AISC 360-10 Wide Flange Warping Constant Calculation

In August this year, we were excited to announce the release of STAAD.Pro SS4.  As with all releases and where we introduce new design codes, we put it through a series of tests to make sure that we achieved the goal of making the code available in time for the release, but unfortunately a number of issues slipped through which we addressed in a patch we posted a few weeks back.

However, since then it has come to light that there is an error in the calculation of the warping constant, Cw for the design of wide flange members.  The code specifies that for doubly symmetric I-shapes with rectangular flanges, it should be taken as ‘Iy/ho^2/4’.  This calculation refers to the inertia of the minor axis, however in STAAD.Pro this is being performed with the major axis inertia and giving a much larger value as displayed in a TRACK 2 output .  This increases the value for rts (Effective Radius of gyration) and thus also leads to an increased value of Lr (Limiting laterally unbraced length for the limit state of inelastic lateral-torsional buckling).  This will impact on the calculation of Mn (Nominal flexural strength) if it should be less than the plastic moment and will tend to overestimate the capacity.  Therefore calculations where lateral torsional buckling for wide flange members is significant, it is suggested that these should be manually checked until an update for STAAD.Pro is published.

I apologise that we did not catch the problem sooner and we will be posting an update to the STAAD.Pro installation very shortly and a notification will be posted on the STAAD.Pro RSS News Feed as soon as it is available for download.