Allowable Shear 1

[zakk]

What percentage of the values for Allowable Stress in Tension (ASME Sec II Part D) is the Allowable Shear Stress for the same material (ambient temperature)? Some souces state 0.7 of allowable tensile stress, others 0.5, etc. I am not talking about welds, strictly base material, i.e. SA516-70 plate loaded in shear.

 

[aggiegrads]

According to vonMises criterion, allowable stress in pure shear (Ss) relates to yield in pure tension (Sy) by:

Ss = Sy / sqrt(3)

or

Ss = 0.577*Sy

Hope this helps. This is from "Mechanical Metallurgy" by George Dieter, 3rd edition, eqn. 3-14.

 

[jte]

zakk-

In addition to the Von Mises formulation, you can consider the Division 2 approach using Stress Intensity (Tresca) which is defined as twice the maximum shear. A detailed explaination is given in Div. 2 Appendix 4, section 4-120. Couple the explaination in the Code and compare to a text book description of Tresca. So if you were working a Division 2 vessel, you would be limited to ½*S. Until the new revision kicks in with Von Mises as a replacement for Stress Intensity...

jt

 

[zakk]

Thanks for the replies.

First, I am dealing with ASME Section VIII Div. 1.

Second, UW-15 provides percentages for groove and fillet weld shear based on allowable stress values and taking into account shear strength, loading and efficiency. Is there a factor that the Code recognizes specifically for base metal shear that can be used directly in Code calculations? In theory, Von Mises will work, but is the 0.577 multiplier appropriate for Code work or are other factors involve also to meet Code requirements?

 

[jte]

Hi zakk-

I figured you were probably dealing with Div. 1; references to Div. 2 are simply to help provide some additional understanding. Div. 2 is a newer code and occasionally provides insight into Div. 1 issues. Take a look at the notes for II-D Table 1A. For SA516-70, notes G10, S1, and T2 apply.

This is all well and good, but you really need to read General note (d): "For Section VIII applications, stress values in restricted shear such as dowel bolts or similar construction in which the shearing member is so restricted that the section under consideration would fail without reduction of area shall be 0.80 times the values in the above Table."

I'm curious as to what type of vessel component you have which would be governed by shear. Any internals or external attachments would not fall under the Code; usually the clips/seats/etc which are attached to the shell cause local bending stress issues, not shear.

jt

 

[zakk]

jte:

It is for construction of a retaining ring similar to Figure UG-34(m). If there is another approach to this, please let me know.

 

[jte]

zakk-

Interesting. I've never seen a vessel with that detail. I usually would expect a flanged head such as those shown in Figure UG-34(j) or (k) for a relatively small vessel. Your vessel is probably just in a different industry than I'm used to dealing with.

jt