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# Thread: Angle Iron Deflection ?

1. ## Angle Iron Deflection ?

Hi working on new gantry router design and intended to use 3"x3"x10'
1/4" angle iron spanning 8-10ft between support legs and predict a load
of approx 100lbs. I am concerned with deflection or twist. if secured
to supports diff and or where my load rides on the angle iron would change
the amount of deflection. If I uploaded pic properly it might give an idea of
what I am trying to do.

2. What accuracy are you looking for. 100 lb on a pair of 10ft L beams is enough to induce noticeable flex. The math for these is simple if you know what you are doing. If not there are some good tables for moment of inertia as well as cantilever beam calculators online. Accurate prediction of deflection is possible, the hard part is determining what is allowable.

A 3x3x0.25 has a moment of inertia of 1.24 inch^4 in both directions (Ix and Iy).

E = modulus of elasticity for steel = 30,000,000 psi

To calculate the max deflection over 10 feet (force concetrated at the center)
= W * length³ / (192 E*I)
= 100lbs * (120 in)³ / (192 * 30,000,000 * 1.24)
= 0.0242"

If the 100 lbs of force is distributed over two pieces of angle, moment of inertia I is doubled and the deflection is cut in half. Still quite a bit deflection at around 0.012".

4. Try these links for calculations... the sites also provide material properties and explanations in varying details for those with less experience with the equations.

engineersedge http://www.engineersedge.com/calculators.htm

efunda http://www.efunda.com/home.cfm

5. Try the freeware "BeamBoy" program. It's great for quickly doing this type of analysis.

6. Unless your angle is loaded through the 'Shear Centre', it will twist as well as deflect vertically. The amount will depend on how the ends of the angle are supported at the ends - 'simple' or 'encastre', or something in between! You really need to have a chat to an engineer friend, if you have one!

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