A or B grade steel

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A or B grade steel

Postby Davidxxx » Mon Jun 22, 2015 2:26 pm

I am using C profile 150x50x3.2 mm (doubled up) for the roof main beam and C profile 115x50x3.2 mm steel for the rafters as designed by the architect. It has to support Diamond concrete tiles. The steel is a major cost of the overall roof and B grade steel to the same dimensions is half the price of A grade.

I don't think the ultimate strength of the steel is relevant in this type of roof, the welded joints are almost certainly the weak point.

Does anyone have experience of using B grade steel - is it B grade because it is re-used or the finish or what ?
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Re: A or B grade steel

Postby Sometimewoodworker » Mon Jun 22, 2015 2:49 pm

The welds should not be the weak point unless you have poor welding techniques being used.

The grades relate to the tensile strength of the steel and the only person qualified to answer your question is the structural engineer who did your design.
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Re: A or B grade steel

Postby Roger Ramjet » Mon Jun 22, 2015 9:23 pm

Davidxxx wrote:Does anyone have experience of using B grade steel - is it B grade because it is re-used or the finish or what ?

On each lot of steel you buy there are numbers stamped on a piece of tin attached to the steel. Here is a list of steel and the numbers you should be looking for: https://en.wikipedia.org/wiki/SAE_steel_grades
Davidxxx wrote:I don't think the ultimate strength of the steel is relevant in this type of roof, the welded joints are almost certainly the weak point.

If the welded joints are done properly, they will be no different from unwelded joints. A lot will depend on the welding rods used, the welder used and the welder who welded the joints.
You may be thinking of downgraded steel. Downgraded steel is steel that has been exposed to the elements, may not be of standard thickness or has been previously used. Here's a website that deals with that: http://www.metalmart.com.au/downgrade-steel
Be careful, one of the members here changed a number of specs on his build and ended up having to reinforce everything twice over. It was his architect's fault but it cost him a lot of money, time and trouble. Story is here: viewtopic.php?f=3&t=1970&start=60
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