Partial fixity of column bases
Two additional types of rotational linear spring are provided to allow partial fixity to be modelled, these are:
- Nominally pinned
- Nominally fixed
These are specifically provided for supports under columns (of any material), but will result in a validation error if placed under walls, or if they are used for any other supports.
The support stiffness is based on the column properties (E*I/L)
- E = Young’s Modulus of the column
- I = relevant bending stiffness (Ixx or Iyy) of the column
- L = distance from the support to the first column point (stack) that is on a Construction Level checked as a Floor in the Levels dialog, i.e. combined length of all the stacks until a floor is found.
Note: Where no Floor has been defined in the column above the support, then L is taken
as total length of column.
Partial fixity spring stiffness is calculated as follows for each of the two bending
releases Mx and My:
- Nominally pinned (spring stiffness) - x% * 4 * E*I/L (default x% = 10%)
- Nominally fixed (spring stiffness) - x% * 4 * E*I/L (default x% = 100%)
Since the spring stiffness is dependent upon stack height and column stiffness (E and I), the spring stiffness will change if any changes are made to column stack height, column E or I values.
In addition, since for steel, Auto Design can change the column size (and hence I value) the spring stiffness will change with any change in column size.