Analysis - Tower Structures.

In the analysis of towers the largest uncertainty is accurate knowledge of the wind loads. Highly sophisticated methods of analysis cannot improve this.A static linear three-dimensional structural analysis is sufficient for almost all lattice tower  structures.

For transmission towers, line break conditions can also be critical. Line breakage will in general induce dynamic loads in addition to any residual static loads.Detailed loading is outside the scope of this section.

For lattice towers with large complicated panel bracing, the secondary bracing forces can be significantly altered by non-linear effects caused by curvature of the panels under the influence of the design loads. Generally the rules in the codes are sufficient, but where structures are of particular importance or where there is much repetition of a design, a non-linear analysis may be necessary.

Dynamic analyses of self-supporting lattice towers are rarely necessary unless there are special circumstances such as high masses at the top, use as a viewing  platform, or circular or almost solid sections of mast which could be responsive to vortex shedding or galloping. Knowledge of the dynamic response is also necessary for assessment of fatigue of joints if this is significant. For guyed towers the non-linear behaviour of the guys is a primary influence and cannot be ignored. The choice of initial tension, for example. can have a very great effect on the deflections (and dynamic behaviour).

The effects of the axial loads in the mast on column stiffness can be significant.Methods of static analysis are given in the main international codes for the design of guyed towers. Guyed towers can also be particularly sensitive to dynamic wind effects especially those with cylin- drical or solid sections.

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