Steel - solid bar or tubular

rampantbunny

I have about a meter of EN24T steel bar. It's solid round @ 25mm outside diameter. When I stand on it it flexes about 1"...I'm looking for something with less flex.

Generally, given the same steel composition and same outside diameter, would hollow round or box section steel be considered more rigid (assuming the walls are not overly thin/weak)?

bonzodog2

1" round pipe or square box wouldn't flex as much over 1m

rampantbunny

bonzodog2 wrote: »

1" round pipe or square box wouldn't flex as much over 1m

Thanks...I'll have a look around for some and try it out.

Coles

bonzodog2 wrote: »

1" round pipe or square box wouldn't flex as much over 1m

Why do you think round tube wouldn't flex as much as solid?

M.T.D

A tube containing the same amount of steel will flex less than a solid bar
A 2" tube with x amount of steel will flex less than a 1" solid bar made with the same quantity of steel.
A 3" bar would flex even less, the larger the tube diameter the more rigid the tube is but if taken too far the wall of the tube gets too thin and it will kink and buckle.

mickward

M.T.D wrote: »

A tube containing the same amount of steel will flex less than a solid bar

so a tube containing the Same amount of steel as a solid 25mm round stock bar, given a wall diameter of 5mm to your tube would have to have an outside diameter of 45mm to "contain the same amount of steel"

rampantbunny

mickward wrote: »

so a tube containing the Same amount of steel as a solid 25mm round stock bar, given a wall diameter of 5mm to your tube would have to have an outside diameter of 45mm to "contain the same amount of steel"

Can you point me to your calculator (online hopefully) or did you do that in your head?

mickward

you need to give a little more information as to what you need.

For example, what weight is going to be applied to the bar, will it be supported on both ends or just one end. Will the weight be hung off the bar of applied from different directions? from one single point of spread out across the bar?

is this to hold your weight such as a chin up bar or something else?

CJhaughey

http://www.wa4dsy.com/robot/bending

M.T.D

The "amount of steel" in the bar and tube can be compared by cross sectional area

for the solid bar pi x r x r - where r is the radius (half the diameter).
For the 25mm (1") approx 3.14(pi) x 12.5 x 12.5 approx 490sqmm

but as pi will be in both calculations it can be ignored for comparison purposes the number we need is 156.25
for the tube think of two solid bars and just subtract area of thinner bar from the thicker one
((outer radius x outer radius)- (inner radius x inner radius)) when this equals 156.25 you have the same amount of steel.

You could of course just compare the tubes and bars by weight.
By using a tube rather than a bar you should be able to have less flex with less steel. i.e a tube tube with similar flex to a bar will contain less steel

rampantbunny

mickward wrote: »

you need to give a little more information as to what you need.

For example, what weight is going to be applied to the bar, will it be supported on both ends or just one end. Will the weight be hung off the bar of applied from different directions? from one single point of spread out across the bar?

is this to hold your weight such as a chin up bar or something else?

Bar supported on one end, with weight hanging from it at other end.
Weight of ooh, lets say 200kg. Can't be more specific I'm afraid but 200kg allows wiggle room.

antiskeptic

rampantbunny wrote: »

I have about a meter of EN24T steel bar. It's solid round @ 25mm outside diameter. When I stand on it it flexes about 1"...I'm looking for something with less flex.

Generally, given the same steel composition and same outside diameter, would hollow round or box section steel be considered more rigid (assuming the walls are not overly thin/weak)?

A pipe of diam 25mm will flex more than a solid bar of 25mm diam. Less material to resist flexing in pipe

Square section 25mm solid. Will flex less than solid round 25mm diameter. More material overall, but critically, far more material at the extremities (top and bottom surface) to resist flex.

Square box section 25mm. Will flex less than solid round 25mm - assuming suitably thick wall, say 5mm. More material at the critical at the extremities (top and bottom surface).

rampantbunny

antiskeptic wrote: »

A pipe of diam 25mm will flex more than a solid bar of 25mm diam. Less material to resist flexing in pipe

Square section 25mm solid. Will flex less than solid round 25mm diameter. More material overall, but critically, far more material at the extremities (top and bottom surface) to resist flex.

Square box section 25mm. Will flex less than solid round 25mm - assuming suitably thick wall, say 5mm. More material at the critical at the extremities (top and bottom surface).

Makes sense...thought that might be the case.