Abstract
The article deals with the peculiarities of calculating bearing capacity for axially loaded timber members under uneven fire action. According to LST EN 1995-1-2 and finite element modelling for determining temperature fields and variations in timber strength under elevated temperature, the method of simple calculations was applied. Calculations are based on the data and results of experimental investigations into the resistance of axially loaded members to fire. Data on variations in timber strength were obtained conducting laboratory tests using the specimens of Lithuanian pine under elevated temperature. Santrauka Atliekant šį tyrimą išnagrinėti netolygiai gaisro veikiamų neapsaugotų liaunų medinių centriškai gniuždomų elementų laikomosios galios skaičiavimo ypatumai, taikant paprastuosius skaičiavimo metodus, pateiktus LST EN 1995-1-2, ir naudojant baigtinių elementų programa nustatytus elemento skerspjūvio temperatūrinius laukus medienos stiprių pokyčiams įvertinti. Skaičiavimo duomenys grindžiami atliktais eksperimentiniais liaunų medinių centriškai gniuždomų strypų atsparumo ugniai tyrimo duomenimis ir rezultatais. Medienos stiprių pokyčiai, naudojami skaičiuojant, paimti remiantis Lietuvoje augančios pušiės medienos stiprių pokyčių bandymo rezultatais.
Highlights
Timber structures in a fire situation are commonly rated as more dangerous if compared with steel and concrete structures
Streiger and Fontana (2005) pointed to the influence of a bending moment on the bearing capacity of timber columns; the results of these investigations were based on data obtained at ambient temperatures and details set out in expressions taken from LST EN 1995-1-1:2005
The analysis of experimental data and calculation results of axially compressed timber members show that some additional factors can be significant and the influence of these factors must be investigated more thoroughly:
Summary
Timber structures in a fire situation are commonly rated as more dangerous if compared with steel and concrete structures. The uneven charring of a timber cross section can induce a bending moment even under axial loading conditions. Streiger and Fontana (2005) pointed to the influence of a bending moment on the bearing capacity of timber columns; the results of these investigations were based on data obtained at ambient temperatures and details set out in expressions taken from LST EN 1995-1-1:2005. The aim of the made calculations was to obtain the influence of eccentricities induced by uneven charring on the behaviour and bearing capacity of a timber member under fire conditions. The calculations of the strength of the members loaded with axial force and bending as well as induced by uneven cross-section charring was based on the remaining cross-section method and experimental charring depth obtained for each side of the member. Eccentricities used in calculations consist of the mean value of the measured bow imperfection equal to 8 mm and eccentricities due to reduction in the cross-section induced by charring (see Fig. 2)
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