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  • 151.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics. Universiti Tun Hussein Onn Malaysia, Faculty of Civil and Environmental Engineering, Department of Infrastructure and Geomatic Engineering.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Franklin, Joel
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Attrition and Fatigue in a Four Waves of Two-Week Travel Diary: A Case Study in Stockholm, SwedenManuscript (preprint) (Other academic)
    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.

  • 152.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics. Universiti Tun Hussein Onn Malaysia, Faculty of Civil and Environmental Engineering, Department of Infrastructure and Geomatic Engineering.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Franklin, Joel
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Subjective Factors Influencing Individual's Response to a New Public Transport ServiceManuscript (preprint) (Other academic)
    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.

  • 153.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics. Universiti Tun Hussein Onn Malaysia, Faculty of Civil and Environmental Engineering, Department of Infrastructure and Geomatic Engineering.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Franklin, Joel
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Liu, Chengxi
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics. VTI.
    Understanding Seasonal Variation in Individual's Activity Participation and Trip Generation by Using Four Consecutive Two-Week Travel DiaryManuscript (preprint) (Other academic)
    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.

  • 154.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Franklin, Joel P.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Examining the effects of out-of-home and in-home constraints on leisure activity participation in different seasons of the year2016In: Transportation, ISSN 0049-4488, E-ISSN 1572-9435, p. 1-25Article in journal (Refereed)
    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.

  • 155.
    Ahmad Termida, Nursitihazlin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Susilo, Yusak O.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Franklin, Joel P.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Observing dynamic behavioural responses due to the extension of a tram line by using panel survey2016In: Transportation Research Part A: Policy and Practice, ISSN 0965-8564, E-ISSN 1879-2375, Vol. 86, p. 78-95Article in journal (Refereed)
    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.

  • 156.
    Ahmadi Achachlouei, Mohammad
    et al.
    School of Engineering, Industrial Engineering Department, Tarbiat Modares University, P.O. Box 14155-4838 Tehran, Iran.
    Chaharsooghi, K.
    School of Engineering, Industrial Engineering Department, Tarbiat Modares University, P.O. Box 14155-4838 Tehran, Iran.
    Developing life-cycle phases for the DoDAF using ISO15704 Annex A (GERAM)2011In: Computers in industry (Print), ISSN 0166-3615, E-ISSN 1872-6194, Vol. 62, no 3, p. 253-259Article in journal (Refereed)
    Abstract [en]

    This paper presents a development of the US Department of Defense Architecture Framework (DoDAF) based on life-cycle concept of the Generalized Enterprise Reference Architecture and Methodology (GERAM) framework/ISO 15704:2000 requirements. Previous research has identified areas of concern within DoDAF by analyzing and evaluating DoDAF against GERAM and potentially assisting in its future development. This paper aims to extend existing architecture description process and artifacts within DoDAF that match the scope of the GERAM life-cycle phases. For this development we use life-cycle aspect of three well-known reference architectures (including PERA, CIMOSA, and GRAI-GIM) that were the basis in formation of GERAM.

  • 157.
    Ahmadi, Alireza
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Discrete element technique for modeling high-speed railway tracks2023Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Discrete element method (DEM) is a methodology to investigatethe interactions among granular materials. It analyzes the behavior of par-ticulate environments by solving force-displacement equations that adhereto Newton’s second law of motion. Despite its usefulness, the DEM is notwithout limitations, and researchers are still facing certain challenges thatrestrict them from performing detailed analyses of granular materials. Thisstudy addresses two issues in DEM modeling of granular materials in rail-way embankments. Firstly, the long computational time required by theDEM for modeling fine angular particles in granular materials is addressedby exploring the effects of particle scaling on the shear behavior of granularmaterial. This study investigates the impact of particle size distribution,particle angularity, and the amount of scaling on the accuracy and compu-tational efficiency of DEM. Secondly, the limitations of DEM in includingthe continuous rail beam structure in the track are addressed by verifyinga DEM model against physical measurements of a full-scale ballasted trackand investigating the influence of including the rail beam structure on high-speed railway ballasted tracks. The results show that the use of particlescaling in the first study significantly improves the computational efficiencyof the DEM while maintaining accuracy, and this method is used in thesecond study to investigate the influence of the rail beam structure on thebehavior of railway tracks.

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  • 158.
    Ahmadi, Zahra
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Building and Real Estate Economics.
    Sundström, Agneta
    The market intelligence impact on strategic performance in declining markets2017In: International Journal of Applied Business and Economic Research, ISSN 0972-7302, Vol. 15, no 15, p. 457-473Article in journal (Refereed)
    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.

  • 159.
    Ahmadiyan, Sara
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Mehari, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Estimation of the characteristic in-situ compressive strength class of concrete structures - A case study of the Skuru bridge2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    It is inevitable that Structures become older and their intended use changes or the structuralcodes regulations change. In some regions the damage from seismic activities is a possibility.It becomes, therefore crucial to assess the structural capacity of such structures. The purposeof this study is to assess the different methods used for testing and estimating thecharacteristic in-situ compressive strength which is the most vital parameter required instructural assessment.

    The focus of the study is for existing structures where there is no prior knowledge about theconcrete strength. This study first investigates and evaluates the merits and demerits of thesemethods for investigation of the condition of in-situ compressive strength of concrete inexisting structures. A case study of the Skuru bridge that was built in 1914 was utilized forthis study. The study is based on information of the construction data and some results fromprior investigation performed by the company COWI. Afterwards, non-destructive tests werecarried out with the UPV and Rebound hammer to assess the quality of the concrete.

    In addition, the study assesses the use of different interpretation methods with regards toreliability and practical application. The results were interpreted in accordance to theEuropean codes, Swedish codes and other interpretation methods. The difference of theresults from the different interpretation methods are compared and evaluated for reliabilityand efficiency.

    The test results confirmed that the concrete consisted of the same strength class. However,the results from the different interpretation methods are dissimilar. The reason for obtainingdifferent results is because the methods depend on different methodologies. The studyshowed that some methods can sometimes overestimate the results and become unsafe forstructural assessment. On the contrary, the other methods can yield lower but safer estimates.

    Moreover, the use of small number of cores is evaluated for various methods. The reasons arebecause in practice, the preference is to avoid large number of cores. As a result, it isrecommended to apply care and proper judgment in selection of the methods andinterpretation of the results. It is also recommended to consider the methods with respect tothe aim of the investigation, their limitations and assumptions.

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  • 160.
    Ahmed, Abdulahi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Construction and Facilities Management.
    Ahmed, Sayidali
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Construction and Facilities Management.
    Implementation of Digital Tools in the Construction Sector in Somalia2022Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The implementation of digital tools, such as building information modeling (BIM) in lowand middle income countries’ (LMIC) infrastructure projects has increased in interest. LMICsuch as Somalia are in need of new road construction and improved infrastructure. The purpose of this thesis study is to explore perceived challenges of implementing digital tools in the construction sector in LMIC. To provide a more detailed and in-depth insight, the thesis study has been performed through an interview study in Somalia.

    Since the interest is in perceptions and experiences about the implementation of digital tools, a qualitative method was chosen. Respondents were selected from the construction sector that has been interviewed about their experiences of the implementation of digital tools. The study has used Kotter's 8-step process for change as an analytical framework to analyze and discuss the empirical findings. 

    The results show that the most critical challenges to implementing digital tools in a LMIC ssuch as Somalia are:- lack of financial resources for investing in digital tools on large infrastructure projects- lack of overall experience and competence in the use of digital tools- lack of regulations for digital tools from the public client

    The study suggests the public client, who in this case is the Ministry of Public Works and Reconstruction and Housing (MPWR) that are responsible for the laws and regulations in the Somalian construction sector to take these critical challenges into consideration. The public client has the overall responsibility and influence over the construction of the infrastructure and in order to increase the implementation of digital tools in the future, it is necessary that the public client establishes follow-ups and evaluations.

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  • 161.
    Ahmed, Abubeker W.
    et al.
    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 Mixtures2013In: International Journal of Pavement Research and Technology, ISSN 1996-6814, Vol. 6, no 6, p. 745-754Article in journal (Refereed)
    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.

  • 162.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. VTI.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. VTI.
    Characterization of heavy traffic axle load spectra for mechanistic-empirical pavement design applicationsIn: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268XArticle in journal (Refereed)
  • 163.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute, Sweden.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. 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 tests2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 1, p. 154-171Article in journal (Refereed)
    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.

  • 164.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Erlingsson, Sigurdur
    Evaluation of permanent deformation models for unbound granular materials using accelerated pavement tests2013In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, no 1, p. 178-195Article in journal (Refereed)
    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.

  • 165.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. 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 measurements2012In: Advances in Pavement Design Through Full-Scale Accelerated Pavement Testing - Proceedings of the 4th International Conference on Accelerated Pavement Testing, 2012, p. 493-503Conference paper (Refereed)
    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.

  • 166.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory. Swedish National Road and Transport Research Institute, Sweden.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory. Swedish National Road and Transport Research Institute, Sweden.
    Numerical validation of viscoelastic responses of a pavement structure in a full-scale accelerated pavement test2017In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 18, no 1, p. 47-59Article in journal (Refereed)
    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.

  • 167.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. VTI.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. VTI.
    Viscoelastic modelling of pavement structure behaviour in a full scale accelerated pavement testManuscript (preprint) (Other academic)
  • 168.
    Ahmed, Abubeker Worake
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Mechanistic-Empirical Modelling of Flexible Pavement Performance: Verifications Using APT Measurements2014Doctoral thesis, comprehensive summary (Other academic)
    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. 

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    Thesis
  • 169.
    Ahmed, Fuad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Tabatabaei Araghi, Pedram
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Radonfritt boende: Stegen till att eliminera radongas med rätt Grundläggningsmetod2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    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.

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  • 170.
    Ahmed, Helin
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Utvärdering av en digital internutbildning för hållbar utveckling inom byggbranschen2024Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the construction sector, education and knowledge transfer play a significant role in promoting sustainability. The impact of the training depends on its implementation and context. A careful evaluation of the use and effectiveness of training is essential to optimize results and provide the necessary knowledge and skills to address sustainability challenges. Unfortunately, a lack of balance between environmental, economic and social aspects in sustainability education can limit the individual's opportunities to effectively deal with sustainability issues in practice. In order to successfully promote sustainability in the construction sector, a deeper understanding of the implementation of education and the integration of knowledge into the work of employees is required. The study aims to investigate how a digital internal training in sustainable development at a large Swedish construction company can be designed and implemented to create opportunities for developed professional practice in the construction industry. Based on this, a qualitative and quantitative data collection method has been implemented to address the study's questions, and various sources have also been used to conduct a literature study. A thematic analysis of the study's qualitative data resulted in a total of twelve themes after interviews with selected individuals with various positions at the construction company were conducted. The results show that there are shortcomings with the construction company's digital sustainability training, which contributes to the fact that the employees do not get the opportunity to develop the desired knowledge, abilities and attitudes in order to achieve the purpose of the training and accomplish sustainable business. A number of central aspects that influence the success and relevance of the training for both the employees and the company as a whole have been identified, which provides valuable insights for future training strategies. These aspects include a lack of social interaction where a community of inquiry is not promoted, outdated content that does not have clear connections to practical sustainability work and a lack of follow-up steps. This resulted in an improvement proposal with parameters that can be addressed and implemented within the training to meet the needs of the construction company, satisfy the needs of employees and achieve high customer satisfaction.

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  • 171. Ahmed, K. M.
    et al.
    Bhattacharya, Prosun
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Hasan, M. A.
    Rahman, M
    von Brömssen, Mattias
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Jacks, Gunnar
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Hossain, Mohammed
    Islam, M. Mainul
    Rahman, Marina
    Rashid, S.M.A.
    Sustainable Arsenic Mitigation (SASMIT) in Bangladesh: The Matlab strategy2010In: Abstracts with programs (Geological Society of America), ISSN 0016-7592, Vol. 42, no 5, p. 652-Article in journal (Other academic)
  • 172. Ahmed, K. M.
    et al.
    Sultana, S.
    Hasan, M. A.
    Bhattacharya, Prosun
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Hasan, M. K.
    Burgess, W. K.
    Hoque, M. A.
    Groundwater quality contrasts between Upper and Lower Dupi Tila Aquifers in Megacity Dhaka, Bangladesh2011In: Groundwater quality contrasts between Upper and Lower Dupi Tila Aquifers in Megacity Dhaka, Bangladesh: Proc. 7th International Groundwater Quality Conference, 2011, p. 71-74Conference paper (Refereed)
    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.

  • 173.
    Ahmed, K. Matin
    et al.
    Univ Dhaka, Dept Geol.
    Bhattacharya, Prosun
    KTH, Superseded Departments (pre-2005), Land and Water Resources Engineering.
    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 overview2004In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 19, no 2, p. 181-200Article in journal (Refereed)
    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.

  • 174.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Impact-type vibration effects on young concrete for tunnelling2016Report (Other academic)
    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.

  • 175.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Laboratorieprovningar av stötbelastade betongprismor vid tidig ålder2015In: Tidskriften Betong, ISSN 1101-9190, no 5, p. 51-54Article in journal (Other academic)
  • 176.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Laboratory simulation of blasting induced bond failure between rock and shotcrete2012Report (Refereed)
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  • 177.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Modelleringsverktyg hittar sprickor2015In: Tidskriften Betong, ISSN 1103-4270, no 5, p. 51-54Article in journal (Refereed)
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  • 178.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Models for analysis of shotcrete on rock exposed to blasting2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In underground construction and tunnelling, the strive for a more time-efficient construction process naturally focuses on the possibilities of reducing the times of waiting between stages of construction. The ability to project shotcrete (sprayed concrete) on a rock surface at an early stage after blasting is vital to the safety during construction and function of e.g. a tunnel. A complication arises when the need for further blasting affects the hardening of newly applied shotcrete. If concrete, cast or sprayed, is exposed to vibrations at an early age while still in the process of hardening, damage that threatens the function of the hard concrete may occur. There is little, or no, established knowledge on the subject and there are no guidelines for practical use.

    It is concluded from previous investigations that shotcrete can withstand high particle velocity vibrations without being seriously damaged. Shotcrete without reinforcement can survive vibration levels as high as 0.5−1 m/s while sections with loss of bond and ejected rock will occur for vibration velocities higher than 1 m/s. The performance of young and hardened shotcrete exposed to high magnitudes of vibration is here investigated to identify safe distances and shotcrete ages for underground and tunnelling construction, using numerical analyses and comparison with measurements and observations. The work focuses on finding correlations between numerical results, measurement results and observations obtained during tunnelling. The outcome will be guidelines for practical use.

    The project involves development of sophisticated dynamic finite element models for which the collected information and data will be used as input, accomplished by using the finite ele­ment program Abaqus. The models were evaluated and refined through comparisons between calculated and measured data. First, existing simple engineering models were compared and evaluated through calculations and comparisons with existing data. 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 beam elements interconnected with springs. The third is a one-dimensional elastic stress wave model. The stress response in the shotcrete closest to the rock when exposed to P-waves striking perpendicularly to the shotcrete-rock interface was simulated. Results from a non-destructive laboratory experiment were also used to provide test data for the models. The experiment studied P-wave propagation along a concrete bar, with proper­ties similar to rock. Cement based mortar with properties that resembles shotcrete was applied on 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.

    Due to the inhomogeneous nature of the rock, the stress waves from the blasting attenuate on the way from the point of explosion towards the shotcrete on the rock surface. Material damping for the rock mass is therefore accounted for, estimated from previous in-situ measurements. The vibration resistance of the shotcrete-rock support system depends on the material properties of the shotcrete and here were age-dependent properties varied to investigate the behaviour of young shotcrete subjected to blast loading. The numerical simulations require insertion of realistic material data for shotcrete and rock, such as density and modulus of elasticity.

    The calculated results were in good correspondence with observations and measurements in-situ, and with the previous numerical modelling results. Compared to the engineering models, using a sophisticated finite element program facilitate modelling of more complex geometries and also provide more detailed results. It was demonstrated that wave propagation through rock towards shotcrete can be modelled using two dimensional elastic finite elements in a dynamic analysis. The models must include the properties of the rock and the accuracy of the material parameters used will greatly affect the results. It will be possible to describe the propagation of the waves through the rock mass, from the centre of the explosion to the reflection at the shotcrete-rock interface. It is acceptable to use elastic material formulations until the material strengths are exceeded, i.e. until the strains are outside the elastic range, which thus indicates material failure. The higher complexity of this type of model, compared to the engineering models, will make it possible to model more sophisticated geometries. Examples of preliminary recommendations for practical use are given and it is demonstrated how the developed models and suggested analytical technique can be used to obtain further detailed limit values.

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  • 179.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Models for analysis of young cast and sprayed concrete subjected to impact-type loads2015Doctoral thesis, comprehensive summary (Other academic)
    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.

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    Thesis
  • 180.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Vulnerability of shotcrete on tunnel walls during construction blasting2018Conference paper (Refereed)
  • 181.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ökad kunskap om sprutbetong ger hållbara tunnlar2012In: Tidskriften Betong, ISSN 1101-9190, no 6, p. 50-52Article in journal (Refereed)
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  • 182.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    A comparison of models for shotcrete in dynamically loaded rock tunnels2010In: Shotcrete: Elements of a System, Informa UK Limited , 2010, p. 11-20Chapter in book (Other academic)
    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. 

  • 183.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    A comparison of models for shotcrete in dynamically loaded rock tunnels2010In: Shotcrete: Elements of a system / [ed] E. Stefan Bernard, Taylor & Francis Group, 2010, p. 1-10Conference paper (Refereed)
    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.

  • 184.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Behaviour of sprayed concrete on hard rock exposed to vibration from blasting operations2014Conference paper (Refereed)
  • 185.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Direct shear strength of high-strength fibre concrete2010In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 62, no 5, p. 379-390Article in journal (Refereed)
    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.

  • 186.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Dynamic measurements for determination of Poisson’sratio of young concrete2017Conference paper (Refereed)
  • 187.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Experimental and numerical investigation of stress wave propagation in shotcrete2011In: Nordic concrete research: Research projects 2011 / [ed] D.H. Bager, 2011, p. 59-62Conference paper (Refereed)
  • 188.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Laboratory investigation of stress waves in young shotcrete on rock2012In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 64, no 10, p. 899-908Article in journal (Refereed)
    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.

  • 189.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Structural dynamic and stress wave models for analysis of shotcrete on rock exposed to blasting2012In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 35, no 1, p. 11-17Article in journal (Refereed)
    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.

  • 190.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Vibration vulnerability of shotcrete on tunnel walls during construction blasting2014In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 42, p. 105-111Article in journal (Refereed)
    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.

  • 191.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Numerical modelling and evaluation of laboratory tests with impact loaded young concrete prisms2016In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, ISSN 1359-5997, Vol. 49, no 11, p. 4691-4704Article in journal (Refereed)
    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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  • 192.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Crack propagation under water pressure2018Report (Refereed)
    Abstract [en]

    Cracks in concrete structures such as a concrete dam can be exposed to water pressure, for example, uplift pressure. The water pressure can be significant and may result in cracks propagating through the structures and thus it may result in reduced service life. However, the knowledge of water pressure within the cracks is relatively limited and is often neglected or just roughly estimated. The influence of crack opening rate on the uplift pressure distribution in the crack and the pressure variation during opening or sudden crack closure are questions needed to investigate. As an attempt to answer those questions, a pilot study presented here describes the possibilities and limitations of the proposed experimental setup; and technology (penetrability meter and tomography) as an examination method for water pressure in propagation concrete cracks. The test specimens examined here are exclusively cylinders cast of concrete with or without an initial crack.

    The penetrability meter can be used to apply water pressure and to visualize the crack opening, X-Ray computed tomography test, was performed. KTH Civil and Architectural Engineering department has organized the laboratory resources.

    The examples reported in this work show that the technology and equipment have great potential for future work on crack propagation, however, sample design and preparation, as well as testing need further development.

  • 193.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Finite element simulation of shotcrete exposed to underground explosions2012In: Nordic Concrete Research, ISSN 0800-6377, no 45, p. 59-74Article in journal (Refereed)
    Abstract [en]

    An elastic finite element model is used tosimulate theinducedstress waves from blasting, propagating in rock towards shotcrete on a tunnel wall. Due to the inhomogeneous nature of the rock, the stress wavesattenuate onitsway from the point of explosiontowardsthe shotcrete on the rock surface. Material damping for the rock-mass is estimated from in-situ measurements. The vibration resistance of the shotcrete-rock support system depends on the material properties of the shotcrete. Age-dependent material properties are varied to investigate the behaviour of young shotcrete subjected to blast loading. Finally, finite element analysis results are presented and verified through comparison with other numerical models, measurements and observations.

  • 194.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Dynamic Measurements for Determining Poisson’s Ratio of Young Concrete2018In: Nordic Concrete Research, ISSN 0800-6377, no 58, p. 95-105Article in journal (Refereed)
    Abstract [en]

    Knowledge of the elastic properties of concrete at early age is often a pre-requisite for numerical calculations. This paper discusses the use of a laboratory technique for determining Poisson’s ratio at early concrete age. A non-destructive test set-up using the impact resonance method has been tested and evaluated. With the method, it has been possible to obtain results already at 7 hours of concrete age. Poisson's ratio is found to decrease sharply during the first 24 hours to reach a value of 0.08 and then increase to approximately 0.15 after seven days.

  • 195.
    Ahmed, Lamis
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Sjölander, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Evaluation and analysis of laboratory tests of bolts-anchored, steel-fiber-reinforced shotcrete linings2017In: Proceedings of the World Tunnel Congress 2017, International Tunnelling Association, 2017Conference paper (Refereed)
    Abstract [en]

    Results from laboratory tests on statically loaded bolt-anchored, steel-fibre-reinforced shotcrete linings in interaction with rock are here evaluated using a 2D finite element model. Calculations are made to determine the state of stress in the rock-shotcrete interface near the rock joints. Plane-stress elements are used with a non-linear material model, capable of describing cracking and de-bonding during loading. The simulated crack position and force-displacement curves are compared with laboratory test results. Since most construction work in underground hard rock involves the use of explosives for excavation work, dynamic load cases are also analysed and compared to results from previous research on vibration resistance of shotcrete. 

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  • 196.
    Ahmed, Samih
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Minchot, Guayente
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Post-tensioned stress ribbon systems in long-span roofs: Case study: Västerås Travel Center2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The stress ribbon system has numerous advantages, that includes but are not limitedto: increasing overall stiffness, control deflections and reduction of materialsconsumption, which in turn, reduces the load and the cost. Nevertheless, its use isusually limited to bridges, in particular, pedestrian bridges; this can be attributedto the insufficient space that buildings’ usually have for end supports, or/and backstayedcables, that can accommodate the expected high pull-out forces occuring atthe cables’ ends.

    In this work, the roof of Västerås Travel Center, which will become one of the longestcable suspended roofs in the world, was chosen as a case study. The aim was toinvestigate the optimal technique to model the post-tensioned stress ribbon systemfor the roof structure using SAP2000, and to assess any possible reduction in thepull-out forces, deflections and concrete stresses. Subsequently, a conventional cablesuspended roof was simulated, using SAP2000, and compared to the post-tensionstress ribbon system in order to examine the potential of the latter. Moreover,the effects of temperature loads and support movements on the final design loadswere examined. Based on the study, a few practical recommendations concerningthe construction method and the iterative design process, required to meet thearchitectural geometrical demands, are stated by the authors.

    The results showed that the post-tensioned stress ribbon system reduces the concretestresses, overall deflections, and more importantly, reduces the pull-out forces by upto 16%, which substantially reduces the design forces for the support structures.The magnitude of these reductions was found to be highly correlated to the appliedprestressing force, making the size of the prestressing force a key factor in the design.

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    Post-tensioned stress ribbon systems in long-span roofs
  • 197.
    Ahmed, Samih
    et al.
    Tyréns AB.
    Minchot, Guayente
    Tyréns AB.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    King, Fritz
    Tyréns AB.
    Hallgren, Mikael
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Post-Tensioned Stress Ribbon Systems in Long Span Roofs2019In: 20th Congress of IABSE, New York City 2019: The Evolving Metropolis - Report2019, International Association for Bridge and Structural Engineering , 2019, p. 534-540Conference paper (Refereed)
    Abstract [en]

    Cable systems have numerous advantages, such as: large column-free areas, and reduced materials consumption, which reduces the load and the cost. Nevertheless, they are rarely used in long span roofs due to large deflections, and the insufficient space for end supports, or/and back-stayed cables. This work suggests the use of post-tension stress ribbon system in long span roofs in order to reduce the pull-out forces, deflections and concrete stresses compared to a conventional cable system. A comparison is carried out through meticulous and accurate finite element simulations, using SAP2000, implemented for the new +200m roof of Västerås Travel Center (Sweden), which will become one of the longest cable suspended roofs in the world, if not the longest. Results confirm the suitability and superiority of stress ribbon systems as it reduces concrete stresses, deflections, pull-out forces and vertical reactions. These reductions are found highly correlated to the applied prestressing forces.

  • 198.
    Ahmic, Edvin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Akbarov, Dosmat
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Klassifikationssystemens påverkan på kalkylarbete: En jämförelse mellan CoClass och BSAB-systemen2018Independent thesis Basic level (university diploma), 180 HE creditsStudent thesis
    Abstract [en]

    As the construction industry shifts to digital information modeling of its projects, the need to coordinate and improve the efficiency of the management of this information increases. A common language in the form of an industry-wide classification system could lead to billions in savings annually. In the calculation, it is important that the correct information management is included in order to provide the most accurate calculation possible.

    The aim of this study is to examine how the three different systems, BSAB 83, BSAB 96 and CoClass, differ and stand in contrast to each other to highlight and demonstrate such differences. The purpose of the study is that it should be used as a basis for how ÅF can create classified calculations with CoClass.

    To achieve the aim of the report and answer the research questions, the examination consisted of literature studies, interviews, a comparative study and a case study. These methods contributed to the following result: ÅF could effectively transfer to the CoClass system. When comparing the systems, it has been shown that CoClass is a more extensive and comprehensive system structured in a different way as opposed to the previous classification systems.

    Based on the results of the study, a calculation structure according to CoClass can be implemented in ÅF's current working methods, where ready-made recipe for building components can still be used. The recommendation is to consider the component table as equivalent to the production result in the calculation work with CoClass structure in the MAP. In the long run, this would have been an efficient strategy, both economically and primarily less time-consuming.

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  • 199.
    Ahne, Alexander
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Wikforss, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Projektering av brandskydd för stålkonstruktioner2005Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 200.
    Ahnlén, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    MAP DESIGN: A development of background map visualisation in Digpro dpPower application2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    What is good map design and how should information best be visualised for a human reader? This is a general question relevant for all types of design and especially for digital maps and various Geographic Information Systems (GIS), due to the rapid development of our digital world. This general question is answered in this thesis by presenting a number of principles and tips for design of maps and specifically interactive digital visualisation systems, such as a GIS.

    Furthermore, this knowledge is applied to the application dpPower, by Digpro, which present the tools to help customers manage, visualise, design and perform calculations on their electrical networks. The visualisation and design of the network was analysed together with the usage of two common background maps, GSD-Fastighetskartan by Lantmäteriet and Primärkartan by the municipalities, whose default appearances are defined by Digpro. The aim was to answer whether there is a more suitable design of the background maps and network to better complement the usage of dpPower and if so, what is the better design?

    When designing interactive systems that will later have various end-users, a user-centred design is important. Therefore, the initial step was to collect user inputs and feedback on the current design via customer interviews. This gave a set of user criteria for good map design of dpPower specifically.

    A study of existing relevant literature and previous work was also performed where several general key principles for good design could be identified.

    Finally, a comparison between the dpPower design and other existing map products, such as e.g. Google Maps and Eniro, was made where key similarities and dissimilarities were identified and discussed.

    These user criteria and design principles could be combined, both to present an answer to the general question “What is good design?” and to present a suggestion of new map appearance in dpPower. Key considerations in the new design suggestions were e.g. to have a toned down background map with all features in the same hue family. However, for GSD-Fastighetskartan the important convention of land classes, blue = water, green = vegetation \& yellow = open land, should be kept. Colour combinations and contrast is the most important design element and since a design cannot be optimally adapted for all types of colour vision deficiencies, the suggestion is to separate the designs to specifically target user groups of different colour vision abilities. Important map information such as e.g. detailed road data should be kept while unnecessary features such as contour lines and polygon borderlines should be hidden. Text positions should also be considered.

    The results were evaluated both via a survey, distributed to users of dpPower, GIT-students and users with no previous experience of GIT or dpPower, and a seminar with employees at Digpro.

    The conclusions drawn from the evaluation was that the presented design suggestions and principles are good, but adjustments should be made. E.g. a use of yellow for low voltage cables, as suggested for Red-Green impaired, is perhaps not the best solution. The results present a good foundation for design of dpPower but more adjustments should be made based on the evaluation and then another evaluation can be performed. It would give an even better result.

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