Design Methodology

The AISI S100-16 follows a capacity-based design procedure. LRFD and ASD are two methods specified in the specification.

Structural members are designed to have strength such that the available strength (factored resistance) Ra, equals or exceeds the required strength (effect due to factored loads), R. Use the METHOD parameter to indicate which design method the program should use (the default method is LRFD).

• Allowable Strength Design (ASD): $R\le R_a , R_a= R_n/\Omega$
• Load and Resistance Factor Design (LRFD): $R_u\le R_a , R_a= \varphi R_n$

  Table 1. Saftey and Resistance factors in AISI 2016

  Force	LRFD: ϕ Factor	ASD: Ω Value
  Tension	0.90	1.67
  Compression	0.85	1.80
  Flexure	0.95 for box sections 0.90 for other sections	1.67
  Shear	0.95	1.60

Tension Resistance

Design of the members subject to axial tension is performed as per Chapter D of AISI S100-16. The tensile strength is calculated with due consideration to both tensile yielding and tensile rupture effects. The design tensile strength, ϕ_tT_n,(LRFD) and the allowable tensile strength, T_n/Ω_t, (ASD) will be calculated as per Chapter D2 and D3 of the code. The nominal tensile strength, T_n shall be the lower value obtained per the limit states of tensile yielding in the gross section and tensile rupture in the net section.

You can control the net area used to calculate the tensile rupture strength by assigning the NSF parameter.

Compression Resistance

Design of the members subject to axial compression is performed as per chapter E of AISI S100-16. The nominal compressive strength is calculated considering compression yielding, global (flexural, flexural-torsional, and torsional) buckling, local buckling, and distortional buckling. The minimum of these three criteria will be used to calculate the compression capacity or strength. The design compressive strength, ϕ_cP_n, (LRFD) and the allowable compressive strength, P_n/Ω_c, (ASD) will be calculated as per chapter E2, E3 and E4 of the specification.

For the calculation of global compression capacities, section E2.1 is applicable for double channels front-to-front. Since this is not a pure box (but like a box), the program does not use E2.1.1. Rather, this built-up shape is treated like a typical section that is not subject to FTB and uses Cl. E2.1-1.

Torsional and flexural torsional buckling are not considered in the determination of compression capacity for L sections (with and without lips) designed about geometric axes. Rather, it is assumed that these members have restraints against torsional and flexural torsional buckling, which is typical in practice.

Flexure Resistance

Design of the members subject to bending about principal axes is performed as per Chapter F of AISI S100-16. The specification applies for bending about one principal axis only.

It is assumed that the member is loaded in a plane parallel to the axis that passes through the shear center or is restrained against twisting.

The nominal flexure resistance is calculated considering flexural yielding, global (lateral-torsional) buckling, local buckling, and distortional buckling. The smallest of these criteria will be used to calculate the flexural capacity or strength. The design flexural strength, ϕ_bM_n, (LRFD) and the allowable flexural strength, M_n/Ω_b, (ASD) will be calculated as per chapter F2, F3 and F4 of the specification.

For calculation of yielding and global (lateral-torsional) buckling, Cl. F2.1.4 is used for double channel front-to-front section.

Shear Resistance

Design of the members subject to shear is dealt with by the module as per chapter G of AISI S100-16. The nominal shear strength, V_n, is calculated for flexural members without transverse stiffeners. The shear buckling force, V_cr, is calculated for for the web of members with transverse stiffeners.

The spacing of transverse stiffeners, if present, is given using the STIFF parameter.

The program ignores any spacing values specified for closed sections such as double channel front-to-front.

Interaction Checks

The program checks members subject to axial force and flexure about one or both axes as well as flexure and shear.

Excluded Checks

The following check are not made as part of the AISI S100-16 design:

• connection design
• design for torsion
• design for stability, ponding, fatigue, or corrosion effects
• web crippling checks
• combined checks for bending and web crippling
• combined checks for bending and torsion
• design for serviceability