ASCE 7-10 1

[Pawel27]

I would like to use combination in section C2.3.5 i.e. 1.2D+1.6L+1.0T. I do not know what resistance factor for design strength should be used. I have spatial stress state (not only tension, compression, shear separately).
What value should be multiplied Nominal Strength to get Design Strength?

 

[JAE]

Tell us more about the material and shape of the elements/framing you are looking at.

 

[Pawel27]

This is SA-387 Gr.11.

 

[JAE]

That is a pressure vessel steel - If this is a pressure vessel then perhaps the design criteria from ASME BPVC code [link (

http://www.asme.org/kb/standards/bpvc-resources/boiler-and-pressure-vessel-code---2013-edition)

]ASME BPVC Link[/url] would be appropriate. The resistance factors are not defined in ASCE 7 - rather they are included in the specific material specification.

For AISC based design (buildings) the resistance factor would be based on considerations of the material type and the member/element type.
For spatial stress checks - if buckling and second order effects are dealt with, then based on that particular steel (that has a fairly good ductility) I would guess a [Φ] = 0.9 as the resistance factor would only consider variations on material properties.

Variations in other parameters that drive a particular [Φ] level, such as variations in dimensions, thicknesses, warping, etc. would not enter into the stress check you seem to be doing (Von Mises?).

 

[Pawel27]

Could You explain sth more where these resistance factors I can find?

 

[Pawel27]

Below notice can be helpful:

Acc. to ASCE7-10, C2.3.5 for self-straining loads below combinations should be used:

1.2D + 1.2T + 0.5L
1.2D + 1.6L + 1.0T

It seems to be LRFD. LRFD use force and moments capacity. How to relate it to my spatial stress state? How to calculate design strength?

 

[JAE]

I think you have to go to the code provisions that govern whatever it is that you are designing.

Is this a building? A pressure vessel? A catwalk? What is it?

There should be a governing code or specification that would provide design criteria for you to use.

The ASME pressure vessel code link -

http://www.asme.org/kb/standards/bpvc-resources/boiler-and-pressure-vessel-code---2013-edition

(The link I posted earlier above is wrong for some reason.)

 

[Pawel27]

This is ash hopper in power plant. The same problem seems to be clear for me using ASD. I would like to focus here on LRFD method with load combinations above.

 

[wannabeSE]

Pawel,
What reference or standard is used to determine the allowable stress for ASD design of the hopper?

For example, structural steel for buildings in the USA is designed with AISC's Specification for Structural Steel Buildings, AISC 360. This current specifcation includes the saftey factors for ASD and the Resistance Factors, [Φ], for LRFD. There is not one [Φ] factor for everything. Shear, bending and weld strength may all have different [Φ] factors. When checking tension there are two differnt [Φ] factors: one for yielding of the gross secion and another for rupture of the net section (eg. net section where bolt holes occur and yieliding is not a concern).

 

[Pawel27]

This is power plant in USA. Could You confirm that this material SA-387Gr.11 is available in this AISC 360? I consider buying this AISC.

 

[Pawel27]

I got ANSI/AISC 360-05 Specification for Structural Steel Buildings. I didn't find answer what is allowable stress.

OK, maybe auxiliary question, which help focus on the point of subject:

In attachment there is a screenshot from book "The structural design of air ducts and gas ducts" (5.1.1, 5.1.2,5.1.3,5.4.6). Section C2.4.4 is from ASCE7-10. There is mentioned about "normal allowables stress". From point 5.1.1 it can be concluded that "normal allowable stress" concerns not only normal stress
(i.e. not only tension/ compression but also shear and bending)? So this normal allowable stress can be used in Combined Stress State like in my analysis? How to determine this "normal allowable stress"?

 

[Pawel27]

One more remark: I think about using 95% of yield stress according to section 5.1.2 as allowable stress in ASD method(see attachment above).

 

[a7x1984]

I am confused. You are designing something without knowing how to design it? Why don't you ask a supervisor?

Before you doing anything creative, make sure the code likes the artwork you are trying to wow the world with.