Thickness Limitations for welded plates 2

[arefinmahadi]

Dear Sir,

Can anybody please help me finding a guideline on plate thickness difference limitations for a welded connections. Such as can i weld a I Beam W.400X6 F.200X8 with a 50 mm thick end plate??

Or can i make a I beam with 5 mm thick web and 24 mm thick flange plates?

Thanks

Arefin

 

[racookpe1978]

You "can make" anything your design requires.

Why you would want to make that odd of a shape is your decision as the design engineer, your budget, and your liability if (when) it fails because your calculations or assumptions were wrong.

Design YOUR welds to accommodate the stresses and strains (movement and fatigue and cycles) you expect. Add an appropriate safety margin based on the codes that you are responsible to meet.

Several thousand years ago, an ancient king killed those engineers whose building fell down and killed someone else. Today? You face a harsher threat: lawyers and bureaucrats.

 

[arefinmahadi]

thanks for the reply. But it is not possible to weld a very thin plate with a heavy one as my fabricators say that. So is there any spec or guideline by any codes ? It will be a great help if anyone can help on this issue.

Thanks
Arefin

 

[thaidavid40]

Certainly, you can weld thin plates to thick ones - if you have the proper weld processes and procedures, and the qualified welders (either human, or robotic). You simply have to account for the factors affecting the weld's heat-affected zone, as well as the base metal(s) chemistry. Maybe what your fabricator is trying to tell you is that they don't know how to make these welds - not that it is impossible to do so. They simply can't do it themselves.
Dave

Thaidavid

 

[hokie66]

arefinmahadi,
Your question is legitimate, but you will find that you get better assistance if we know more about you.

It is apparent that you work for a steel fabricator. What is your position in that company? Are you an engineer? Who designs the steel sections which you are fabricating? Where are you located geographically? What is the source of the steel plate which you are using? What grades of plate are being welded? And what type equipment is being used in the fabrication facility?

One further thing. This site frowns on double posting, so in the future please restrict your posts to a single forum. In this case, either forum which you have used is appropriate, but you need to choose one.

 

[arefinmahadi]

Dear Hokie ,

Thanks for your assistance. I was just looking for general specs on this regards. Any specific code reference or manual.

I am working as the design engineer in a PEB farm. i am from Bangladesh. We use ASTM A572 50 grade steel plates. Now for designing built up plates my previous boss told me to follow few thumb rules for selection of web flange thicknesses. He worked for Zamil Steel in middle east.

web thickness = web depth/180 (not less)
flange thickness = flange width/33 (not less)
flange thickness/web thickness = 2.4 (not more)

We use AISC - 360/05 for design purpose and that segregates sections in compact, non compact and slender sections and i can select any section and design according to these segregation. So why the limitations mentioned above? when i asked my boss he replied that these are thumb rules for fabrication limitations regarding welding. We have Shielded Metal Arch Welding and Submerged Arch Welding (auto) facilities in our shop. I dont have much knowledge on AWS. Now where can i find general specs on this regards.

I was not aware of the double posting issue. I am really sorry for that. It will not hapen in the future.

Thanks & Regards

Arefin

 

[hokie66]

Arefin,
Now you have asked a properly formulated question, but one which I can't answer without some research. As to your previous boss's rules of thumb, the flange/web ratio seems about right, but the web and flange thickness limits are too thin for my liking.

This does sound similar to the way "preengineered metal buildings" are built in North America, so perhaps some of our PEMB contributors can assist.

 

[arefinmahadi]

thanks hokie for your quick response. Please post if u find out anything handy.

Arefin

 

[vhengr]

As your basic query is about welding - refer the welding Bible - "AWS" welding code.

I hope everybody has attempted your welding query here.

Though the main objective of PEB structure to optimise the steel weight; I also feel web and flange plates are too slender as per your rules of thumb. These structures may land in deep trouble with long-term durability problem after a time, mainly in highly corrosive and coastal areas. A concern is to overlook serviceability requirement of the structure.

For guidelines PEB design and detailing you can refer the latest MBMA (Metal Building Manufacturers Association) Design Manual based on IBC.


Cheers! -VH

 

[arefinmahadi]

"I also feel web and flange plates are too slender as per your rules of thumb."

Then it will be considered as slender section element and designed that way. Isn't it??

"These structures may land in deep trouble with long-term durability problem after a time, mainly in highly corrosive and coastal areas. A concern is to overlook serviceability requirement of the structure."

Can u just help me finding exactly where in MBMA or any other codes where section thickness is related with building serviceability ?

It will be a great help if u share your standards of choosing section thicknesses or references.


Thanks
Arefin

 

[vhengr]

"building serviceability" - here I mean Long term durability of the structure.
The only reason I asked first you to check min. plate thickness to be used for your structure as per code which you referring.


Cheers! -VH

 

[arefinmahadi]

its not about the minimum plate thickness. Its about width to thickness ratio. As per AISC i can find compact non compact and slender elements.
One more thing. Which is plate girders. If my section elements are slender its strength is reduced as per code. But it does not restrict thickness selection.

Arefin

 

[vhengr]

Slender section elements :

"Then it will be considered as slender section element and designed that way. Isn't it?" - Agreed (code will guide you)

THIN section elements :

"These structures may land in deep trouble with long-term durability problem after a time, mainly in highly corrosive and coastal areas." - Your engineering call or as per customer demand.



Cheers! -VH