Bolting of the follow sections 10

[Bozo_Sam]

Hi there,

could someone provide some general guidance on how to bolt together multiple hollow sections? I am using only rectangular sections.

Also, I attached the figure below and am interested in which of the two ways is the "correct" one, when it comes to connecting two rectangular sections side by side.

Many thanks,

Uroš

 

[desertfox]

Hi
The top picture is better but the problem is reaching down into the sections to tighten them, you could I suppose put cutouts into the walls of the section to access them but that reduces the section strength.
If you use the bottom figure you will end up crushing inwards the section walls as you tighten the bolt

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

Agree with desertfox, the top sketch is OK but the lower one potentially problematic.

Will there be access issues due to length of the tubes?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[MintJulep]

It depends so very much on what the loads are, what direction the loads are applied and what you are trying to do.

They both have details that are sub-optimal "in general", but those weaknesses may or may not be critical for whatever you are doing.

 

[drawoh]

Bozo_Sam,

Your first drawing with the inside walls bolted together is good. Your other drawing is very bad. Bolts are easily able to crush thin-walled tubes. If bolts are not clamped down hard, they come loose.

Consider drilling through the tubes, welding a solid round bar through the holes, and drill your bolt clearance holes through the bars. Now, you have a solid, clamped section.

--
JHG

 

[BrianE22]

Another way would be to use 2 bolts: One by the top wall and one by the lower wall. You'll still get some crushing.

 

[kingnero]

Solid round bar + drilling? I've seen tubes welded in SHS, same effect but much less work...

 

[drawoh]

kingnero,

It has to have a hole in it. I won't ask the welder how it got there. Drilling a hole through a bar is potentially more accurate.

--
JHG

 

[SwinnyGG]

You'll get much stronger and stiffer results if you bolt through external flanges welded to the tube walls. Even if you weld in a spacer to prevent crushing of the tubes, the load path from the section into the bolt passes through the region of the section with the lowest stiffness.

 

[Bozo_Sam]

Hi guys,

thanks for the extensive replies. This has been most helpful. If I try to summarize the suggestions, it would be better to have the option with the short screw.

If possible the best way would be to weld an additional cylinder on both sections as in the figure below. This would provide stiffness and stability to the connection.

 

[desertfox]

Hi Bozo Sam

Yes that configuration will work but just make sure the tubes you put through the section are just below the surface of the section.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Tmoose]

Sam, in your haste to post you left the annotations and notes off your 7 Aug 20 08:22 posted image, and in so doing added vast mysteries.

I am scratching my head about what is welded to what, and what the hatched ( tube ?) and un-hatched (tube) do in the arrangement.

 

[robyengIT]

why not like this (the spacer pipe is already on the lathe to be cut) ? And you need few tack-weldings just to keep the spacer pipe in position during assembly/erection.

 

[MJCronin]

Bozo ....

I would just clamp the tubes together and run an intermittent stitch weld along the top corners and bottom corners where the two tubs were in contact.

But now your gonna tell me that the tubes must be able to be dis-assembled ?... Right ?

And that you forgot to tell us this before ....


MJCronin
Sr. Process Engineer

 

[Bozo_Sam]

Hi guys and thanks again for the effort.

Do you think having a 2mm chamfer as a preparation for the filled weld would be reasonable?

Sorry for the confusing figure before.

 

[BrianE22]

You should look at how the external loads are applied to the tubes. One center bolt versus other methods will have different stress/deflections/friction clamping.

 

[drawoh]

Bozo_Sam,

Are you the welder or the designer?

Specify that you want the bar/tube welded through your rectangular tube. Welders are skilled, and will find a good way to do it. When you inspect it, it will be two pieces of metal, ground flat on both faces.

Get Mongo the installer to install the bolts.

--
JHG

 

[robyengIT]

Too many welds that, at the end before assembly, have to be ground together with the head of the pipes. No reason to do this, also because after assembly the weld don't do anything : it is enough the pipes to avoid crushing of hollow sections

 

[mfgenggear]

robyengIT (Mechanical)
7 Aug 20 19:04
Too many welds that, at the end before assembly, have to be ground together with the head of the pipes. No reason to do this, also because after assembly the weld don't do anything : it is enough the pipes to avoid crushing of hollow sections

agreed! the sleeve over the bolt is to prevent crushing the tubing or pipe.
it needs to a tad smaller to let the bolt compress properly.
once torque it should be fine.

 

[r13]

If it is accessible, weld the short sleeves with end plates that having predrilled hole should work. Sizing the sleeve for compression.