In the previous article, I had explained the structural design, analysis, how does burj khalifa resist storms, buttresses support, crosswalls and I-shaped section, mechanical floors and other concepts of burj khalifa. In this article I will explain why the burj khalifa has a unique shape, its lightning protection and how they built this building upto 830 meter on loose sandy soil. So let's start with its unique shape.
Have you ever wondered why the burj khalifa is an asymmetrical design? Consider two designs(refer fig 1a) - One with symmetrical steps and another with asymmetrical steps.
The reason behind the asymmetrical design is vortex shedding(refer fig 1b). This phenomenon occurs when the wind passes around a structure and leads to very beautiful and dangerous vibrations in the building and can collapse the building. This is dangerous because the vortices are fluctuating. This generates fluctuating force on this building. If the natural frequency of vibration of this building is the same as the frequency of these fluctuations in force, the building will violently oscillate. A phenomenon called resonance. These oscillations will continue to increase and eventually the burj khalifa may fail completely.
The interesting thing is that around 70% of the burj khalifa is supported by the concrete core. The top 25% does not have any concrete core support. It is a steel structure. The burj khalifa mainly resists bending, but the top of this superstructure is allowed to bend and sway by about six feet in windy storms as shown in fig 6. The steel can easily resist tensile loads.
Did you notice the beautiful flower-like petals just above the base of the building? This structural design, especially the petals, was inspired by one of dubai’s most widely cultivated flowers: the spider lily(refer fig 5a).
These lightning strikes on the burj khalifa are fascinating. At the very top of this building, there is a small, fantastic device that prevents the burj khalifa from burning down. That device is a lightning arrester. This dome is connected to a sensor equipment which is powered by a tiny battery. As soon as it detects a super-charged cloud nearby, the dome immediately generates opposite charges on its surface to attract the lightning towards it(refer fig 5b). The electron flow of lightning is then passed through the outer column’s steel structure and dissipated into the earth pits via the steel inside the foundation piles(refer fig 5c).
The electrons travel only through the external columns due to the skin effect. burj khalifa is Dubai’s lighting rod. Its lightning arrester collects the lightning strokes of almost the entire dubai.
Thanks for reading!