Non structural beam in staad to apply linear loads to bent

[Paul8]

I am designing a series of bents as pipe racks and am wondering if there is an easier way to apply loads. I am currently converting all my linear loads from pipes to point loads for each bent. This is tedious becuase not all bents are equally spaced. Is there a way to have a beam run between all my bents on which I could apply a kinear load, without having it contribute structurally to the model?

 

[BAretired]

Usually, you would take the worst situation, i.e. the bent which carries the largest tributary length of pipe, design the bent for that and make the others all identical.

BA

 

[SteveGregory]

BA has the right idea. However, you could use simple span beams from bent to bent and load them up to model the pipe loads.

 

[Ron]

Agree with BAretired. Pick one bent and apply highest load, assuming the bent has lateral support. If not, either use a pipe as a beam with everything except the vertical condition released or similar with a dummy beam.

Are you providing X-bracing between bents?

 

[delagina]

how lazy can you be. you are just putting loads based on pipes operating/dead/test weight. you can assume 40 psf if all pipe diameters are 8" or less.

designing piperack based on just one bent is OLD and nobody should be using it anymore since you have Staad and can come up will more exact calculation. You may have problems with that with connection design and foundation design.

 

[BAretired]

delagina,

designing piperack based on just one bent is OLD and nobody should be using it anymore since you have Staad and can come up will more exact calculation.

You can come up with a more exact calculation if you know the exact loading, but usually in a plant, the loading can vary over the years. Someone may decide to use more pipes or larger pipes. You don't want to be unnecessarily confined by too tight a design.

Having a standard bent is good planning as it permits them to be moved around in the future without having to re-calculate the strength in a slightly changed situation. It also avoids the very real possibility of workers installing a bent in the wrong place.

And finally, the cost of pipe support bents is a minor cost in a plant compared to the cost of mechanical equipment and the cost of collapse.

BA

 

[delagina]

BAretired,

i guess i didnt read the question well. if he is designing the bents only as in 2D with fixed support then yes, i guess designing just one bent is better.

But if he is designing a piperack with braced bay then 3d design is better in my opinion than just one bent.

 

[dhengr]

Delagina,
BA’s thinking is right on the money, the potential of mis-locating a particular bent and the installation and inspection labor for 20 slightly different bents will be a killer. Furthermore, when you go out to get these 20 slightly different bents fabed, that price will skyrocket. BA is right that the cost of the pipe support bents should not be a large percentage of the project’s total cost, but the way you propose going at it, they certainly well be very costly to save pennies on materials weights. Finally, ask your boss if he wants you spending his fees on 20 different bent designs, when one design will save him and the client money and headaches. You need more ‘think a little’ OLD fashioned though that may be, and less Staad, to really become a better engineer.

 

[delagina]

dhengr, haha i'll try to think OLD fashioned.

but seriously if it's a piperack with braced bay it should be modeled as 3d. it's easier for connection and foundation design later also when piping department starts giving you anchor loads. bent frame can still be similar sizes though.

 

[bootlegend]

Delagina,

Since you mentioned designing the bents as 2d with fixed supports I assume you are trying to accoutn for the out of plane loads. Typically a bent is designed for the gravity loads and in plane lateral loads as a 2D structure. The top is braced out of plane by the supported structure (pipes, conveyor, etc). So there is not necessarily a need to fix the supports to model it as 2D.

I got 350 heads on a 305 engine; I get ten miles to the gallon, I ain't got no good intentions.

 

[delagina]

can you explain to me if you just design 1 bent what percent of loads you will transfer to the braced bay due to pipe friction/anchor loads. what tension you will assume for the strut beam design/connection. what loads you will provide for the foundation. what axial you will assume for the brace bay vertical brace.

because all of these i can easily get if i modeled it in 3d.

fyi also i never said bent frames should be different sizes.