Through-bolting of Aluminium SHS with Steel side plates

• Aug 28, 2023

• #2

SWComposites

Aerospace

Nov 6, 2000

3,376

You should add bolt sleeves or blocks inside the HSS to directly react the bolt clamping force. Otherwise the bolts are apt to lose preload over time. Or the HSS could be crushed if bolts over tightened.

 

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• Aug 28, 2023

• #3

M

MintJulep

Mechanical

Jun 12, 2003

9,916

This is an awful design.

Destined to fall.

Start over.

Sorry if that blunt truth isn't the answer that you were hoping for.

 

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• Aug 28, 2023

• #4

SWComposites

Aerospace

Nov 6, 2000

3,376

Yep, “snug tight” or loose bolts and dynamic loads are a prescription for problems.

 

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• Aug 28, 2023

• Thread starter
• #5

Struct2Mech

Civil/Environmental

Aug 27, 2023

3

It is a challenge to strike a balance on this one.

I could add a bolt sleeve (in red) by passing it through a larger hole in one side of the SHS although I won't be able to weld it into place.

I'd still be stuck with a snug-tight fit sadly.

I'll keep thinking on it.

Thanks for the advice guys.

 

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• Aug 28, 2023

• #6

dik

Structural

Apr 13, 2001

25,752

The nylock or locktite red should keep the assembly together. The design isn't good for any serious loading. Transfer of load is by bearing and by shear on the fastener, and it only has to be 'finger snug tight' to achieve that. The tightness of the connection is not by 'clamping' tension. Any galvanic corrosion issues?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

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• Aug 28, 2023

• #7

SWComposites

Aerospace

Nov 6, 2000

3,376

Is it just a single bolt or multiple bolts?
Can you share a picture of the overall assembly and how loaded?
Is the bolt supposed to be removable? Nylock nuts are really only good for a few installs.

 

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• Aug 28, 2023

• #8

dvd

Mechanical

Nov 12, 2001

1,948

A shoulder bolt with the shoulder bearing on the angle is another possibility.

Snug tight is an odd constraint to impose on yourself with the expectation of solving the problem with a threaded fastener.

 

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• Aug 28, 2023

• #9

dik

Structural

Apr 13, 2001

25,752

With normal structural steel construction, 'snug tight' has a specific meaning and the force on the bolt may be too great and may collapse the aluminum tube. 'Snug tight' is actually a significant torque, and with 3/4" bolts can be several hundred foot-lbs. For 'finger tight' connections I generally spec 20 ft-lbs and are used generally for slotted holes in vertically slotted connections.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

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• Aug 28, 2023

• #10

BrianE22

Specifier/Regulator

Mar 21, 2010

1,066

I'd use 2 bolts - one near the upper wall of the tube and one near the bottom.

 

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• Aug 28, 2023

• Thread starter
• #11

Struct2Mech

Civil/Environmental

Aug 27, 2023

3

Dik said:

Any galvanic corrosion issues?

Click to expand...

Likely minimal risk with all parts being powder coated.

Dik said:

'Snug tight' is actually a significant torque, and with 3/4" bolts can be several hundred foot-lbs. For 'finger tight' connections I generally spec 20 ft-lbs

Click to expand...

You make a good point. I had assumed my layman would be able to achieve "snug tight" with a wrench but you are likely right and this is more inline with finger tight.

SWComposites said:

Is it just a single bolt or multiple bolts?
Can you share a picture of the overall assembly and how loaded?
Is the bolt supposed to be removable? Nylock nuts are really only good for a few installs.

Click to expand...

Two bolts in this instance are sharing the applied load. Load is applied downwards on the outside edge of the angle top flange. I cannot share the design sorry.
The bolt can be removed if needed but its primarily a bolted connection to allow the parts to be easily transported and assembled on site. It is unlikely to be disassembled.

BrianE22 said:

I'd use 2 bolts - one near the upper wall of the tube and one near the bottom.

Click to expand...

I had considered this option but I had also hoped to reduce the overall bolt count.

Appreciate all the assistance!

 

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• Aug 29, 2023

• #12

TugboatEng

Marine/Ocean

Nov 1, 2015

11,462

Powder coating is the worst. Aluminum requires specialized primers such as chromate conversion coatings. Powder coaters tend to skip this step and the powder coating ends up accelerating corrosion by crevice corrosion. However, if your product isn't exposed to a lot of moisture three things shouldn't be a concern.

I am curious to see a discussion of solutions to the problem of bolting across boxed tubing. You provided a possible option that people seem to be talking around.

 

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• Aug 29, 2023

• #13

dik

Structural

Apr 13, 2001

25,752

For light loads, I don't generally sleeve... just a finger tight bolt with the threads wrecked. I know with powder coating with Al, you have to take special precautions, or it simply doesn't work.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

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• Aug 30, 2023

• #14

r6155

Mechanical

Jan 12, 2010

2,770

Please, send us dimensions.

Regards

 

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