| 1. |
- Darabi, H., et al.
(author)
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Development of a novel hybrid multi-boosting neural network model for spatial prediction of urban flood
- 2021
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In: Geocarto International. - : Taylor and Francis Ltd.. - 1010-6049 .- 1752-0762.
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Journal article (peer-reviewed)abstract
- In this study, a new hybridized machine learning algorithm for urban flood susceptibility mapping, named MultiB-MLPNN, was developed using a multi-boosting technique and MLPNN. The model was tested in Amol City, Iran, a data-scarce city in an ungauged area which is prone to severe flood inundation events and currently lacks flood prevention infrastructure. Performance of the hybridized model was compared with that of a standalone MLPNN model, random forest and boosted regression trees. Area under the curve, efficiency, true skill statistic, Matthews correlation coefficient, misclassification rate, sensitivity and specificity were used to evaluate model performance. In validation, the MultiB-MLPNN model showed the best predictive performance. The hybridized MultiB-MLPNN model is thus useful for generating realistic flood susceptibility maps for data-scarce urban areas. The maps can be used to develop risk-reduction measures to protect urban areas from devastating floods, particularly where available data are insufficient to support physically based hydrological or hydraulic models.
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| 2. |
- Javed, Saqib, 1978
(author)
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Development of Modelling and Simulation tools for Geothermal Basements and Deep Foundations in Soft Clays
- 2016
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Reports (other academic/artistic)abstract
- Pile heat exchangers are fast emerging as a potentially viable alternative to the more prevalent borehole heat exchangers for the provision of space heating and cooling. In the last decade or so, the use of geothermal piles has increased sharply in many countries including Belgium, China, Japan, Switzerland, the Netherlands, United Kingdom, and United States, among others. In Sweden, however, interest in geothermal piles has been surprisingly scant. This is despite the fact that most of the infrastructure and buildings in Sweden are founded on piled foundations. Early estimates suggest that approximately 75 % of heating requirements and 90 % of cooling requirements of a typical Swedish office building could be provided by geothermal piles. Initial studies also indicate quick payback and large carbon savings. On the other hand, as several Swedish cities are founded in areas with very soft soil conditions with high groundwater tables, there are concerns that pile heat exchangers with cyclic thermal loading could trigger excessive creep deformations. Most of the Swedish research on geothermal piles and cyclic thermal loading dates back to 1980s. Today, both analysis and test methods for understanding soft clay behaviour have improved significantly. Hence, there is a need to revisit the topic of cyclic heating and cooling of Swedish soft clays to fully understand the implications of the use of geothermal piles.This project, funded by Swedish Energy Agency, has dealt with the development of mathematical models for thermal modelling of geothermal piles in Swedish soft clay conditions. The new models include a method to determine the thermal impact of the building on the underlying pile heat exchangers, and calculation methods to evaluate the thermal resistance of the pile heat exchangers. An existing borehole model has also been updated for modelling of irregular configurations of geothermal piles. The mathematical models developed in this project can be implemented in any computer code to be incorporated in existing building energy simulation software. The models can also be used to develop controllers and control schemes to maximize the performance of pile heat exchangers. The project has also demonstrated the application of driven steel and precast pile heat exchangers in Swedish soft clays and has established the importance of acquiring in-situ measurements to determine key design parameters. The results from the project have been presented in seven journal and conference proceeding papers, three research reports, and one book chapter.
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| 3. |
- Persson, Peter, et al.
(author)
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Effect of structural design on traffic-induced building vibrations
- 2017
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In: Procedia Engineering. - : Elsevier BV. - 1877-7058. ; 199, s. 2711-2716
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Journal article (peer-reviewed)abstract
- Population growth and urbanization results in densified cities, where new buildings are being built closer to existing vibration sources, and new transportation systems are constructed closer to existing buildings. Potential disturbing vibrations are one issue to consider in planning urban environments and densification of cities. Vibrations can be annoying for humans but also for sensitive equipment in, for example, hospitals. In determining the risk for disturbing vibrations, the distance between the source and the receiver, the ground properties, and type and size of the building are governing factors. In the paper, a study is presented aiming at investigating the influence of various parameters of the building’s structural design on vibration levels in the structure caused by ground surface loads, e.g. traffic. Parameters studied are related to the type of construction material (if it would be a light or heavy structure), and to the slab thickness. The study is limited to the structural response at frequencies near the first resonance frequency of the soil. The finite element method is employed for discretizing the building structure that is coupled to a semi-analytical model considering a layered ground.
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| 4. |
- Persson, Peter
(author)
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Vibrations in a Built Environment : Prediction and Reduction
- 2016
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Doctoral thesis (other academic/artistic)abstract
- Vibrations in a built environment can exceed the requirements for sensitive equipment in a building or can cause annoyance to residents. Hence, there is often a need for reducing such vibrations. The vibrations can originate from ambient sources such as motorway traffic, or from internal sources such as people walking inside the building. Disturbing vibrations can be reduced by reduction measures. Vibration-reduction measures can be evaluated numerically, with for instance the finite element method, to avoid construction of expensive mock-ups. In the thesis, large finite element models involving several physical domains (e.g. road, soil, bedrock, and building parts) were developed to study the effect of vibration-reduction measures.Ground vibrations can be reduced by installing a wave barrier between an external source and a receiver. As concluded in the thesis, an empty barrier (i.e. a trench) installed in the soil has the ability to reduce the ground-vibration level by approximately 60%. If the barrier contains a solid material, however, the level of reduction is reduced to approximately 30%. At long distances, at around 500 m and longer, from the vibration source, an amplification in vibration is observed. At such distances, moreover, the ground motion follows the motion of the bedrock. Another example of a wave obstacle that is studied in the thesis involves shaping the landscape surrounding a building. The topsoil that is usually transported from the construction site can be used to construct hills and valleys that constitute the shaped landscape. However, this can result in anything from an appreciable reduction to an appreciable amplification in the ground-vibration levels, depending on how the landscape is formed. If constructed properly, the reduction in the level of vibration can reach approximately 35%. Vibrations from both external and internal sources can be reduced by modifying the properties of the concrete slabs and the soil underneath. The soil properties can be improved by mixing the soil with a binder, in order to stiffen the soil. Is is shown in the thesis that by using stabilised soil underneath a concrete slab, vibrations originating from motorway traffic can be reduced by almost 60%, and up to 80% for an internal pedestrian load. By using a time-efficient numerical model developed in the thesis, the effect by using different positions for the supports of a water-pipe system on vibrations transmitted to other parts of buildings was studied. Because frequency peaks can be avoided, a marked change of vibration characteristics can be achieved. A reduction of more than 60% in the transmitted vibrations was observed. The general methods and measures presented in the thesis are exemplified by the conceptual design process of the MAX IV Laboratory, a vibration-sensitive research facility. This laboratory exhibited the phenomena needed for selecting it as a comprehensive example case.
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| 5. |
- Bjurström, Henrik, et al.
(author)
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Comparative Seismic Laboratory and Non-Contact Field Measurements of Asphalt Concrete
- 2016
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In: 2016 Structural Materials Technology Paper Summaries.
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Conference paper (peer-reviewed)abstract
- Non-contact acoustic field measurements are performed on a newly built highway to characterize the real part of the dynamicmodulus of the asphalt concrete (AC) top layer. The in situ measurements are performed using an array of 48 micro-electromechanicalsystem (MEMS) sensors. Cores extracted from the field measurement positions are then examined in a laboratory usingseismic modal testing for comparison. The laboratory testing allows master curves to be constructed to characterize the AC over awide temperature and frequency range. It is demonstrated that the real parts of the dynamic moduli are consistent at the fieldtemperatures using the two test methods. The in situ measurements are also shown to be highly repeatable. The presentedcomparative study indicates a possible application for assuring the quality of AC based on mechanical properties using fast noncontactin situ measurements.
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| 6. |
- Andersen, Lars Vabbersgaard, et al.
(author)
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Variation in models for simple dynamic structure–soil–structure interaction problems
- 2017
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In: Procedia Engineering. - : Elsevier BV. - 1877-7058. ; 199, s. 2306-2311
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Conference paper (peer-reviewed)abstract
- To account for dynamic cross-coupling of structures via the soil, a computational model must be accurate enough to provide the correct overall behaviour of the scattered wave field. However, simplicity is also important when a model should be used for design purposes, especially in the early design stages and feasibility studies. The paper addresses the accuracy of simple models in which an array of structures is simplified into blocks placed on the ground surface or embedded within the soil. Comparisons are made between models that account or do not account, in a proper manner, for the inertia and embedment of the structures. Especially, the limitations of simplified models are discussed regarding their capability to quantify the insertion loss accurately.
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| 7. |
- Draganovic, Almir, et al.
(author)
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Ultrasonic dispersion of hard dispersed ultrafine milled cement-based grout for water sealing of fractured hard rock
- 2022
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 317
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Journal article (peer-reviewed)abstract
- Ever higher demands on the sealing of rock around underground structures drive the development of cement based grouts. The results of the previous study demonstrated that it is possible to mill cement to approximately 20 to 25 mu m and use it to seal fracture aperture down to approximately 70 mu m. Further milling deteriorates the penetrability of the grouts due to the flocculation of the fine particles. This study investigates ultrasound as a technique to improve dispersion of grouts based on ultrafine milled cement. The grout tested is based on cement where 95% of the cement mass has particles smaller than 12 mu m and is very hard to disperse. Dispersion with ultrasound is compared with a conventional laboratory mixer equipped with a disk and rotor-stator system. The dispersion efficiency of this mixing equipment was tested by a filter pump. The results confirmed that a conventional laboratory mixer equipped with a disk is not at all suitable for dispersion of this grout. The laboratory mixer equipped with a rotor-stator system is much better than a disc but still cannot disperse this fine milled grout properly. Ultrasound was found to be the most effective method. The dispersion achieved, measured with a filter pump, was around 54 mu m which indicates that it is possible to seal fracture aperture now down to 54 mu m, which is a significant improvement.
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| 8. |
- Adamson, Bo, et al.
(author)
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Bjälklag på jord : grundläggningsdjup
- 1973
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Reports (other academic/artistic)abstract
- Grundläggning med "platta på mark" eller riktigare "bjälklag på jord" kan ske med kantförstyvad platta eller med platta och grundmurar. Enligt Svensk Byggnorm 67 är grundläggningsdjupet enligt huvudregeln 0,25 m. Grundläggningsdjup måste emellertid knytas till ett stort antal förutsättningar. Genom tillgång till datorberäkningsmetoder och stora datorer har det blivit möjligt att noga teoretiskt studera temperaturer och frostnedträngning. I rapporten granskas olika faktorers inverkan på frostnedträngningen. Intill en byggnad ges möjlighet till en mera nyanserad bedömning av frostnedträngning och grundläggningsdjup. Ett förslag till ändring av Svensk Byggnorm ges också. Genom ett stort antal diagram, baserade på datorberäkningar, ges läsaren möjlighet till bedömning av egna okonventionella konstruktioner. En uppföljning av rapporten sker i "Bjälklag på jord - värmeisolering och golvtemperaturer", R41 :1973.
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| 9. |
- Bergström, Anders, et al.
(author)
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Field test of a floating thermal pile in sensitive clay
- 2021
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In: Geotechnique. - 0016-8505 .- 1751-7656. ; 71:4, s. 334-345
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Journal article (peer-reviewed)abstract
- The response of floating pile foundations in deep deposits of soft clay is governed by the settlements within the clay deposit surrounding the piles. A long-duration thermal response test (TRT) has been performed to assess the impact of heating and cooling on the geotechnical performance of a vertically loaded slender tubular steel pile in a deep deposit of sensitive clay. The results from the instrumented test site indicate that negligible excess pore water pressures, up to 3 kPa during heating and down to -1·1 kPa during cooling, were generated in the soil adjacent to the pile for a 50 W/m heat flux. The heating rate was sufficiently low to facilitate the drainage of pore water. The influence radius for the excess pore water pressures, however, extended beyond the soil volume affected by temperature change. The absence of thermally triggered creep settlements could be explained by the overlap between the remoulded zone resulting from pile installation, the extent of the heating, and the low creep susceptibility of remoulded sensitive clay for moderate temperature changes. Furthermore, no difference in the ultimate bearing capacity was found between the thermal pile and the reference pile, which was only loaded with a serviceability load during the test series. The current test data, therefore, indicate that driven floating piles in a deep deposit of soft clay also function as heat exchanger piles with minimal detrimental effects, for similar operational conditions as used in the TRT. It should be noted, however, that other pile types that do not extensively remould the clay adjacent to the pile shaft may show more significant influence of the thermal changes.
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| 10. |
- Bjurström, Henrik, et al.
(author)
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Field and laboratory stress-wave measurements of asphalt concrete
- 2016
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In: Construction and Building Materials. - : Elsevier. - 0950-0618 .- 1879-0526. ; 126, s. 508-516
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Journal article (peer-reviewed)abstract
- Abstract Non-contact surface wave measurements are performed on a new asphalt concrete (AC) pavement using 48 micro-electro-mechanical system (MEMS) sensors as receivers to estimate the real part of the dynamic moduli of the AC top layer. Laboratory measurements of core samples, extracted from the field measurement positions, are used to construct master curves for comparison with the field measurements. The real parts of the dynamic moduli from the two test methods are consistent at the field measurement temperatures, and the non-contact field measurements are highly repeatable. These results indicate a possible application for quality assurance of AC based on mechanical properties.
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