| 1. |
- Nasr, Amro, et al.
(författare)
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Probabilistic analysis of climate change impact on fungal decay of timber elements in ground contact and their long-term structural performance
- 2022
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Ingår i: Wood Material Science and Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280.
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Tidskriftsartikel (refereegranskat)abstract
- Climate change can substantially affect infrastructure performance and safety. In this article, the impact of climate change on fungal decay of wooden infrastructure in ground contact is investigated. For this purpose, projections of three different climate change scenarios are used to assess the impact of climate change on fungal decay rate of untreated clear wood elements in ground contact in Sweden. The highest increase in the average decay rate is observed for four counties located in mid-Sweden, i.e. Örebro, Värmland, Västmanland, and Gävleborg. Furthermore, two illustrative examples are presented to demonstrate the impact of the increased decay rates on the structural performance and long-term reliability of timber elements in four selected counties, Skåne (southernmost Sweden), Örebro, Värmland, and Västmanland. In the first illustrative example, the impact of climate change on the bending moment capacity of untreated timber utility poles is assessed while in the second the impact on the long-term reliability of axially loaded untreated columns is investigated. In the four studied counties, it is found that climate change can have considerable impacts on the structural performance and long-term reliability of timber elements in ground contact.
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| 2. |
- Bayat Pour, Mohsen, et al.
(författare)
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A Literature Review of Probabilistic Hygrothermal Assessment for Building Envelopes
- 2024
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Ingår i: Building and Environment. - 0360-1323. ; 261
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Forskningsöversikt (refereegranskat)abstract
- This study presents a state-of-the-art review of the evolution of probabilistic hygrothermal assessments of building envelopes. First, relevant literature was identified by employing a systematic methodology, including scoping and systematic searches, quality assessment, and study analysis. The analysis, based on 143 selected publications, provides statistical insights into uncertainty propagation and sensitivity analysis methods, geographical distributions, climatic conditions, sustainability perspectives, uncertain parameter groups, employed metamodels, hygrothermal analysis tools, model dimensions, building usage, and moisture-related damage models. The results illustrate that the majority of probabilistic hygrothermal assessment studies, exceeding 95%, are not explicitly incorporating sustainability perspectives, including environmental, economic, and societal. Also, to enhance the accuracy in this field, it is important to integrate hygrothermal functions as uncertain input variables, given their potential to significantly impact hygrothermal performance compared to single material properties. While 90% of studies are confined to 1D modelling, extending research to 2D and 3D is advised to capture more complicated details. Moreover, case studies in tropical climates, where moisture-related issues can be prevalent, are noticeably lacking. Sensitivity analysis faces limitations due to its transient nature and variable interactions, necessitating identification of methods capable of non-linear and interactive analyses with low computational costs. Furthermore, several studies neglect ambient conditions and building usage considerations as stochastic variables, highlighting the need for comprehensive analyses. Lastly, understanding the merits and limitations of metamodeling methods is crucial for achieving reliable and robust hygrothermal analyses. The paper concludes by outlining the identified gaps and offering recommendations for future research in this field.
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| 3. |
- Bayat Pour, Mohsen, et al.
(författare)
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Mould reliability analysis combined with mould health risks for decision support
- 2023
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Ingår i: AIP Conference Proceedings. ; 2918
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Konferensbidrag (refereegranskat)abstract
- Common solutions for building energy-efficient buildings constitute e.g., double-glazed windows, airtight building envelopes and highly insulated walls. These solutions may improve the indoor environment/comfort but can also lead to adverse effect, e.g., mould at the surface of the construction components and consequently human health problems. With this study, a mould risk assessment including health consequences, a decision analysis and their adaptation to different types of building envelopes are developed. Within the frame of a mould risk and decision analysis, a physics and biology-based mould reliability analysis is combined with a medical science-based health occurrence and consequence model on an interdisciplinary basis. For the minimization of the expected consequences, an Inutility Decision Analysis (IDA) including an objective function is introduced and applied to a case study. An external wooden frame wall in a residential building is analysed and optimized with IDA quantitatively modelling the expected life cycle costs and the mould induced health risk of design alternatives. The calculation of the probability of mould occurrence is based on hygrothermal and mould reliability analysis. The health consequences are calculated with the conditional probability of asthma as inferred from the odds ratio in medical literature. The costs of choosing a type of external wall, are modelled based on the costs of the materials and works related to assembling them. The design alternative with the minimum aggregated risks and expected cost, i.e., expected inutility is selected. Within the assumptions of the example, it is demonstrated that mould health consequences constitute an important part of the expected inutilities.
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| 4. |
- Bayat Pour, Mohsen, et al.
(författare)
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Robust probabilistic modelling of mould growth in building envelopes using random forests machine learning algorithm
- 2023
-
Ingår i: Building and Environment. - 0360-1323. ; 243
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Tidskriftsartikel (refereegranskat)abstract
- Probabilistic methods can be used to account for uncertainties in hygrothermal analysis of building envelopes. This paper presents methods for robust mould reliability analysis and identification of critical parameters. Mould indices are calculated by probabilistic hygrothermal analysis, followed by the application of the "Finnish mould growth model." To increase the robustness of the mould growth analysis, a random forests metamodel is first trained on the dataset and then used to expand the number of simulations. Finally, the reliability is calculated based on the probability of exceeding a given maximum mould index limit state. Critical parameters are identified through a sensitivity analysis based on linear and non-linear dependencies between inputs and maximum mould index. The methods are demonstrated by analysing three external wall assemblies. In conclusion, the mould reliability analysis method helps to assess the robustness of the hygrothermal analysis and mould assessment by investigating the influence of hygrothermal variables' uncertainties on the maximum mould index. By combining a metamodel with probabilistic analysis, it is possible to significantly reduce the amount of time required to evaluate a large number of scenarios.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Hosseini, Seyyed Hasan, et al.
(författare)
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Moisture prediction of timber for durability applications using data-driven modelling
- 2023
-
Ingår i: World Conference on Timber Engineering 2023 (WCTE 2023). - 9781713873273 ; , s. 3808-3815
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Konferensbidrag (refereegranskat)abstract
- Durability and service life assessment is a major challenge for the design and use of timber in outdoor weather exposed environments. Rate of deterioration by fungal decay is closely linked to variations in wood moisture content. The objective of the present paper is to test and evaluate different data-driven models based on the multilinear regression (MLR) and artificial neural network (ANN) approach. Moisture content was predicted at the surface and core of a rain-exposed wooden element in the context of durability and service life assessment. Synthetic data stemming from a numerical model were used to fit time-series weather variables, including different combinations of time-lagged daily precipitation, relative humidity, and temperature, to temporal variations of daily average wood moisture content. Based on a set of statistical and qualitative analyses, using the weather variables lagged by 0 – 11 days as input variables for 11 mm depth moisture prediction, ANN showed the highest accuracy and least sensitivity to its initial setups, and could significantly outperform the MLR with the same input variables. The resulting models for surface and core moisture prediction were then tested against two different datasets consisting of measured data from wood specimens subjected to outdoor exposure.
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| 10. |
- Kahangi Shahreza, Seyedmohammad, et al.
(författare)
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Novel water penetration criterion for clay brick masonry claddings
- 2022
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 353
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Tidskriftsartikel (refereegranskat)abstract
- Despite the impact of water penetration on the performance of building envelopes, no general agreement is available on implementing water penetration due to wind-driven rain (WDR) in hygrothermal and moisture safety analyses. This study proposes a novel criterion for water penetration in clay brick masonry that depends on the water content level of masonry. An experimental campaign investigating water penetration in clay brick masonry exposed to uniform water spray is conducted on masonry triplets prepared from bricks with different water absorption properties and three mortar joint profiles. During each test, water absorption and water penetration are registered continuously. The results show that no water penetration occurs unless the water content of the specimens is above 90% of their saturation capacity. The saturation level at which penetration starts is consistent across all joint profiles and brick types. Accordingly, exposure to driving rain at levels below the threshold may not lead to water penetration. The utility and implications of the proposed criterion are briefly demonstrated by analyzing water content and water penetration in a clay brick masonry façade. The resulting water penetration is compared with the results obtained using a commonly accepted reference model that assumes one percent of all wind-driven rain deposited on the façade to penetrate the clay brick cladding. By linking water penetration in clay brick masonry to the water content, the proposed criterion is an attempt to logically explain a phenomenon of high scientific and practical relevance for moisture analyses of a frequently used type of building envelope.
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| 11. |
- Marais, Brendan N., et al.
(författare)
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Modelling in-ground wood decay using time-series retrievals from the 5th European climate reanalysis (ERA5-Land)
- 2023
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Ingår i: European Journal of Remote Sensing. - 2279-7254. ; 56:1
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Tidskriftsartikel (refereegranskat)abstract
- This article presents models to predict the time until mechanical failure of in-ground wooden test specimens resulting from fungal decay. Historical records of decay ratings were modelled by remotely sensed data from ERA5-Land. In total, 2,570 test specimens of 16 different wood species were exposed at 21 different test sites, representing three continents and climatic conditions from sub-polar to tropical, spanning a period from 1980 until 2022. To obtain specimen decay ratings over their exposure time, inspections were conducted in mostly annual and sometimes bi-annual intervals. For each specimen’s exposure period, a laboratory developed dose–response model was populated using remotely sensed soil moisture and temperature data retrieved from ERA5-Land. Wood specimens were grouped according to natural durability rankings to reduce the variability of in-ground wood decay rate between wood species. Non-linear, sigmoid-shaped models were then constructed to describe wood decay progression as a function of daily accumulated exposure to soil moisture and temperature conditions (dose). Dose, a mechanistic weighting of daily exposure conditions over time, generally performed better than exposure time alone as a predictor of in-ground wood decay progression. The open-access availability of remotely sensed soil-state data in combination with wood specimen data proved promising for in-ground wood decay predictions.
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| 12. |
- Meyer-Veltrup, Linda, et al.
(författare)
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Design and performance prediction of timber bridges based on a factorization approach
- 2018
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Ingår i: Wood Material Science and Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280.
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Tidskriftsartikel (refereegranskat)abstract
- Service life of timber bridges is predominantly affected by the site-specific climatic conditions in terms of moisture and temperature over time, the overall design, the design of details, and the choice of materials. In recent years, a performance-based methodology has been developed to predict (1) the material climatic conditions within timber components from macro climate data and comparison between design details, (2) decay intensity from material climate data, and (3) the material resistance as a combined effect of wood-inherent properties and its moisture dynamics. Within the WoodWisdomNet project ‘Durable Timber Bridges’ we emphasized on utilizing exposure, decay, and resistance models for a comprehensive guideline for the design of timber bridges. Therefore, a factorization approach is presented based on dose–response relationship between wood material climate and responding fungal decay. The concept does also allow for quantifying the material resistance of untreated, modified, and preservative-treated wood using factors based on laboratory and field durability tests and short-term tests for capillary water uptake, adsorption, and desorption dynamics. The findings from the present study have the potential to serve as an instrument for design and service life prediction of timber structures and will be implemented in an engineering design guideline for timber bridges.
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| 13. |
- Molnár, Miklós, et al.
(författare)
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Energi- och resurseffektiva murade ytterväggar
- 2019
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Ingår i: Bygg & teknik. - 0281-658X. ; :4/19
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- EUs Energieffektiviseringsdirektiv innebär en skärpning av kraven på byggnaders energiprestanda. För murverksbranschens del har man identifierat ett behov av att utveckla ytterväggskonstruktioner med 30 procent lägre U-värde jämfört med idag vanligt förekommande murade ytterväggslösningar. Utveckling av välisolerade murade ytterväggskonstruktioner med tunna, ytförstärkta bärande delar förefaller vara ett attraktivt alternativ eftersom U-värdet kan förbättras utan ytterligare ökning av väggtjockleken.
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| 14. |
- Molnár, Miklós, et al.
(författare)
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Energy efficient buildings by use of reinforced masonry walls : An experimental study
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Användning av ytförstärkning har undersökts som ett led i att förbättra murade ytterväggars energiprestanda. De experimentella undersökningarna genomförda vid Lunds tekniska högskola visar att genom användning av ytförstärkning kan tjockleken på den bärande delen i en yttervägg minskas med mellan 30 - 50 procent jämfört med dagens väggtyper. Väggarnas bärförmågan kan samtidigt bibehållas eller rentav ökas. Det insparade utrymmet kan nyttjas till mer termisk isolering, vilket medför att ytterväggens energiprestande förbättras utan ytterligare ökning av dess totala tjocklek.
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| 15. |
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| 16. |
- Niklewski, Jonas, et al.
(författare)
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Durability of rain-exposed timber bridge joints and components
- 2016
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Ingår i: WCTE 2016. - 9783903024359 ; , s. 4667-4675
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Konferensbidrag (refereegranskat)abstract
- The design of details is an important aspect in durability design of rain-exposed timber structures. Joints are considered the weak-points of these structures as they accumulate moisture and facilitate deterioration by decay. The present study aims to study the influence of detail design, and its effect on the service life, by estimating the decay rate in a number of rain-exposed timber components and joints, typically found in timber bridges. A test-setup was exposed outdoors over a period of one year while the moisture content was measured in specific measuring points. The test-setup included groups of beams, columns and joints commonly found in timberbridges. For the beams and columns, the effectiveness of typical protective measures was also tested. The annual decay rate was estimated using two different decay prediction models. Compared to a reference beam, the results show that structural protection reduced the risk of decay while joints and end-grain tended to be at increased risk. The lowest service life, estimated to 3-4 years, was found close to end-grain where drying was hindered but moisture could accumulate. In general, the discrepancy between the two decay models was large for low to medium exposure and decreased with increasing exposure.
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| 17. |
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| 18. |
- Niklewski, Jonas
(författare)
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Durability of timber members : Moisture conditions and service life assessment of bridge detailing
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The longevity of timber structures in exposed outdoor environments is often perceived to be unreliable as compared with that of concrete and steel structures. This situation is exacerbated to some extent by the fact that the European commission for standardization (CEN) currently provides no quantitative method for service life assessment of timber structures. To counteract this, the present thesis deals with methods for the quantitative service life assessment of timber in outdoor above-ground construction.Wood moisture content and temperature, i.e. the material climate involved, are two fundamental indicators of decay activity of wooden members. Performance based service life assessment of wood is largely comprised of two parts: (1) establishing the relationship between the environmental conditions and the material climate, and (2) establishing the relationship between the material climate and the rate of deterioration. The former depends on factors such as weather parameters, material properties and the design of details.Two experimental trials were conducted in order to acquire data concerning the relationship between the environmental conditions and the moisture content of the wood. The aim of the first experiment was to study typical details utilized for timber bridges with respect to their variation in moisture content. The type of detailing employed was shown to have a great effect on the moisture conditions, with the exposed contact areas and the end-grain being subject to increased levels of moisture content. The second experiment focused on the effects of long-term superficial damage on the moisture conditions of wood. It was shown that superficial damage caused by photo degradation and checking lead to increased moisture absorption and consequently to a longer duration of surface wetness. The relationship between environmental conditions and material climate was estimated through numerical modelling, which involves the explicit modelling of moisture transport within the wooden member and the exchange of moisture at the surfaces that are exposed. The model was applied to one-dimensional transverse moisture transport as well as to multi-dimensional transport in the case of simple details, such as side-grain to side-grain contact areas. The numerical model was then coupled with decay prediction models so as to map the relative decay hazard in European climates.
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| 19. |
- Niklewski, Jonas, et al.
(författare)
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Energieffektiva murade väggar med slimmad tjocklek
- 2020
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Ingår i: Bygg & teknik. - 0281-658X. ; :2/20, s. 47-49
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Glasfibernät och stål som appliceras i putsen eller fästes mekaniskt direkt mot väggytan möjliggör en minskning av den bärande väggens tjocklek i murade ytterväggar. Det insparade utrymmet kan användas till mer isolering och därmed bygga mer energieffektiva murade ytterväggar utan att öka den totala väggtjockleken. Väggarnas klimatavtryck minskar.
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| 20. |
- Niklewski, Jonas, et al.
(författare)
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Evaluation of moisture and decay models for a new design framework for decay prediction of wood
- 2021
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- Performance-based, service-life design of wood has been the focus of much research in recent decades. Previous works have been synthesized in various factorized design frameworks presented in the form of technical reports. Factorization does not consider the non-linear dependency between decay-influencing effects, such as between detail design and climate variables. The CLICKdesign project is a joint European effort targeting digital, performance-based specification for service-life design (SLD) of wood. This study evaluates the feasibility of using a semi-empirical moisture model (SMM) as a basis for a digital SLD framework. The performance of the SMM is assessed by comparison against a finite element model (FEM). In addition, two different wood decay models (a logistic, LM, and simplified logistic model (SLM)) are compared. While discrepancies between the SMM and FEM were detected particularly at high wood moisture content, the overall performance of the SMM was deemed sufficient for the application. The main source of uncertainty instead stems from the choice of wood decay model. Based on the results, a new method based on pre-calculated time series, empirical equations, and interpolation is proposed for predicting the service life of wood. The method is fast and simple yet able to deal with non-linear effects between weather variables and the design of details. As such, it can easily be implemented as part of a digital design guideline to provide decision support for architects and engineers, with less uncertainty than existing factorized guidelines.
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| 21. |
- Niklewski, Jonas, et al.
(författare)
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Livslängddimensionering av träkonstruktioner : Utveckling av nytt verktyg
- 2020
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Ingår i: Bygg & teknik. - 0281-658X. ; 2020:5
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Trä som byggnadsmaterial används till allt från trädäck och möbler till broar och höghus. Enbart i Sverige används 5-6 miljoner m3 sågade barrträvaror årligen varav ungefär hälften används i byggtillämpningar [2]. Till bärande konstruktioner inom hus- och brobyggnad nyttjas framförallt gran och furu men för trädäck och träpanel finns det en uppsjö av olika träslag och behandlingar på marknaden. Vilket material som lämpar sig för ett specifikt byggprojekt beror bland annat på önskad livslängd, planerat underhåll och vilken grad av slitage som är acceptabelt. Valet av material är alltså långt ifrån trivialt. EU-projektet ClickDesign jobbar mot att öka och sprida kunskap om beständighetsfrågor inom träbyggnad.
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| 22. |
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| 23. |
- Niklewski, Jonas, et al.
(författare)
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Moisture conditions of rain-exposed glue laminated timber members: the effect of different detailing : the effect of different detailing
- 2018
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Ingår i: Wood Material Science and Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 13:3, s. 129-140
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Tidskriftsartikel (refereegranskat)abstract
- In performance-based durability design, relating the in-use conditions of wooden members to their moisture content is an important step. In the present study, the effects of detail design on the wood moisture content of glulam members are investigated experimentally. The moisture content of glulam members, designed with various connection details and structural protection, was monitored at 18 different measuring points (n = 3) by use of resistance-type moisture sensors for a period of a year. The effects of detail design are studied by comparing the moisture content of various details to that of a freely exposed beam. As expected, the design of the details was clearly reflected by their moisture content. Efforts to protect the wood were favourable in most cases, although only complete shelter kept the moisture content consistently below the level critical for the occurrence of decay. In order to relate the effects of moisture traps to the climate, a three-parameter empirical model was constructed and fitted to the experimental results. The model was able to capture the main features of the measurements and was used in order to characterize the performance of details in terms of their response to weather.
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| 24. |
- Niklewski, Jonas, et al.
(författare)
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Moisture content prediction of rain-exposed wood: Test and evaluation of a simple numerical model for durability applications
- 2016
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Ingår i: Building and Environment. - : Elsevier BV. - 1873-684X .- 0360-1323. ; 97:February, s. 126-136
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in FrenchDecay-prediction models can be used to predict the service life of wooden components. However, knowledge of how the material climate, i.e. moisture content and material temperature, varies with time is required. A reliable material climate prediction model is therefore crucial in situations when measurements are not viable. The aim of this paper is to develop and assess the performance of a simple numerical moisture transport model for rain-exposed wood. The main focus is on the influence of rain and moisture transport in the transversal direction.First, a model based on Fick’s second law of diffusion was calibrated against laboratory measurements where wooden boards were exposed to artificial rain. Second, the model was tested against field-test measurements on wooden boards in use-class 3.1, i.e. above-ground, exposed to rain and free to dry. The influence of rain was investigated by studying the difference between sheltered and exposed specimens over time. Finally, the model was applied to a number of Swedish climates and two different decay-prediction models were used to assess the output.The main conclusion is that the influence of rain can be reproduced with sufficient accuracy for the particular application. The error between the numerical result and measurements tends to increase with decreasing temperature and at high moisture contents. However, the total error is reduced when the moisture content history is post-processed in a decay-prediction model as the rate of decay decreases with decreasing temperature.
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| 25. |
- Niklewski, Jonas, et al.
(författare)
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Numerical study on the effects of macro climate and detailing on the relative decay hazard of Norway spruce
- 2021
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Ingår i: Wood Material Science and Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 16:1, s. 12-20
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Tidskriftsartikel (refereegranskat)abstract
- The durability of wood depends on its in-use environmental conditions. The aim of this study was to estimate the effects associated with macro climate and detail design as well as their interdependence. A numerical moisture model and two different decay prediction models were utilized for assessing the decay risk of a horizontal member and a joint exposed at 300 sites scattered across Europe. In general, the results obtained with both decay models exhibited strong similarities to the Scheffer climate index. Distinct discrepancies were however observed in regions with much precipitation where one model stood out as less dependent on precipitation and more dependent on relative humidity. The projected decay rate of the joint was about two to four times higher than that of the horizontal board, depending on the model employed. One of the models indicated that the relative difference between the horizontal member and the joint decreased with increasing amounts of precipitation. Due to lack of reliable experimental data, no inference regarding the model accuracy could be made. Future studies should focus on collecting empirical data on relative decay risk in different climates, preferably focusing on regions where the difference in projected decay depends on the model employed.
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| 26. |
- Niklewski, Jonas, et al.
(författare)
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Simplified environmental analysis of the long-term performance of wood cladding and decking
- 2023
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Ingår i: 13th World Conference on Timber Engineering, WCTE 2023. - 9781713873273 - 9781713873297 ; 1, s. 549-557
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Konferensbidrag (refereegranskat)abstract
- The performance of timber in exposed environments is affected by several biotic and abiotic factors. For timber cladding and decking, two important aspects include reduced structural performance due to fungal decay and aesthetical changes resulting from superficial effects such as photodegradation and moulds. Predicting the long-term performance of timber is important because it enables rational material (species and treatment) and design (detailing) choices and reduce the risks of unexpected repairs and premature replacement of timber products. In this paper, we use available data on material performance in conjunction with environmental analysis to model, in a simplified way, (1) the time until onset of fungal decay and (2) the long-term aesthetical appearance of timber facades and decking. The results demonstrate how the analysis canbe used on a detailed geometry where wooden boards were modelled as separate objects and the choice of material affects the outcome. Several steps needing further development were identified, including a dose model linking microclimate to colour change and a better model for predicting moisture content. The study is part of a long-term effort to make holistic performance-based assessment of wood available for public use through easy-to-use procedures and accessible open-source software.
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| 27. |
- Niklewski, Jonas, et al.
(författare)
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Strengthened clay brick and lightweight aggregate concrete block walls tested under eccentric axial loading – a feasibility study on different strengthening techniques
- 2020
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Ingår i: Brick and Block Masonry - From Historical to Sustainable Masonry : Proceedings of the 17th International Brick and Block Masonry Conference - Proceedings of the 17th International Brick and Block Masonry Conference. - : CRC Press. - 9780367565862 - 9781003098508 ; , s. 987-993
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Konferensbidrag (refereegranskat)abstract
- Strengthening of masonry walls is a means to improve the energy performance of modern external masonry walls without further increasing their total thickness. The present paper evaluates the feasibility - here refer-ring to ease-of-application and structural performance - of several techniques aimed at strengthening mason-ry walls subjected to eccentric axial loading. Four full scale walls made of solid clay bricks and lightweight aggregate concrete blocks were strengthened using externally bonded reinforcement of conventional steel mesh, high-strength steel wire, masonry reinforcement and mechanically fastened strips of steel sheet. Each of the studied strengthening techniques is feasible from a structural perspective. Mechanically fastened steel strips require the least work, and no render is required since the steel is not exposed to fire. Steel mesh can be applied directly on the wall surface, which lowers the thickness of the render layer. Continued research with more replicates will confirm the presented conclusions.
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| 28. |
- Niklewski, Jonas, et al.
(författare)
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The effect of weathering on the surface moisture conditions of Norway spruce under outdoor exposure
- 2023
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Ingår i: Wood Material Science and Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 18:4, s. 1394-1404
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Tidskriftsartikel (refereegranskat)abstract
- Understanding wood surface moisture variations is fundamental to the modelling of moisture content. Exposure to sunlight, fluctuating temperature and rain leads to superficial deterioration and reduced surface hydrophobicity. Here, the effect of weathering was studied through monitoring the surface and global moisture content of axially matched pre-weathered and planed sets of specimens exposed outdoors over 18 months. The difference in surface conditions was characterised by analysing the rain-induced peaks. The results suggest that, following precipitation, weathered surfaces remain wet over a longer time period. No effect was observed through the global moisture content. After one year of exposure, the difference between pre-weathered and planed surfaces was small to insignificant. In service life modelling, it is therefore unnecessary to consider the unweathered state and simulations should target the behaviour of weathered wood. Numerical simulations were able to capture the general behaviour of the surface and global moisture content, but discrepancies over individual peaks were observed. Finally, the study demonstrates how peak analysis and signal analysis can be used for isolating subtle differences between time-series of surface moisture content. The same techniques can be used in future studies to characterise other factors influencing surface conditions, such as wood species and detailing.
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| 29. |
- Niklewski, Jonas, et al.
(författare)
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The effects of joints on the moisture behaviour of rain exposed wood: a numerical study with experimental validation
- 2021
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Ingår i: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 16:1, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Joints in timber structures are particularly vulnerable to degradation due to their tendency to trap moisture. The mechanisms involved, and their effect on the moisture conditions of wood, are here investigated numerically. The horizontal member of a rail and post-type configuration is modelled numerically by a two-dimensional diffusion model with material properties for Norway spruce. Contact areas are assumed to be fully wetted when the specimen is exposed to free water but are unable to interact with the ambient air. Water that is absorbed through such areas cannot dry out through the same surface and is instead redistributed. The model was validated against experimental data, both previously unpublished data and data obtained from the literature, including both laboratory and outdoor exposure. The numerical solutions were, in general, consistent with the measured data. The model provides a simple, yet accurate, method to estimate the moisture conditions in certain types of wood joints. In addition, the spatial distribution of time spent above 25% moisture content was calculated, in order to investigate the suitability of the model for durability applications.
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| 30. |
- Ranefjärd, Oskar, et al.
(författare)
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Investigating the Potential of Latent Heat in Hygroscopic Insulating Materials
- 2022
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Ingår i: Thermal Performance of the Exterior Envelopes of Whole Buildings XV International Conference. - 2166-8469. - 9781955516280 ; , s. 85-94
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Konferensbidrag (refereegranskat)abstract
- Energy from buildings accounts for almost 40% of global energy-related carbon emissions. A way to reduce both energy consumption in buildings as well as their environmental impact is to use bio-based insulation materials such as cellulose, wood or hemp fiber insulation. Experiences from modern buildings built with a timber-frame structure and insulated with bio-based materials show that these buildings have lower energy needs in the operational phase than what was initially expected from energy simulation models. However, these experiences have thus far been anecdotal, and they have not yet been validated through measurements. It is common that energy models only focus on thermal properties of materials and thermal flows through the building envelope, without considering moisture loads or hygrothermal behavior of building materials. A relevant difference between bio-based insulation materials and their polystyrene or mineral wool-based counterparts is that the former is more hygroscopic, with a generally high moisture capacity. It is hypothesized that latent heat and moisture transfer from the higher hygroscopicity of bio-based insulation materials could account for the discrepancy between modelled energy needs and measured energy needs in the operational phase. A numerical study was conducted to evaluate the energy performance of materials with varying hygroscopic properties. A numerical model of an exterior wall assembly with hygroscopic insulation materials was created in COMSOL, enabling parameters to be varied, without the manual input commonly required by some other commercial programs. Studied parameters included moisture buffering capacity and insulation thickness. Furthermore, the influence of the indoor and outdoor climate on the hygrothermal performance of the wall assembly was studied. The output evaluated focused primarily on the heat flux through the wall from the interior side. Results of the study showed that there is a potential for energy saving using hygroscopic insulation materials, as their higher moisture capacity could contribute to reduced energy needs for space heating. Results from this study also indicate that latent heat should be evaluated when insulation materials with hygroscopic properties are used in the building envelope, otherwise the energy use from heating could be underestimated.
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| 31. |
- Shahreza, Seyedmohammad Kahangi, et al.
(författare)
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Experimental investigation of water absorption and penetration in clay brick masonry under simulated uniform water spray exposure
- 2021
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Ingår i: Journal of Building Engineering. - : Elsevier BV. - 2352-7102. ; 43, s. 102583-102583
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we performed an experimental investigation of water absorption and penetration in clay brick masonry exposed to cyclic water spraying by employing a newly developed test setup. Several parameters, including brick absorption properties and different mortar joint profiles, were investigated. The specimens were exposed to a uniform water spray rate ranging between 1.7 and 3.8 l/m2/h, and water absorption and dampness patches on the non-exposed backside (the protected side) of the specimens monitored continuously. The results indicate that the amount of absorbed water is highly dependent on the water absorption coefficient and absorption capacity of the bricks, whereas the mortar joint profiles do not influence water absorption. The first dampness patches on the specimens' backside appeared in the vicinity of the head joint, and the time until the first patch appeared correlated well with water content levels. Accordingly, the first visible dampness patches appeared on the specimens' backside at water content levels corresponding to 50%–60% of full saturation level. Additionally, the specimens' backside reached 90% dampness at water content levels corresponding to 95% of full saturation level. As a feature attributed to the absence of known defects and zero differential air pressure, no measurable amounts of penetrated water could be collected at the specimens’ backside. The newly developed test setup might facilitate verification of moisture simulations and provide a basis for rational decision-making concerning clay brick masonry design and maintenance.
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| 32. |
- van Niekerk, Philip Bester, et al.
(författare)
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Estimating the service life of timber structures concerning risk and influence of fungal decay—A review of existing theory and modelling approaches
- 2021
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 12:5
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Forskningsöversikt (refereegranskat)abstract
- Wood is a renewable resource and a promising construction material for the growing bio-based economy. Efficiently utilising wood in the built environment requires a comprehensive understanding of the dynamics regarding its usability. Durability is an essential property to consider, as various types of exposure create conditions for the deterioration of wood through biotic and abiotic agents. Biodegradable materials introduce increased complexity to construction and design processes, as material decomposition during a structure’s lifetime presents a physical risk to human health and safety and costs related to repairs and maintenance. Construction professionals are thus tasked with utilising wooden elements to accentuate the material’s beneficial properties while reducing the risk of in-service decomposition. In this paper, only the cause and effect of fungal induced decay on the service life of wooden buildings and other wood-based construction assets are reviewed. The service life of wood components can thus be extended if suitable growing conditions are controlled. Multiple existing modelling approaches are described throughout the text, with special attention given to the two most comprehensive ones; TimberLife and the WoodExter. In choosing an appropriate model for a specific application, the authors recommend evaluating the model’s regional specificity, complexity, practicality, longevity and adaptability.
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| 33. |
- Van Niekerk, Philip B., et al.
(författare)
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Mapping the biotic degradation hazard of wood in Europe - Biophysical background, engineering applications, and climate change-induced prospects
- 2022
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 76:2, s. 188-210
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Tidskriftsartikel (refereegranskat)abstract
- Construction using timber has seen a resurgence in light of global climate mitigation policies. Wood is a renewable resource, and engineered wood products are proving to be competitive against concrete and steel while having several advantages. However, while the renewable nature of wood in construction is a beneficial property for climate mitigation policies, the process of biodegradation introduces a challenge for service life planning. A review of hazard mapping is presented while developing contemporary hazard maps, occurrence maps and projected hazard maps for 2050 using representative concentration pathways (RCP) 2.6 and 8.5. The risk of timber decay is expected to increase in most of Europe as the temperatures rise, with a decrease expected in dryer regions. Termites are likely to experience a range expansion as more areas become suitable, while human activity and an increase in extreme weather events like floods are expected to facilitate dispersion. Marine borer species already present a risk in most European coastal regions; however, the effect of changes in water temperatures are likely to shift the boundaries for individual borer species. Overall, warmer climates are expected to increase the metabolic activity of all of these organisms leading to a general reduction in service life.
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