Aluminum Rod with Weld subjected to Moment and Shear - HAZ Zone Reduction Calculation 2

[N G P]

Dear All,

I have been involved in the verification of a cantilever aluminum rod of 45mm diameter which shall be subjected to a lateral force and subsequent moment. The end of the rod is proposed as welded to the base plate by fillet weld by a client.

I understand that aluminum will be softened by the welding and reduction of the section capacity need to be considered in the design check. The maximum moment will end up exactly at the location of the weld as it is a cantilever. While referring to BS 8118 section 4.4, I came to note that the thickness need to be reduced by the factor of kz. The material proposed is 6063 T6 and the kz is found as 0.45 from table 4.5.

As far I understand, I may need to reduce the thickness by 0.45t for the calculation of section modulus. This may result in substantial reduction in the member. Since it is a round rod rather than tube or other type of extrusion, is it the correct way to calculate the net effective section?

could some one help on this regard.?

 

[phamENG]

I can't speak to that code, but the Aluminum Design Manual (the subject code in the US and jurisdictions spring the "International Building Code" addresses the issue by reducing the yield and tensile stressed of the martial.

For a rod that size (a little less than 2"), I would expect it to be nearly useless as a cantilever of welded.

 

[dvd]

Read this

 

[ClearCalcs]

Depending how long the rod is, you may be able to do a post-weld heat treatment somewhat easily - though I haven't seen much literature for something as thick as 45mm. Aluminum cantilevers in general are brutal because of the HAZ. I dealt with this before for railing anchorage.

Depending on your moment demands, manufacturers do offer base plate solutions, typically casted and where you fasten the aluminum with screws. I would probably suggest looking in that direction. Example here:

https://www.keesafety.ca/safety-railings/kee-lite

-Laurent

http://www.ClearCalcs.com

 

[N G P]

Thank you all for the response.

This circular rod section is in fact proposed by the client for the hand rail support posts with welding to the base plate. I have to verify and give them a verdict whether it is feasible or not.

phamENG,
I referred the aluminum design manual. Although it looked sophisticated initially, it has clearly provided the allowable stress for the welded alloys. I will use the recommended values for verifying the sections.

 

[RenHen]

I think your chances of showing that detail working for a handrail support post are pretty slim.

 

[N G P]

It didn't pass. I was worried about the deflection before. However, upon considering the welded alloy properties, it fails in the flexural strength and deflection seems okay as the elastic modulus can be considered as the same. The allowable strength for flexural compression reduced to 6.5 ksi from 20 ksi ( AA ADM VII Table 2-24).

Apart from changing the section dimensions, other options which I can quickly imagine are;
- Casted base plate as clear calcs mentioned. However, I think it may be difficult to obtain the items within the tight time schedule
- Stainless steel option which may lead to higher cost
- Galvanized steel might be resulting in corrosion issue as the location is near to the sea
- Change the grade of aluminium which has higher strength( Weldable grade)

 

[phamENG]

You haven't mentioned what this is for, but I'm assuming you are unable to change the size or the spacing. Never mind. I see the handrail reference. If they are dead set on aluminum, reduce the spacing of the posts until it works. Also, take a look at this document. It gives some simplified hand calc methods for accounting for participation from multiple hand rails.

Given that you're near salt water, stainless is certainly the way to go. It will be worth the higher cost. Galvanized is a viable option, but it needs to be galvanized after fabrication and care taken in not damaging the coating. If it is damaged, it should be touched up appropriately. If specified properly, it can be used with success. Though stainless (of the appropriate grade!) will have a longer service life.