| 1. |
- Andersson, Ronny, et al.
(författare)
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Calculating CO2 Uptake for Existing Concrete Structures during and after Service Life
- 2013
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 1520-5851 .- 0013-936X. ; 47:20, s. 11625-11633
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a model that can calculate the uptake of CO2 in all existing concrete structures, including its uptake after service life. This is important for the calculation of the total CO2 uptake in the society and its time dependence. The model uses the well-documented cement use and knowledge of how the investments are distributed throughout the building sector to estimate the stock of concrete applications in a country. The depth of carbonation of these applications is estimated using two models, one theoretical and one based on field measurements. The maximum theoretical uptake potential is defined as the amount of CO2 that is emitted during calcination at the production of Portland cement, but the model can also, with some adjustments, be used for the other cement types. The model has been applied on data from Sweden and the results show a CO2 uptake in 2011 in all existing structures of about 300 000 tonnes, which corresponds to about 17% of the total emissions (calcination and fuel) from the production of new cement for use in Sweden in the same year. The study also shows that in the years 2030 and 2050, an increase in the uptake in crushed concrete, from 12 000 tonnes today to 200 000 and 500 000 tonnes of CO2, respectively, could be possible if the waste handling is redesigned.
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| 2. |
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| 3. |
- Häglund, Martin, et al.
(författare)
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Load combination of moisture induced eigenstresses in timber
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents and suggests a load combination factor for moisture induced stress (MIS) when MIS and snow load are combined. It is argued that MIS may be considered as an ordinary load to be combined with other structural actions, for example snow load. This outlook is not new but till now the load combination factor issue has not been investigated. Based on measured snow depths and calculated MIS at four different locations in Sweden it is suggested that the load combination factor for MIS is set to 0.2.
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| 4. |
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| 5. |
- Häglund, Martin
(författare)
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Moisture content penetration in wood elements under varying boundary conditions
- 2007
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 1432-5225 .- 0043-7719. ; 41:6, s. 477-490
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of effects of moisture exposure on timber structures is important for serviceability and load bearing capacity of timber elements and systems. Varying climate affects the moisture content profiles in timber as the relative humidity changes in the ambient air. This paper presents methods for calculation of diffusion based moisture transport and corresponding results on how timber responds to varying moisture with regard to moisture penetration and distribution. The calculations are based on measured outdoor relative humidity and temperature at different climatic locations in Sweden. No remarkably large deviations between the different climatic locations were found in general, which is positive in a design code perspective.
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| 6. |
- Häglund, Martin
(författare)
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Moisture Induced Stress Perpendicular to Grain in Timber Structures
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Timber structures and wooden element are in general affected by moisture and moisture variation in different ways. Their hygroscopic properties result in adsorption of water when wetted and in desorption when dried. Because the volume of wood is not constant but varies with the moisture content, uneven distribution of moisture will result in induced eigen-stresses because of internal restraint hygroexpansion. Since cross-sectional forces must self-balance, drying causes tensile and compressive stresses near the surface and the middle of a beam, respectively; the opposite applies for wetting. In the design of timber structures today, effects of moisture are considered in a rather summary way. A structural element is assigned to a certain service class and each class has its specific constant strength reduction factor (i.e. the wetter the climate, the larger the reductions). Nevertheless, one concern with such a method it that noting is said about the moisture variation—the selection of service class is only based on anticipated moisture equilibrium levels. It is verified by experiment that moisture induced eigen-stress, which adds to the mechanical stress from external loading, may cause stress fields that significantly reduce the load bearing capacity. In view of the significant importance of moisture on the behavior of wood structures, there is an apparent lack of precise characterization of the climatic condition as a basis for design of timber structures. In order to improve design codes it has been suggested that moisture effects should may be considered as an action to be combined with other ordinary loads (such as snow and live load) instead of being recognized in form of strength reduction factors. In order to further explore this line of suggestion, investigation of climatic conditions and determination of moisture and stress profiles were performed, and the outcome was evaluated by application of e.g. statistical extreme value analysis. This thesis presents background and new findings on moisture induced stress perpendicular to grain. The five appended papers address climate modeling, moisture penetration, development of eigen-stresses and consideration of moisture as an action. In short, some of the findings are: higher stress-levels are induced in larger cross-sections than in smaller ones, summer seasons cause more induced eigen-stresses than winter seasons, induced tensile stress can reach well above the characteristic strength (0.5 MPa), proper surface coating effectively reduces moisture gradients (and thus hinder potential stresses to fully develop), and finally, it is suggested that a load combination factor for moisture induced stress should be equal to 0.2.
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| 7. |
- Häglund, Martin, et al.
(författare)
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Onset of mould growth – the effect of climate variability and different geographic locations
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a study on how climate conditions at numerous locations in Sweden affect the risk of onset of mould on wood sheltered outdoors. The results indicate that the risk is clearly higher in the south compared to the north of Sweden. These differences are mainly explained by colder and dryer winter periods in the north which is unfavorable for development of mould. The results also show that the climate effect with respect to risk for mould growth has a significant variation between different years. Thus, the risk for unfavorable effects cannot be solely based on predictions for a so-called normal year without considering years with more extreme climate effects. Based on the results it is argued in favor of developing a quantitative method to assess the risk of mould growth using probabilistic methods and reliability analysis. Such a method should be simple enough for the general engineer to implement and serve as a valuable tool in order to avoid inappropriate design and potential health related problems.
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| 8. |
- Häglund, Martin
(författare)
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Parameter influence on moisture induced eigen-stresses in timber
- 2010
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 68:4, s. 397-406
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Tidskriftsartikel (refereegranskat)abstract
- Moisture induced stress in timber is dependant on many factors. The driving force behind is the moisture variation in the surrounding air which causes induced stress due to restraint of hygro-expansion within timber elements (this can to some extent be seen analogous to thermally induced stress in steel). Today's computational power together with advanced constitutive models offers aaEuro-aEuro-valuable tool towards understanding and determining moisture actions on timber. However, it seems that the issue concerning uncertainties of the input parameters is seldom addressed. This paper presents results on how various factors affect the resulting moisture induced stress by aaEuro-aEuro-parametric study of the input values. A small numerical change of one parameter may possibly result in aaEuro-aEuro-major change of calculated stress levels. It is for example, shown that coating (paint) and cross-sectional dimensions play an important role for spatial stress distribution.
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| 9. |
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| 10. |
- Häglund, Martin, et al.
(författare)
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Time-series modeling of moisture exposure on timber structures
- 2007
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Ingår i: Building and Environment. - : Elsevier BV. - 1873-684X .- 0360-1323. ; 42:3, s. 1515-1521
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a methodology with the purpose of modeling and simulating outdoor temperature and relative humidity (vapor concentration) related to moisture exposure on timber structures. The methodology is based on time-series analysis with recorded meteorological data used as input. In situations where recorded data is missing or consists of limited sequences, this methodology offers the possibility to use synthetic data instead. It was found that temperature and vapor concentration could be modeled by a combination of deterministic functions and stochastic processes, which consider the dynamics of the climate, including slow seasonal variations and fast daily changes. Specifically, a model for temperature and vapor concentration in Stockholm, Sweden, is presented together with simulation results. It is shown that the model produces simulated sequences with statistical properties close to the real recorded ones. (c) 2006 Elsevier Ltd. All rights reserved.
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