Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	Modeling Solutions
	Subarea:	Properties
	Original Author:	SANJIB DAS

 

What is the difference between "Prismatic" and "General Section" and which method to use while exporting the section from Section Wizard?

Answer : Whenever you are creating any built-up section in Section-Wizard, you have two options to export it in STAAD 

1. Prismatic
2. General.

When it is exported via “PRISMATIC”, program only reads the 6 sectional properties AX, AY,AZ ,IX ,IY  and IZ which are the only necessary parameters for the analysis and calculate sectional deformation and corresponding forces.

There is not enough information within that option for STAAD to recognize elements of the cross section such as a flange, web, etc., terms which are critical for deciding whether the section is compact, non-compact, slender, etc. 

Consequently, the design of PRISMATIC sections had to be based on certain rules of thumb like 0.6Fy for allowable compressive bending stress.

The second method is via “GENERAL”. Here, the program reads the 6 sectional properties as in prismatic section but apart from that, you have the options for specifying the thickness, depth of web and flange of its equivalent I section using terms like TD, B, TB, etc. STAAD then uses the rules for design of I shapes for designing General sections.

Design of prismatic sections are not supported in STAAD.Pro due to reasons mentioned above. So if you intend to design the section in STAAD.Pro you should export as a general section.