| 1. |
- Ah Shenga, Pedro, et al.
(författare)
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3D Phase-shift Laser Scanning of Log Shape
- 2014
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 9:4, s. 7593-7605
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a portable scanner to determine the 3D shape of logs was evaluated and compared with the measurement result of a computer tomography scanner. Focus was on the accuracy of the shape geometry representation. The objective is to find a feasible method to use for future data collection in Mozambique in order to build up a database of logs of tropical species for sawing simulations. The method chosen here was a 3D phase-shift laser scanner. Two logs, a birch log with bark and a Scots pine log without bark, were scanned, resulting in 450 cross sectional “images” of the pine log and 300 of the birch log. The areas of each point cloud cross section were calculated and compared to that of the corresponding computer tomography cross section. The average area difference between the two methods was 2.23% and 3.73%, with standard deviations of 1.54 and 0.91, for the Scots pine and birch logs, respectively. The differences in results between the two logs are discussed and had mainly to do with presence of bark and mantle surface evenness. Results show that the shape measurements derived from these methods were well correlated, which indicates the applicability of a 3D phase-shift laser scanning technology for gathering log data.
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| 2. |
- Ahmed, Sheikh Ali, et al.
(författare)
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Anatomical properties and process parameters affecting blister/blow formation in densified European aspen and downy birch sapwood boards by thermo-hygro-mechanical compression
- 2013
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 48:24, s. 8571-8579
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Tidskriftsartikel (refereegranskat)abstract
- Approximately, 13.5 % of the standing volume of productive forest land in Sweden is covered by birch and aspen, which provides the vast potential to produce value-added products such as densified wood. This study shows whether it is possible to densify those species with a thermo-hygro-mechanical (THM) process using heat, steam, and pressure. In this process, transverse compression on thin European aspen (Populus tremula) and downy birch (Betula pubescens) boards was performed at 200 ºC with a maximum steam pressure of 550 kPa. To obtain a theoretical 50 % compression set, the press’s maximum hydraulic pressure ranged from 1.5 to 7.3 MPa. Preliminary tests showed that ~75 % of the birch boards produced defects (blisters/blows) while only 25 % of the aspen boards did. Mainly, radial delamination associated with internal checks in intrawall and transwall fractures caused small cracks (termed blisters) while blows are characterized by relatively larger areas of delamination visible as a bumpy surface on the panel. Anatomical investigations revealed that birch was more prone to those defects than aspen. However, those defects could be minimized by increasing the pre-treatment time during the THM processing.
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| 3. |
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| 4. |
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| 5. |
- Björngrim, Niclas, et al.
(författare)
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Factory Mounted and Retrofit Passive Resistance Sensors Adapted to Monitor Moisture Content in Timber Bridges
- 2017
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Ingår i: BioResources. - : North Carolina State University. - 1930-2126. ; 12:4, s. 7218-7227
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Tidskriftsartikel (refereegranskat)abstract
- The biggest threats to the longevity of a timber bridge are rot and decay. Wood protection by design, inspections, and monitoring of the bridge for elevated moisture content will ensure that the full service life of the structure can be achieved. Today's sensors for moisture content measurements are limited in their functionality and range. This paper presents a sensor that can be both factory installed and retrofitted, which can measure the moisture content through the cross-section of the member in a timber bridge. The sensor has been mounted on Sundbron bridge during manufacturing and retrofitted on Gislaved bridge. The ensuing measurements helped to adjust a design flaw on Gislaved bridge. Monitoring of Sundbron showed that the bridge deck dried up after the bridge had been exposed to sleet and snow during the on-site assembly of the stress laminated bridge deck
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| 6. |
- Björngrim, Niclas, et al.
(författare)
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Health monitoring of a cable-stayed timber footbridge
- 2011
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Konferensbidrag (refereegranskat)abstract
- This paper presents a structural health monitoring system to a timber bridge that will be built in Skellefteå during 2011. The bridge is a cable-stayed timber footbridge spanning 130 meters. The main objectives of using the health monitoring system are to verify the structural design and the long-term behavior of the bridge. The structural health monitoring system consists of GNSS receivers, MEMS accelerometers, laser positioning systems, wireless moisture content sensors, strain gauges and weather stations.
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| 7. |
- Björngrim, Niclas, et al.
(författare)
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Health monitoring of a cable-stayed timber footbridge
- 2011
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Ingår i: Proceedings of SHATIS'11 International Conference on Structural Health Assessment of Timber Structures. - : Laboratório Nacional de Engenharia Civil – LNE.
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Konferensbidrag (refereegranskat)
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| 8. |
- Björngrim, Niclas, et al.
(författare)
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Moisture Content Monitoring of a Timber footbridge
- 2016
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 11:2, s. 3904-3913
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Tidskriftsartikel (refereegranskat)abstract
- Construction of modern timber bridges has greatly increased during the last 20 years in Sweden. Wood as a construction material has several advantageous properties, e.g., it is renewable, sustainable, and aesthetically pleasing, but it is also susceptible to deterioration. To protect wood from deterioration and ensure the service life, the wood is either treated or somehow covered. This work evaluates a technology to monitor the moisture content in wood constructions. Monitoring the moisture content is important both to verify the constructive protection and for finding areas with elevated levels of moisture which might lead to a microbiological attack of the wood. In this work, a timber bridge was studied. The structure was equipped with six wireless sensors that measured the moisture content of the wood and the relative humidity every hour. Data for 744 days of the bridge are presented in this paper. Results show that the technology used to monitor the bridge generally works; however, there were issues due to communication problems and malfunction of sensors. This technology is promising for monitoring the state of wood constructions, but a more reliable sensor technology is warranted continuous remote monitoring of wood bridges over long periods of time.
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| 9. |
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| 10. |
- Björngrim, Niclas, et al.
(författare)
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Multivariate Screening of the Weather Effect on Timber Bridge Movements
- 2016
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 11:4, s. 8890-8899
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Tidskriftsartikel (refereegranskat)abstract
- Monitoring displacements and weather impact of complex structures such as a large cable stayed footbridge generates large amount of data. In order to extract, visualize and classify health-monitoring data to get a better comprehension multivariate statistical analysis is a powerful tool. This paper is a screening to evaluate if principal component analysis is useful on health monitoring data. Principal component analysis (PCA) and projections to latent structures by means of partial least squares (PLS) modeling were used to achieve a better understanding of the complex interaction between bridge dynamics and weather effects. The results show that principal component analysis (PCA) give good overview of the collected data, and PLS modeling show that winds from east and west best explain bridge movements.
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