2) Determine the allowable capacity (service) of the built up member shown below
ID: 1712153 • Letter: 2
Question
2) Determine the allowable capacity (service) of the built up member shown below, which is utilized as a compression member in a large railroad truss bridge. The member is pinconnected at each end and has an unbraced length of 21’-0”. The channels are C10x15.3s. Assume the member is made of A36 steel. You may neglect the effects of the rivets and associated holes. Check the following :
a. Global buckling of each channel
b. Global buckling of the built up member
2) Determine the allowable capacity (service) of the built up member shown below, which is utilized as a compression member in a large railroad truss bridge. The member is pin connected at each end and has an unbraced length of 21'-0". The channels are C10x15.3s. Assume the member is made of A36 steel. You may neglect the effects of the rivets and associated holes. Check the following: Global buckling of each channel Global buckling of the built up member a. b. END TIE PLATE SINGLE LACING 8.0 CHANNELS BUILT UP COLUMN N.TS 8.0Explanation / Answer
a)Individual channel section buckling:
Unbraced length of channel section in minor axis = 8"
Unbraced length of channel section in major axis=21'=252"
Moment of inertia of channel about major axis=67.4 in4
moment of inertia of channel about minor axis = 2.28 in4
Modulus of elasticity of steel=29000ksi
Buckling capapcity about major axis = (pi2*29000*67.4)/2522 = 303.78 kips
Buckling capapcity about minor axis = (pi2*29000*2.28)/82 =10196.5 kips
Therefore, buckling capapcity of each channel section = 303.78 kips
b) The unbraced length of builtup column=21 '
moment of inertia of built up section about centroidal horizontal axis = 2*[2.28 +4.49*(3.3662)]=106.3in4
moment of inertia of built up section about centroidal vertical axis = 2*67.4=134.8 in4
Buckling cpapcity of built up section = pi2*29000*106.3/2522 = 479.1 kips
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