G.6 Member Properties
The following types of member property specifications are available in STAAD.Pro.
- Prismatic Sections - four basic geometric shapes where the principal section properties are calculated from shapes dimensions or defined.
- Standard Sections - the principal dimensions and section properties from obtained from published documents and supplied in STAAD.Pro as standard databases
- User-Defined Tables - the principal dimensions and some section properties for 10 different shape types which can be included in the model or located in an external file
- Tapered Sections - either tapered I shaped or tapered tube sections defined by the dimensions at either end of the member for which the properties are calculated
- Assigned Sections - a standard section profile from one of the standard database is used
- Steel Joists and Joist Girders - standard joist or joist girders from publications
- Composite Sections - the section properties for standard steel profiles that have the additional effect of increased stiffness due to a positive connection to a concrete slab
- Curved Members - the stiffness is calculated and modified based on the curvature of the member between the start and end nodes
Shear Area for members refers to the shear stiffness effective area. Shear stiffness effective area is used to calculate shear stiffness for the member stiffness matrix.
As an example: for a rectangular cross section, the shear stiffness effective area is usually taken as 0.83 (Roark) to 0.85 (Cowper) times the cross sectional area. A shear area of less than the cross sectional area will reduce the stiffness. A typical shearing stiffness term is
Phi (Φ) is usually ignored in basic beam theory. STAAD will include the PHI term unless the SET SHEAR command is entered.
Shear stress effective area is a different quantity that is used to calculate shear stress and in code checking. For a rectangular cross section, the shear stress effective area is usually taken as two-thirds (0.67x) of the cross sectional area.
Shear stress in STAAD may be from one of three methods.
(Shear Force)/(Shear stress effective area)
This is the case where STAAD computes the area based on the cross section parameters.
(Shear Force)/(Shear stiffness effective area)
This is the case where STAAD uses the shear area entered.
(V Q)/(I t)
In some codes and for some cross sections, STAAD uses this method.
The values that STAAD uses for shear area for shear deformation calculation can be obtained by specifying the command PRINT MEMBER PROPERTIES.
The output for this will provide this information in all circumstances: when AY and AZ are not provided, when AY and AZ are set to zero, when AY and AZ are set to very large numbers, when properties are specified using PRISMATIC, when properties are specified through a user table, when properties are specified through from the built-in-table, etc.