Effects of natural ageing on selected physical and mechanical properties of structural timber

Les je po poseku in uporabi za konstrukcije izpostavljen staranju, ki je med drugim odvisno od pogojev izpostavitve. V času življenjske dobe oz. uporabe je les izpostavljen fotodegradaciji, biodegradaciji, površinskim in notranjim strukturnim spremembam in staranju, ki se kaže v spremembi barve, kemijske sestave, higroskopnosti, dimenzijske stabilnosti ter nekaterih mehanskih lastnosti. Podajamo pregled literature, s posebnim poudarkom vpliva pogojev izpostavitve na spremembe lastnosti lesa ter pregled kemijskih in mikrostrukturnih sprememb ter sprememb barve, sorpcijskih in mehanskih lastnosti. V splošnem so spremembe zaradi staranja lahko zelo počasne in jih je težko ovrednotiti tudi zaradi velike naravne variabilnosti lesnih lastnosti. Poznavanje sprememb v naravno staranem lesu je ključno pri ohranjanju kulturne dediščine. Pri načrtovanju vzdrževanja, konzerviranja ter pri obnovi kulturne dediščine, z upoštevanjem staranja konstrukcijskega lesa bolje razumemo strukturne spremembe, vlažnostna in napetostno-deformacijska stanja lesenih konstrukcij ter interakcije z drugimi gradbenimi materiali.After harvesting, wood in constructions undergoes an ageing process that depends, among other things, on exposure conditions. During its lifetime wood is subject to photodegradation, biodegradation, surface and internal structural changes, and ageing, which is reflected in changes in colour, chemical composition, hygroscopicity, dimensional stability, and mechanical properties. We present a literature review, with particular emphasis on the influence of exposure conditions on changes in wood properties, chemical and microstructural changes, and changes in colour, sorption, and mechanical properties. In general, ageing-related changes can be very slow and difficult to detect, in part because of the wide natural variability in wood properties. Knowledge of the changes in naturally aged wood is critical for preserving cultural heritage, evaluating the safety of wood structures, and planning their conservation. When planning maintenance, conservation, and restoration of cultural heritage, we can better understand the structural changes, moisture and stress deformation states of wood structures, and interactions with other building materials if we consider the ageing of structural wood