Assign/Clear Foundation Springs
Foundation springs can be set according to options provided in this dialog. Based on member choice from Assign/Clear At, springs are inserted or deleted at column or brace bases by the help of this dialog.
At a foundation node, six components of a spring can be defined. These are three translational (linear) springs and three rotational springs.
To assign springs at column bases, first choose Assign Foundation Spring and then pick Column Base from Assign/Clear At, The next step is to define orientation. Two options are provided to set the orientation of springs at column base:
- Angle from Global X-axis (deg) : By default, a spring is defined in global frame. In this case, three components of linear and rotational springs are along global X-, Y-, and Z-direction. This set-up can be modified in such a way that it can be rotated around global Z-axis by specified angle measured counter-clockwise. Rotated springs are also graphically indicated on screen.
- Same as Column : This option is only valid for column bases. In this case, the springs are rotated with the same as column does, and again it is measured counter-clockwise from global X-axis.
- By default, all stiffness values are grayed out. It means that at these degrees of freedom, the spring stiffness coefficient is infinitely large (i.e., this degree of freedom is fixed).
- To set any particular degree of freedom free and then assign a stiffness value, first pick check box, and then enter stiffness value at available box next to your pick.
- For rotational stiffness values, there are two options: either enter stiffness value directly, or use % of Column Minor Stiffness or % of Column Major Stiffness. If the latter is chosen, type a value between 0 and 100. This value is multiplied with column major or minor stiffness to obtain rotational spring stiffness value as follows:
whereRx = (a/100) × 4EI/L - I
= - the major or minor moment of inertia of the column
- L
= - the length of the column
- E
= - the modulus of elasticity
- a
= - the user-defined percentage value
If Brace Base is chosen in Assign/Clear At, all settings specifically used for columns are grayed out. Therefore, the options Same as Column, % of Column Minor Stiffness and % of Column Major Stiffness are not available for braces. Other rules applied to column as explained above are also valid for springs at brace bases.
To delete springs at column or brace bases, first choose Clear Foundation Spring and then pick Column Base or Brace Base from Assign/Clear At to remove springs at column or brace bases, respectively.
Calculated stiffness values and other related information about foundation springs are tabulated in the Model Data report.
More controls provided about showing springs and their values on screen by invoking View - Foundation Springs from main menu.