss were instrumented to measure the distribution, and the floor joists in the downstream lane were instrumented to establish possible redundancy paths. Using an FE model in combination with the measured strain data, it was found that redundant load paths only existed at the level of the deck. The bottom chord members experienced non-zero strains once the control vehicle was past the span, possibly indicating some level of redundancy. The members believed to relieve a portion of the bottom chord tensile forces included the car joists, edge joists, and the timber deck. The amount of force transferred from the bottom chord to the deck members was found by FE analysis to be highly related to the lateral stiffness of the floor beams. The FE model was adjusted to match the measured results by modifying various modelling parameters. The most important features of the model were that all deck elements were modelled to be located at the elevation of the bottom chord, that the lateral stiffness of the floor beams was reduced by 50% to best represent the transfer of forces to deck elements, and that the stiffness of bottom chord members was reduced to 80% of their pristine values. In combination with calibrated modification factors applied to the measured values, this FE model is believed to be a useful tool to represent the behaviour of the structure to assist in detecting further damage by modelling the strain differential between members, and components of members

Caution in cryptotephra correlation: resolving Lateglacial chemical controversies at Sluggan Bog, Northern Ireland

Tephra layers are valuable stratigraphic and chronological markers in palaeoenviromental studies. Establishing robust linkages require complete comparative databases of eruptive events to ensure that potential correlatives are not overlooked. This is achieved through the construction of tephrostratigraphical inventories proximal to the volcanic source. Proximally-characterised ash layers are frequently detected thousands of kilometres from source alongside limited numbers of tephras with no apparent proximal correlative. Despite the inability to correlate to a specific eruption, source volcanoes can be proposed and many of these far-field occurrences have become well-established stratigraphic markers. However, careful scrutiny is essential to verify the primary and instantaneous fallout origin of these distant occurrences. Here we present new data which proposes explanation for the long-standing controversy surrounding the source of Late-glacial age cryptotephras within Sluggan Bog, Northern Ireland. Chemical analysis of glass shards detected within this sequence are proposed to originate from an obsidian exposure located 11 km from the site, rather than from a contemporaneous eruptive event. This discovery highlights the importance of giving appropriate consideration to the enclosing geology of a particular palaeorecord. We suggest locations where geological sources might complicate air-fall recor

Spatial, sectoral and temporal trends in A8 migration to the UK 2004-2011. Evidence from the worker registration scheme

Since the enlargement of the European Union on 1st May 2004, large numbers of migrants from the A8 countries (Poland, Czech Republic, Latvia, Lithuania, Slovakia, Slovenia, Hungary and Estonia) have joined the UK labour market and East-Central Europe has become one of the principal source regions of migrants to Britain. Nationals from these states now constitute some of the largest foreign-born populations in the country. As part of the transitional arrangements following accession, A8 migrants were required to register under the Worker Registration Scheme (WRS) if they took up employment in the UK for one month or longer. The WRS operated between May 2004 and April 2011. The WRS represents a uniquely detailed source of information on East-Central European labour migration to the UK in terms of the employment taken up by A8 migrants immediately after arrival in the UK. The research presented here analysed administrative data from the WRS in order to shed light on spatial, sectoral and temporal trends in registration flows. The findings in this report can help inform understanding of migration patterns, and responses to them, at the national and local government levels.The volume of labour migration flows from East-Central Europe has been substantial, with 1,133,950 registrations recorded over the lifetime of the WRS (May 2004 – April 2011). These flows have been concentrated in particular segments of the labour market, with most A8 migrants engaging with the hospitality and agricultural sectors and often working through recruitment agencies as opposed to directly for employers. The volume of new arrivals from the A8 countries has decreased since the onset of the recession in 2008 but still remained substantial at the end of the WRS period. The demand for migrant labour has been relatively consistent in agriculture compared to other sectors of the economy during the recession, suggesting that employers in this sector may still require overseas workers as they struggle to source labour regardless of prevailing labour market conditions. In other sectors the requirement for overseas workers had receded to a large extent by 2011. Conceptually this points to A8 migrant labour serving distinct ‘functions’ in the UK labour market

Analysis of prehistoric brown earth paleosols under the podzol soils of Exmoor, UK

The deforestation of the upland landscapes in southwest Britain during prehistory is an established archaeological narrative, documenting human impacts on the environment and questioning the relationship of prehistoric societies to the upland landscapes they inhabited. Allied to the paleoenvironmental analyses of pollen sequences, which have provided the evidence of this change, there has been some investigation of prehistoric paleosols fossilized under principally Bronze Age archaeological monuments. These analyses identified brown earth soils that were originally associated with temperate deciduous woodland, on occasion showing evidence of human impacts such as tilling. However, the number of analyses of these paleosols has been limited. This study presents the first analysis of a series of pre‐podzol brown earth paleosols on Exmoor, UK, two of which are associated with colluvial soil erosion sediments before the formation of peat. This study indicates these paleosols are spatially extensive and have considerable potential to inform a more nuanced understanding of prehistoric human impacts on the upland environments of the early‐mid Holocene and assess human agency in driving ecosystem change

Changes in marital quality over 6 years and its association with cardiovascular disease risk factors in men: findings from the ALSPAC prospective cohort study

Background: Marital relationship quality has been suggested to have independent effects on cardiovascular health outcomes. This study investigates the association between changes in marital relationship quality and cardiovascular disease (CVD) risk factors in men. Methods: We used data from The Avon Longitudinal Study of Parents and Children, a prospective birth cohort study (Bristol, UK). Our baseline sample was restricted to married study fathers with baseline relationship and covariate data (n=2496). We restricted final analysis (n=620) to those with complete outcome, exposure and covariate data, who were married and confirmed the study child’s father at 6.4 years and 18.8 years after baseline. Relationship quality was measured at baseline and 6.4 years and operationalised as consistently good, improving, deteriorating or consistently poor relationship. We measured CVD risk factors of blood pressure, resting heart rate, body mass index, lipid profile and fasting glucose at 18.8 years after baseline. Results: Improving relationships were associated with lower levels of low-density lipoprotein (−0.25 mmol/L, 95% CI −0.46 to −0.03) and relative reduction of body mass index (−1.07 kg/m2, 95% CI −1.73 to −0.42) compared with consistently good relationships, adjusting for confounders. Weaker associations were found between improving relationships and total cholesterol (−0.24 mmol/L, 95% CI −0.48 to 0.00) and diastolic blood pressure (−2.24 mm Hg, 95% CI −4.59 to +0.11). Deteriorating relationships were associated with worsening diastolic blood pressure (+2.74 mm Hg, 95% CI 0.50 to 4.98). Conclusions: Improvement and deterioration of longitudinal relationship quality appears associated with respectively positive and negative associations with a range of CVD risk factors

Response to: 'On the approach for determining association between changes in marital quality and cardiovascular disease risk factors' by MM Pike

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Genetic exchange in <i>Trypanosoma brucei</i>: evidence for mating prior to metacyclic stage development

It is well established that genetic exchange occurs between Trypanosoma brucei parasites when two stocks are used to infect tsetse flies under laboratory conditions and a number of such crosses have been undertaken. Both cross and self-fertilisation can take place and, with the products of mating being the equivalent of F1 progeny in a Mendelian system and. Recently, analysis of a large collection of independent progeny using a series of polymorphic micro and minisatellite markers, has formally demonstrated that the allelic segregation at loci on each of the 11-megabase chromosomes conforms to ratios predicted for a classical diploid genetic system involving meiosis as well as independent assortment of markers on different chromosomes. Further extensive analysis of these F1 progeny, using a large panel of micro and minisatellite markers, has led to the construction of a genetic map of one parasite stock A. MacLeod, A. Tweedie and S. McLellan et al., The genetic map of Trypanosoma brucei, Nucleic Acids Res 33 (2005), pp. 6688–6693. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (10)

Allelic segregation and independent assortment in <i>T. brucei</i> crosses: proof that the genetic system is Mendelian and involves meiosis

The genetic system on Trypanosoma brucei has been analysed by generating large numbers of independent progeny clones from two crosses, one between two cloned isolates of Trypanosoma brucei brucei and one between cloned isolates of T. b. brucei and Trypanosoma brucei gambiense, Type 2. Micro and minisatellite markers (located on each of the 11 megabase housekeeping chromosomes) were identified, that are heterozygous in one or more of the parental strains and the segregation of alleles at each locus was then determined in each of the progeny clones. The results unequivocally show that alleles segregate in the predicted ratios and that alleles at loci on different chromosomes segregate independently. These data provide statistically robust proof that the genetic system is Mendelian and that meiosis occurs. Segregation distortion is observed with the minisatellite locus located on chromosome I of T. b. gambiense Type 2 and neighboring markers, but analysis of markers further along this chromosome did not show distortion leading to the conclusion that this is due to selection acting on one part of this chromosome. The results obtained are discussed in relation to previously proposed models of mating and support the occurrence of meiosis to form haploid gametes that then fuse to form the diploid progeny in a single round of mating