A variety of materials can be used to construct a typical water tower; steel and reinforced or pre-stressed concrete are most often used (with wood, fiberglass, or brick also in use), incorporating an interior coating to protect the water from any effects from the lining material.

Very high volumes and flow rates are needed when fighting fires. With a water tower present, pumps can be sized for average demand, not peak demand; the water tower can provide water pressure during the day and pumps will refill the water tower when demands are lower.

Architects and builders have taken varied approaches to incorporating water towers into the design of their buildings. On many large commercial buildings, water towers are completely hidden behind an extension of the facade of the building.

Eigenvalue Buckling Analysis

An Eigenvalue Buckling analysis predicts the theoretical buckling strength of an ideal elastic structure. The imperfections and nonlinearities prevent most real-world structures from achieving their theoretical elastic buckling strength. Therefore, an Eigenvalue Buckling analysis often yields quick but non-conservative results.

A more accurate approach to predicting instability is to perform a nonlinear buckling analysis. This involves a static structural analysis with large deflection effects turned on.

A gradually increasing load is applied in this analysis to seek the load level at which your structure becomes unstable. Using the nonlinear technique, your model can include features such as initial imperfections, plastic behaviour, gaps, and large-deflection response.

Eigenvalue Buckling in ANSYS Mechanical

In Mechanical, an Eigenvalue Buckling analysis is a linear analysis and therefore cannot account for nonlinearities. It employs the Linear Perturbation Analysis procedure of MAPDL. This procedure requires a pre-loaded environment from which it draws solution data for use in the Eigenvalue Buckling analysis.

An Eigenvalue Buckling analysis must be linked to (proceeded by) a Static Structural Analysis. This static analysis can be either linear or nonlinear and the linear perturbation procedure refers to it as the "base analysis" (as either linear or nonlinear).

A structure can have an infinite number of buckling load factors. Each load factor is associated with a different instability pattern. Typically the lowest load factor is of interest.

Based upon how you apply loads to a structure, load factors can either be positive or negative. The application sorts load factors from the most negative values to the most positive values.

The minimum buckling load factor may correspond to the smallest eigenvalue in absolute value.

Buckling mode shapes do not represent actual displacements but help you to visualize how a part or an assembly deforms when buckling.

The procedure that the MAPDL solver uses to evaluate buckling load factors is dependent upon whether the pre-stressed Eigenvalue Buckling analysis is linear-based (linear pre-stress analysis) or nonlinear-based (nonlinear pre-stress analysis).

Conclusion

For a linear upstream Static Structural Analysis, you can define loading conditions only in the upstream analysis.

The results calculated by the Eigenvalue Buckling analysis are buckling load factors that scale all of the loads applied in the Static Structural analysis.

Thus for example if you applied a 10 N compressive load on a structure in the static analysis and if the Eigenvalue Buckling analysis calculates a load factor of 1500, then the predicted buckling load is 1500x10 = 15000 N. Because of this it is typical to apply unit loads in the static analysis that precedes the buckling analysis.

The buckling load factor is to be applied to all the loads used in the static analysis.