Aluminum Tube Effective Properties

[ron9876]

I need to analyze an existing aluminum gate and I don't have much experience with aluminum. Is the effective moment of inertia of aluminum tubes the same as steel tubes? I need to calculate deflections of 3x2x1/8 6063-T5 tubes.

 

[MiketheEngineer]

Of the course the moment of inertia is the same - just calculate it as you would any section. BUT E is about one third that of steel - usually around 10,000,000

Check with your supplier

 

[ash060]

Aluminum does use effective moment inertia for deflection calc's but not for stress calc's where they use any effective stress. Check the AA code section 4.7.6 they have the equations for the effective width used to calculate properties. Use the tables in part VII of the code to make things easier.

Than the light gauge manual has some examples for calculating the effective properties. Most aluminum extrusions do not have fillets just sharp corners so it makes the calc easier.

So after you calc the stress for strength; check for the effective width at that stress level; and than calc the effective properties.

Remember to check for both local buckling and LTB for strength not such a big deal for deflection. Usually not a problem for steel HSS but can be for aluminum.

Sometimes I just use about 75% of the Igross to save time because it is a good estimate and usually conservative. Unlike light gauge no supplier will give you those properties.

 

[ron9876]

Thanks for the input.

 

[Ron]

If the aluminum sections are standard and not special extrusions, the geometric properties are given in the Aluminum Design Manual (ADM 2000 or ADM 2005).

Be careful with welded sections as the properties in design are significantly different within 1-inch of the weld (assumed heat affected zone).

The ADM covers both ASD and LRFD approaches.