ML20138M298

Provides Position on Interpretation & Application of Combined Stress Equations in Section 1.6, Combined Stress, in American Inst of Steel Const Manual,Per 850521 Telcon

ML20138M298
Person / Time
Site:	LaSalle
Issue date:	05/25/1985
From:	Hartzman M Office of Nuclear Reactor Regulation
To:	Galambos T MINNESOTA, UNIV. OF, MINNEAPOLIS, MN
Shared Package
ML20138M288	List: ML20138M284 ML20138M290 ML20138M298 ML20138M304 ML20138M308
References
NUDOCS 8511010067
Download: ML20138M298 (2)

Text

. ,

[pR AtC o, UNITED STATES y g NUCLEAR REGULATORY COMMISSION g  : E WASHINGTON, D. C. 20555 o, ~

~

"% /  ;

2,5; l9K f Professor T. V. Galambos Department of Civil and Mineral Engineering University of Minnesota Minneapolis, Minnesota

Dear Professor Galambos:

This letter follows up our telephone conversation of May 21, 1985, regarding the interpretation and application of the combined stress equations in Section 1.6

" Combined Stresses" of the Specification contained in the AISC Manual of Steel Construction, 7th and 8th Editions.

The issues regarding these equations are as follows:

1. To which cross-sectional axes are these equations referred to, i.e. ,

geometric axes or principal axes?

2. Should equations 1.6-la of 1.6-2 be evaluated at various points on a cross-section? ,

3. On which bending moments shot.id the maximum bending stresses be based, i.e. the moments occurring at. a given cross-section or the maximum incividual moments occurring anywhere along the number?

My position regarding these issues are as follows:

1. Equation 1.6-la and 1.6-2 are referenced to the principal axes of a cross-section.

2. These equations are not evaluated at a given point on a cross-section.

Rather, the maximum bending stress due to each principal moment acting separately is determined. Since there are two principal moments, the maximum stress due to these moments may occur at the same or different points on a cross-section. They will occur at the same point if the section is doubly-symmetric. They may occur at different points if the section is singly symetric, such as equal angle or tee sections.

3. The principal moments from which the maximum bending stresses are determined do not necessarily have to occur at the same cross-section. That is, the largest principal bending moment about the major axis may occur at one section of the member while the largest principal bending moment about the minor axis may occur at a different section along the member.

4. The allowable stresses are determined from the behavior of the whole member in each principal direction separately. For example, for an equal 8511010067 851022 PDR ADOCK 05000373 P PDR

angle member the allowable stress for bending in the plane of the minor axis will depend on the length of the member, to account for possible lateral / torsional instability. For bending in the plane of the major axis the allowable stress will depend only on the properties of the material.

I would appreciate your opinion regarding my position on these issues.

Sincerely, Mark Hartzman, Ph.D.

Mechanical Engineering Branch Division of Engineering l

Office of Nuclear Reactor Regulation l

1 0

_- - - - - -