Through-bolting of Aluminium SHS with Steel side plates

[Struct2Mech]

Hi,

I'm looking to use a through-bolt to join two steel angle sections to an aluminum SHS (as pictured).

The bolt will be subject to both shear and tension (some prying) and largely dynamic loads (vibration and impact). The bolt will also only likely be snug tight (reliant on a layman to tighten the bolt with hand tools).

I'm struggling to know how to check the connection for strength. For snug tight through-bolts in HSS subject to mostly static loads, a bolt should be treated as a pin. As this isn't a static load, I'm unsure how to proceed and I'm struggling to find any relevant literature.

I'm also concerned about the bolts loosening and I'd appreciate any referrals to text that might help me there too.

Can anyone point me in the right direction?

Thanks heaps!

 

[SWComposites]

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.

 

[MintJulep]

This is an awful design.

Destined to fall.

Start over.

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

 

[SWComposites]

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

 

[Struct2Mech]

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.

 

[dik]

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

 

[SWComposites]

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.

 

[dvd]

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.

 

[dik]

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

 

[BrianE22]

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

 

[Struct2Mech]

Any galvanic corrosion issues?

Likely minimal risk with all parts being powder coated.

'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

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.

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.

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.

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

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

Appreciate all the assistance!

 

[TugboatEng]

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.

 

[dik]

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

 

[r6155]

Please, send us dimensions.

Regards