A new lift tower was to be designed and to be fixed to an existing stair case connected to a boiler’s structure.

Several three dimensional FEM models were developed for the lift tower’s sensitivity analysis using software package Robot™ Structural Analysis Professional 2013, by Autodesk®. The main differences between the models were the support conditions on the side of the existing stair case (connection points for the walkways). Each model represented an attempt to simulate in a realistic way the stiffness of the stair case structure and its influence on the stress distribution of the lift tower’s structure. Fully pinned, fully released and non-linear gap supports were tested.

In order to have a structural system for the lift tower that was not excessively dependent on the support provided by the stair case, nor to create unacceptable strain on the foundation anchor bolts, final design was based on a non-linear gap support model for one direction. The resulted stress distribution on the steel profiles proved to be adequate and reasonable.

Load cases and combinations were the same for every model and both service and ultimate limit states were verified. Figure 1 shows an image of the final design model, which was also used for the structure’s dynamic analysis. Natural frequencies and vibration modes configuration were determined and excessive vibration risk was assessed.