Handbook of Civil Engineering Calculations

FIGURE 35. Interaction diagram for axial force and moment.

The interaction diagram is readily analyzed by applying the following relationships:
dPldg =fyt\ dMpldg = -V2fytg\ .'. dPldMp = -2Ig. This result discloses that the change in
slope along CB is very small, and the curvature of this arc is negligible.

5. Replace the true interaction diagram with a linear one
   Draw a vertical line AD = QA5Py, and then draw the straight line CD (Fig. 35). Establish
   the equation of CD. Thus, slope of CD = -Q.85Py/Mp; P = - 0.85/y^J/M^, or Mp =
   1.18(1-PXPpM,.
   The provisions of one section of the AISC Specification are based on the linear inter-
   action diagram.


6. Ascertain whether the data are represented by a point on AD
   or CD; calculate M'p> accordingly
   Thus, Py = Afy= 13.24(36) = 476.6 kips (2.119.92 kN); PlPy = 84/476.6 = 0.176; therefore,
   apply the last equation given in step 5. Thus, Mp = 55.0(36)712 = 165 ft-kips (223.7
   kN-m); Mp = 1.18(1 - 0.176)(165) = 160.4 ft-kips (217.50 kN-m). This result differs from
   that in part a by 4.6 percent.

Load and Resistance Factor Method

Abraham J. Rokach, MSCE, Associate Director of Education, American Institute of Steel

Construction, Inc., writing in Theory and Problems of Structural Steel Design, McGraw-

Hill, states "In 1986 a new method of structural steel design was introduced in the United

States with the publication of the Load and Resistance Factor Design Specification for

Corein web

Core beyond

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