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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Development of a Logit model of the transition effect to public transport

Ziedén, Therése January 2017 (has links)
The importance of traffic planning has, throughout the years, been in- creased, providing sustainable developments of traffic and infrastructural investments. The analysis of the current traffic situation and the evalua- tion of the effects of a future investment are crucial for the socio-economic benefits maintenance. These analyses and evaluations are most commonly done using traffic simulation models. One of the main traffic planning aims, nowadays, is to increase the number of public transport users against the number of private car users. This change in mode choice is called transition effect and could be beneficial both from an environmental and socio-economic perspective. This thesis aims to evaluate and improve the macroscopic traffic demand and transition model, used fot the city of Norrköping. Additionally, the thesis investigates if a general transition Logit model can be developed and which parameters are the most important to be included in a modal choice estimation. For the needs of this study, the traffic planning software Visum is used. The travel mode distribution is calculated by Logit models coded in Python-scripts integrated in Visum. Then, a traffic assignment is performed by Visum, computing new travel times as inputs to the Logit model and this iterative procedure continues until the system reaches an equilibrium. The thesis aims for a more reliable prediction of the transition effect by correcting the Python-scripts and estimating the parameters of the Logit model using data from surveys. The study shows that travel times is the most important factor for realistic results generation. However, the data used for the estimation of the Logit model parameters did not include sufficient information of travel times. The travel times had to be calculated, using two different methods, in order to be included in the estimation of new parameters. Although these methods could not provide any positive effects on the transition, they did prove the importance and significance travel time have when developing a traffic model. The result of the study invokes the importance to further develop the method of calculating travel times, when the input data is not sufficient, and shows that the travel time parameters are case specific.
2

Modelling masonry spires : An investigation / Modellering av murade tornspiror : En utredning

Lillemo, Dennis January 2021 (has links)
Masonry spires are a typical part of church architecture. Since it is rare that masonry is used as a load-bearing material in the western world today, it is important to maintain and increase the knowledge of modelling masonry structures both from a maintenance point of view and to build new masonry structures. The purpose of this master thesis is to look at and evaluate some different methods to model masonry spires exposed to common loads such as gravity, settlement and wind. The spire of the Salisbury Cathedral is used as a template regarding geometry and mechanical properties for the modelling methods. Two modelling methods are used in the master’s thesis. The first one is the limit analysis method applied to masonry. It is used to calculate a critical thickness for the masonry of the spire for a severe wind load. The second method is the Finite Element Method (FEM). The commercial finite element software Abaqus is used to create the model and the discretization used with the FE modelling is the macro-modelling approach. Concrete Damage Plasticity (CDP) in Abaqus is used as the material model and adapted to masonry. The finite element model consists of the spire itself along with the supporting structure beneath it down to the piers. Four different simulations (jobs) are run with varying wind direction and two of them have settling piers. The results from the finite element simulations indicate that the membrane stresses in the spire faces for the various jobs were not significantly different from one another. One of the jobs with settling piers could not be completed because the tensile stresses in the arches reached the tensile strength capacity of the material. The other simulation with a settlement that did complete did not have any significant difference in stress compared with the simulations without settlements. While the arches and the piers underwent plastic straining the spire itself did not. The stress levels there remained in the linear range for all the completed simulations. The finite element results also agree with the limit analysis. These findings call into question some of the modelling choices. The inclusion of the structure beneath the spire in the finite element model, as a way to study the effect of settlements, did not give more insight into the spire’s behaviour. Furthermore, the method to implement settlements was too inaccurate and another approach should be used to study the effect of settlements on the state of spires. Further work needs to be done on that topic. Improvements can also be made regarding how CDP was adapted for masonry. / Murade tornspiror är en vanlig takkonstruktion inom kyrkoarkitekturen. Eftersom det numera är sällsynt att murverk fungerar som lastbärande material i västvärlden, är det viktigt att upprätthålla och utöka kunskapen om murverkskonstruktioner för både underhåll och nybyggnation. Syftet med denna masteruppsats är att betrakta och utvärdera några olika modelleringsmetoder för murade tornspiror som är utsatta för några typiska laster såsom egentyngd, sättningar och vind. Katedralen i Salisbury används som en modelleringsmall i uppsatsen med avseende på katedralens geometri och materialegenskaper. Två modelleringsmetoder används i uppsatsen. Den första är gränsanalys tillämpad på murverkskonstruktioner. Den används för att beräkna en kritisk tjocklek för tornspiran under en stor vindlast. Den andra metoden är Finita Elementmetoden (FEM). Den kommersiella finita elementprogramvaran Abaqus används för finita elementanalysen och diskretiseringen som används för murverket i finita elementmodellen är makromodellering. Concrete Damage Plasticity (CDP) i Abaqus används som materialmodell och anpassas för murverk. Finita elementmodellen består utav själva tornspiran inklusive de bärande delarna under spiran och ned till pelarna. Fyra olika simuleringar ("jobb") körs med vindlast som angriper från olika riktningar och två av simuleringarna har pelare som sätter sig. Resultaten från simuleringarna visar att membranspänningarna i tornspirans väggar, för de olika jobben, inte skilde sig i någon betydelig grad från varandra. Ett av jobben med pelare som satte sig kunde inte köras klart eftersom dragspänningarna i valvbågarna överskred draghållfastheten på murverket i modellen. Den andra simuleringen med sättningar som kördes klart uppvisade inte några avsevärda skillnader i spänningar i tornspiran jämfört med simuleringarna utan sättningar. Medan plastiska töjningar uppkom i både valvbågarna och pelarna i modellen, uppkom de inte i tornspiran. Spänningsnivåerna i tornspiran var inom det linjära intervallet för alla simuleringar. Resultaten från finita elementanalysen stämde överens med resultaten från gränsanalysen. Analysresultaten ifrågasätter vissa av modelleringsvalen. Att inkludera de bärande delarna under tornspiran i finita elementmodellen, för att undersöka effekten av sättningar, gav inte en större insikt i hur sättningar påverkar tornspiran. Dessutom, var metoden för att tillämpa sättningar för oprecis och en annan metod borde användas. Mer arbete måste utföras vad gäller det ämnet. Sättet att tillämpa CDP för murverk kan också förbättras.

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