Hull i brukt konstruksjonsvirke
Bachelor thesis
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https://hdl.handle.net/11250/3079117Utgivelsesdato
2023Metadata
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Sammendrag
Vi ble tildelt oppgaven med å utføre testing av brukte treplanker med ulike plasseringer av hull for å undersøke effekten og sammenligne resultatene med forslaget til ombrukstandarden. Disse førsøkene og funnene vil kunne hjelpe til videre med å kartlegge veiene til en sirkulær økonomi for treverk og et redusert utslipp. For å oppnå dette formålet gjennomførte vi en firepunkts bøyetest på tretti 2x4 (48 mm x 98 mm) planker som var tørre og befant seg i god stand. Dimensjonene valgte vi ut ifra det mest brukte konstruksjonsvirke som vil ha en størst retur i fremtiden fremover. Testingen ble utført i to omganger, der vi først testet stivheten og deretter bruddstyrken med hull plassert i ulike soner. Hulldiameterne var hovedsakelig utvalgt for å etterligne det mest realistiske utfallet med boring til trekkrør i stendere.Resultatene av testingen viste at materialet fortsatt hadde betydelig styrke til tross for tilstedeværelsen av hull. Imidlertid hadde hullene en innvirkning på bruddforløpet, da store spenninger ble overført til hullområdet på grunn av redusert tverrsnitts areal. Dette resulterte i en økning av spenningskonsentrasjonen rundt hullene. Dette gjør derfor at virket deformerer seg lettere, spesielt i strekksonen til planken. This bachelor thesis researches the viability of reusing old wooden planks, in this case 2x4 with holes. The assignment was issued by a collective group of partners working on the new Norwegian standard for allowing old wood to be re-graded as construction timber. Omtre, Treteknisk and Standard Norge, guided us along the way with other partners such as Horisont Miljøpark give us the materials needed. The goal of this project is to help with research for re-grading timber to reduce the carbon emissions connected to production of production of new wood. Therefor we got to know if old planks are as good as new. To find compassion values for old and new timber, we had to carry out a test which gave us the values needed. A four-point bending test would give us the necessary data to make conclusions and comparisons. Before we started testing, we visually graded the timber based on standards for new wood. After the documentation of the physical condition and other reasonable factors we carried out the four-point bending test. The setup was in two parts, one part where none of the timber had holes, and the stiffness was measured. The second part was holes of 18mm in 5 different heights in the middle of the beam’s length, and a 35mm hole. This was to look at the tensile and compression effect with holes in zones called ‘constructive zone’ and ‘non-construction zone’.The result showed us that a lot of timber gets graded significantly lower than its actual strength. We also learned that old timber in this case, doesn’t lose a lot of bending strength, but they lose about 15% elasticity. The holes of 18mm in the upper section on the compression side had small to no effect, but the same hole on the lower tensile side had a bigger effect. Drilling holes decrease the stiffness but will increase if placed in the center with a maximum diameter of 2/4 of the height. We concluded with used timber kept dry after demolition can be reused. The holes will make a weaker point in the cross section where tensile stress occurs. Bending a material still rely on the strength of knots and annuals rings and should avoid drilling holes close to weak points.