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  • 101.
    Ahlberg, Jesper
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Biogeofysik.
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Biogeofysik.
    Distributed snow modelling integrating ground penetrating radar data for improved runoff predictions in a Swedish mountain basin2009Ingår i: EGU General Assembly 2009, 2009Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Operational forecasts of snow melt runoff in Sweden are currently running with precipitation and temperature as the main input variables and calibrated with runoff data, and there is an interest to make better use of new measurement systems for distributed snow data. At the same time, various data assimilation techniques are becoming more frequently used in hydrological modeling, in order to reduce uncertainties related to both model structure errors and errors in input and calibration data. Thus, it is important to address not only what type of snow data that can be used to improve the model predictions, but also what type of input data and model structures that are optimal in relation to the available snow data. The objective of this study is to investigate to what extent the runoff predictions can be improved by assimilation of temporal and spatially distributed snow data, and if the improvements depend on the choice of model structures, for instance the use of energy balance or day-degree snow models. In order to achieve these objectives a new distributed snow model has been implemented into the hydrological modeling framework HYSS/HYPE. This model can easily be setup with either an energy balance model or a day-degree model for the snow pack calculations, and it is easy to run the model with different spatial resolutions. In the fully distributed case, snow drift processes are implicitly included in the model through a precipitation distribution model, based on topographical information and wind direction. The model was applied to a mountain basin in northern Sweden used for hydropower production, where extensive snow measurements were taken during the last two winters 2007-2009. A climate station is located at the outlet of the regulation lake, including automated point measurements of snow depth, snow mass (snow pillow), snow wetness and snow temperature. Distributed snow cover data was sampled using ground-penetrating radar from snow mobiles. Measurements were taken at the time of the maximum snow cover, providing a data set with snow depth, snow density, snow water equivalent along 20 km long transects in representative areas of the basin. The precipitation distribution model was calibrated using the distributed SWE data from the GPR measurements. Application of the calibrated model to previous years without available snow data show that the runoff predictions was improved compared to calibrations without the distributed snow data, however the improvements were larger for the energy balance compared to the day-degree model. Further developments will include assimilation of the temporal and spatial snow data to adjust the distribution of various input variables, for instance air temperature and wind speed.

  • 102.
    Ahlfors, JOhanna
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Häggdahl, Josefin
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Framtidens modulskola: En jämförande studie av arbetsmiljön i en tillfällig och en befintlig skolbyggnad2016Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
  • 103.
    Ahlgren, Max
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    Goldmann, Jacob
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    The Internationalization of Swedish SMEs: how does internationalization affect individual firm’s capital and credit risk structure?2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this master thesis we examine how the level of internationalization, i.e. a firm’s relative exposure to foreign sales, affects individual SMEs in Sweden. Since it is conducted using a data sample with Swedish SMEs its applicability in other countries may vary. The aspects concerned in which the internationalization affects the firm’s structure is limited to the areas of capital structure, credit risk and the factors affecting credit risk. Altman’s Z-score model is employed to approximate a firm’s credit risk and the debt ratio represents the firm’s capital structure. The purpose of the thesis is to increase the knowledge and provide insights on how internationalization affects SMEs in general and in Sweden in particular. Knowledge on how internationalization affects firms is scarce and by this thesis we have extended the known area of the topic and shed light on this relatively unexplored SME aspect. Our hope is that by highlighting differences (and similarities) in credit risk attributes of high and low internationalized firms SMEs this will improve their financial transparency and ease their attracting and access to external sources of capital. To examine the effects of internationalization on Swedish SMEs we have employed statistical techniques, most importantly regression analysis.

    Our study has not only implications for academics, but for all parts that has any interest in efficient credit scoring models and to understand credit risk characteristics and how internationalization affects SMEs. Banks, policy makers and credit rating agencies are constantly pursuing improvements in the efficiency and accuracy of quantifying credit risk by developing credit-scoring models. Banks because they want to minimize credit losses and maximize profitability and policy makers to secure a viable business environment for companies to nurture economic growth, employment, innovation and the country’s competitiveness. The SME segment has received extra attention lately due to the financing barriers they are facing.

    Our results are contradictory to some earlier research in the area and in line with other. This implies that the characteristics and relationship of SMEs credit risk and internationalization changes over time and/or differs between countries, perhaps even between regions within national borders. For example we arrived at the conclusion that our basic model indicates a positive relationship between internationalization and credit risk, in line with both Rugman (2009) and Caves (2007). Our analysis shows no significant difference in the firm’s capital structure depending on the internationalization, although younger companies tended to have a higher level of internationalization. This finding is contradictory to the research conducted by Burgman (2009) and the reports carried out by the European Commission whose report reaches the conclusion that older firms had a higher level of international exposure. 

  • 104.
    Ahlin, Rikard
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Brinck, Viktor
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Klimatkalkylering2014Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta är en studie om klimatpåverkan i samband med anläggandet av järnvägsbroar i syfte att ta fram nyckeltal (moment, material, mängder) för att effektivt kunna reducera utsläppen av växthusgaser. Till grund för studien har vi arbetat med Trafikverkets verktyg klimatkalkyl 2.0. Det har granskats utifrån användarvänlighet och riktighet i indata och emissionsomräkningsfaktorer. Det för att se till skillnaden mellan modellen och ett unikt anläggningsprojekt, var skiljer sig Trafikverkets typvärden mot de projektspecifika förutsättningarna samt vilka blir dess konsekvenser?

    Studien har kommit fram till att utan viss försiktighet vid arbete i klimatkalkyl 2.0 finns risk för inkorrekta resultat. Dessutom har studien påvisat tvivelaktiga standardvärden för betydande poster.

    Utöver dessa resultat har studien konstaterat att de mest betydande delarna för det unika anläggningsprojektets utsläpp är reduktion av mängden stål och betong samt att hitta leverantörer som kan bevisa låga emissionsfaktorer. Med relativt enkla åtgärder skulle det unika anläggningsprojektets totala utsläpp av koldioxidekvivalenter minskas med nästan 20%.

  • 105.
    Ahlroth, Sofia
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö.
    Convergent validity test of structural benefit transfer: the case of water qualityManuskript (preprint) (Övrigt vetenskapligt)
  • 106.
    Ahlroth, Sofia
    KTH, Tidigare Institutioner                               , Anläggning och miljö.
    Correcting NDP for SO2 and NOx emissions: Implementation of a theoretical model in practice2003Ingår i: The Review of Income and Wealth, ISSN 0034-6586, E-ISSN 1475-4991, nr 3, s. 425-440Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The theoretical and the practical studies in the field of environmental accounting are often two separate lines of work. In this study, we develop an optimal control theory model for adjusting NDP for the effects of SO2 and NOx emissions, and subsequently insert empirically estimated values. The model includes correction entries for the effects on welfare, real capital, health and the quality and quantity of renewable natural resources. In the empirical valuation study, production losses were estimated with dose-response functions. Recreational and other welfare values were estimated by the contingent valuation (CV) method. Effects on capital depreciation are also included. For comparison, abatement costs and environmental protection expenditures for reducing sulfur and nitrogen emissions were estimated. The theoretical model was then utilized to calculate the adjustment to NDP in a consistent manner. The estimated damage value of sulfur is close to the Swedish sulfur tax.

  • 107.
    Ahlroth, Sofia
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys.
    Costs and benefits of climate change : a bottom-up analysisManuskript (preprint) (Övrigt vetenskapligt)
  • 108.
    Ahlroth, Sofia
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys.
    Finnveden, Göran
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys.
    Ecovalue08-a new valuation method for environmental systems analysis toolsManuskript (preprint) (Övrigt vetenskapligt)
  • 109.
    Ahlroth, Sofia
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys.
    Höjer, Mattias
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö.
    Sustainable energy prices and growth: Comparing macroeconomic and backcasting scenarios2007Ingår i: Ecological Economics, ISSN 0921-8009, E-ISSN 1873-6106, Vol. 63, nr 4, s. 722-731Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    How do results from the sustainability research world of backcasting relate to the macroeconomic scenarios used for policy evaluation and planning? The answer is that they don't, mostly - they come from different scientific traditions and are not used in the same contexts. Yet they often deal with the same issues. We believe that much can be gained by bringing the two systems of thinking together. This paper is a first attempt to do so, by making qualitative comparisons between different scenarios and highlighting benefits and limitations to each of them. Why are the pictures we get of the energy future so different if we use a macroeconomic model from when using a backcasting approach based on sustainable energy use? It is evident that the methods for producing those two kinds of scenarios differ a lot, but the main reason behind the different results are found in the starting points rather than in the methods. Baseline assumptions are quite different, as well as the interpretations and importance attached to signals about the future. in this paper, it is discussed how those two types of scenarios differ and how they approach issues such as energy prices and growth. The discussion is based on a comparison between Swedish economic and sustainability scenarios. The economic scenarios aim at being forecasts of the future and are used as decision support for long-term policies. But are the assumptions in the economic scenarios reasonable? The sustainability scenarios are explicitly normative backcasting scenarios. They do not take the issue of growth and consumption fully into account. Could they be developed in this respect? The comparison between the scenarios is also used to look closer at the issue of energy prices in a society with sustainable energy use. One of the questions raised is if a low energy society calls for high energy prices. Moreover, the effects of tradable permits versus energy taxes is analysed in the context of how energy use could be kept low in a growing economy.

  • 110.
    Ahlroth, Sofia
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys.
    Nilsson, Måns
    SEI.
    Finnveden, Göran
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys.
    Hjelm, Olof
    Linköpings universitet.
    Hochschorner, Elisabeth
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Miljöstrategisk analys.
    Weightning and valuation in environmental systems analysis toolsManuskript (preprint) (Övrigt vetenskapligt)
  • 111.
    Ahlsten, Anton
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Karlsdotter, Ellen
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Numeriska simuleringar av betongplattor på mark med gradientkrympning och sprickfördelande armering2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Betongplattor på mark är en ofta använd grundläggningsmetod. Trots detta är sprickbildning ett vanligt problem där kraven på maximala sprickvidder ofta inte uppfylls. De sprickor som bildas i plattorna uppkommer bl.a. till följd av dess uttorkning, och då olika fuktförhållanden råder på var sida om plattan utvecklas en krympning som varierar med en gradient över tvärsnittet. Vid dimensionering av armeringen för denna inre last och sprickbildningen den orsakar, finns endast otillräckliga analysermetoder att tillgå i normer. Att analysera det tvång som uppstår vid krympningen är mycket svårt, speciellt då betongen spricker och lastfallet blir statiskt obestämt.

    I detta arbete undersöks sprickbildningen i krympande betongplattor på mark så att noggrannare dimensionering av den sprickfördelande armeringen skall kunna utföras. Analyserna har utförts med numeriska simuleringar i FEM-programmet Atena 2D där ett antal olika plattor med varierande betongklass, armeringsinnehåll och platthöjd undersökts. Arbetet omfattar en jämförelse av de erforderliga sprickfördelande armeringsinnehållen samt de analytiskt beräknade sprickvidder som erhålls dels enligt huvuddokumentet för Eurokod 2 och dels enligt huvuddokumentet och den tyska nationella bilagan. Armeringen har då dimensionerats utifrån en spänningsfördelning som varierar linjärt över tvärsnittet, på samma sätt som krympningen varierar. Studien behandlar även en jämförande undersökning av sprickutvecklingen vid inre respektive yttre last för att påvisa skillnader i sprickbeteendet.

    De numeriska simuleringarna visade att en ökad sprickfördelande förmåga och en minskning av sprickvidder erhålls då armeringsinnehållet i en platta ökas. Av de undersökta plattorna nås armeringens flytspänning inte i något fall, vilket tyder på att mängden armering kan minskas ytterligare utan att s.k. single cracks uppstår. Även vid underarmering, då armeringen minskas till 64 % av vad Eurokods huvuddokument anger, behålls den sprickfördelande funktionen. Undersökningarna visade att den sprickbildning som sker av den inre lasten vid krympning är beroende av uppsprickningen, till skillnad från sprickbildning vid yttre last. Den jämförande studien över armeringsinnehåll enligt Eurokod 2 visar att dimensionering enligt tyska nationella bilagan under verkan av inre last ger en reducerad erforderlig armeringsarea med 20 % i förhållande till huvuddokumentet. De analytiska beräkningarna över sprickvidder tyder på att beräkningsmetoden enligt Eurokod 2 ger större sprickvidder än den som beräknats enligt den tyska nationella bilagan.

  • 112.
    Ahlund, Rasmus
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Jord- och bergmekanik.
    Ögren, Oscar
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Jord- och bergmekanik.
    Pore pressures and settlements generated from two different pile drilling methods2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    För pålningsarbeten i känsliga jordar och speciellt i innerstadsprojekt är det viktigt att vara medveten om befintliga metoder och välja den mest gynnsamma av dessa för att på så sätt minimera de risker som är sammankopplade med arbetet. Sänkhammarborrning är en relativt säker påldrivningsmetod och kan delas upp i luftdriven borrning och vattendriven borrning. Det här arbetet jämför dessa två metoder och visar att formationspåverkan vid luftdriven borrning är större än den vid vattendriven borrning.

    Arbetet baseras på en fältstudie där totalt 4 pålar borrades, två med luftdriven borrning och två med vattendriven borrning. Borrningen genomfördes i en formation med lera ovanpå silt och ren friktionsjord och jorddjupet på platsen varierade mellan 12-15 meter. För att undersöka formationspåverkan mättes sättningar på djupet och på markytan och portryck mättes mitt i lerlagret. Arbetet kunde urskilja två huvudsakliga problem vid borrning i den här typen av formation. Det första är risken för överborrning i friktionslager och det andra är risken för portrycksökning i tätare lerlager. Båda dessa fenomen observerades när luftborrning utfördes men inget av dem kunde urskiljas då vattenborrning utfördes. Sammanfattningsvis kan sägas att vattendriven borrning påverkar jorden mindre i den mening att den ger upphov till mindre portrycksökning och orsakar mindre korttidssättningar.

  • 113.
    Ahmad, Arslan
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Mark- och vattenteknik.
    Evaluation of organic residues and their mixtures with Peepoos to produce fertilizer.2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Peepoo, self-sanitising, biodegradable toilet is characterized by low carbon to nitrogen (C-N) ratio and low dry matter (DM) content. Principal nutrients (nitrogen (N), phosphorous (P) and potassium (K)) are also not in a balance as required by most crops. It was expected that the mixing of used Peepoos with other organic materials might balance its chemical characteristics. In this thesis, availability and suitability of common organic materials produced in Kenya has been investigated for mixing with used Peepoo bags to obtain a balanced fertilizer product from the crop nutrition aspect. Seven organic residues were selected from the list of 13 on the basis of their availability near the processing site in Nairobi. The selected residues were then chemically analyzed for their individual plant nutrient content. The analysis results were used subsequently to simulate the chemical composition of a wide range of Peepoo-Residue mixtures. The evaluation of the theoretical mixtures based on DM content, C-N ratio and NPK ratio showed that the majority of investigated mixtures had DM content below 60 %. Majority of the mixtures showed C-N ratio between 10-1:1. All the mixtures deviated from the common nutrient uptake ratio of crops (1:0.5:1.4). Composite mixtures with more than 2 ingredients resulted in a balanced fertilizer product. The study concludes and recommends that the composite mixtures with more than two ingredients should be considered for practical processing of Peepoos into a commercial fertilizer product.

  • 114.
    Ahmad, Roman
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Chammoun, Johan
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Optimering av den svenska metoden fördimensionering av betongbeläggningar på flygfält2017Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Sverige har länge använt beläggningsytor av asfalt på grund av dess flexibla

    egenskaper som är lämpliga för det svenska klimatet. Historiskt sett har Sverige

    haft låg trafikmängd vilket inte gett utrymme för utvecklingen av betong som

    beläggning i vägar.

    Trafikmängden har sedan ett par år tillbaka ökat markant och det kan därför hända

    att det kommer att byggas betongvägar i huvudleder. Emellertid är erfarenheten i

    Sverige så pass låg att utveckling av nuvarande metoder fordras. USA har länge

    brukat betongvägar i stor skala och har betydligt större mängd betongvägar i

    motsats till Sverige, som har mindre än 1 %. Den ökade trafikmängden speglas

    även på flygplatser.

    I den här studien jämförs den svenska dimensioneringsmetoden för

    betongbeläggning på flygfält (Strand, 2016) med den amerikanska

    dimensioneringsmetoden i syfte att optimera den svenska metoden.

    Den svenska dimensioneringsmetoden (Strand, 2016) som denna studie behandlar

    är förenklad och baserad på gamla teorier. Metoden framställs genom äldre

    litteraturstudier men kombineras även med aktuell litteratur. Den amerikanska

    metoden används genom dess egna datorprogram kallad FAARFIELD där alla

    beräkningar görs med hänsyn till dess normer och krav.

    Dimensioneringen sker för lasten från Airbus A380 med 365 avgångar per år

    enligt Swedavias förväntningar. Oarmerade betongplattor med 350 till 450 mm

    tjocklek med betongkvaliteten C35/45 klarar inte av utmattningskriteriet. Däremot

    klarar likadana plattor med betongkvalitén C60/75 utmattningskraven och

    fungerar utmärkt som beläggning på uppställningsplatser och rullbana. Vid

    dimensionering enligt den amerikanska metoden visar resultaten att plattorna blir

    både tjockare och tunnare än den svenska metoden beroende på vilken

    betongkvalite som används.

    Den svenska metoden förutsätter en del förenklingar vid dimensionering av

    betongbeläggningar och därför blir inte beräkningen helt korrekt. Resultaten som

    denna studie visar är därför preliminära. Optimering av den svenska

    beräkningsgången är ett steg i rätt riktning men det praktiska utförandet av arbetet

    och erfarenheten av detta är något som måste byggas ut för en fulländad och

    fungerande metod i praktiken.

  • 115.
    Ahmad Termida, Nursitihazlin
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi. Universiti Tun Hussein Onn Malaysia, Faculty of Civil and Environmental Engineering, Department of Infrastructure and Geomatic Engineering.
    Understanding Individuals' Learning and Decision Processes in a Changing Environment by Using Panel Data2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    When a new transport service is introduced, people have to learn and familiarize themselves with the new service before they decide to adopt it. These processes are developed over time, thus produce dynamics in individuals’ behavioural responses towards the service. This affects the demand of the new service, thus affect revenues. Available studies have examined the factors influencing these responses from microeconomic perspectives. The influence of the theory-based subjective factors has not been examined empirically. Understanding these would assist transport and urban planners to design a better marketing strategy to increase the market share of the new service. A change in seasons affect individuals’ activity-travel decisions, thus produce dynamics in activitytravel patterns in different seasons. Individuals’ constraints, in a form of mandatory activities (working/studying), are influencing individuals’ decisions to participate in day-to-day nonmandatory activities (leisure and routine activities). The interdependency between travel demand, time allocation and mode choice that considers interactions between mandatory and non-mandatory activities, in different seasons is less explored. Understanding these would assist transport planners and operators to manage travel demand strategies across different seasons of the year and provide better transportation systems for all individuals. This thesis includes five papers. Paper I explores individuals’ characteristics of the quick-response and the adopters of the new public transport (PT) service and examines the temporal effects. Paper II investigates the subjective factors influencing a quick-response to the new PT service by proposing a modified attitude-behaviour framework. Paper III and IV analyse the effects of seasonal variations and individuals’ constraints on their day-to-day activity-travel decisions and patterns. Paper V analyses the attrition and fatigue in the two-week travel diary panel survey instrument.

  • 116.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi. Universiti Tun Hussein Onn Malaysia, Faculty of Civil and Environmental Engineering, Department of Infrastructure and Geomatic Engineering.
    Susilo, Yusak
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi.
    Franklin, Joel
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi.
    Attrition and Fatigue in a Four Waves of Two-Week Travel Diary: A Case Study in Stockholm, SwedenManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    This paper describes a four-wave panel survey design and implementation collected on individual level, consisting of three survey’s instrument namely, self-reported two-week travel diary, on-line psychological questionnaire, and self-reported mental map-related questions. The panel survey is built with the aim to examine individuals’ behavioural changes when a new tram extension line in western sub-urban areas of Stockholm, Sweden, was introduced in October 2013. The survey duration took approximately seven months’ period and the data collected covers all four different seasons of the year, which make it wealth of information. The analysis of attrition and fatigue was done on the two-week travel diary survey instrument only. It is found that the overall attrition rate is 34.3% of the total participants (102 individuals) in the Wave 1 survey, which is considered large. The attrition rate between consecutive waves, however, is considered low which is within the range of 7% to 10%. Based on the binary logit models, there are no systematic tendencies of the dropouts’ characteristics from wave to wave to be found, indicating attrition is purely random. There is no correlation between immobile days and missing trips per day are to be found between-waves. The results of the binary logit model on missing trip show that personal attributes, temporal factors (e.g. weekdays and waves) and travel characteristics (e.g. home-based trip, trip purpose, travel distance and number of inter-modal transfers) significantly affect the missing trip but no indication of fatigue appears.

  • 117.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi. Universiti Tun Hussein Onn Malaysia, Faculty of Civil and Environmental Engineering, Department of Infrastructure and Geomatic Engineering.
    Susilo, Yusak
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi.
    Franklin, Joel
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi.
    Subjective Factors Influencing Individual's Response to a New Public Transport ServiceManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The timing and nature of people’s responses can be expected to vary when a new element enter their environment. For example, when an individual is provided with a new or modified transport service. This time-scale of behavioural responses will affect the patronage of, and short- and long-term demands on the new service over time. Understanding the underlying factors that influence an individual’s response over time to a new or modified transport service would enable us to identify trigger factors that make the new service attractive from an individual’s point of view. Chatterjee (2001) and Douglas (2003) argued that motives other than instrumental factors related to public transport use, such as attitudes, awareness, travel habits and learning processes, can influence individual responses over time to changes in the travel environment. Unfortunately, despite their importance, there have been few studies that examined this argument empirically. To address this research gap, this paper aims to investigate the influences of subjective factors on individuals’ responses to the introduction of a modified public transport (PT) service over time by proposing and testing an alternative model that modifies the theory of planned behaviour (TPB) model framework. This paper also aims to investigate the behavioural change in terms of attitudes and perceptions on individuals’ resources and constraints in using a modified PT service over time after its introduction. The case study involves the new extension of a tram line connecting the suburbs of Alvik and Solna Centrum in Stockholm, Sweden. Four waves of a panel survey were conducted with 96 individuals who lived along the new service, from just before the new service was introduced and until seven months after its introduction. A structural equation modelling technique was used to estimate the relationships between behavioural constructs and panel data, then incorporate them into a discrete choice model. The results show that intention influences individual’s quick-response choice. The panel analysis shows that past behaviour in using the new service influenced current behaviour, and that perceived walking distance in using the service consistently influenced the frequency of using the new service over time.

  • 118.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi. Universiti Tun Hussein Onn Malaysia, Faculty of Civil and Environmental Engineering, Department of Infrastructure and Geomatic Engineering.
    Susilo, Yusak
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi.
    Franklin, Joel
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi.
    Liu, Chengxi
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi. VTI.
    Understanding Seasonal Variation in Individual's Activity Participation and Trip Generation by Using Four Consecutive Two-Week Travel DiaryManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    This paper explores the interactions between travel demand, time allocation and mode choice in different seasons by jointly modeling the work and/or study, routine and leisure activity-travel engagements of 67 individuals in Stockholm, Sweden. A longitudinal panel two-week travel diary data collected in four consecutive waves over a span of seven months period that covers all four different seasons; autumn, winter, spring and summer, were analysed by using simultaneous Tobit models. The model was applied to explore the interactions among each activity-travel indicator, and individuals’ unique characteristics and endogeneity in activity-travel engagements between different seasons were also considered in the model system. The results of models reveal clear trade-offs between mandatory activities (work and/or study) and non-mandatory activities (routine and leisure), regardless of any seasons, although the magnitudes vary between seasons. There is also a positive mutual endogeneity relationship between number of trips and activity duration within the same activity type. The trade-offs between work and/or study trips towards routine and leisure trips are larger in winter and spring respectively, than in other seasons. It is also found that mode effects on travel time for conducting mandatory activity are much larger in spring than in other seasons. However, the effects of public transport and slow modes on travel time for leisure activities are much larger in summer than in other seasons.

  • 119.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap.
    Susilo, Yusak
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap.
    Franklin, Joel P.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap.
    Examining the effects of out-of-home and in-home constraints on leisure activity participation in different seasons of the year2016Ingår i: Transportation, ISSN 0049-4488, E-ISSN 1572-9435, s. 1-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using multi-day, multi-period travel diaries data of 56 days (four waves of two-week diaries) for 67 individuals in Stockholm, this study aims to examine the effects of out-of-home and in-home constraints (e.g. teleworking, studying at home, doing the laundry, cleaning and taking care of other household member[s]) on individuals’ day-to-day leisure activity participation decisions in four different seasons. This study also aims to explore the effects of various types of working schedules (fixed, shift, partial- and full-flexible) on individuals’ decisions to participate in day-to-day leisure activities. A pooled model (56 days) and wave-specific models (14 days in each wave) are estimated by using dynamic ordered Probit models. The effects of various types of working schedules are estimated by using 28 days of two waves’ data. The results show that an individual’s leisure activity participation decision is significantly influenced by out-of-home work durations but not influenced by in-home constraints, regardless of any seasons. Individuals with shift working hours engage less in day-to-day leisure activities than other workers’ types in both spring and summer seasons. The thermal indicator significantly affects individuals’ leisure activity participation decisions during the autumn season. Individuals exhibit routine behaviour characterized by repeated decisions in participating in day-to-day leisure activities that can last up to 14 days, regardless of any seasons.

  • 120.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Transportplanering, ekonomi och teknik.
    Susilo, Yusak O.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Transportplanering, ekonomi och teknik.
    Franklin, Joel P.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Transportplanering, ekonomi och teknik.
    Observing dynamic behavioural responses due to the extension of a tram line by using panel survey2016Ingår i: Transportation Research Part A: Policy and Practice, ISSN 0965-8564, E-ISSN 1879-2375, Vol. 86, s. 78-95Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using a four-wave panel survey of individuals' trips and psychological attributes collected among residents along a new tram line extension in the city of Stockholm, Sweden, this study aims to investigate factors that determine the individuals' learning and decision-making processes in using a new transport option. This includes investigating which group of travellers have used the new tram extension earlier than others, and integrated the tram extension as a part of their daily travel patterns. This paper also describes the design and construction of the four-wave panel data collection, which was collected from two weeks before and up to seven months after the opening of the new option. Descriptive analysis shows that within a seven-month period, 79% of the respondents tried the new tram extension but only 14.9% of them adopted the new option as their daily travel mode. During the observed period, about 49.3% of the respondents migrated between travel modes for non-discretionary trips. Further multivariate analysis shows that middle-income travellers and travellers who owned car(s) used the new tram extension earlier than others. The effect of past experience on the current use of the tram extension on a day-to-day basis was also examined by using a mixed logit model with panel data. The purpose of the model is to examine whether individuals' daily experiences with the new tram extension that result from repeated previous choices would affect their decisions to maintain using the new option in subsequent waves.

  • 121.
    Ahmadi, Zahra
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande, Bygg- och fastighetsekonomi.
    Sundström, Agneta
    The market intelligence impact on strategic performance in declining markets2017Ingår i: International Journal of Applied Business and Economic Research, Vol. 15, nr 15, s. 457-473Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study examines how companies in declining markets operate in the context of market intelligence, responding to customer needs and applying them to strategic performance. A quantitative survey was sent to 214 public housing companies. The results indicate that market intelligence creates commitment and is significant. A positive relationship was found between data gathering, dissemination, and responsiveness, which indicates that the companies comprehend market needs but companies have difficult to manage construction strategies that improve strategic performance. There was a low value of strategic performance; a link between market intelligence and the chosen strategy was not confirmed. Companies know what the market wants but base their decision on previous strategic performance on economic conditions in the municipality instead.

  • 122.
    Ahmed, Abubeker W.
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik. Swedish National Road and Transport Research Institute (VTI).
    Biligiri, Krishna Prapoorna
    Department of Civil Engineering Indian Institute of Technology Kharagpur .
    Hakim, Hassan
    Swedish National Road and Transport Research Institute (VTI).
    An Algorithm to Estimate Rational Values of Phase Angles and Moduli of Asphalt Mixtures2013Ingår i: International Journal of Pavement Research and Technology, ISSN 1996-6814, Vol. 6, nr 6, s. 745-754Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this study was to develop and evaluate an algorithm based on Fast Fourier Transform (FFT) that can calculate rational values of phase angle (f) and moduli of the variants of asphalt mixtures for the data obtained from the different frequency sweep tests. f and moduli for ten different asphalt mixtures resulting in over 690 data points collected from both USA and Sweden were computed using FFT. Theoretical observations revealed that there were significant differences for f between FFT and other methods to the order of 10-50%; however, there was no difference in moduli estimates for any mix and was independent of the test. Precisely, the FFT method produced rational f for mixtures that deviate from conventional mixture properties. Furthermore, statistical comparisons corroborated the predicted f estimates indicative of significant differences between the analysis techniques; but, the moduli were unaffected by the analysis methods. The study successfully illustrated the FFT technique, a user-friendly analytical procedure that can obviate the errors in the rational estimation of the acutely sensitive viscoelastic parameters.

  • 123.
    Ahmed, Abubeker W.
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik. VTI.
    Erlingsson, Sigurdur
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik. VTI.
    Characterization of heavy traffic axle load spectra for mechanistic-empirical pavement design applicationsIngår i: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268XArtikel i tidskrift (Refereegranskat)
  • 124.
    Ahmed, Abubeker W.
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap. Swedish National Road and Transport Research Institute, Sweden.
    Erlingsson, Sigurdur
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap. Swedish National Road and Transport Research Institute, Sweden.
    Evaluation of a permanent deformation model for asphalt concrete mixtures using extra-large wheel tracking and heavy vehicle simulator tests2015Ingår i: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, nr 1, s. 154-171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper evaluates a mechanistic–empirical permanent strain model for asphalt concrete mixtures. The evaluation was carried out based on two different types of tests: an extra-large wheel-tracking (ELWT) test and a full-scale accelerated pavement test using a heavy vehicle simulator (HVS). Asphalt slabs from three different types of asphalt mixtures were prepared for the ELWT test and tested at several pavement temperatures and tyre inflation pressures. Lateral wandering was also incorporated. The measured permanent deformations in the asphalt slabs were thereafter modelled using the permanent strain model from the US Mechanistic-Empirical Pavement Design Guide and model parameters were estimated for the three types of mixes. For validation, data from an HVS tested pavement structure consisting of the same asphalt mixtures as those tested using the ELWT were used. A set of calibration factors for the three mixtures were therefore obtained between the two tests. In all cases, the calibration factors were within ±20% from unity. Differences in geometry, scale, wheel loading configuration as well as the speed of loading between the two test devices could be the possible reasons for the differences in observed calibration factors.

  • 125.
    Ahmed, Abubeker W.
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Erlingsson, Sigurdur
    Evaluation of permanent deformation models for unbound granular materials using accelerated pavement tests2013Ingår i: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, nr 1, s. 178-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mechanistic-empirical (M-E) pavement design methods have become the focus of modern pavement design procedure. One of the main distresses that M-E design methods attempt to control is permanent deformation (rutting). The objective of this paper is to evaluate three M-E permanent deformation models for unbound granular materials, one from the US M-E pavement design guide and two other relatively new models. Two series of heavy vehicle simulator (HVS) tests with three different types of base material were used for this purpose. The permanent deformation, wheel loading, pavement temperature, and other material properties were continuously controlled during the HVS tests. Asphalt concrete layers were considered as linear elastic where stress-dependent behaviour of unbound materials was considered when computing responses for the M-E permanent deformation models with a nonlinear elastic response model. Traffic wandering was also accounted for in modelling the traffic by assuming it was normally distributed and a time-hardening approach was applied to add together the permanent deformation contributions from different stress levels. The measured and predicted permanent deformations are in general in good agreement with only small discrepancies between the models. Model parameters were also estimated for three different types of material.

  • 126.
    Ahmed, Abubeker W.
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik. Swedish National Road and Transport Research Institute, Pavement Technology, VTI, Linköping, Sweden .
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Pavement Technology, VTI, Linköping, Sweden .
    Modeling of flexible pavement structure behavior - Comparisons with Heavy Vehicle Simulator measurements2012Ingår i: Advances in Pavement Design Through Full-Scale Accelerated Pavement Testing - Proceedings of the 4th International Conference on Accelerated Pavement Testing, 2012, s. 493-503Konferensbidrag (Refereegranskat)
    Abstract [en]

    A response model to be employed in a mechanistic-empirical pavement performance prediction model based on multilayer elastic theory has been developed.An iterative approach using a method of successive over-relaxation of a stress dependency model is used to account for the nonlinear behavior of unbound materials. Asphalt and subgrade materials are assumed to be linear elastic. The response model was verified against two series of Heavy Vehicle Simulator (HVS) response measurements made under a variety of wheel load configurations and at different pavement temperatures.A comparison with FallingWeight Deflectometer (FWD) data was also carried out. The model was subsequently used to predict permanent deformation from the HVS testing using simplework hardening models.Atime hardening approach has been adopted to combine permanent deformation contributions from stress levels of different magnitude.The response model outputs and the predicted permanent deformations were generally in good agreement with the measurements.

  • 127.
    Ahmed, Abubeker W.
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vägtekniks laboratorium. Swedish National Road and Transport Research Institute, Sweden.
    Erlingsson, Sigurdur
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vägtekniks laboratorium. Swedish National Road and Transport Research Institute, Sweden.
    Numerical validation of viscoelastic responses of a pavement structure in a full-scale accelerated pavement test2017Ingår i: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 18, nr 1, s. 47-59Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper demonstrates the application of a generalised layered linear viscoelastic (LVE) analysis for estimating the structural response of flexible pavements. A comparison of the direct layered viscoelastic responses with approximate solutions based on the linear elastic (LE) and LVE collocation methods was also carried out. The different approaches were implemented by extending a layered elastic program with an improved computational performance. The LE and LVE collocation methods were further extended for analysis of pavements under moving loads. The methods were illustrated by analysing a pavement structure subjected to moving wheel loads of 30, 50, 60 and 80kN using a Heavy Vehicle Simulator (HVS). The various responses (stresses and strains) in the pavement, at pavement temperatures of 0, 10 and 20 degrees C, were measured using various types of sensors installed in the structure. It was shown that the approximated LVE solution based on the LE collocation method agreed very well with the measurements and is computationally the least expensive.

  • 128.
    Ahmed, Abubeker W.
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik. VTI.
    Erlingsson, Sigurdur
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik. VTI.
    Viscoelastic modelling of pavement structure behaviour in a full scale accelerated pavement testManuskript (preprint) (Övrigt vetenskapligt)
  • 129.
    Ahmed, Abubeker Worake
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Mechanistic-Empirical Modelling of Flexible Pavement Performance: Verifications Using APT Measurements2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Mechanistic-Empirical  (M-E)  pavement  design  procedures  are  composed  of  a  reliable  response model to estimate the state of stress in the pavement and distress models in order to predict the different types of pavement distresses due to the prevailing traffic and environmental conditions. One of the main objectives of this study was to develop a response model based on multilayer elastic  theory   (MLET)  with  improved  computational  performance  by   optimizing  the   time consuming parts of the MLET processes. A comprehensive comparison of the developed program with  two  widely  used  programs  demonstrated  excellent  agreement  and  improved  computational performance.  Moreover,  the  program  was  extended  to  incorporate  the  viscoelastic  behaviour  of bituminous materials through elastic-viscoelastic correspondence principle. A procedure based on collocation of linear viscoelastic (LVE) solutions at selected key time durations was also proposed that improved the computational performance for LVE analysis of stationary and moving loads. A comparison  of  the  LVE  responses  with  measurements  from  accelerated  pavement  testing  (APT) revealed a good agreement. Furthermore the developed response model was employed to evaluate permanent deformation models  for  bound  and  unbound  granular  materials  (UGMs)  using  full  scale  APTs.  The  M-E Pavement  Design  Guide  (MEPDG)  model  for  UGMs  and  two  relatively  new  models  were evaluated  to  model  the  permanent  deformation  in  UGMs.  Moreover,  for  bound  materials,  the simplified  form  of  the  MEPDG  model  for  bituminous  bound  layers  was  also  evaluated.  The measured  and  predicted  permanent  deformations  were  in  general  in  good  agreement,  with  only small discrepancies between the models. Finally, as heavy traffic loading is one of the main factors affecting the performance of flexible pavement, three types of characterizations for heavy traffic axle load spectrum for M-E analysis and design of pavement structures were evaluated. The study recommended an improved approach that enhanced the accuracy and computational performance. 

  • 130.
    Ahmed, Fuad
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    Tabatabaei Araghi, Pedram
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    Radonfritt boende: Stegen till att eliminera radongas med rätt Grundläggningsmetod2012Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    People who live in northern part of the world spend much more time indoors than those who live in warmer countries. In addition that home should be safe, it should also protect one against heat, cold, sunlight and pollution. The indoor environment is affected by installations, material and how the building is formed. Those anomalies that are visible, felt or smelled can be noticed and be rectified. But it’s much more difficult if these abilities are missing. Building houses in Sweden means that you have restrictions to follow. One has to adapt its house so that Swedish standards are maintained. Planning’s Building Regulation must be followed. Planning and Building Act and regulations must be met. Account has been takes for these provisions during the planning and design stage of the house. The following thesis will describe how various parameters have interacted for the design of the house. In depth the essay will illustrate how to build a radon resistant house and address how the air we inhale in our homes may eventually be harmful and finally how this problem is seen globally. International studies show that radon gas in indoor air increases the risk of getting lung cancer. By 2020, all single-family homes and public facilities must be remediated to a statutory value annual average level. It is one of sixteen environmental requirements that the parliament has set as a target for indoor environment. The National Board of health and Welfare has a guideline as a recommendation for indoor radon for existing homes while Planning´s Building Regulation has a limit for new constructions, which is binding. The quality of accommodation differs worldly. According to the Radiation Authority radon gas is attributed to 15 % of all peace lung cancer cases per year in Sweden. The percentage increases with population. Radon gas enters through foundation, through well water used in household and through building materials. Planning

    and Building Regulations survey 2010 showed that people are exposed to the highest radon levels at home. Consumers are becoming more aware of the risk of exposure to high radon levels over long period. New dwellings of radon resistant homes would benefit both producers and consumers. Before this goal will be achieved one has to know the significance choice of foundation. Result show that crawlspace is the most effective foundation method to radon build radon resistant homes.

  • 131. Ahmed, K. M.
    et al.
    Bhattacharya, Prosun
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Miljögeokemi och ekoteknik.
    Hasan, M. A.
    Rahman, M
    von Brömssen, Mattias
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Miljögeokemi och ekoteknik.
    Jacks, Gunnar
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Miljögeokemi och ekoteknik.
    Hossain, Mohammed
    Islam, M. Mainul
    Rahman, Marina
    Rashid, S.M.A.
    Sustainable Arsenic Mitigation (SASMIT) in Bangladesh: The Matlab strategy2010Ingår i: Abstracts with programs (Geological Society of America), ISSN 0016-7592, Vol. 42, nr 5, s. 652-Artikel i tidskrift (Övrigt vetenskapligt)
  • 132. Ahmed, K. M.
    et al.
    Sultana, S.
    Hasan, M. A.
    Bhattacharya, Prosun
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik (flyttat 20130630), Miljögeokemi och ekoteknik.
    Hasan, M. K.
    Burgess, W. K.
    Hoque, M. A.
    Groundwater quality contrasts between Upper and Lower Dupi Tila Aquifers in Megacity Dhaka, Bangladesh2011Ingår i: Groundwater quality contrasts between Upper and Lower Dupi Tila Aquifers in Megacity Dhaka, Bangladesh: Proc. 7th International Groundwater Quality Conference, 2011, s. 71-74Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dhaka is one of the fastest growing megacities of the world and is set to become the third largest by 2025. Currently about 86% of the municipal water supply comes from over 500 wells drilled in the Dupi Tila aquifers underlying the city. The Upper Dupi Tila aquifer (UDTA) is overexploited and a large part has been dewatered; abstractions from the lower Dupi Tila started only recently. Results of water analysis and EC surveys have been used to decipher the variations in groundwater quality in the UDTA and LDTA. EC surveys reveal a systematic deterioration of water quality in the vicinity of the Buriganga River in southeast Dhaka. The UDTA is more widely affected by anthropogenic processes than the LDTA, which still largely exhibits its intrinsic water quality characteristics. Regular monitoring and proper management practices are essential to protect the quality of this precarious resource.

  • 133.
    Ahmed, K. Matin
    et al.
    Univ Dhaka, Dept Geol.
    Bhattacharya, Prosun
    KTH, Tidigare Institutioner, Mark- och vattenteknik.
    Hasan, Md. Aziz
    Univ Dhaka, Dept Geol.
    Akhter, S. Humayun
    Univ Dhaka, Dept Geol.
    Alam, S. M. Mahbub
    Univ Dhaka, Dept Geol.
    Bhuyian, M. A. Hossain
    Univ Dhaka, Dept Geol.
    Imam, M. Badrul
    Univ Dhaka, Dept Geol.
    Khan, Aftab A.
    Univ Dhaka, Dept Geol.
    Sracek, Ondra
    Masaryk Univ, Fac Sci, Dept Mineral Petrol & Geochem.
    Arsenic enrichment in groundwater of the alluvial aquifers in Bangladesh: an overview2004Ingår i: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 19, nr 2, s. 181-200Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arsenic in the groundwater of Bangladesh is a serious natural calamity and a public health hazard. Most groundwater from the shallow alluvial aquifers (<150 m), particularly in the Holocene plain lands, are vulnerable to As-enrichment. Delta plains and flood plains of the Ganges-Brahmaputra river system are moderately to severely enriched and more than 60% of the tube wells are affected. Shallow aquifers in the Meghna river basin and coastal plains are extremely enriched with more than 80% of the tube wells affected. Aquifers in the Pleistocene uplands and Tertiary hills are low in As. The vertical lithofacies sequence of the sediments from highly enriched areas of the country show two distinct lithofacies associations-a dominantly sandy channel-fill association and a fine-grained over bank association. The sediments can be grouped into 4 distinct lithofacies, viz. clay, silty clay, silty sand and sand. Thin section petrography of the As-enriched aquifer sands shows that the sands are of quartzolithic type and derived from the collision suture and fold thrust belt of the recycled orogen provenance. Groundwater is characterized by circum-neutral pH with a moderate to strong reducing nature. The waters are generally of Ca-Mg-HCO3 or Ca-Na-HCO3 type, with HCO3- as the principal anion. Low SO42- and NO3-, and high dissolved organic C (DOC) and NH4+ concentrations are typical chemical characteristics of groundwater. The presence of dissolved sulfides in these groundwaters indicates reduction Of SO4. Total As concentration in the analyzed wells vary between 2.5 and 846 mug l(-1) with a dominance of As(III) species (67-99%). Arsenic(III) concentrations were fairly consistent with the DOC and NH4+ contents. The HNO3 extractable concentrations of As (As-NO3) in the sediments (0.5-17.7 mg kg(-1)), indicate a significant positive correlation with Fe-NO3, Mn-NO3, Al-NO3 and P-NO3. The concentrations Of S-NO3 (816-1306 mg kg(-1)) peaked in the clay sediments with high organic matter (up to 4.5 wt.%). Amounts of oxalate extractable As (As..) and Fe (Fe x) ranged between 0.1-8.6 mg kg(-1) and 0.4-5.9 g kg(-1), respectively. Arsenic(ox) was positively correlated with Fe-ox, Mn-ox, and Al-ox in these sediments. Insignificant amounts of opaque minerals (including pyrite/arsenopyrite) and the presence of high As contents in finer sediments suggests that some As is incorporated in the authigenically precipitated sulfides in the reducing sediments. Moreover, the chemical extractions suggest the presence of siderite and vivianite as solid phases, which may control the aqueous chemistry of Fe and PO43-. Reductive dissolution of Fe oxyhydroxide present as coatings on sand grains as well as altered mica (biotite) is envisaged as the main mechanism for the release of As into groundwater in the sandy aquifer sediments.

  • 134.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    Impact-type vibration effects on young concrete for tunnelling2016Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The strive for a time-efficient construction process naturally put focus on the possibility of reducing the time of waiting between stages of construction, thereby minimizing the construction cost. If recently placed concrete, cast or sprayed, is exposed to impact vibrations at an early age while still in the process of hardening, damage that threatens the function of the hard concrete may occur. A waiting time when the concrete remains undisturbed, or a safe distance to the vibration source, is therefore needed. However, there is little, or no, fully proven knowledge of the length of this distance or time and there are no established guidelines for practical use. Therefore, conservative vibration limits are used for young and hardening concrete exposed to vibrations from e.g. blasting.

    As a first step in the dynamic analysis of a structure, the dynamic loads should always be identified and characterized. Here it is concluded that impact-type loads are the most dangerous of possible dynamic loads on young and hardening concrete. Shotcrete (sprayed concrete) on hard rock exposed to blasting and cast laboratory specimens subjected to direct mechanical impact loads have been investigated using finite element models based on the same analysis principles. Stress wave propagation is described in the same way whether it is through hard rock towards a shotcrete lining or through an element of young concrete.

    Within this project, work on evaluating and proposing analytical models are made in several steps, first with a focus on describing the behaviour of shotcrete on hard rock. It is demonstrated that wave propagation through rock towards shotcrete can be described using two-dimensional elastic finite element models in a dynamic analysis. The models must include the material properties of the rock and the accuracy of these parameters will greatly affect the results. It is possible to follow the propagation of stress waves through the rock mass, from the centre of blasting to the reflection at the shotcrete-rock interface. It is acceptable to use elastic material formulations until the strains are outside the elastic range, which thus indicates imminent material failure. Comparisons are made between numerical results and measurements from experiments in mining tunnels with ejected rock mass and shotcrete bond failure, and with measurements made during blasting for tunnel construction where rock and shotcrete remained intact. The calculated results are in good correspondence with the in situ observations and measurements, and with previous numerical modelling results. Examples of preliminary recommendations for practical use are given and it is demonstrated how the developed models and suggested analytical technique can be used for further detailed investigations.

  • 135.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Laboratorieprovningar av stötbelastade betongprismor vid tidig ålder2015Ingår i: Tidskriften Betong, ISSN 1101-9190, nr 5, s. 51-54Artikel i tidskrift (Övrigt vetenskapligt)
  • 136.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Laboratory simulation of blasting induced bond failure between rock and shotcrete2012Rapport (Refereegranskat)
  • 137.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Modelleringsverktyg hittar sprickor2015Ingår i: Tidskriften Betong, ISSN 1103-4270, nr 5, s. 51-54Artikel i tidskrift (Refereegranskat)
  • 138.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Models for analysis of shotcrete on rock exposed to blasting2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Inom undermarks- och tunnelbyggande leder strävan efter en mer tidseffektiv byggprocess till fokus på möjligheten att reducera väntetiderna mellan byggetapper. Möjligheten att projicera sprutbetong på bergytor i ett tidigt skede efter sprängning är avgörande för säkerheten under konstruktionen av t.ex. en tunnel. En komplikation uppstår när behovet av ytterligare sprängning kan påverka härdningen av nysprutad betong. Om betong, gjuten eller sprutad, utsätts för vibrationer i ett tidigt skede under härdningsprocessen kan skador som hotar funktionen hos den hårdnade betongen uppstå. Kunskapen i ämnet är knapphändig, eller obefintlig, och det finns inga etablerade riktlinjer för praktisk användning.

    Slutsatsen från tidigare undersökningar visar att sprutbetong kan tåla höga vibrationer (partikelhastigheter) utan att allvarliga skador uppstår. Oarmerad sprutbetong kan vara oskadd efter att ha utsatts för så höga vibrationsnivåer som 0,5–1 m/s medan partier med förlorad vidhäftning till berget kan uppträda vid vibrationshastigheter högre än 1 m/s. Funktionen hos ung och hårdnande sprutbetong som utsätts för höga vibrationsnivåer undersöks här för att identifiera säkra avstånd och sprutbetongåldrar för undermarks- och tunnelbyggande, med hjälp av numeriska analyser och jämförelser med mätningar och observationer. Arbetet fokuserar på att finna samband mellan numeriska resultat, mätresultat och observationer från tunnelbyggande. Det slutliga resultatet kommer att vara riktlinjer för praktisk användning.

    Projektet omfattar utveckling av sofistikerade dynamiska finita elementmodeller för vilka insamlad information och data kommer att användas som indata för det finita elementprogrammet Abaqus. Modellerna utvärderades och förfinats genom jämförelser mellan beräknade och uppmätta resultat. Först jämfördes befintliga enkla mekaniska, ingenjörsmässiga modeller vilka utvärderades genom beräkningar och jämförelser med befintliga data. Den första modellen är en strukturdynamisk modell bestående av massor och fjäderelement. Den andra är en modell uppbyggd av finita balkelementet sammankopplade med fjädrar. Den tredje är en endimensionell elastisk spänningsvågsmodell. Spänningstillståndet i sprutbetongen närmast berget, utsatt för vinkelrätt inkommande P-vågor simulerades. Resultat från icke-förstörande laborationsprovningar användes också som testdata för modellerna. Experimentellt studerades P-vågsutbredning i en betongbalk med egenskaper likvärdiga med berg. Cementbruk med egenskaper liknande sprutbetong applicerades på balkens ena ände medan en hammare användes i den andra. Formen hos den genererade spänningsvågen som propagerade mot sprutbetongänden registrerades med accelerometrar utplacerade längs balken.

    På grund av bergets inhomogena karaktär kommer spänningsvågorna från sprängningen att dämpas ut på vägen från detonationspunkten till sprutbetongen på bergytan. Materialdämpningen hos bergmassan måste därför beaktas och kan uppskattas utifrån resultat från fältmätningar. Vibrationståligheten hos förstärkningssystem av sprutbetong och berg beror av materialegenskaperna hos sprutbetongen och i den här studien varierades de åldersberoende egenskaperna för att undersöka beteendet hos nysprutad och hårdnande sprutbetong utsatt för sprängbelastning. De numeriska simuleringarna kräver realistiska materialdata för sprutbetong och berg, som t.ex. densitet och elasticitetsmodul.

    De beräknade resultaten var i god överensstämmelse med observationer och mätningar i fält plats, och med de tidigare numeriska resultaten. Jämfört med de mekaniska modellerna kan ett sofistikerat finit elementprogram underlätta modellering av mer komplexa geometrier och också ge mer detaljerade resultat. Det visades att vågutbredning genom berg och fram emot sprutbetong kan beskrivas med tvådimensionella elastiska finita element i en dynamisk analys. Modellerna måste beskriva bergets egenskaper och noggrannheten i dessa parametrar kommer att ha stor inverkan på resultaten. Det kommer att vara möjligt att beskriva vågutbredningen genom bergmassan, från detonationspunkten till reflektionen vid bergytan, det vill säga gränssnittet mellan sprutbetong och berg. Det är acceptabelt att använda elastiska materialformuleringar tills materialet elasticitetsgräns överskrids tills töjningar utanför det elastiska området nås, vilket därmed indikerar materialbrott.

    Den högre komplexiteten hos den här typen av modell, jämfört med de mekaniska modellerna, kommer att göra det möjligt att analysera mer komplexa tunnelgeometrier. Exempel på preliminära rekommendationer för praktiskt bruk ges och det visas hur de utvecklade modellerna och den föreslagna analysmetodiken kan användas för att fastställa ytterligare detaljerade gränsvärden.

  • 139.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Models for analysis of young cast and sprayed concrete subjected to impact-type loads2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The strive for a time-efficient construction process naturally put focus on the possibility of reducing the time of waiting between stages of construction, thereby minimizing the construction cost. If recently placed concrete, cast or sprayed, is exposed to impact vibrations at an early age while still in the process of hardening, damage that threatens the function of the hard concrete may occur. A waiting time when the concrete remains undisturbed, or a safe distance to the vibration source, is therefore needed. However, there is little, or no, fully proven knowledge of the length of this distance or time and there are no established guidelines for practical use. Therefore, conservative vibration limits are used for young and hardening concrete exposed to vibrations from e.g. blasting.

    As a first step in the dynamic analysis of a structure, the dynamic loads should always be identified and characterized. Here it is concluded that impact-type loads are the most dangerous of possible dynamic loads on young and hardening concrete. Shotcrete (sprayed concrete) on hard rock exposed to blasting and cast laboratory specimens subjected to direct mechanical impact loads have been investigated using finite element models based on the same analysis principles. Stress wave propagation is described in the same way whether it is through hard rock towards a shotcrete lining or through an element of young concrete. However, the failure modes differ for the two cases where shotcrete usually is damaged through loss of bond, partly or over larger sections that may result in shotcrete downfall. Cracking in shotcrete due to vibrations only is unusual and has not been observed during previous in situ tests. The study of shotcrete is included to demonstrate the need of specialized guidelines for cases other than for mass concrete, i.e. structural elements or concrete volumes with large dimensions in all directions.

    Within this project, work on evaluating and proposing analytical models are made in several steps, first with a focus on describing the behaviour of shotcrete on hard rock. It is demonstrated that wave propagation through rock towards shotcrete can be described using two-dimensional elastic finite element models in a dynamic analysis. The models must include the material properties of the rock and the accuracy of these parameters will greatly affect the results. It is possible to follow the propagation of stress waves through the rock mass, from the centre of blasting to the reflection at the shotcrete-rock interface. It is acceptable to use elastic material formulations until the strains are outside the elastic range, which thus indicates imminent material failure. The higher complexity of this type of model, compared with mechanical models using mass and spring elements, makes it possible to analyse more sophisticated geometries. Comparisons are made between numerical results and measurements from experiments in mining tunnels with ejected rock mass and shotcrete bond failure, and with measurements made during blasting for tunnel construction where rock and shotcrete remained intact. The calculated results are in good correspondence with the in situ observations and measurements, and with previous numerical modelling results. Examples of preliminary recommendations for practical use are given and it is demonstrated how the developed models and suggested analytical technique can be used for further detailed investigations.

    The modelling concept has also been used for analysis of impact loaded beams and concrete prisms modelled with 3D solid elements. As a first analysis step, an elastic material model was used to validate laboratory experiments with hammer-loaded concrete beams. The laboratory beam remained un-cracked during the experiments, and thus it was possible to achieve a good agreement using a linear elastic material model for fully hardened concrete. The model was further developed to enable modelling of cracked specimens. For verification of the numerical results, earlier laboratory experiments with hammer impacted smaller prisms of young concrete were chosen. A comparison between results showed that the laboratory tests can be reproduced numerically and those free vibration modes and natural frequencies of the test prisms contributed to the strain concentrations that gave cracking at high loads. Furthermore, it was investigated how a test prism modified with notches at the middle section would behave during laboratory testing. Calculated results showed that all cracking would be concentrated to one crack with a width equal to the sum of the multiple cracks that develop in un-notched prisms. In laboratory testing, the modified prism will provide a more reliable indication of when the critical load level is reached.

    This project has been interdisciplinary, combining structural dynamics, finite element modelling, concrete material technology, construction technology and rock support technology. It is a continuation from previous investigations of the effect on young shotcrete from blasting vibrations but this perspective has been widened to also include young, cast concrete. The outcome is a recommendation for how dynamic analysis of young concrete, cast and sprayed, can be carried out with an accurate description of the effect from impact-type loads. The type of numerical models presented and evaluated will provide an important tool for the work towards guidelines for practical use in civil engineering and concrete construction work. Some recommendations on safe distances and concrete ages are given, for newly cast concrete elements or mass concrete and for newly sprayed shotcrete on hard rock.

  • 140.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Vulnerability of shotcrete on tunnel walls during construction blasting2018Konferensbidrag (Refereegranskat)
  • 141.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ökad kunskap om sprutbetong ger hållbara tunnlar2012Ingår i: Tidskriften Betong, nr 6, s. 50-52Artikel i tidskrift (Refereegranskat)
  • 142.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    A comparison of models for shotcrete in dynamically loaded rock tunnels2010Ingår i: Shotcrete: Elements of a system / [ed] E. Stefan Bernard, Taylor & Francis Group, 2010, s. 1-10Konferensbidrag (Refereegranskat)
    Abstract [en]

    During blasting in tunnels and mines, the shotcrete-rock interaction is influenced by propagating stress waves. Shotcrete support in hard rock tunnels is here studied through numerical analysis and comparisons with previous numerical results, measurements and observations in situ. The stress response in the shotcrete closest to the rock when exposed to P-waves striking perpendicularly to the shotcrete-rock interface is simulated. The first model tested is an elastic stress wave model, which is onedimensional with the shotcrete assumed linearly elastic. The second is a structural dynamic model that consists of masses and spring elements. The third model is a finite element model implemented using the Abaqus/Explicit program. Two methods are used for the application of incident disturbing stress waves: as boundary conditions and as inertia loads. Results from these three types of models are compared and evaluated as a first step before a future extension to more detailed analyses using 3D models.

  • 143.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Behaviour of sprayed concrete on hard rock exposed to vibration from blasting operations2014Konferensbidrag (Refereegranskat)
  • 144.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Direct shear strength of high-strength fibre concrete2010Ingår i: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 62, nr 5, s. 379-390Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental and theoretical study of the shear behaviour of steel-fibre-reinforced concrete is presented. Twenty-seven direct shear push-off tests were carried out on high-strength concrete, with and without steel fibre reinforcement. The test series contained uncracked and precracked specimens for the study of the slipping response and the shear stress that can be transferred across an open crack. The test variables were the fibre content and the reinforcement ratio. The test results were compared with information provided by the available codes and other, previous results. The test results indicated that incorporation of steel fibres and bars in concrete members subjected to shear leads to an improved mechanical behaviour before failure. Based on the presented experimental results, an equation governing the direct shear strength is proposed and verified against test results from other test series.

  • 145.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Dynamic measurements for determination of Poisson’sratio of young concrete2017Konferensbidrag (Refereegranskat)
  • 146.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Experimental and numerical investigation of stress wave propagation in shotcrete2011Ingår i: Nordic concrete research: Research projects 2011 / [ed] D.H. Bager, 2011, s. 59-62Konferensbidrag (Refereegranskat)
  • 147.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Laboratory investigation of stress waves in young shotcrete on rock2012Ingår i: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 64, nr 10, s. 899-908Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To study the behaviour of shotcrete under dynamic load, a non-destructive laboratory experiment was set up with P-wave propagation along a concrete bar, with properties similar to rock. Cement-based mortar with properties that resemble shotcrete was applied to one end of the bar with a hammer impacting the other. The shape of the stress waves travelling towards the shotcrete was registered using accelerometers positioned along the bar. Finite-element modelling was used to verify the test results, which showed that the laboratory model with an impacting hammer could be used to initiate the same type of stress waves that result from blasting in good-quality rock. Previously recommended maximum allowed peak particle vibration velocities were verified.

  • 148.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Structural dynamic and stress wave models for analysis of shotcrete on rock exposed to blasting2012Ingår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 35, nr 1, s. 11-17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During blasting in tunnels and mines, the interaction between shotcrete (sprayed concrete) and rock is influenced by propagating stress waves. Shotcrete support in hard rock tunnels is studied here through numerical analysis using three different modelling approaches. The stress response in the shotcrete closest to the rock when exposed to P-waves striking perpendicularly to the shotcrete–rock interface is simulated. The first model tested is a structural dynamic model that consists of masses and spring elements. The second is a model built up with finite element beam elements interconnected with springs. The third is a one-dimensional elastic stress wave model. The models give comparable results, although the definition of the dynamic loads is different. The analysis results can be used to estimate whether the shotcrete will fail or not for a prescribed distance to detonating explosives inside the rock.

  • 149.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Vibration vulnerability of shotcrete on tunnel walls during construction blasting2014Ingår i: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 42, s. 105-111Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect on shotcrete from blasting operations during tunnelling is studied, with focus on young and hardening shotcrete. A finite element model specially adapted for analysis of the shotcrete behaviour is tested, it is able to describe stress wave propagation in two dimensions which is important for cases where shear stresses are dominant. The modelling results are compared with in situ measurements and observations, from construction blasting during tunnelling through hard rock. The comparison shows that the model gives realistic results and can be used to investigate the vulnerability of shotcrete, aiming at compiling recommendations and guidelines for practical use. The given recommendations emphasize that blasting should be avoided during the first 12 h after shotcreting and that distance and shotcrete thickness are important factors for how much additional time of waiting is possibly needed.

  • 150.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Malm, Richard
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Numerical modelling and evaluation of laboratory tests with impact loaded young concrete prisms2016Ingår i: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, ISSN 1359-5997, Vol. 49, nr 11, s. 4691-4704Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Numerical modelling in combination with in situ measurements, observations and laboratory testing will be important to future establishment of reliable guidelines for efficient civil and engineering work involving concrete casting close to e.g. blasting operations. Results from laboratory tests with impact loaded young concrete prisms are here evaluated using a 3D finite element model. Solid elements are used and a non-linear material model implemented, capable of describing cracking during stress wave propagation. The position of cracks and measured particle vibration velocities are calculated and compared with laboratory test results. The damaging effect of impact vibrations is evaluated using crack width and fracture energy as damage criteria. Alternative geometry for the test prisms, with a notched section, is analysed. This will give one wide crack at the centre of the prism instead of two or three cracks distributed over its length which will make future laboratory test more efficient and reliable. Recommended damage limits at concrete ages of 4, 6, 8 and 12 h are given, based on numerical calculations for concrete strength class C25 and C50.

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