Moment of Inertia of Trapezoid Beam
Moment of Inertia of Trapezoid Beam
(OP)
Its been days since I have been struggling to get the right second moment of area for a composite beam.
Attached is the section in question. Concrete slab on top of a steel trapezoid girder. I just can't get the moment of inertia for the two inclined webs of the steel girder. Tried every method, even subtracting the inner empty area's inertia from the full trapezoidal inertia but still not the right answer.
Here is the right answer for the total composite section.
Elastic Neutral Axis after Concrete Transformation: 695.5mm from bottom of the girder.
Total Elastic Moment of Inertia of the Entire Section: 1.201-e10 mm4
Does anyone know any method to calculate the Moment of Inertia for this section? Thanks a million for your help.
Attached is the section in question. Concrete slab on top of a steel trapezoid girder. I just can't get the moment of inertia for the two inclined webs of the steel girder. Tried every method, even subtracting the inner empty area's inertia from the full trapezoidal inertia but still not the right answer.
Here is the right answer for the total composite section.
Elastic Neutral Axis after Concrete Transformation: 695.5mm from bottom of the girder.
Total Elastic Moment of Inertia of the Entire Section: 1.201-e10 mm4
Does anyone know any method to calculate the Moment of Inertia for this section? Thanks a million for your help.






RE: Moment of Inertia of Trapezoid Beam
I have no connection with IES, Inc. except as a satisfied use.
Jim
RE: Moment of Inertia of Trapezoid Beam
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Moment of Inertia of Trapezoid Beam
RE: Moment of Inertia of Trapezoid Beam
iv
RE: Moment of Inertia of Trapezoid Beam
Top and bottom plates are straightforward. The side plates may be considered as two vertical plates with a height of 711mm and a thickness of 9.5/cos36 or a single vertical plate of 19/cos36 = 23.485mm.
The area is 1981*13 + 25*608 + 23.485*711 = 75,651mm2, slightly less than found by iv63.
The moment of inertia and centroid may be calculated in the usual manner.
BA
RE: Moment of Inertia of Trapezoid Beam
BA
RE: Moment of Inertia of Trapezoid Beam
I get a slightly lower I value of 1.15E10 with my hand calc. That's not that difficult of a hand calc. The trickiest part is calculating the moment of inertia of the inclined web. It should be:
I(inclined) = (I_sa + Iwa)/2 + ((Isa-Iwa)/2)*cos(2*theta)
RE: Moment of Inertia of Trapezoid Beam
=)
RE: Moment of Inertia of Trapezoid Beam
I hope this helps you.
RE: Moment of Inertia of Trapezoid Beam
RE: Moment of Inertia of Trapezoid Beam
RE: Moment of Inertia of Trapezoid Beam
This probably is much more easier then downloading any specific software for calculating properties. Ofcourse this wont give you detailed properties but still not bad. Thanks.