Assigning Foundation Springs at Column Base

To assign springs at column bases, select Column Base in Assign/Clear At. Two options are provided to set the orientation of springs at column base:

Setting	Description
Angle from Global X-axis (deg)	By default, a spring is defined in the global system: three components of linear and rotational springs are defined along the global X-, Y-, and Z-axes. This orientation can be modified in such a way that it can be rotated around the global Z-axis by a specified angle measured counter-clockwise from the Global X-axis. The orientation of rotated springs is graphically indicated on screen.
Same as Column	This option is valid only for column bases. The springs are rotated such that their orientation aligns with the column orientation angle.

The stiffness values for linear and rotational springs at column bases are determined according to the following rules:

By default, all of the spring stiffness values are infinitely large (i.e., these degrees of freedom are fixed).
To specify a stiffness value associated with any degree of freedom, first select the option box for that degree of freedom and then enter the spring stiffness value.
For rotational or torsional stiffness values, there are two options: either enter stiffness value directly, or use % of Column Minor Stiffness, % of Column Major Stiffness, or % of Column Torsional Stiffness. If the latter option is chosen, a value between 0 and 100 is expected. This value is used to calculate rotational or torsional spring stiffness values as follows:
$K_{r x} = (\frac{a}{100}) \frac{4 E I_{x}}{L}$

$K_{r y} = (\frac{a}{100}) \frac{4 E I_{y}}{L}$

$K_{r z} = (\frac{a}{100}) \frac{G J}{L}$
where
I_x
=
major moment of inertia
I_y
=
minor moment of inertia
J
=
section torsional constant
E
=
modulus of elasticity
G
=
shear modulus
L
=
column length

Note: The coefficient a is the percentage value input by user.

It should be noted that if a column is pinned at its base and rotational springs are also defined at the same base, these springs have no effect in the analysis results. In this case, the column does not transmit any moment because it is free to rotate at its base. To activate the rotational springs, the column should be defined as fixed at its base.

I_x	=	major moment of inertia
I_y	=	minor moment of inertia
J	=	section torsional constant
E	=	modulus of elasticity
G	=	shear modulus
L	=	column length