Section wizard

Dear team

I am trying to model a Z purlin in staad using polygn command. When i enter the TD and Tb value as 0.002mm the utilization ratio is 99999. 

Please share your observation. How do i desgin a z purlin in STAAD?

  • I believe you are using some hot rolled steel design code like IS800 2007 where we report 99999 for the case when slender flange is subjected to bending as slender flanges has very less bending capacity and code has not provided any clear guideline for that. Now, the thickness being 2mm, the flange becomes slender and you see that infinity ratio. As TD and TB values are used in determination of section classification only, you can use a higher TD or TB value to make the flange and web non-slender but that may not be accepted by all. As all the other sectional properties like area, MOI etc remains as per 2mm thick element I do not see any adverse problem with changing TD and TB value for making them non-slender if they really are as per your engineering judgement. Though this is a workaround, this should not be used if you have doubt.

    Also 2mm is very less thick and in that range may be cold formed sections are used. If that is the case, you can use any cold formed steel design code like IS801 code, and the design will be done without such error.

    Thanks & Regards,
    Abhisek Mandal
    Global Technical Support