MAINMAST is a computer programme developed by Ramboll for analysis and design of cantilever towers, guyed masts, monopoles and chimneys exposed to wind and ice load. MAINMAST is probably the most sophisticated computer package for analysis of mast and towers in the world.

The MAINMAST programme is able to analyse guyed masts and towers by the following different methods:

Static analysis, including patch wind loading according to the EC3 part 3.1: "Towers and Masts" and BS 8100: "Lattice Towers and Masts" model

Static analysis, including patch wind loading according to the IASS model
Eigen mode (free vibration) analysis of the structure exposed to wind and ice load
Stochastic analysis of the Maximum Dynamic Response (MDR)
Stochastic fatigue analysis and lifetime estimation of the response from vortex shedding
Analysis of the rupture of a guy rope
Analysis methods

MAINMAST is based on the Finite Element Method (FEM) of second order and all kinds of loads and load combinations, eccentricities, guy arrangements etc. may be taken into account.

The static analysis is carried out in two steps:

An initial step where the structure is exposed to the initial load, e.g. dead load, initial guy tension, initial wind load corresponding to the initial guy tension etc. This step is very convenient if guys are non symmetric or special guy arrangements appears.
A second part where the structure is exposed to the rest of the total load, e.g. ice load, wind load. The second part can be divided into several load steps.

The free vibration (eigen mode) analysis is carried out in the following steps:

A static analysis of the mast exposed to dead and wind load
A determination of the eigen modes of the loaded mast

The Maximum Dynamic Response (MDR) is carried out in the following steps:

An eigen mode analysis of the mast exposed to the mean wind
A stochastic part where the RMS response and the peak factor are determined based on the eigen modes of the mast exposed to the mean wind
Integrating in the frequency domain carries out the Maximum Dynamic Response, using a number of modes.

The fatigue analysis is integration over the wind direction and the wind speed, where the response for vortex shedding is determined in each step. The method is based upon Vickery's theory of negative aerodynamic damping.

Analysis results

The results from a MAINMAST analysis will be:

Node displacements
Sectional forces in the mast
Reaction at the mast foundation
Guy forces and guy reactions on mast and foundation
Lattice forces
Pipe stresses
Summary of total load on mast and guy elements
Eigen frequencies
Modal masses
Life times

The forces in the lattice sections are determined on the assumptions that the legs carry the axial force as well as the bending moments. For conical sections the legs carries a part of the shear forces as well. The diagonals carry the remaining shear forces and the torsional moment.