| 1. |
- Akbari, Camilla, et al.
(författare)
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Long-term major adverse liver outcomes in 1,260 patients with non-cirrhotic NAFLD
- 2024
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Ingår i: JHEP Reports. - : Elsevier. - 2589-5559. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- Background & AimsLong-term studies of the prognosis of NAFLD are scarce. Here, we investigated the risk of major adverse liver outcomes (MALO) in a large cohort of patients with NAFLD.MethodsWe conducted a cohort study with data from Swedish university hospitals. Patients (n = 1,260) with NAFLD without cirrhosis were diagnosed through biopsy or radiology, and had fibrosis estimated through vibration-controlled transient elastography, biopsy, or FIB-4 score between 1974 and 2020 and followed up through 2020. Each patient was matched on age, sex, and municipality with up to 10 reference individuals from the general population (n = 12,529). MALO were ascertained from Swedish national registers. The rate of events was estimated by Cox regression.ResultsMALO occurred in 111 (8.8%, incidence rate = 5.9/1,000 person-years) patients with NAFLD and 197 (1.6%, incidence rate = 1.0/1,000 person-years) reference individuals during a median follow up of 13 years. The rate of MALO was higher in patients with NAFLD (hazard ratio = 6.6; 95% CI = 5.2–8.5). The risk of MALO was highly associated with the stage of fibrosis at diagnosis. In the biopsy subcohort (72% of total sample), there was no difference in risk between patients with and without non-alcoholic steatohepatitis. The 20-year cumulative incidences of MALO were 2% for the reference population, 3% for patients with F0, and 35% for F3. Prognostic information from biopsy was comparable to FIB-4 (C-indices around 0.73 vs. 0.72 at 10 years).ConclusionsThis study provides updated information on the natural history of NAFLD, showing a high rate of progression to cirrhosis in F3 and a similar prognostic capacity of non-invasive tests to liver biopsy.Impact and implicationsSeveral implications for clinical care and future research may be noted based on these results. First, the risk estimates for cirrhosis development are important when communicating risk to patients and deciding on clinical monitoring and treatment. Estimates can also be used in updated health-economic evaluations, and for regulatory agencies. Second, our results again highlight the low predictive information obtained from ascertaining NASHstatus by histology and call for more objective means by which to define NASH. Such methods may include artificial intelligence-supported digital pathology. We highlight that NASH is most likely the causal factor for fibrosis progression in NAFLD, but the subjective definition makes the prognostic value of a histological NASH diagnosis of limited value. Third, the finding that prognostic information from biopsy and the very simple Fibrosis-4 score were comparable is important as it may lead to fewer biopsies and further move the field towards non-invasive means by which to define fibrosis and, importantly, use non-invasive tests as outcomes in clinical trials. However, all modalities had modest discriminatory capacity and new risk stratification systems are needed in NAFLD. Repeated measures of non-invasive scores may be a potential solution.
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| 2. |
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| 3. |
- Bader, Thomas K., 1980-, et al.
(författare)
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Path dependence in OSB sheathing-to-framing nailed connection revealed by biaxial testing
- 2018
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Ingår i: Journal of Structural Engineering. - Reston, VA : American Society of Civil Engineers (ASCE). - 0733-9445 .- 1943-541X. ; 144:10
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Tidskriftsartikel (refereegranskat)abstract
- OSB sheathing-to-wood framing connection, as typically used in light-frame shear walls, was experimentally examined in a novel biaxial test setup with respect to possible path dependence of the load-displacement relation. The connection with an annular-ringed shank nail was loaded under displacement control following nine different displacement paths within the sheathing plane, which coincided at a number of points. In intersection points, resultant connection force, its orientation and work performed on the connection system to reach the specific point were calculated and compared. Evaluation of experiments revealed significant path dependence with respect to orientation of force resultants at path intersection points. However, magnitude of the forces and the work carried out showed relatively small dependence of the displacement path undertaken. Comparison of uniaxial connection tests with the European yield model demonstrated strong contribution of withdrawal resistance of the ringed shank nail to its lateral strength. Results of this type are a valuable basis to build better models when simulating such connections in wood structures.
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| 4. |
- Caprolu, Giuseppe, et al.
(författare)
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Analytical and experimental evaluation of the capacity of the bottom rail in partially anchored timber shear walls
- 2012
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Ingår i: World Conference on Timber Engineering 2012 (WCTE 2012). - : WCTE 2012 Committee. - 9781622763054 ; , s. 157-166, s. 157-166
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Konferensbidrag (refereegranskat)abstract
- Kallsner and Girhammar have developed plastic design methods for light-frame timber shear walls that can be used for determining the load-carrying capacity when the shear walls are partially anchored. For such walls, the leading stud is not fully anchored against uplift and tying down forces are developed in the sheathing-to-framing joints. Since the forces in the anchor bolts and the sheathing-to-framing joints do not act in the same vertical plane, the bottom rail will be subjected to cross-wise bending, leading to possible splitting along the bottom side of the rail. Another possible brittle failure mode is splitting along the edge of the bottom rail in line with the sheathing-to-framing fasteners. An experimental program has been conducted using different anchor bolt locations, washer sizes and pith orientations. A fracture mechanics approach for the two failure modes is used to evaluate the experimental results. The comparison shows a good agreement between the experimental and analytical results. The failure mode is largely dependent on the distance between the edge of the washer and the edge of the bottom rail. The size of the washer seems also to have some influence on the failure load. The fracture mechanics models seem to capture the essential behaviour of the splitting modes and to include the decisive parameters. These parameters can easily be adjusted to experimental results and be used in design equations for bottom rails in partially anchored shear walls.
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| 5. |
- Florisson, Sara, et al.
(författare)
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A numerical study of the effect of green-state moisture content on stress development in timber boards during drying
- 2019
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Ingår i: Wood and Fiber Science. - : Society of Wood Science and Technology. - 0735-6161. ; 51:1, s. 41-57
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Tidskriftsartikel (refereegranskat)abstract
- Timber boards manufactured with a traditional sawing pattern often contain both heartwood andsapwood. In such boards, internal constraints can occur during drying because of a radial variation in greenstate(GS) MC between the heartwood (30-60%) and sapwood region (120-200%). Despite such knowledge,the initial MC is seldom considered when evaluating kiln-drying schedules. The effect of GS MC on thedevelopment of tangential tensile stress during drying is studied for four types of timber boards. A numericalmodel was developed that can simulate transient nonlinear orthotropic moisture flow and moisture–inducedstress and distortion in wood with the use of the finite element method. The stress analysis considers elastic,hygroscopic, and mechano-sorptive strain. The study shows that the GS MC does not significantly influencethe maximum stress state, but that it does influence the time at which the maximum tangential tensile stressoccurs at different exchange surfaces. This results in several periods in the drying schedule where unfavorablehigh stress situations in the tangential direction arise, which could lead to crack propagation.
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| 6. |
- Florisson, Sara, et al.
(författare)
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A three-dimensional numerical analysis of moisture flow in wood and of the wood's hygro-mechanical and visco-elastic behaviour
- 2021
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Ingår i: Wood Science and Technology. - : Springer. - 0043-7719 .- 1432-5225. ; 55:5, s. 1269-1304
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional numerical model was employed in simulating nonlinear transient moisture flow in wood and the wood's hygro-mechanical and visco-elastic behaviour under such conditions. The model was developed using the finite element software Abaqus FEA, while taking account of the fibre orientation of the wood. The purpose of the study was to assess the ability of the model to simulate the response of wood beams to bending and to the climate of northern Europe. Four-point bending tests of small and clear wood specimens exposed to a constant temperature and to systematic changes in relative humidity were conducted to calibrate the numerical model. A validation of the model was then performed on the basis of a four-point bending test of solid timber beams subjected to natural climatic conditions but sheltered from the direct effects of rain, wind and sunlight. The three-dimensional character of the model enabled a full analysis of the effects of changes in moisture content and in fibre orientation on stress developments in the wood. The results obtained showed a clear distinction between the effects of moisture on the stress developments caused by mechanical loads and the stress developments caused solely by changes in climate. The changes in moisture that occurred were found to have the strongest effect on the stress state that developed in areas in which the tangential direction of the material was aligned with the exchange surface of the beams. Such areas were found to be exposed to high-tension stress during drying and to stress reversal brought about by the uneven drying and shrinkage differences that developed between the outer surface and the inner sections of the beams.
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| 7. |
- Florisson, Sara, et al.
(författare)
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Analysis of hygro-mechanical behavior of wood in bending
- 2021
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Ingår i: Wood and Fiber Science. - : International society of wood science and technology (SWST). - 0735-6161. ; 53:1, s. 27-47
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Tidskriftsartikel (refereegranskat)abstract
- The empirical test developed as validation for a newbeamelementmodel that can account for bothmechanical and environmental load action in finite element analysis is presented. The testing protocol allowsfor the identification and analysis of contributing deflection components in bending under varying MCconditions, including mechano-sorption. The components of deflection in the shear-free span of a four-pointbending test and their responses to varyingmoisture are evaluatedwith an analytical procedure. The experimentwas conducted on clear, straight-grained sapwood and heartwood specimens of Norway spruce (Picea abies)(30 15 640 mm3). The program consisted of three phases: 1) long-term (LT) experiments under constanttemperature of 60°C and RH cycles between 40% and 80%, 2) a short-term static experiment to determine thevariation in the sample set and the load level of the LT experiment on end-matched specimens, and 3) creeptests at 60°C and constant humidity at either 40%or 80%to determine the effect ofmoisture on the viscoelasticcreep. Mass changes and hygro-expansion measured on matched specimens were used in the analyticalmethod. Constitutive models used for describing the material-level response to loads and moisture changeswere applied to the shear-free segment of the specimens disregarding actual moisture gradients and fiberorientation inside the test specimens. A successful identification of each deflection component and isolation ofmechano-sorption component was accomplished. In the 90 da of testing, the dominant component of the totaldeflection was the elastic component, followed by the mechano-sorptive component. Creep was found to benonnegligible and important in the correct description of mechano-sorption. The effect of moisture on theviscoelastic behavior showedmost important during loading and first stages of decreasing deflection rate phase.
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| 8. |
- Florisson, Sara, et al.
(författare)
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Modelling of mechano-sorption in clear wood by using an orthotropic non-linear moisture flow and stress model
- 2018
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Ingår i: WCTE 2018 - World Conference on Timber Engineering. - : World Conference on Timber Engineering (WCTE).
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Konferensbidrag (refereegranskat)abstract
- The European design standard for timber structures provides, besides obligatory safety requirements, a set of general serviceability requirements. Despite their generality, they have been proven important in design of timber structures, especially in varying climatic conditions, where the time dependent deflection can have a dominant role in long term performance. The total deformation consists of instantaneous elastic deformation, hygroscopic deformation, time dependent creep and mechano-sorptive deformation. The three latter deformations are influenced by climate, and when the change in climate is considerable over time, the deflection will significantly increase. In this paper a test-setup is created to study the effect of mechano-sorption on the global deflection of clear wood samples. The samples are loaded in a three-point bending test subjected to a constant mechanical load combined with a cyclic climatic load. The moisture induced stress and bending distortion were simulated by taking into account elastic, hygroscopic and mechano-sorptive strain. The non-linear moisture flow was simulated using Fick’s law. A parametric study was performed to obtain a better understanding of the constitutive equation, especially the term related to the moisture and temperature dependent diffusion coefficient. In addition to the simulations, an experiment was performed to verify the global deflection and mass change. The obtained results show that the mechano-sorption behaviour of the tested clear wood samples can be modelled, but an improvement of both the experimental setup and the model is required to come to more accurate conclusions on this type of long-term material behaviour.
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| 9. |
- Florisson, Sara
(författare)
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Moisture-induced stress and distortion of wood : A numerical and experimental study of wood's drying and long-term behaviour
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the current advances made in three-dimensional modelling of wood, it is possible to provide an overall picture of moisture flow, and moisture-induced stress and deformations, whereas previously, experiments only provided local measurements. The main aim of the doctoral thesis is to investigate the possibilities of the developed three-dimensional numerical model to predict the behaviour of wood when simultaneously exposed to a mechanical load and a particular climate. Three applications in the fields of wood drying and long-term behaviour of wood are considered: 1) the effect of green-state moisture content on the drying behaviour of timber boards, 2) the calibration of the numerical model based on a long-term four-point bending tests using small wood beams subjected to a constant temperature and systematic relative humidity (RH) changes, and 3) the validation of the numerical model by means of a long-term four-point bending test on solid timber beams subjected to Northern European climate. As part of the second application, an experimental methodology and analytical method were designed. The numerical model was developed in finite element software Abaqus FEA® and consists of several user-subroutines to include material orientation (i.e. annual ring pattern, conical shape and spiral grain), and the selected constitutive behaviour and required boundary conditions. To simulate the moisture flow, a nonlinear single-Fickian approach was combined with a nonlinear Neumann boundary condition, which describes the flux normal to the exchange surface based on a moisture and temperature dependent surface emission coefficient. A strain relation was used that accounts for hygro-expansion, and the elastic, creep and mechano-sorptive behaviour. The analytical method describes the elastic and creep deflection in the constant moment area of the four-point bending setup, and was used to isolate and assess the mechano-sorption deflection in the cumulative moisture content domain. The results show that the three-dimensional character of the numerical model contributed to the analysis and visualisation of the different stress states and deformations that are affected by material properties that vary (i.e. from pith to bark, between heartwood and sapwood, and due to temperature and moisture content), fibre orientation and climate. The simulations made on timber boards clarified phenomena, such as stress reversal and casehardening associated with wood drying, and showed that the green-state moisture content affected the time, size and frequency with which extremes in tangential tensile stress developed inside the timber during drying. The results of the calibration and validation indicated that the numerical model is able to describe moisture change and gradients in the considered temperature and relative humidity ranges (between -2-60℃ and 40-80% RH), as well as the deflection. The experimental methodology and analytical method led to a successful identification of each deflection component and isolation of the mechano-sorptive deflection curves. The experimental methodology benefitted the calibration of the numerical model. In conclusion, the presented three-dimensional numerical model compatible with Abaqus FEA® provides a powerful tool for scientists and timber engineers to study the combined effect of load and climate on stress state and deformations of various timber products in a wide field of applications.
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| 10. |
- Florisson, Sara, et al.
(författare)
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Three-dimensional orthotropic nonlinear transient moisture simulation for wood : analysis on the effect of scanning curves and nonlinearity
- 2020
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Ingår i: Wood Science and Technology. - : Springer. - 0043-7719 .- 1432-5225. ; 54, s. 1197-1222
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces, with the development of user-subroutines in the finite-element software Abaqus FEA (R), a new practical analysis tool to simulate transient nonlinear moisture transport in wood. The tool is used to revisit the calibration of moisture simulations prior to the simulation of mechanical behaviour in bending subjected to climate change. Often, this calibration does not receive sufficient attention, since the properties and mechanical behaviour are strongly moisture dependent. The calibration of the moisture transport simulation is made with the average volumetric mass data experimentally obtained on a paired specimen of Norway spruce (Picea abies) with the dimensions 30x15x640 mm(3). The data, from a 90-day period, were measured under a constant temperature of 60 degrees C and systematic relative humidity cycles between 40 and 80%. A practical method based on analytical expressions was used to incorporate hysteresis and scanning behaviour at the boundary surface. The simulation tool makes the single-Fickian model and Neumann boundary condition readily available and the simulations more flexible to different uses. It also allows for a smoother description of inhomogeneity of material. The analysis from the calibration showed that scanning curves associated with hysteresis cannot be neglected in the simulation. The nonlinearity of the analysis indicated that a coherent set of moisture dependent diffusion and surface emission coefficient is necessary for the correct description of moisture gradients and mass transport.
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