(a) Explain what is meant by lateral torsional buckling.
(b) A floor system in a steel framed building comprises a reinforced concrete slab
supported on simply supported steel universal beam sections spanning 7.2m and
orientated such that they are in bending about their major axes of bending. The
beam sections are 406 imes 140 imes 39 UB's. In the initial design, the concrete slab
was deemed to provide lateral restraint to the full length of the compression
flanges of the beams. A design detail revision being proposed would result in
lateral restraint being provided to the compression flanges only at both ends of
the beam and mid-span. Calculate the reduction is bending moment capacity of
the beams if this design revision is to be implemented. Assume a Class 1 section
and a design strength of 275MPa. You may also assume C_(1)=1.0 for the
determination of M_(cr).
The relevant section properties and material data are as follows:
E=210,000(N)/(m)m^(2),G=81,000(N)/(m)m^(2),f_(y)=275(N)/(m)m^(2)
h=398mm,b=141.8mm,W_(pl,y)=724 imes 10^(3)mm^(3)
I_(z)=410 imes 10^(4)mm^(4),I_(w)=0.155 imes 10^(12)mm^(6),I_(T)=10.7 imes 10^(4)mm^(4)
(a)
Explain what is meant by lateral torsional buckling
(20%)
(b)
A floor system in a steel framed building comprises a reinforced concrete slab supported on simply supported steel universal beam sections spanning 7.2 m and orientated such that they are in bending about their major axes of bending. The beam sections are 406 x 140 x 39 UB's. In the initial design, the concrete slab was deemed to provide lateral restraint to the full length of the compression flanges of the beams. A design detail revision being proposed would result in lateral restraint being provided to the compression flanges only at both ends of the beam and mid-span. Calculate the reduction is bending moment capacity of the beams if this design revision is to be implemented. Assume a Class l section and a design strength of 275 MPa. You may also assume Ci=1.0 for the determination of Mer. (80%)
The relevant section properties and material data are as follows:
E = 210.000 N/mm2 G = 81,000 N/mm2 fy = 275 N/mm2 h = 398 mm b = 141.8 mm Wpl,y = 724x103 mm3 Iz=410x104 mm4 Iw =0.155x1012 mm6 IT = 10.7x104 mm4
