Collapse of aluminum lattice mast as an effect of design and executive errors

Abstract

Masts – as tall and slender structures – are usually analysed in an idealized scheme of a multi-span beam supported on a central hinge and from several to over ten elastic supports formed by successive levels of guy ropes. Such a structure has a relative low material usage, but needs a large area for the guy ropes foundation. Although historically there have been many failures of masts, nowadays, they are very technologically advanced structures, constructed by high-level specialist, hence it is very rarely that there are any problems with them. However, this article presents the case of the 80-meter aluminium mast, which collapsed a few months after being put into service. During the period of the use of the mast, the wind speed did not exceed 70 % of its nominal value, and on the day of the catastrophe it was relatively low, within 40–50 % of standard value. A detailed investigation allowed to identify basic damages within the guy ropes, the foundations, and the trunk, which was damaged secondarily, as a result of falling on the ground. The assessment of the rigidity of the trunk-guy ropes system were made using calculations of the load capacity of the elements and the state of displacement of the system under the action of wind. All conducted analyses indicated a large number of design and execution errors, as, for example, application of standards related to steel structures to make calculations for the aluminum structure, omission of the action of wind on the guy ropes, completely incorrect location and anchoring of the guy ropes. Finally, it was stated that the executed structure was significantly different from the assumed one, as it had a dramatically reduced stiffness of the resilient intermediate supports. The outcome was a severe swaying of the mast in the direction perpendicular to the wind, which damaged the guy ropes, resulted in the collapse of the facility.