Statične mehanske lastnosti starega konstrukcijskega lesa

Škorjanc, Jani (author), Straže, Aleš (mentor)

V diplomski nalogi smo preučili vpliv naravnega aerobnega staranja na strukturne, kemijske in statične mehanske lastnosti smrekovega (Picea abies Karst.) konstrukcijskega lesa. Z več objektov smo dendrokronološko datirali les s starostjo do 272 let. Vzorcem smo s FT-IR spektroskopijo kemometrično določali relativni delež hemiceluloz, relativni delež lignina ter stopnjo kristaliničnosti celuloze. Statično, 4-točkovno upogibno testiranje čistih laboratorijskih preizkušancev (10 mm × 7 mm × 170 mm, R × T × L) smo izvedli v suhi (20 °C/20 %) in vlažni klimi (20 °C/88 %). Ugotovili smo, da ima stari konstrukcijski les v primerjavi z recentnim lesom nižji relativni delež hemiceluloz, medtem ko delež lignina ostaja na isti ravni. Pri nekaterih vzorcih starega konstrukcijskega lesa smo ugotovili tudi višjo stopno kristaliničnosti celuloze. Proces staranja ni vplival na upogibno trdnost in togost konstrukcijskega lesa; povišala pa se je variabilnost mehanskih lastnosti. Opazili smo, da je pri starem konstrukcijskem lesu specifični modul elastičnosti bolj odvisen od spreminjanja vlažnosti lesa (2,26 %/%) kot pri recentnem lesu (< 2,0 %/%).

• Language: Slovenian
• Keywords: les, konstrukcijski les, staranje, mehanske lastnosti
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: BF - Biotechnical Faculty
• Publisher: [J. Škorjanc]
• Year: 2023
• PID: 20.500.12556/RUL-150419
• UDC: 630*833:630*812.7
• COBISS.SI-ID: 166528003
• Publication date in RUL: 17.09.2023

Secondary language

• Language: English
• Title: Static mechanical properties of old structural timber

Abstract

In the thesis, the influence of natural aerobic aging on the structure and static-mechanical properties of Norway spruce (Picea abies Karst.) structural timber was studied. Several objects were dendrochronologically dated to an age of up to 272 years. Samples were determined chemometrically by FT-IR spectroscopy for the relative proportion of hemicelluloses, the relative proportion of lignin, and the degree of crystallinity of cellulose. Static 4-point bending tests on small clear specimens (10 mm × 7 mm × 170 mm, R × T × L) were performed in both dry (20°C/20%) and humid climates (20°C/88%). It was found that the old structural wood had a lower relative content of hemicelluloses than the recent wood while the lignin content remained the same. A higher degree of crystallinity of cellulose was also observed in some samples of old structural wood. The aging process did not affect the flexural strength and stiffness of the structural timber but the variability of the mechanical properties increased. The specific modulus of elasticity of old structural timber was found to be more dependent on the change in wood moisture content (2.26%/%) than that of recent timber (< 2.0%/%).

• Keywords: wood, structural timber, aging, mechanical properties