Vpliv staranja na fizikalno-mehanske lastnosti lesa stropne konstrukcije : diplomsko delo - univerzitetni študij

Ifko, Beno (author), Gorišek, Željko (mentor), Straže, Aleš (comentor), Čufar, Katarina (reviewer)

Na odvzetem lesu navadne smreke (Picea abies (L.) Karst.), iz lesene stropne konstrukcije v kapeli Graščine Preddvor, smo ovrednotili vpliv staranja na osnovi izbranih fizikalno-mehanskih lastnosti vgrajenega lesa (gostote, ravnovesne vlažnosti, dimenzijske stabilnosti, statičnega in dinamičnega modula elastičnosti, upogibne, tračne in strižne trdnosti trdnosti). Z dendrokronološkimi raziskavami smo časovno umestili odvzete vzorce. Datirali smo jih v sredino 19. stoletja. Starost odvzetih preizkušancev za mehansko testiranje je tako med 160 in 170 leti. Povprečna gostota v absolutno suhem stanju lesa stropne konstrukcije je bila 398 kg/m3, povprečna gostota zračno suhega lesa pa je znašala 429 kg/m3. Povprečna ravnovesna vlažnost naših preizkušancev je bila v zgornjem higroskopskem območju (% = 87%), v procesu adsorpcije 17,8 % in v procesu desorpcije 19,1%. Na spodnji meji kvazilinearnega območja (% = 33 %) pa je bila ravnovesna vlažnost v procesu adsorpcije 8,4 % in v procesu desorpcije 9,6 %. Kazalniki dimenzijske stabilnosti so normalni, razen sorpijskega kvocienta in anizotropije, ki sta neugodna. Upogibna trdnost je bila 72,3 MPa, elastični modul iz upogiba pa je pri tem bil 9,4 GPa. Dinamični elastični modul v vzdolžni smeri pri frekvenčnem odzivu je bil 12,3 GPa. Prečni dinamični elastični modul je bil nižji in je znašal 10,9 GPa. Tlačna trdnost vzporedno z vlakni je bila 40,5 MPa. Strižna trdnost v vzdolžno radialni ravnini je bila za odvzete preizkušance 8,6 MPa. Vse te vrednosti ne izkazujejo drastičnega znižanja in s tem poslabšanja nosilnosti lesa stropne konstrukcije. Les bi lahko služil svojemu namenu še več stoletij, če ne bi prišlo do lokalnega razkroja, zaradi intenzivnega zamakanja skozi streho.

• Language: Slovenian
• Keywords: smrekovina, staranje, dendrokronologija, fizikalne lastnosti, mehanske lastnosti
• Work type: Undergraduate thesis
• Typology: 2.11 - Undergraduate Thesis
• Organization: BF - Biotechnical Faculty
• Place of publishing: Ljubljana
• Publisher: [B. Ifko]
• Year: 2016
• Number of pages: X, 63 f.
• PID: 20.500.12556/RUL-117867
• UDC: 630*561.24
• COBISS.SI-ID: 2679177
• Publication date in RUL: 31.07.2020

Secondary language

• Language: English
• Title: Effect of aging on physical-mechanical properties of wood of a ceiling construction

Abstract

From the specimens of the wood Norway spruce (Picea abies (L.) Karst.), taken from the wood ceiling construction in the chapel of the Preddvor manor, we evaluated the influence of aging on the basis of the selected physical-mechanical properties of the inbuilt wood. Dendrochronological investigation helped us to identify the felling dates of the wood. The dating showed that the construction is derived from the middle of the 19th century. The age of the tested material is between 160 and 170 years. The average density of the oven dry massive ceiling wood was 398 kg/m3. The average density of the air dry wood was 429 kg/m3. The average value of equilibrium moisture content was in the upper quasi-linear area (% = 87 %), in the process of adsorption 17.8 % and in the process of desorption 19.1 %. The indicators of dimension stability are normal, but the ratio of sorption and anisotropy are unfavourable. The modulus of elasticity was determined for the equilibrated specimens using a 3-point bending test and dynamic excitation in the longitudinal and transverse direction. The correspondence between the methods was good, with the coefficient of determination greater than 0.85. The bending strength was 72.3 MPa and the modulus of elasticity from bending was 9.4 GPa. The dynamic elastic modulus in the longitudinal direction was 12.3 GPa and in the transverse direction 10.9 GPa. The compressive strength parallel to grain was 40.5 MPa. The shear strength in the longitudinal radial plane was 8.6 MPa. All these values do not show a drastic reduction and thus deterioration of the load-carrying capacity of the wood ceiling construction. The wood could serve its purpose for more centuries to come if the intensive roof leakage had not led to local degradation.

• Keywords: spruce wood, ageing, dendrocronology, physical properties, mechanical properties