bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Temperature on Ladderane Lipid Distribution in Anammox Bacteria
Authors: Rattray Jayne E. , van de Vossenberg Jack , Jaeschke Andrea , Hopmans Ellen C. , Wakeham Stuart G. , Lavik Gaute , Kuypers Marcel M. M. , Strous Marc , Jetten Mike S. M. , Schouten Stefan , Sinninghe Damsté Jaap S.
Published: January 2010

Anaerobic ammonium-oxidizing (anammox) bacteria have the unique ability to synthesize fatty acids containing linearly concatenated cyclobutane rings, termed “ladderane lipids.” In this study we investigated the effect of temperature on the ladderane lipid composition and distribution in anammox enrichment cultures, marine particulate organic matter, and surface sediments. Under controlled laboratory conditions we observed an increase in the amount of C
20
[5]-ladderane fatty acids compared with the amount of C
18
[5]-ladderane fatty acids with increasing temperature and also an increase in the amount of C
18
[5]-ladderane fatty acids compared with the amount of C
20
[5]-ladderane fatty acids with decreasing temperature. Combining these data with results from the natural environment showed a significant (
R
2
= 0.85,
P
= <0.0001,
n
= 121) positive sigmoidal relationship between the amounts of C
18
and C
20
[5]-ladderane fatty acids and the
in situ
temperature; i.e., there is an increase in the relative abundance of C
18
[5]-ladderane fatty acids at lower temperatures and
vice versa
, particularly at temperatures between 12°C and 20°C. Novel shorter (C
16
) and longer (C
22
to C
24
) ladderane fatty acids were also identified, but their relative amounts were small and did not change with temperature. The adaptation of ladderane fatty acid chain length to temperature changes is similar to the regulation of common fatty acid composition in other bacteria and may be the result of maintaining constant membrane fluidity under different temperature regimens (homeoviscous adaptation). Our results can potentially be used to discriminate between the origins of ladderane lipids in marine sediments, i.e., to determine if ladderanes are produced
in situ
in relatively cold surface sediments or if they are fossil remnants originating from the warmer upper water column.
Ecology of Speciation in the Genus
Bacillus
Authors: Connor Nora , Sikorski Johannes , Rooney Alejandro P. , Kopac Sarah , Koeppel Alexander F. , Burger Andrew , Cole Scott G. , Perry Elizabeth B. , Krizanc Danny , Field Nicholas C. , Slaton Michèle , Cohan Frederick M.
Published: January 2010

Microbial ecologists and systematists are challenged to discover the early ecological changes that drive the splitting of one bacterial population into two ecologically distinct populations. We have aimed to identify newly divergent lineages (“ecotypes”) bearing the dynamic properties attributed to species, with the rationale that discovering their ecological differences would reveal the ecological dimensions of speciation. To this end, we have sampled bacteria from the
Bacillus subtilis
-
Bacillus licheniformis
clade from sites differing in solar exposure and soil texture within a Death Valley canyon. Within this clade, we hypothesized ecotype demarcations based on DNA sequence diversity, through analysis of the clade's evolutionary history by Ecotype Simulation (ES) and AdaptML. Ecotypes so demarcated were found to be significantly different in their associations with solar exposure and soil texture, suggesting that these and covarying environmental parameters are among the dimensions of ecological divergence for newly divergent
Bacillus
ecotypes. Fatty acid composition appeared to contribute to ecotype differences in temperature adaptation, since those ecotypes with more warm-adapting fatty acids were isolated more frequently from sites with greater solar exposure. The recognized species and subspecies of the
B. subtilis
-
B. licheniformis
clade were found to be nearly identical to the ecotypes demarcated by ES, with a few exceptions where a recognized taxon is split at most into three putative ecotypes. Nevertheless, the taxa recognized do not appear to encompass the full ecological diversity of the
B. subtilis
-
B. licheniformis
clade: ES and AdaptML identified several newly discovered clades as ecotypes that are distinct from any recognized taxon.
Conserved Symbiotic Plasmid DNA Sequences in the Multireplicon Pangenomic Structure of
Rhizobium etli
Authors: González Víctor , Acosta José L. , Santamaría Rosa I. , Bustos Patricia , Fernández José L. , Hernández González Ismael L. , Díaz Rafael , Flores Margarita , Palacios Rafael , Mora Jaime , Dávila Guillermo
Published: January 2010

Strains of the same bacterial species often show considerable genomic variation. To examine the extent of such variation in
Rhizobium etli
, the complete genome sequence of
R. etli
CIAT652 and the partial genomic sequences of six additional
R. etli
strains having different geographical origins were determined. The sequences were compared with each other and with the previously reported genome sequence of
R. etli
CFN42. DNA sequences common to all strains constituted the greater part of these genomes and were localized in both the chromosome and large plasmids. About 700 to 1,000 kb of DNA that did not match sequences of the complete genomes of strains CIAT652 and CFN42 was unique to each
R. etli
strain. These sequences were distributed throughout the chromosome as individual genes or chromosomal islands and in plasmids, and they encoded accessory functions, such as transport of sugars and amino acids, or secondary metabolism; they also included mobile elements and hypothetical genes. Sequences corresponding to symbiotic plasmids showed high levels of nucleotide identity (about 98 to 99%), whereas chromosomal sequences and the sequences with matches to other plasmids showed lower levels of identity (on average, about 90 to 95%). We concluded that
R. etli
has a pangenomic structure with a core genome composed of both chromosomal and plasmid sequences, including a highly conserved symbiotic plasmid, despite the overall genomic divergence.
Intranasal Vaccinations with the
trans
-Sialidase Antigen plus CpG Adjuvant Induce Mucosal Immunity Protective against Conjunctival
Trypanosoma cruzi
Challenges
Authors: Giddings O. K. , Eickhoff C. S. , Sullivan N. L. , Hoft D. F.
Published: January 2010

Trypanosoma cruzi
is an intracellular protozoan parasite capable of infecting through mucosal surfaces. Our laboratory has previously elucidated the anatomical routes of infection after both conjunctival and gastric challenge in mice. We have shown that chronically infected mice develop strong immune responses capable of protecting against subsequent rechallenge with virulent parasites through gastric, conjunctival, and systemic routes of infection. We have also shown that intranasal immunizations with the unique
T. cruzi trans
-sialidase (TS) antigen protect against gastric and systemic
T. cruzi
challenge. In the current work we have investigated the ability of purified TS adjuvanted with CpG-containing oligonucleotides to induce immunity against conjunctival
T. cruzi
challenge. We confirm that intranasal vaccinations with TS plus CpG induce TS-specific T-cell and secretory IgA responses. TS-specific secretory IgA was detectable in the tears of vaccinated mice, the initial body fluid that contacts the parasite during infectious conjunctival exposures. We further show that intranasal vaccinations with TS plus CpG protect against conjunctival
T. cruzi
challenge, limiting local parasite replication at the site of mucosal invasion and systemic parasite dissemination. We also provide the first direct evidence that mucosal antibodies induced by intranasal TS vaccination can inhibit parasite invasion.
Pore Formation Triggered byLegionellaspp. Is an Nlrc4 Inflammasome-Dependent Host Cell Response That Precedes Pyroptosis
Authors: Silveira Tatiana N. , Zamboni Dario S.
Published: January 2010

Legionella pneumophila, the etiological agent of Legionnaires disease, is known to trigger pore formation in bone marrow-derived macrophages (BMMs) by mechanisms dependent on the type IVB secretion system known as Dot/Icm. Here, we used several mutants ofL. pneumophilain combination with knockout mice to assess the host and bacterial factors involved in pore formation in BMMs. We found that regardless of Dot/Icm activity, pore formation does not occur in BMMs deficient in caspase-1 and Nlrc4/Ipaf. Pore formation was temporally associated with interleukin-1β secretion and preceded host cell lysis and pyroptosis. Pore-forming ability was dependent on bacterial Dot/Icm but independent of several effector proteins, multiplication, andde novoprotein synthesis. Flagellin, which is known to trigger the Nlrc4 inflammasome, was required for pore formation asflaAmutant bacteria failed to induce cell permeabilization. Accordingly, transfection of purified flagellin was sufficient to trigger pore formation independent of infection. By using 11 differentLegionellaspecies, we found robust pore formation in response toL. micdadei,L. bozemanii,L. gratiana,L. jordanis, andL. rubrilucens, and this trait correlated with flagellin expression by these species. Together, the results suggest that pore formation is neitherL. pneumophilaspecific nor the result of membrane damage induced by Dot/Icm activity; instead, it is a highly coordinated host cell response dependent on host Nlrc4 and caspase-1 and on bacterial flagellin and type IV secretion system.
Suppression ofPlasmodium cynomolgiin Rhesus Macaques by Coinfection withBabesia microti
Authors: van Duivenvoorde Leonie M. , Voorberg-van der Wel Annemarie , van der Werff Nicole M. , Braskamp Gerco , Remarque Edmond J. , Kondova Ivanela , Kocken Clemens H. M. , Thomas Alan W.
Published: January 2010

BothPlasmodiumandBabesiaspecies are intraerythrocytic protozoans that infect a wide range of hosts, including humans, and they elicit similar inflammatory responses and clinical manifestations that differ markedly in severity. We recently reported that a rhesus macaque that was chronically infected withBabesia microtiwas able to control infection withPlasmodium cynomolgi(a parasite of macaques with characteristics very similar to those ofPlasmodium vivax) better than naïve monkeys. To confirm this and to investigate the underlying immunopathology, six naïve rhesus monkeys were infected withB. microti. After 24 days, four of these monkeys and four naïve rhesus monkeys were challenged withP. cynomolgiblood-stage parasites.B. microtipersisted at low levels in all monkeys, and the clinical parameters were comparable to those of noninfected controls. There was a significant decrease inP. cynomolgiparasitemia in animals coinfected withB. microticompared to the parasitemia in animals infected withP. cynomolgialone. This decrease inP. cynomolgiparasitemia correlated with increases in the levels of proinflammatory monocytes at the time ofP. cynomolgiinfection and with higher C-reactive protein (CRP) serum levels 1 week after malaria infection. Therefore, we conclude that ongoing infection withB. microtiparasites leads to suppression of malaria infection.
The Ferrichrome Uptake Pathway inPseudomonas aeruginosaInvolves an Iron Release Mechanism with Acylation of the Siderophore and Recycling of the Modified Desferrichrome
Authors: Hannauer Mélissa , Barda Yaniv , Mislin Gaëtan L. A. , Shanzer Abraham , Schalk Isabelle J.
Published: January 2010

The uptake of iron intoPseudomonas aeruginosais mediated by two major siderophores produced by the bacterium, pyoverdine and pyochelin. The bacterium is also able of utilize several heterologous siderophores of bacterial or fungal origin. In this work, we have investigated the iron uptake inP. aeruginosaPAO1 by the heterologous ferrichrome siderophore.55Fe uptake assays showed that ferrichrome is transported across the outer membrane primarily (80%) by the FiuA receptor and to a lesser extent (20%) by a secondary transporter. Moreover, we demonstrate that like in the uptake of ferripyoverdine and ferripyochelin, the energy required for both pathways of ferrichrome uptake is provided by the inner membrane protein TonB1. Desferrichrome-55Fe uptake inP. aeruginosawas also dependent on the expression of the permease FiuB, suggesting that this protein is the inner membrane transporter of the ferrisiderophore. A biomimetic fluorescent analogue of ferrichrome, RL1194, was usedin vivoto monitor the kinetics of iron release from ferrichrome inP. aeruginosain real time. This dissociation involves acylation of ferrichrome and its biomimetic analogue RL1194 and recycling of both modified siderophores into the extracellular medium. FiuC, anN-acetyltransferase, is certainly involved in this mechanism of iron release, since its mutation abolished desferrichrome-55Fe uptake. The acetylated derivative reacts with iron in the extracellular medium and is able to be taken up again by the cells. All these observations are discussed in light of the current knowledge concerning ferrichrome uptake inP. aeruginosaand inEscherichia coli.
Calibration of the Ontario Highway Bridge Design Code 1991 edition
Authors: Nowak Andrzej S. , Grouni Hid N.
Published: January 2010

The paper describes the calculation of load and resistance factors for the Ontario Highway Bridge Design Code (OHBDC) 1991 edition. The work involved the development of load and resistance models, the selection of the reliability analysis method, and the calculation of the reliability indices. The statistical models for load and resistance are reviewed. The considered load components include dead load, live load, and dynamic load. Resistance models are developed for girder bridges (steel, reinforced concrete, and prestressed concrete). A reliability analysis is performed for selected representative structures. Reliability indices are calculated using an iterative procedure. The calculations are performed for bridge girders designed using OHBDC 1983 edition. The resulting reliability indices are between 3 and 4 for steel girders and reinforced concrete T-beams, and between 3.5 and 5 for prestressed concrete girders. Lower values are observed for shorter spans (up to 30–40 m). The acceptance criterion in the selection of load and resistance factors is closeness to the target reliability level. The analysis confirmed the need to increase the design live load for shorter spans. Partial resistance factors are considered for steel and concrete. The criteria for the evaluation of existing bridges are based on the reliability analysis and economic considerations. Key words: bridge code, calibration, load factor, resistance factor, reliability index.
Application of two-layer hypothesis to fully developed flow in ice-covered curved channels
Authors: Urroz Gilberto E. , Ettema Robert
Published: January 2010

Presented herein are the results of a study in which the two-layer hypothesis is applied in the formulation of flow in curved ice-covered channels. In accordance with this hypothesis, ice-covered flow can be treated as two free-surface flows: one associated with the bed and the other with the ice cover. The two-layer hypothesis is customarily used in analysis of flow in straight ice-covered channels. The results of the analysis are compared with measurements of flow velocity made using a simulated ice jam formed in a curved flume. The comparison reveals that the formulation is adequate only as a means of obtaining preliminary estimates of order-of-magnitude and direction of streamwise and transverse components of flows. It does not facilitate satisfactory detailed simulation of the inherent three-dimensionality of curved-channel flows. Key words: ice-covered rivers, river bends.
Evaluation of piezoelectric weigh-in-motion system
Authors: Ali N. , Trogdon J. , Bergan A. T.
Published: January 2010

The analysis presented deals with the accuracy of a piezoelectric weigh-in-motion system installed on Interstate 19 in the state of Oregon. Axle weights for 5-axle tractor semi-trailer trucks were measured by the piezoelectric weigh-in-motion system and then compared with the static weights. An analysis of variance and Dunnett's test were conducted in order to determine if there existed a significant difference between data. The analysis showed no significant difference for steering axle and tandem axle weights. However, the analysis did indicate that a significant difference existed for trailing tandem. Key words: weigh-in-motion, dynamic weight, static weight, highways, piezoelectric weigh-in-motion.
Vehicle classification from weigh-in-motion data: the progressive sieving algorithm
Authors: Fekpe E. S. K. , Clayton A. M.
Published: January 2010

A classification procedure has been developed, based on the concept of progressive sieving of weigh-in-motion data through a series of criteria designed to separate, identify, and classify vehicles by their axle arrangement. The procedure is demonstrated to be feasible, and is capable of identifying all major types of vehicles quite accurately. The procedure together with a nomenclature provides a classification system that is open-ended having an infinite number of classes. The system is universal and could be used by any jurisdiction. It facilitates evaluation of vehicle weight and dimension policy alternatives and their impacts on the highway system. The procedure has the capability of translating data from one classification system into another. Key words: classification, sieving, axle spacing, vehicle configuration.
Finite element investigation of fibre-reinforced concrete deck slabs without internal steel reinforcement
Authors: Wegner Leon D. , Mufti Aftab A.
Published: January 2010

Experimental tests on half-scale models have demonstrated that polypropylene-fibre-reinforced concrete (PFRC) bridge deck slabs completely devoid of conventional steel reinforcement will fail by punching shear under concentrated loads considerably greater than those specified for design, provided the top flanges of the supporting girders are adequately restrained from moving laterally. Similar models were analyzed using nonlinear finite element techniques in order to reproduce experimentally observed load–deflection behaviours and failure loads. Commonly available concrete failure criteria for plain concrete was incorporated into the material model used for the PFRC deck slab. Results of the finite element analyses are presented. It is shown that while predicted load–deflection paths were less than satisfactory, accurate predictions of failure loads were achieved, but only after considerable tuning of various modelling parameters. Key words: nonlinear finite element method, bridge decks, fibre-reinforced concrete.
Pounding of buildings during earthquakes: a Canadian perspective
Authors: Filiatrault André , Cervantes Mario , Folz Bryan , Prion Helmut
Published: January 2010

The main objective of this paper is to provide information to structural engineers on how to consider and mitigate the phenomenon of pounding between adjacent structures during earthquakes. The first part of the paper reviews the problem of seismic pounding; observations of damage from pounding during recent earthquakes are described as well as the pounding potential for buildings in large Canadian cities. A review of literature on analytical and numerical studies of earthquake pounding is presented along with methods that have been proposed to mitigate pounding. In the second part of the paper, the seismic behaviour of three closely spaced, Canadian code designed, plane steel frames is investigated. Nonlinear time-step dynamic analyses and nonlinear elastic gap elements, to model pounding, are used for this purpose. Several parameters, such as separation distances, pounding locations, and ground motion characteristics, are considered. Key words: dynamics, earthquakes, impacts, pounding, seismic.
Impacts cumulatifs du développement hydro-électrique sur le bilan d'eau douce de la baie d'Hudson
Authors: Anctil François , Couture Richard
Published: January 2010

This paper discusses the consequences on the marine environment, more specifically on the fresh water balance, of the hydroelectric development of several tributaries of Hudson Bay, including James Bay and Foxe Basin. The fresh water balance is determined by identifying, at different scales, the modifications caused by each complex. The main inputs are the freezing and thawing of the ice cover, runoff water, and mass exchange at the air–water interface. Three spatial scales were used to obtain the resolution required to document the cumulative effects of fresh water balance modifications on the water surface layer: the Hudson Bay, the Hudson Strait, and the Labrador Sea. Finally, the addition of the proposed Grande-Baleine hydroelectric complex is examined from the available information and forecasts. Key words: hydroelectric development, impact, marine environment, fresh water balance, ice cover, runoff water, mass exchange.[Journal translation]
An empirical study of vehicular headways in urban areas
Authors: Abdelwahab Walid M. , Ehm Renate , Mah Mike
Published: January 2010

Conventional statistical distribution models (e.g., Poisson) are known to perform satisfactorily in predicting the number of crossing opportunities in a traffic stream of certain characteristics. However, in many traffic studies, one is interested in estimating the number of crossing opportunities under traffic and roadway conditions that are not typical of any known statistical distribution. A typical example is the number of crossing opportunities across a two-way, multilane traffic stream within a signalized corridor. There does not appear to be a single distribution capable of adequately describing the vehicular headway distribution under a variety of traffic and roadway conditions.This paper demonstrates that carefully developed regression models can be used to accurately predict the number of crossing opportunities in a traffic stream under various roadway and traffic conditions. Compared with conventional statistical functions, the regression models are easy to use, transferable, and volume-based, thus allowing the user to predict the number of crossing opportunities using readily available traffic count data. It was found that, depending on the traffic conditions under consideration, conventional statistical distributions, such as the Poisson function, can underestimate the number of crossing opportunities by approximately one third. Typical applications of these models are in the area of development of warrants for vehicular and pedestrian traffic control devices. Key words: crossing opportunities, vehicular headway, arrival patterns, empirical models.
Aguamilpa underground penstocks — excavation phase
Authors: Méndez Fidencio
Published: January 2010

The Aguamilpa hydroelectric project is one of a number of hydroelectric schemes currently being constructed along the course of the Santiago River in western Mexico. Aguamilpa, with a total cost of $750 million U.S., is a 960 MW installation scheduled for operation by October 1993. As the most important plant in the complex, Aguamilpa qualifies as one of the more spectacular engineering construction jobs of the decade in Mexico. The facility is composed of a complex set of tunnels, including the underground penstocks, the powerhouse and surge chamber caverns, the tailrace tunnel, and temporary tunnels. In the initial design, most of the tunnelling work was to have been of a permanent nature. However, as the date of completion was brought forward, it became necessary to open up more working faces and as such a number of temporary tunnels were started. This paper presents the sequences of underground penstocks excavation, the construction methods developed, and the equipment employed. Also, the complex patterns of tunnels that were drilled initially for access and to facilitate later excavation of the underground penstocks are described. Key words: tunnels, underground penstocks, powerhouse, construction methods.
Influence of site effects and period-dependent force modification factors on the seismic response of ductile structures
Authors: Hosni Shamel , Heidebrecht Arthur C.
Published: January 2010

A foundation factor, F, is incorporated in the National Building Code of Canada (NBCC) design base shear formula to account for amplification of bedrock ground motions as these propagate upwards through the local soil deposit (site effects). In the NBCC, the value of F is specified as a function of the local soil type and depth, irrespective of the ductility capacity for which the structure situated at the surface of the soil deposit is to be designed and detailed. On the other hand, the ductility capacity of the structures is taken into account in the code by the force modification factor, R, for which values are specified depending on the type of the structural system. The current study investigates the influence of the ductility capacity of engineering structures in mitigating the site effects. Simple bilinear single-degree-of-freedom models are used to simulate the seismic response of structures, underlain by soft or stiff soil deposits and subjected to seismic ground motions. These structural models are also used to investigate the effects of the period-dependent force modification factors on the seismic response of structures.The results show that site effects are less significant for ductile structures, as compared with structures that respond elastically. The results are then used to evaluate the current code provisions for site effects. The current study also shows that using period-dependent force modification factors to derive the code design base shear not only is recommended for short period structures but also is necessary to provide a realistic simulation of the seismic response of these structures. Key words: site, seismic, ductility, structure, foundation, factor, base, shear, amplification, soil, period.
A parametric study of perfobond rib shear connectors
Authors: Oguejiofor E. C. , Hosain M. U.
Published: January 2010

This paper summarizes the results of 40 push-out test specimens with a new type of shear connector called perfobond rib. This connector is a flat steel plate with a number of holes punched through. The test specimens were designed to study the effect of a number of parameters on the shear capacity of the connection. These were the number and spacing of rib holes, transverse reinforcement, and compressive strength of concrete. The main objective of this study was to derive an expression for predicting the capacity of perfobond rib connector based on the results of the parametric study.The test results indicate that the shear capacity of the perfobond rib connector increases with the number of rib holes as long as the hole spacing is at least 2.25 times the diameter of the holes. The effect of increasing the transverse reinforcement ratio from 0.27% to 0.36% was an increase of approximately 16% in the shear capacity of the connection. Similarly, an increase of 36% in the shear connection capacity was achieved due to a 63% increase in concrete strength.An expression for computing the shear capacity of perfobond rib connectors is proposed. A regression analysis, which is based on a model that takes into account the contributions of concrete dowels formed by the rib holes, the transverse reinforcement, and the strength of concrete, was used in the derivation. Key words: composite beam, perfobond rib connector, headed stud, push-out test, compressive strength of concrete, transverse reinforcement.
A rapid seismic screening procedure for existing bridges in Canada
Authors: Filiatrault André , Tremblay Stéphane , Tinawi René
Published: January 2010

The seismic behaviour of existing bridges in Canada remains an important problem, since most of these structures have been built before modern seismic provisions. Recent earthquakes around the world have demonstrated that such older structures can behave poorly under even a moderate ground excitation. The cost for a systematic evaluation and retrofit of bridges in Canada would be prohibitive and therefore such an operation is impractical. As an alternative, this paper presents a rapid seismic screening procedure for existing bridges in Canada. The main goal of the procedure is to allow owners to prioritize their structures for further detailed seismic evaluations. The procedure can also be used to provide data for a postearthquake inspection of bridges located in the epicentral region. Special care has been taken to make the method rapid and simple. Technical personnel without any specific knowledge of seismic design should correctly perform the screening evaluation. The procedure can also be easily incorporated in an existing bridge inspection program. The paper describes the various parameters of the screening procedure. Screening examples of bridges in the Montreal metropolitan area are also presented. Key words: bridges, earthquakes, evaluation, seismic screening.
Damage from 20th century earthquakes in eastern Canada and seismic vulnerability of unreinforced masonry buildings
Authors: Bruneau Michel , Lamontagne Maurice
Published: January 2010

This paper has been prepared as a reminder of past damaging earthquakes in eastern Canada and as a testimony of the damage suffered; isoseismal maps of five selected eastern Canadian earthquakes are presented as well as illustrations of their effects. Although features of the four older historical events reviewed herein are reasonably well documented (although not to present standards), data of engineering significance needed to perform accurate seismic-resistance evaluations have been for the most part lost owing to the time elapsed. Hence, the damage examples presented herein should not be construed as a comprehensive survey but rather as a sampling of noteworthy failures. Since most of the structural damage produced by these earthquakes was suffered by unreinforced masonry buildings, an overview of the seismic risks they constitute and their main modes of failure is presented. The first step of a coordinated seismic risk reduction plan is also formulated; its application is recommended for the mitigation of economic and human losses in future eastern Canadian earthquakes. Key words: case histories, earthquakes, eastern Canada, seismic risk reduction plan, structural damage, unreinforced masonry buildings.
Laboratory study of frazil distribution in a flow
Authors: Tsang Gee , Cui Wei
Published: January 2010

Laboratory experiments were conducted in a circular flume to study the formation, flocculation, and distribution of frazil in a turbulent flow from a Lagrangian frame of reference. The evolution of frazil was studied with video taping and frazil concentrations were measured at multiple points under different hydrothermal conditions. The experiments showed that the average vertical distribution of frazil could be approximated with a functional relationship of the error function type. The empirical equation contains three parameters, which specify the maximum concentration gradient of frazil, the position where it takes place, and the depth gap over which significant changes in frazil concentration occur. These parameters were found to be well-defined functions of the total frazil content in the water column, the flow Reynolds number, and the relative boundary roughness. Frazil accumulated mainly within a thin surface layer. Continued production of frazil contributed more to a higher concentration than a thicker surface layer. Key words: frazil, vertical distribution, laboratory experiments.
Discussion: Grouted anchorages for aramid fibre reinforced plastic prestressing tendons
Authors: Benmokrane Brahim
Published: January 2010

not available
Relaxation behaviour of prestressed wood assemblies. Part 2: Theoretical study
Authors: Quenneville Pierre , Van Dalen Karl
Published: January 2010

Transverse prestress has been found to increase significantly the strength and stiffness of laminated timber bridge decks and timber joints using timber connectors. A fundamental requirement to the successful use of prestressing with timber is the ability to predict the reduction of prestress with time for transversely prestressed timber applications. The loss of prestress with time for transversely prestressed assemblies was studied experimentally and analytically. The analytical study consisted of developing a model that takes into account the effects of constant and changing relative humidity and stressing frequency. Analytical relaxation curves derived from the model were compared with experimental relaxation curves. The model was also used to predict prestress losses in different scenarios. Results show that the proposed relaxation model can be used effectively to predict prestress losses taking into account the effects of constant and changing relative humidity and stressing history. Key words: connections, wood, prestress, Douglas fir, rheology.
On the use of finite element programs in structural evaluation and development of design charts
Authors: Mufti A. A. , Tadros G. , Agarwal A. C.
Published: January 2010

In many phases of structural design and analytical evaluation, the solution of stress and strain distribution in an elastic continuum is required. Special cases of such problems may range from two-dimensional plane stress or plain strain distribution, plate bending to analysis of fully three-dimensional solids. The finite element programs are often used to predict the critical regions for stress analysis and design. Stresses are generally of greater practical importance than displacements for structural design and evaluation. Most of the finite element computer programs calculate element stresses at the centroids, integration points, or nodes of elements. In this paper, examples of bridge deck analysis are used to illustrate the stress interpretation using the finite element programs. It is demonstrated that the stresses at nodes calculated by some finite element programs violate the equilibrium conditions and do not converge to the correct answers. These calculated stresses at nodes are usually too low and lead to unsafe designs and evaluations. Key words: finite element method, finite element programs, structural analysis, least square smoothing, stress interpolation.
Road accident severity analysis: a micro level approach
Authors: Nassar S. A. , Saccomanno F. F. , Shortreed J. H.
Published: January 2010

A comprehensive understanding of the relationship between road accident occurrence and severity of consequences permits the formulation of safety measures that are most cost-effective. A disaggregate model of road accident severity based on sequential logit models is presented. The sequential binary approach is able to account for the dependency between different levels of severity. Factors that affect the level of damage experienced by individuals involved in road accidents include the following: accident dynamics, seating position, vehicle condition, vehicle size, driver condition, and driver action. Separate models are calibrated for three accident situations: single-vehicle accidents, two-vehicle accidents, and multi-vehicle accidents. Ontario road accident police reports are used to calibrate and validate the models. The results of a simple application of the models to a safety protocol involving the effectiveness of passenger restraint devices are presented. Key words: road accident severity, personal injury, logit.
Performance of L-moments and nonparametric flood frequency analysis
Authors: Gingras Denis , Adamowski Kaz
Published: January 2010

A simulation study was undertaken to compare parametric L-moments and nonparametric approaches in flood frequency analysis. Data of various sample lengths were generated from a given generalized extreme value distribution and the quantiles estimated using the fixed-kernel nonparametric method and from a generalized extreme value distribution fitted by L-moments. From the resulting root-mean-square errors for various quantiles, it was concluded for unimodal distributions that nonparametric methods are preferable for large return period floods estimated from short (<30 years) samples while parametric methods are preferable in other circumstances. It was also pointed out that nonparametric methods are more suitable for mixed distributions. Key words: frequency analysis, L-moments, nonparametric methods, simulation.
Seismic loading for buildings with setbacks
Authors: Wong C. M. , Tso W. K.
Published: January 2010

Dynamic analysis is in general accepted as the best method to obtain the seismic load distribution for buildings with a setback. However, most building codes require the base shear obtained by dynamic analysis to be calibrated by the static base shear obtained using the code's equivalent static load procedure. In obtaining the code static base shear, two issues often arise among the design professionals. First, it is unclear whether the code static base shear is applicable for buildings with setbacks because the period prescribed by the code to be used in the base shear formula is in general not pertinent to buildings with setbacks. Second, it is uncertain whether the higher mode period should be used in computing the base shear when the modal weight of a higher mode is larger than that of the fundamental mode — a case often encountered in designing buildings with setbacks. This paper is an attempt to resolve the above issues. For the first issue, modification factors were derived for adjusting the code period formula so that it can provide a more reasonable estimate for the period of a building with a setback. For the second issue, it was demonstrated in this paper that for cases where the modal weight of a higher mode is larger than that of the fundamental mode, using the higher mode period for base shear calculation will result in unnecessarily conservative design. Key words: earthquake, seismic, irregular buildings, setback, dynamic analysis.
Risk-based bridge management: optimization and inspection scheduling
Authors: Cesare M. , Santamarina J. C. , Turkstra C. J. , Vanmarcke E.
Published: January 2010

Bridge management based on reliability methods permits the selection of the set of repair projects that minimizes the total network risk in a planning horizon. This approach, previously proposed by the authors, uses the Markovian model for the decay of structural components, evaluates the overall reliability of the bridge as a system, and computes risk by taking into consideration the consequences of reduced function. This paper presents important additional aspects of risk-based bridge management. First, genetic algorithms are proposed as an alternative optimization strategy; small and large bridge networks are solved, guiding the solution towards minimum risk. Second, Markovian transition matrices for deterioration and post-inspection Bayesian updating are combined to schedule inspections so that the overall reliability of the bridge network is maximized for a given inspection budget. Results from a simulation study using a real bridge network are presented and compared with current inspection practice. Key words: bridge management, reliability, risk assessment, optimization, inspection scheduling.
Review of vibration guidelines for suspended concrete slabs
Authors: Caverson Robert G. , Waldron Peter , Williams Martin S.
Published: January 2010

As spans and slenderness ratios increase, suspended concrete floor slabs are becoming increasingly susceptible to vibration problems. The dynamic behaviour of such floors is currently poorly understood, and there are no established design procedures to deal with vibrations. This paper reviews the existing vibration guidelines for all types of floors and discusses how they may be applied to suspended concrete slabs. Results from a program of field testing of concrete floors are presented and compared with a number of these guidelines. Key words: vibration, concrete, floor slabs, prestressing, natural frequencies, damping, human perception.
Analyse non linéaire par éléments finis des pièces comprimées et fléchies à parois minces
Authors: Boudjelal M. T. , Beaulieu D. , Fafard M.
Published: January 2010

A finite element analysis of the ultimate strength of steel thin-walled beam–columns is discussed in this paper. The numerical model used was developed by Akoussah, Beaulieu, and Dhatt and is based on a Lagrangian formula of thin-walled bars. In this model, the law of multiaxial elastic–plastic behaviour was adopted and incorporated on the section's surface by Radau or Gauss type points. Case studies were performed in which different parameters likely to influence the behaviour of beam–columns were used. Corresponding interaction curves were plotted. The results obtained were compared with those of other authors for H sections under biaxial bending, for square or rectangular tubular sections under biaxial bending, and for H sections bended in relation to each of the principal axes. The results emphasize the key role played by shear stress on the bearing capacity of open section compressed members under bending. Key words: shear, compression, finite elements, bending, interaction, elasticity, plasticity.
Observations and modelling of soil water content changes around trees
Authors: Silvestri V. , Tabib C. , Behidj F.
Published: January 2010

This paper presents the results of a 5-year study of water content variations in a clay soil due to tree roots and evapotranspiration. The site of the study program is Maisonneuve Park which is located in the eastern area of Montreal, in the heart of a zone known for settlement problems experienced by lightweight buildings supported on shallow foundations. The clay deposit around several trees (both isolated and in a row) has been monitored by means of several arrays of 3–5 m long thin aluminium tubes, spaced from 0.1H to about 3H from the trees, where H represents the height of the trees. The volumetric water contents around the tubes have been measured by means of a neutron probe. The study shows that while for some trees, the effects of the roots are confined to a volume of soil located at a distance less than the height of the tree, in other cases, the zone affected by the trees is of much greater extent, reaching as far as 1.5H. In addition, for some of the trees studied, their effect extends to depths exceeding 4 m. Water content changes have also been estimated using the Versatile Soil Moisture Budget model, which was developed at Agriculture Canada. Comparisons between soil moisture readings in the field with estimates from the model show the feasibility of estimating soil moisture changes from standard meteorological data. Key words: water content changes, clay deposit, tree roots, evapotranspiration, observations, modelling.
Joint effects of access and geometry on two-lane rural highway safety in British Columbia
Authors: Li Jian , Abdelwahab Walid , Brown Gerald
Published: January 2010

This paper examines the safety impact of access type, access density, traffic volume, and road geometry on two-lane rural highways in British Columbia. Documented accident to access relationships were reviewed and found to be in poor agreement with observed accident experience within the Province. The nontransferability of accident to access relationships, the lack of studies of traffic and road geometry interaction effects, and the need for a tool to predict the impact of access on highway safety led to the development of the models described in this paper. A comprehensive and disaggregate data base was constructed for some 560 km of the provincial primary arterial highway network. Highway access was classified into four groups: public road intersection, business access, private access, and roadside pullout. Various geometric data, traffic volume, and posted speed limit were included in the data base. Different measures of accidents were chosen to develop the models, including accident rate, accident frequency, severe (fatal plus injury) accident rate, and severe accident frequency. The statistical analyses indicated that when viewed as a disaggregated set of multivariate elements, all access types were significantly correlated with accidents. The joint effects of access and geometry, such as the combination of private access and horizontal curvature, intensify the effect of access on accidents. As a result, relative weightings of all access types in terms of their impact on safety were empirically derived, with business access weighted as 0.5 and private access weighted as 0.10 of public road intersections. Key words: highway access, geometry, accidents, rural highways, two-lane highways, multivariate regression.
Étude sédimentologique de sites de dépôt de matériaux de dragage dans le fleuve Saint-Laurent. I. Modélisation numérique tridimensionnelle du panache de dispersion des sédiments retenus dans la colonne d'eau
Authors: Khelifa Ali , Ouellet Yvon
Published: January 2010

Within the sedimentological study of disposal sites of dredged materials along the St. Lawrence River between Sorel and Saint-Pierre-les-Becquets, a three-dimensional numerical model (SED3D) has been developed to reproduce the dispersion of sediments maintained in the water column during an open-water discharge operation. This model is based on the extension of the Douglas–Wang finite element formulation to discretize the steady three-dimensional advection–diffusion equation. The space discretization is quadratic using 20 nodes hexahedron elements (H20). Results of SED3D model applied to Cap-de-la-Madeleine disposal site show that suspended sediments settle in a domain less than 200 m of the disposal point by 50 m and so they can not reach the seaway. The qualitative validity of these results was demonstrated by the analysis of some sediment samples taken in the St. Lawrence River at Cap-de-la-Madeleine. Key words: dredging, sediments, St. Lawrence River, advection–diffusion, numerical model, Douglas–Wang, finite element.
Étude sédimentologique de sites de dépôt de matériaux de dragage dans le fleuve Saint-Laurent. II Analyse quantitative de la stabilité des sédiments déposés
Authors: Khelifa Ali , Ouellet Yvon
Published: January 2010

This paper presents the second part of a sedimentological study on four disposal sites of dredged material along the St. Lawrence River between Sorel and Saint-Pierre-les-Becquets. A quantitative analysis of the stability of non-cohesive sediments disposed at those sites comprises, on one hand, a study of the erosion process by currents at those sites and, on the other hand, of the erosion by currents and waves at Yamachiche in Lake St-Pierre. The results show that the daily eroded quantity at the site of Cap-de-la-Madeleine varies from 0.1 to 6 times the capacity of a barge of 500 m3 when the river discharge varies from low-water to flood conditions with a 20-year recurrence. When wave conditions corresponding to a significant height of 0.5 m and a peak period of 3.5 s (event with a probability of the order of 10%) are superposed on currents at the Yamachiche site, the calculated erosion corresponds to 0.7 to 2.5 barges. Under high-wave conditions of 0.7-m height and 4 s period (event with a probability of the order of 0.1%), the erosion rises to about 2.5 to 7 barges. These results are in good agreement with measures taken at Cap-de-la-Madeleine and Yamachiche. Key words: dredging, sediments, St. Lawrence River, Lake St-Pierre, erosion, waves.