1,721,030 research outputs found
Publication no. 74, Load reduction on buried rigid pipes
No full textPublication no. 74, Load reduction on buried rigid pipesBuried culverts are extensively used in road construction. Arching is a soil-structure interaction concept that plays a key role in most of the culvert installations. In effect, arching is the behaviour of the soil-structure system involving redistribution of soil stresses around the structure from the values that would occur if the structure were not present. In positive arching a portion of the load over the structure is transmitted to the soil around the condiut. Negative arching is unfavourable and implies that the culvert is drawing more load than the column weight of soil over it. Terziahgi described arching action in soils as "One of the most universal phenomena encountered in soils both in field and in the laboratory. Since arching is maintained solely by shearing stresses in the soil, it is no less permanent than any other state of stress in the soil wich depends on the existence of shearing stresses, such as the state of stress beneath the footing of a column. " Terziaghi also stated that the amount of arching can only be obtained by direct measurement on full scale structures in the field. Arching is important in two types of buried culverts: • long-span flexible steel culverts • imperfect ditch culverts. The imperfect ditch method involves incorporating a compressible layer within the backfill above a rigid culvert. As the backfill is placed, the soft zone compresses more than the surrounding soil and thus induces positive arching above the culvert. Two flexible steel culverts, two concrete pipes and one east in place box culvert are instrumented for monitoring the behaviour during construcion and on a long-term basis. Expanded polystyrene is used as compressible material in the fill above the rigid culverts. A shorter version of the second paper "Load reduction on rigid culverts beneath high fills. Long-term behaviour" received the K. B. Woods award at the 73rd annual meeting at the Transportation Research Board in Washington in January 1994. The K. B. Woods award is presented for the outstanding paper in the field of design and construction of transportation facilities. The work in the first paper was published in Pipeline Crossing Proceedings, Special Conference, Pipeline Division ASCE, Denver Colorado March 25-27, 1991. The work in the second paper was published in Transportation Research Record no. 1415, Transportation Research Board, National Research Council, Washington D. C. 1993. The work in the third paper was published in Transportation Research Record no. 1231, Transportation Research Board, National Research Council, Washington D.C. 1989. The county roads offices in Buskerud, Hordaland, Oppland and Telemark are greatly acknowledged for making it possible to perform instrumentation on the field installations. Tor Helge Johansen and Willy Holm are greatly acknowledged for their careful work on the instrumentation and field operations
Influence of Subsoil Conditionson the Design and Performance of Flexible Pavements
Get PDFThe effect of subsoil conditions is one of the prominent factors that control both the design and performance of flexible pavement structures. Despite having a wide range of empirical methods from measurements and experience, the quantification of the short-term and long-term physical processes of geo-materials in roads is not yet fully understood. Particularly, subgrade soils have not got the required attention in the characterization of pavement materials although they are known as the “foundation” of the pavement structure. This conception has raised — partly due to the notion that the stress from the traffic is low at the subgrade level — and partly, due to existence of a wide variety of soils, in contrast to standardized materials for asphalt, base, and sub-base layers. Lowtraffic volume roads, however, have often thin asphalt layer, and the stress magnitude from the traffic loads can be significant at the subgrade level. In addition, subgrade soils are most susceptible to the variation of local and environmental conditions.
With the fact that the subgrade layer is an integral part of pavement analysis, this thesis aimed to address the main important issues of characterization of subgrade soils in mechanistic pavement design methods. The objectives of this research have been classified within three main themes: (1) to propose numerical models to characterise subgrade soils for practical mechanistic-empirical pavement design method, (2) to enhance the quantitative characterisation of subgrade soils — instead of the widely used qualitative characterizations in practice, (3) to use finite element method to optimise road design and maintenance practices.
The main contributions of this study are: First, an overview of research literature is provided on the existing methods and knowledge of characterization of subgrade soils in flexible pavement design. The geotechnical aspects in pavement design are outlined to identify the research needs and to formulate the main research questions. Second, a method for formulation and implementation of a nonlinear resilient modulus model is presented. The method in this study has been found to be more versatile than the existing methods for characterization of subgrade soils since it considers the effects of both confining pressure and deviator stress. The implications of this method were found to be important aspects of pavement design for low-traffic volume roads.
Third, a constitutive model is proposed to predict the long-term deformation of subgrade soils. The model is formulated based on the plastic strain from first loading cycle, and an additional parameter that accounts for the proximity of the applied stress to the static strength of the soil. The predicted results from the proposed model showed a good agreement with laboratory tests for deviator stress level up to 50% of the static strength of the soil. Fourth, based on finite element modelling of soil compaction, the lift thickness of fine-grained soils has been observed to be defined as a function of cohesion and friction angle. This study suggested the optimisation technique of lift thickness depending on the strength parameters of soils to improve the rolling strategy of soil compaction during road construction.
Finally, a finite element modelling technique is presented for prediction of spring thawing in frozen subgrade soils. Since there are no well-established methods for modelling of the thawing process, analytical solutions are used to validate the numerical methods for simplified boundary conditions. Further, the application of finite element method is extended to model multi-layer pavement structures with the thermal and physical properties of each layer and varying surface temperature. In this study, the thaw depth is observed to be linearly proportional to time for sinusoidal surface temperature variation — in contrast to the existing knowledge of thaw rate for homogeneous frozen layers where the thaw depth is proportional to the square root of time.PhD i bygg, anlegg og transportPhD in Civil and Transport Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Military terrain-mobility : sedentary peat
Get PDFMilitær terrengmobilitet kan betraktes med et makroperspektiv og et mikroperspektiv. Makroperspektivet er overveiende når det kommer til ressursbruk og forskning for militær terrengmobilitet, nasjonalt og internasjonalt. Det er lite militært arbeid i nyere tid som fokuserer på presis bruk av ingeniørteknologi med kunnskap og ferdigheter på avdelingsnivå. Denne studien fokuserer på mikroperspektivet.
Sedentær torv er en utfordring for mekaniserte landstyrker fordi dette er en betydelig andel av et nordisk manøverrom. Kvalifiserte ingeniørrekognoserings soldater bør kunne måle, tolke og kalkulere områder med torv for mobilitet. Dette med hensyn på sin tradisjonelle rolle som ingeniørsoldater.
Studien søker å finne drivende faktorer som enkelt kan måle og tolke torv med feltmålinger som gir tilstrekkelig informasjon til å kalkulere bæreevnen til torv.
Studien belyser behov for kunnskap og orienterer mot en løsning for å svare på problemformulering; hvordan enkelt måle, tolke og kalkulere torvs bæreevne for korttidslast?
Dette i den hensikt å muliggjøre konservative vurderinger for å sikre egne landstyrkers mobilitet.
Innledningsvis har litteraturstudien innen grunnleggende geoteknikk og terramechanics lagt vekt på teorier om bæreevne og drivende faktorer som kan måles med enkle feltmålinger.
Dette har ført til utvikling av en manuell målemetode og modifisering av et Cone Penetration Test-apparat. Dette er benyttet under feltforsøk for å måle stivheten i underliggende torv lag. Feltforsøket med analyse viser lovende resultater. Det er lagt vekt på at testen eventuelt skal kunne utføres av militært personell med enkle hjelpemidler.
Resultatene i studien er et teoretisk potensiale forfattet som et testdesign for innsamling av målbare data med et bevameter. Hvis testene i testdesignet gjennomføres og data analyseres vil sannsynligvis dette kunne løse problemformuleringen empirisk. Det er favorisert løsninger hvor militært personell med enkelt materiell kan utdannes og trenes til å kalkulere kortidslast på torv.
Resultatene definerer også utviklingspotensialer av testdesignet som kan bidra til å løse flere utfordringer ved terrengmobilitet enn torv alene.Military mobility in the terrain can be viewed at as a macro perspective and a micro perspective. The macro perspective is predominant when it comes to the use of resources and research for military terrain-mobility, nationally and internationally. There haven’t been a lot of military work in recent times that focuses on the precise use of engineering technology with knowledge and skills, at the level of subunits. This study focuses on this micro perspective.ForsvaretsubmittedVersionM-V
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Soil-structure interaction and load distribution on buried concrete pipes
Get PDFThe efficiency of transport plays an important role in human welfare and the food industry. The vehicles are travelling with a higher speed and are transporting even larger loads than before. An increased understanding of the traffic load distribution is vital to meet the current and future challenges.
The main focus in this thesis is the comparison of the traffic loads by railway and roads. It focuses on the distribution of the loads, and the significance of traffic loads effect on pipelines with minimum and maximum soil covers. A method is presented to optimize the pipe design. For the optimization the software PLAXIS 2D is used, a finite element program that simulates geotechnical problems with a better approach to reality. The results of the optimization are compared with calculations made according to the current regulations. The problem is answered by creating a case, placing the pipes with different soil covers.
The results for the vertical accelerations match the expectations, other full-scale trials and previous research. The vertical accelerations presented, show that there is a rapidly decreasing effect. This will be a critical factor for pipes with minimum soil covers.
The comparison of hand calculations and the calculations done in PLAXIS shows opportunities to increase the utilization of the pipe construction. The potential of the maximum and minimum soil covers is great. FEM programs proves to be helpful with the challenges that arise in reality and provides a good indication in solving complex issues.Effektivisering av transportmidler spiller en viktig rolle for menneskets velferd og næringssektoren. Dette fører til at kjøretøyene skal kjøre med høyre hastighet og transportere større laster enn noen gang. For å imøtekomme utfordringer knyttet til fremtidige og nåværende problemer kreves økt forståelse av påkjenningene nedgravde rørkonstruksjoner utsettes for, og også hvordan jorden oppfører seg som en følge av trafikklastene.
Målet med denne oppgaven er å sammenlikne trafikklaster fra jernbane og veg. Det er fokusert på hvordan kreftene fordeler seg og hvilken betydning en trafikklast som beveger seg utgjør for rør som legges ved minimum og maksimum overdekningen. Det er også fremlagt en metode for optimalisering av rørkonstruksjonen som dimensjoneres ved bruk av PLAXIS 2D, et finite element program som simulerer geotekniske problemer med en bedre tilnærming til virkeligheten. Resultatene sammenliknes med beregninger gjort etter dagens regelverk for å se mulighetene for optimalisering av rørkonstruksjoner ved bruk av en ny teknologisk tilnærming. Det er tatt i bruk et case-studie der røret legges ved ulike overdekninger for å svare på problemstillingen.
Resultatene for de vertikale akselerasjonene som er funnet stemmer godt overens med forventninger, andre fullskalaforsøk og tidligere forsking. De vertikale akselerasjonene som er presentert viser å ha en raskt nedtrappende effekt og vil for rør anlagt med liten overdekning være en kritisk faktor. Beregningene gjennomført etter dagens regelverk sammenliknet med beregningene i PLAXIS viser gode muligheter for å øke utnyttelsen til rørkonstruksjonene. Resultatene viser et spesielt stort forbedringspotensial ved største og minste overdekning som er testet. FEM-programmer viser seg å være et godt hjelpemiddel til å gjenskape de utfordringene som oppstår i virkeligheten og gir gode indikasjoner på hvordan komplekse problemer kan løses.BasalM-B
Buried flexible structures : modeling and field behavior
Get PDFThe future utilization of long-span buried structures requires improved theoretical understanding of the constructions. The physical dimensions are increasing and the mechanical features grow more complex. FEM modeling serves as a good tool to explore the earth pressure and the internal forces in the steel structure.
The main goal of t his thesis is to investigate the reliability of FEM modeling compared to short- and long- term measurements, with a main focus on the the pressure distribution and internal forces in the steel structure. To perform the study two existing buried structures in Norway were examined; a horizontal ellipse and an arch footed in concrete. Measurements on the horizontal ellipse included earth pressure and deformation, and measurements on the arch included earth pressure, axial force and moment. The model was contrived in PLAXIS 2D based on theoretical material properties and structure geometry.
The earth pressure on the steel structure will increase in a long-term perspective. It is therefore preferred that the modelled earth pressure coincide this accretion. The results show overall good correspondence. At the ellipse structure the modelled arching effect was higher than measured. Laboratory tests are required in order to achieve a more accurate soil model, thereby improving the results. The modelled axial stress was inverted from the measured axial stress. The measured axial force and moment were also higher than the modelled values. The measurements are based on five locations in the steel structure and it remains unclear whether or not they represent the total stress distribution. It is likely that the modelled values present a better estimation on the stress distribution. However, further investigation and additional measurements are necessary to investigate this assumption. The measurements on deformation suggested that peaking occurred during construction. Controlled peaking in buried structures is desired when the internal stress caused by deformation don’t exceed the yield point. The modelled deformation estimated that the span increased. An alternative solution for obtaining a better estimate is to insert a line-load on each backfill layer in order to imitate the compression performed during backfill.
Overall the model in PLAXIS 2D produced adequate estimations of the earth pressure and internal forces. The detailed monitoring of the construction presented in the model could prove useful in future soil-steel structures. Obtaining a representative model of the selected structures will however require some additional adjustments
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
