ESDU 18003:2019

$22.75

Form Factors for Flanged Sections Under Combined Bending and Axial Load

Published By	Publication Date	Number of Pages
ESDU	2019-04	16

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Category: ESDU

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Description

INTRODUCTION

This Data Item presents form factor, K, curves to calculate the maximum permissible bending moments, M_max, for sections that are symmetrical about the x-axis and Z-sections (see Sketch 2.1). For sections symmetrical about the x-axis and Z-sections constrained to bend about the x-axis, the presence of axial loading, in addition to bending, reduces the permissible bending moment. An estimate of the effect of an axial load, P, acting in this sense on the permissible bending moment, M_max, of Z-sections and other sections symmetrical about the x-axis may be made by use of the K curves (Figures 1 to 6) presented in this Data Item. The form factor K is plotted against Ph/M for various values of b/d for six values of t/h. For convenience the form factor has been related to the 0.2 per cent proof stress of the material. Values of K taken from the curves give directly the value of the maximum permissible bending moment appropriate to a given constant ratio of bending moment and axial load as represented by Ph/M. For other cases a process of successive approximation is necessary. The values of K for Ph/M=0 correspond to pure bending.

This Data Item supersedes ESDU Struct 01.06.02. The form factors provided in this Data Item incorporate the Ramberg-Osgood formula to define the stress-strain curve of the material which replaces the idealised stress-strain curve approach used in ESDU Struct 01.06.02. This Data Item also presents values of K for values of Ph/M up to 20 in all of its figures. No account has been taken of any type of instability, the possibility of which must also be considered (see, for example, ESDU Struct 01.01.08 and 01.01.09).

For sections symmetrical about the x-axis and Z-sections, this Data Item applies only when they are constrained to bend about the x-axis shown in Sketch 2.1.

Sketch 2.2 supports the conclusion reached in Derivation 2 that K values are not very sensitive to the variation of the material characteristic m (gradually yielding to sharply yielding). K values are presented in Figures 1 to 6 of this Data Item for a material with a typical value of the material characteristic m. For a material with a specific value of the material characteristic m ESDU 90004 can be used to obtain more accurate results.

For other polygonal shapes ESDU 90004 and its computer program can be used to calculate the maximum permissible bending moments, M_max.

Additional information