Second Moment Area of Moment Frame with Shear Truss
Second Moment Area of Moment Frame with Shear Truss
(OP)
Hi there,
I am trying to calculate the deflection of a moment frame made up with a shear truss.

Each bay is 3 metres, so total height is 12 metres. I am using a static horizontal load of 10000 N/m.
I am modelling it as a cantilever beam using stiffness 'K' as (8*E*I)/L^4
I need to find the second moment area of the structure. For the shear truss alone I get the correct deflection. In the literature I have found that the second moment of area is 0.9*(2*(A*1.5^2)). A is the cross-sectional area of the column, 1.5 is the distance in metres from the neutral axis. Using this I get the correct answer. However, when I add unbraced bays to each side I do not.
I guessed that the new second moment area of the total structure is 0.9*(2*(A*1.5^2)) + 2*(A*4.5^2), but I don't get the correct answer from this.
So, Could somebody please tell me what the second moment of area for this structure is, please?
Best wishes
I am trying to calculate the deflection of a moment frame made up with a shear truss.

Each bay is 3 metres, so total height is 12 metres. I am using a static horizontal load of 10000 N/m.
I am modelling it as a cantilever beam using stiffness 'K' as (8*E*I)/L^4
I need to find the second moment area of the structure. For the shear truss alone I get the correct deflection. In the literature I have found that the second moment of area is 0.9*(2*(A*1.5^2)). A is the cross-sectional area of the column, 1.5 is the distance in metres from the neutral axis. Using this I get the correct answer. However, when I add unbraced bays to each side I do not.
I guessed that the new second moment area of the total structure is 0.9*(2*(A*1.5^2)) + 2*(A*4.5^2), but I don't get the correct answer from this.
So, Could somebody please tell me what the second moment of area for this structure is, please?
Best wishes
RE: Second Moment Area of Moment Frame with Shear Truss
You could use the program to compute the drift at the top and back-calculate an "effective second moment of the area."
For example, apply P = 50 kips laterally at the top, and calculate the drift, Delta. Then use Delta = PL^3 / 3EI to back out Ieff. That's the closet thing to what you're asking.
RE: Second Moment Area of Moment Frame with Shear Truss
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Second Moment Area of Moment Frame with Shear Truss
RE: Second Moment Area of Moment Frame with Shear Truss
https://en.wikipedia.org/wiki/Cremona_diagram
Known in the UK by a completely different name. Anyway the crucial feature is that loads are only applied at joints, which are assumed to be pinjoints. There are many google hits
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?