# Modal buckling analysis wizard

Buckling is an eigenanalysis to find the load factors and modes of buckling.

## Definition

**Number of Modes**

The number of modes required from the eigenanalysis.

**Maximum No. Iterations**

All eigensolvers are iterative. This is used to set up the maximum number of iterations that will be allowed. For some buckling analyses this value may need to be increased. The maximum number of iterations can also be set in the Advanced Settings dialog.

**Load Factor Shift**

The load factor shift specifies the load factor around which the modes are calculated. For example, a load factor shift of 5 will find the buckling cases closest to 5 times the applied load. The frequency shift currently only works with the subspace iteration eigensolver. If a non-zero shift is added, this will automatically select subspace iteration. See Advanced Solver Settings > Eigensolution for how to change the eigensolver.

**Load Factor Cut-offs**

The cut-offs allows for load factors outside the range of interest to be discarded. These buckling modes will still be calculated but the results are discarded rather than stored. A lower cutoff of zero will ensure that negative modes (i.e. buckling due to load reversal) are ignored. Note that these are absolute values and not relative to the load factor shift.

**P-delta Case**

The basis on which the geometric stiffness is calculated.. This can either be a load definition (e.g. 1.2L1 + 1.2L2) or an analysis or combination results case (e.g. A3 or C4). When a load description is specified, GSA first analyses the structure under this load and generates a geometric stiffness from the resulting forces/moments. When an analysis or combination case is specified the geometric stiffness is constructed from the results in this analysis or combination case. Combination cases can only be simple combination cases (i.e. of the form $a.A_a + b.A_b + ...$ )

## Advanced options

For advanced options on buckling analysis see