Plates and bars go up to 100 ksi yield stress per A514. Structural shapes go up to 70 ksi yield per A913. Haven't seen anything in AISC for high strength steels above that
All I know is P/A and Mc/I
RE: Allowable stress in Ultra high strength steels
The relevant AISC section lists the ASTM steels that the specification applies to.
The commentary states: "This Specification lists those products/materials that are commonly useful to structural engineers and those that have a history of satisfactory performance. Other materials may be suitable for specific applications, but the evaluation of those materials is the responsibility of the engineer specifying them. In addition to typical strength properties, considerations for materials may include, but are not limited to strength properties in transverse directions, ductility, formability, soundness, weldability including sensitivity, coatings, and corrosivity."
So it appears that if you specify something that is not listed in AISC 360, Section A3.1a, it is up to you to do the research to verify that your use of the material, and application to it in design with respect to safety factors, etc. is appropriate. Sort of hard to do with limited resources, time, fee, etc.
Building codes such as IBC typically incorporate AISC-360 by reference. So if the material is not in AISC-360, then AISC-360 cannot be complied with and therefore the building code won't allow use of the material.
All I know is P/A and Mc/I
RE: Allowable stress in Ultra high strength steels
I believe this is an intentional oversight in the current AISC codes. Some quick thoughts about this:
1) Inherent in the AISC provisions are considerations of residual stresses. The question then becomes if the residual stresses from rolling or welding higher strength materials would be on par with the assumptions in the current code equations or would they need to be revised. This affects inelastic buckling and direct analysis method, maybe more things.
2) The phi and omega values in the code are based on the types of failures we see in the current code materials. Is it possible that when yield and fracture are not separate by very much then the phi or omega values would need to be altered somewhat to ensure the desired factor of safety?
I know Ben Schaeffer from John Hopkins (who is involved in both AISI and AISC) is interested in extremely high strength steels. My belief is that he's leading an ad-hoc committee to explore what it would take to allow some consideration for higher strength materials into AISC. But, my impression is that it's pretty early in the process and that we're at least a code cycle away from having any major results from this group. I don't even know what those results would be.... Maybe some AISC sponsored research, engineering journal articles, design guide, a new appendix, or code commentary.
RE: Allowable stress in Ultra high strength steels
We had the same type of issues come up years ago when high strength concrete was starting to show up for bridge designs.
At the time I was doing bridge designs (not anymore thankfully) and we had a project with two twin bridges - one was constructed of "typical" concrete and the other with high strength concrete in both the deck and the precast girders....the idea being to study the long term differences between them.
One issue came up in design was how to determine the appropriate transfer length of the girder tendons at the ends - simply use the AASHTO methods?
One consultant kept insisting that we were unconservative using the development lengths for 5000 psi concrete in girders with 12,000 psi strengths.
Some charts in the AISC (like the 95/SQRoot Fy) go up to Fy 100ksi. 1.9.1.2. Even in my older green AISC manual. This implies that the basic rules could still apply for SOME or even various Utra high strength steels.
But in other areas they have caveats Like (Except for hybrid members and A514 steel)1.5.1.4.1 bending. The most important section. Although most Ultra HSS may not adhere to A514, A514 has some large tensile strengths of 140KSI.
This application is not for a bridge or building, it is for a telescopic boom with a conveyor on top.
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RE: Allowable stress in Ultra high strength steels
All I know is P/A and Mc/I
RE: Allowable stress in Ultra high strength steels
The commentary states: "This Specification lists those products/materials that are commonly useful to structural engineers and those that have a history of satisfactory performance. Other materials may be suitable for specific applications, but the evaluation of those materials is the responsibility of the engineer specifying them. In addition to typical strength properties, considerations for materials may include, but are not limited to strength properties in transverse directions, ductility, formability, soundness, weldability including sensitivity, coatings, and corrosivity."
So it appears that if you specify something that is not listed in AISC 360, Section A3.1a, it is up to you to do the research to verify that your use of the material, and application to it in design with respect to safety factors, etc. is appropriate. Sort of hard to do with limited resources, time, fee, etc.
Check out Eng-Tips Forum's Policies here:
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RE: Allowable stress in Ultra high strength steels
All I know is P/A and Mc/I
RE: Allowable stress in Ultra high strength steels
2) The phi and omega values in the code are based on the types of failures we see in the current code materials. Is it possible that when yield and fracture are not separate by very much then the phi or omega values would need to be altered somewhat to ensure the desired factor of safety?
I know Ben Schaeffer from John Hopkins (who is involved in both AISI and AISC) is interested in extremely high strength steels. My belief is that he's leading an ad-hoc committee to explore what it would take to allow some consideration for higher strength materials into AISC. But, my impression is that it's pretty early in the process and that we're at least a code cycle away from having any major results from this group. I don't even know what those results would be.... Maybe some AISC sponsored research, engineering journal articles, design guide, a new appendix, or code commentary.
RE: Allowable stress in Ultra high strength steels
At the time I was doing bridge designs (not anymore thankfully) and we had a project with two twin bridges - one was constructed of "typical" concrete and the other with high strength concrete in both the deck and the precast girders....the idea being to study the long term differences between them.
One issue came up in design was how to determine the appropriate transfer length of the girder tendons at the ends - simply use the AASHTO methods?
One consultant kept insisting that we were unconservative using the development lengths for 5000 psi concrete in girders with 12,000 psi strengths.
Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies
RE: Allowable stress in Ultra high strength steels
TKS for the input.
Some charts in the AISC (like the 95/SQRoot Fy) go up to Fy 100ksi. 1.9.1.2. Even in my older green AISC manual. This implies that the basic rules could still apply for SOME or even various Utra high strength steels.
But in other areas they have caveats Like (Except for hybrid members and A514 steel)1.5.1.4.1 bending. The most important section. Although most Ultra HSS may not adhere to A514, A514 has some large tensile strengths of 140KSI.
This application is not for a bridge or building, it is for a telescopic boom with a conveyor on top.