Opinions on using Mill Certificates for Yield Strength 1

[EngDM]

I have been getting a lot of guardrails requesting to use A500 steel pipes on quite a few jobs lately due to availability, but most EOR's spec G40.21 350W Class C. The steel book puts A500 round at 317MPA, but the fabricator provided me with a certificate showing a yield strength of 480MPa for the steel he will be sourcing. I don't intend on using anywhere close to the 480MPa, but what are you opinions on using something higher than 317MPa? I'm not really sure if I'm stuck to using the book values or not here. It's for a guardrail for Pete's sake.

 

[SWComposites]

The cert is likely for a very small sample from the mill lot. Is the fabricator going to test every pipe to ensure it has some minimum strength? Is the fabricator buying the pipe to a specification that ensures a minimum strength value?

 

[EngDM]

The cert is likely for a very small sample from the mill lot. Is the fabricator going to test every pipe to ensure it has some minimum strength? Is the fabricator buying the pipe to a specification that ensures a minimum strength value?

Good questions. Given that it is for a guardrail I imagine they wouldn't be doing the extra work required to ensure the strength everywhere. I guess the book value is the minimum they have to fabricate to for the A500 standard so it's my safest bet.

Thanks for the input.

 

[WinelandV]

Did the fabricator provide you with a yield strength, or a tensile strength? I'm unfamiliar with any HSS shapes coming in at 480MPa (70ksi).

What exactly is the EOR specifying G40.21 350W Class C for guardrails specifically or is that just a standard note for round tubes on the plan set? My experience with guardrail calcs is that since they are a delegated design (in the US at least), the EOR won't care what you use, as long as you meet the loading requirements.

Please note that is a "v" (as in Violin) not a "y".

 

[CDLD]

Snippet from CSA S16-14.

 

[LittleWheels]

Isn't the design intent for guard rail to develop tension along the guard rail and the posts just hold the guard rail at the right height until it gets hit? There are wire rope crash barriers with only 'nominal' posts that are a more extreme version of the same design intent.

 

[JStephen]

From this link:

https://www.aisc.org/globalassets/modern-steel/archives/2022/june2022.pdf

, Pages 16-17
"The preferred material specification for rectangular hollow structural sections (HSS) is ASTM A500 Grade C (Fy = 50 ksi, Fu = 62 ksi). Two notable options for HSS are A1065 and A1085. A1085 (Fy = 50 ksi, Fu = 65 ksi) provides actual wall thickness and tighter corner radii tolerances for design. Additional benefits include a maximum yield stress of 70 ksi for A1085 and a defined standard for Charpy V-notch material toughness."

Note that the higher yield may require different weld procedures than you'd normally use.

 

[EngDM]

Isn't the design intent for guard rail to develop tension along the guard rail and the posts just hold the guard rail at the right height until it gets hit?

I should have clarified, its a people guardrail with the loading as per NBCC.

Did the fabricator provide you with a yield strength, or a tensile strength?

Yes, they specify both yield and tensile.

"The preferred material specification for rectangular hollow structural sections (HSS) is ASTM A500 Grade C (Fy = 50 ksi, Fu = 62 ksi).

The HSC Blue book specifies a lower yield for round hollow sections of 45ksi.

Snippet from CSA S16-14.

Aaaaand we have a winner.