Define a New Purlins

Before inserting purlins, trusses/beams/ steel frame members must be defined. 

To define purlins:

1.  Click on the "Purlin" button from toolbar or you can use command line at right bottom corner. There are two purlin insertion methods; Insert Using Two Members or Insert Using Multiple Members.
    
2.  To Insert Using Two Members, select the first truss or frame member followed by the second one where the purlins will be inserted. Intermediate trusses/beams/frame members will be automatically detected. In order to consider purlins as simple beams, there should not be any intermediate trusses/beams. Otherwise, purlins are considered as continuous beams.  
   
3.  To Insert Using Multiple Members, press ENTER after selecting all the truss or frame members. This function allows you to pick a specific frame members as the supporting members. 
4.  Purlin dialog will be loaded, purlin geometry and input loading can be specified by following:                                                                                                                                                                                      
   
5. In the Geometry dialog
   
   • Profile/ Section of the purlins: Select purlins section for top chord & bottom chord. 
     
   • Section Alignment (e.g On the section/ Under the section/ Center etc.)
     
   • Section Alignment on the Top Chord : Section Alignments "On the Section", "Under the Section", "Centered", "Align to Top", "Align to Bottom" 
     
   • Section Alignment on the Bottom Chord : Section Alignments "On the Section", "Under the Section", "Centered", "Align to Top", "Align to Bottom"
     
   • Continuous Purlin. You can specify the Maximum Member Length (Cut Length) for purlins in the Settings Center from Steel Settings > Member Design.
     
   • Generation method (Purlins to be placed on truss joints or by spacing)
     
   • Layout Style: In the case of different length trusses, purlins maybe aligned according to short member or long member. User can use "Perpendicular From Shorter" or "Perpendicular from Longer" options.    
     
   • Delete First Member
     
   • Delete Last Member
     
   • Left & right cantilever length of purlin 
     
   • Gap Between Continuous Purlins
     
   • Set first and last purlin offset.
     
     
6.  Click "Sag Rods" under General options to model edit geometric properties of sag rods. 
   Sag rods decreases the buckling length of purlins and girts. You can include effects of sag rods into building analysis by checking "Include in Analysis" option. 
   
   
   
                                                                                                                                                                                              
7. "Autofit" or "Manual" can be used as Insertion Method. You can delete the sag rods by using "None" option. 
   
   In case of, autofit selected as insertion method, user must set the "Rod Count". 
   
   You can change the geometric properties of sag rods and profile hangers from below menu.
   
   
   
   
   

Sad rods are secondary members that provides restraints to the purlin in the plane of the roof. They are important if you want to design the purlins within ProtaStructure.   Purlins are usually cold-formed members and the design of cold formed members is out of scope of ProtaStructure.  Hence, if you do not intend to design purlin within ProtaStructure, then there is no need to insert sag rods.  In addition, sag rods will increase the size of the model considerably if there are many purlins.