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D13.C.2 Member Capacities

D13.C.2.1 Axial Tension Members

Stress in a section of an axial tension member shall not exceed design strength Ry of the selected steel multiplied by the coefficient of service conditions, γc (input by the GAMC1 and CAMC2 parameters), take from table 1 of SP 16.13330.2011.

The slenderness of tension members shall not exceed the slenderness limit, λu indicated in table 33 of SP 16.13330.2011 as equal to 150. This limit may be specified using the CMM parameter, which defaults to 150.

The net section factor (the ratio of Anet/Agross ) is specified by the NSF parameter and is used for tension members to allow for the reduction of design cross-section area.

D13.C.2.2 Axial Compression Members

All axial compression members are calculated as long bars (i.e., with allowance for slenderness - λ = l0/imin , where l0 is the effective length of the element). Calculation is performed in accordance with clause 7.1.1 of SP 16.13330.2011, with the buckling coefficient ϕ determined by equation 8. Effective lengths of elements (within and out-of plane) take into account role and location of the bar in the structure, as well as fixity of the ends (l0 = μ1 ), are determined according the requirements of section 10.3 of SP 16.13330.2011 and are set by the user specification of the members. Slenderness parameters, μx(z) and μy are set using the parameters KZ and KY, respectively. If the slenderness parameters of an element is not precisely known, then the effective length can be specified using the LY and LZ parameters, instead. The ultimate slenderness of compression members shall now exceed the limit values given in table 32 of SP 16.13330.2011, or a user-specified value provided through the CMN parameter. The value of the coefficient α used in Table 32 is taken within the limits of 0.5 and 1.0. The limiting slenderness value in compression elements depends on stress acting the member, buckling coefficient, and design resistance of the steel.

Since the slenderness can be different in various planes, the greatest slenderness ratio is assumed in calculations. A warning is given if the slenderness ratio of a compression element exceeds the limit, but the calculations are continued. If the slenderness ratio exceeds the limit value, the output line containing the slenderness check is preceded by a # (pound or hash symbol).

The calculations of single members are performed in this manner. If the member is subjected to axial forces and bending moment (e.g., due to self weight), then the calculation of load bearing capacity will be done taking into account the axial force and bending moments and the buckling resistance only under the axial compression according to clause 7.1 of SP 133330.2011. Local buckling of the web and flanges of centrally loaded members is checked. Stiffener ribs are recommended if necessary.

D13.C.2.3 Flexural Members

Member subjected to bending moments and shear forces are called flexural members.

There are three classes of flexural elements:

  1. Elastic - in cross-section, the stress in the extreme compression fiber of the steel member –assuming an elastic distribution of stresses– can reach the yield strength. σ ≤ Ry , where σ is the absolute value of the stress.
  2. Elasto-plastic - in on part of the cross-section, the stresses are σ ≤ Ry and in another σ = Ry .
  3. Plastic state (i.e., conditional plastic hinge) - across the entire cross-section, the stresses are σ = Ry .

The parameter TB is used to specify either class 1 (elastic) or class 2 (elasto-plastic).

The calculation of flexural members consists of verification of strength, stability, and deflection.

Normal and tangential stresses are verified by strength calculations of members. Normal stresses are calculated in the outermost section fibers. Tangential stresses are verified in the neutral axis zone of the same section. If the normal stresses do not exceed design steel strength and tangential stresses do not exceed the design value of steel shear strength, Rsγs , then according to clause 8.2.1 of SP 16.13330.2011 the principal stresses are checked.

For elements subjected to biaxial bending moments according to clauses 8.2.1 and 8.4.1 of SP 16.13330.2011

D13.C.2.4 Eccentrically Compressed/Tensioned Members

Eccentrically compressed or tensioned members are subjected to simultaneous action of axial force and bending moment. Bending moment appears to eccentrically applied longitudinal force or due to transverse force.