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PART 7 MEMBERS SUBJECT TO COMBINED ACTIONS<br />
D7.1 SCOPE<br />
This part of the Tables contains the interaction formulae which must be used to design members subject<br />
to combined actions in accordance with Section 8 of AS 4100.The table below provides the location of<br />
design capacities and reference points within this publication for checking interaction effects on member<br />
capacities.<br />
Design<br />
Capacity Description Reference<br />
Nomx Elastic flexural buckling load of a member, about the principal x- axis Tables 7.3.2-1 to D7.3.2-4<br />
Nomy Elastic flexural buckling load of a member, about the principal y- axis Tables 7.3.2-1 to D7.3.2-4<br />
φNc Nominal member capacity in compression Tables D5.2-1(A) to D5.2-4<br />
φNs Design section capacity in axial compression Tables D3.1-1 to D3.1-4<br />
φNt Design section capacity in axial tension Tables D3.1-1 to D3.1-4<br />
φMs Design section moment capacity (SHS) Tables D3.1-1 to D3.1-4<br />
φMsx, φMsy φMs about x- and y- axes (RHS) Tables D3.1-1 & D3.1-3<br />
φMrx (comp) φMsx reduced by axial compression force (RHS) Section D7.4.1.1<br />
φMrx (tens) φMsx reduced by axial tension force (RHS) Section D7.5.1.1<br />
φMry φMsy reduced by axial force (RHS) Section D7.4.2.1 & D7.5.2.1<br />
φMr (comp) φMs about a principal axis reduced by axial compression force Section D7.4.1.1<br />
φMr (tens) φMs about a principal axis reduced by axial tension force Section D7.5.1.1<br />
φMb Design moment capacity (RHS) Tables D4.1-1 to D4.1-2<br />
φVv Design shear capacity of a web (SHS) Table D3.1-2 & D3.1-4<br />
φVvx φVv for bending about x- axis (RHS) Table D3.1-1 & D3.1-3<br />
φVvy φVv for bending about y- axis (RHS) Table D3.1-1 & D3.1-3<br />
φMz Design torsional section moment capacity Tables D3.1-1 to D3.1-4<br />
D7.2 METHOD<br />
Section D7.3 describes the use and determination of moment amplification factors and the determination<br />
of the elastic buckling load for braced or sway members. The elastic buckling load required for combined<br />
bending and axial compression when the moment is amplified by the moment amplification factors δ b and<br />
δ s .<br />
Sections D7.4 and D7.5 give the interaction formulae for combined bending and axial compression and<br />
combined bending and axial tension respectively. Each section describes the method for uniaxial bending<br />
about the major principal x-axis, for uniaxial bending about the minor principal y-axis, and for biaxial<br />
bending. Section D7.6 gives the interaction formulae for biaxial bending without axial forces. In every<br />
case both the section capacity and the member capacity must be checked.<br />
D7.3 MOMENT AMPLIFICATION<br />
For a member subjected to combined bending and axial compression force, irrespective of whether that<br />
member is an isolated statically determinate member or part of a statically indeterminate frame the bending<br />
moments will be amplified by the presence of axial compression force. Such amplification can be accounted<br />
for by a variety of means and these are now considered in relation to braced and sway members.<br />
Braced Member - the member is braced such that its ends cannot move relative to one another.<br />
If a first order elastic analysis is conducted then δ b (Clause 4.4.2.2 of AS 4100) must be used to amplify<br />
the design action effects between the ends of the member. However, when the moment amplification<br />
factor is greater than 1.4, a second order elastic analysis must be carried out (see Appendix E of AS<br />
4100).<br />
DuraGal DESIGN CAPACITY TABLES<br />
DCTDHS/06<br />
D7-2 for STRUCTURAL STEEL HOLLOW SECTIONS MARCH 2002
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