During a member check, various factors are calculated. In most cases, these factors are largely dependent on the moments at the ends of the segment under consideration. Some of them, however depend on the values of moments and/or displacements at mid or quarter points along the segment. It is not always possible to have stations positioned exactly at the mid or quarter points required because even though stations are positioned at mid and quarter points between adjacent flange restraints, segments do not always extend between adjacent flange restraints (particularly when the critical flange changes due to moment reversal). In such cases, SPACE GASS simply takes the moment and/or displacement values from the station nearest to the required point.
For the AS4100 and NZS3404 modules, am is calculated using the formula in clause 188.8.131.52(a)(iii) when the segment is restrained at both ends.
If the segment is unrestrained at one end, AS4100 and NZS3404 require the bending moment diagram to be matched to one of the three diagrams shown in table 5.6.2. This is very difficult when the bending moment diagram could be any conceivable shape. Therefore, SPACE GASS uses am = 0.25 if there is a non-zero moment at the unrestrained end, am = 2.25 if the mid-segment moment is less than 25% of the restrained end moment, am = 1.25 if the mid-segment moment is less than 50% of the restrained end moment or otherwise am = 1.0. This is less conservative than the approach adopted in v12.25.334 and earlier versions.