AS 4100 Parameters

The implementation of the AS 4100 requires that the engineer provide additional design criteria. These criteria refer to the manufacturing process used for hollow structural sections to be used on the project, and the location load is applied to a beam between brace points. Both these criteria are discussed in detail below, but both pieces of information are provided to the program in the Australia Parameters dialog located in the RAM Manager Criteria menu (these parameters are used in other modules as well).

Load Location

When loads are applied transverse to a member (typically gravity loads applied to a beam) the engineer should indicate where those loads are applied for consideration in member capacity calculations (Table 5.6.3(2) in AS 4100-98). In the RAM Manager , the engineer can designate if loads applied transverse to a member are applied at the shear center or top of section. This setting will only affect the capacity of a beam in segments in which they are not braced laterally (i.e., they are subject to lateral torsional buckling).

Residual Stress Welded Shapes

When calculating member capacity (See Section 5 of AS 4100-98), it is necessary to know the residual stresses in the section which are a function of the manner in which the section is created. For welded sections the engineer can specify the manufacturing method used to create the section. Rolled I sections are assumed to be Hot Rolled (HR) per table 5.2. Rolled tubes and pipes are assumed cold formed (CF) per Steel Designer Handbook. All other welded sections must be designated as either Heavy Welded (HW) or Light Welded (LW) in the RAM Manager .

Assumptions

Member design in RAM Steel Beam considers the provisions of AS 4100 section 5.1 considering section and lateral torsional buckling capacity.

Each unbraced segment is considered to be restrained laterally, this includes cantilever ends of beams. No axial load is considered in the design of the beams in RAM Steel Beam.

The ends of a unbraced beam segment are assumed to be unrestrained rotationally. This will conservatively result in a kr factor of 1.0 being used in the calculation of le.

The twist restraint factor, kt, is conservatively set to 1.1 according to the recommendations and examples of the Steel Design Handbook.

The load height factor will be determined based on load being applied within an unbraced segment length, assuming laterally restrained end conditions (LL) and according to the selection of the loading position in the RAM Manager - Criteria - Australia Parameters dialog as previously described. This k_l factor used by the program will therefore be either 1.0 (loads applied at shear centre) or 1.4 (loads applied at top flange).

The effective length of the member for lateral torsional buckling capacity calculation per 5.6.3:

le = k_tk_lk_rl

The unbraced length, l, is shown on the reports, not the effective length le.

Section capacity for unbraced segments of a beam are calculated according to section 5.6.1.1 of symmetric I and C sections, per 5.6.1.2 for unsymmetrical I sections and per 5.6.1.4 for hollow sections.