Effective cross section size after 30 minutes fire exposure on all sides: d_ef=β_n∙t+k_0∙d_0=0,70 mm/min∙30min+1,0∙7mm=28mm Size of the effective cross section: Width b: 133 mm - 2∙28 mm = 77 mm Height h: 400 mm - 2∙28 mm = 344 mm Beam properties of the effective cross section after 30min fire exposure: Bending strength edgewise fm,0,edge,k = 44 N/mm2 Shear strength edgewise fv,0,edge,k = 4,2 N/mm2 Compression perpendicular to grain edgewise fc,90,edge,k = 6 N/mm2 Modulus of elasticity E0,k = 11 600 N/mm2 Modulus of rigidity G0,edge,mean = 400 N/mm2 Area of cross section A =b∙h = 26488 mm2 Section modulus Wy = b∙h2/6 = 1,52∙106 mm3 Moment of inertia Iy = b∙h3/12 = 2,61∙107 mm4 Moment of inertia Iz = h∙b3/12 = 1,31∙107 mm4 Torsion moment of inertia Itor = 0,3∙h∙b3 = 4,71∙107 mm4 Modification factor kmod,fi = 1,0 Modification factor kfi = 1,1 Material safety factor γM,fi (default value in EC5) = 1,0 Size effect factor kh = (300/344)0,15 = 0,98 9. CALCULATION EXAMPLES OF LVL STRUCTURES c,90,d = c,90,d ef = c,90,d ∙ ( + 30 mm) = 15,2kN 150 mm ∙ (51 mm+ 30 mm) = 1,3N/mm2 kc,90 is 1,4 for LVL-P flatwise and fc,90,k is 2,2 N/mm2. c,90 ∙ c,90,flat,d =1,4∙ 1 1 , , 1 2∙ 2,2 m N m2 = 2,8 N/mm2 > c,90,d →OK ef = n ∙ + 0 ∙ 0 = 0,70 mmmin∙ 30min+1,0∙ 7mm=28mm 9.11 MAIN BEAM OF ROOF STRUCTURE IN 30MIN FIRE EXPOSURE Single-span main beam of a flat roof structure is GLVL 48 P beam 133x400 mm. Span length is L = 4000 mm, width of the loading area 8000 mm and roof purlins are on the top of the beam. Support length is 100 mm. Snow load sk is 2,5 kN/m2, own weight of the roof structure is 1,0 kN/m2 and own weigh of the beam is 0,2 kN/m. The structure fulfils the ULS and SLS requirements in normal temperature where wnet,fi ≤ L/300 has been the most critical requirement. The fire resistance R30 of the beam needs to be verified for fire exposure on all sides of the beam. LVL Handbook Europe 211
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