The recent Myanmar earthquake of M7.7 of last March 28 continues to be al Center of global media attentionespecially by reason of the important and growing number of victims caused and gods structural collapses observed, which involved several skyscrapers, some even under construction. The effects of the earthquake are documented not only by the collapses, but also by the video recordings of the showy horizontal oscillations of several skyscrapers and come on effects of wave motion of the waters of the Towing poolspresent at altitude in many of these buildings. It arises spontaneously to ask what the effect and role of the swimming pools on the structural behavior Of these skyscrapers and how dangerous it can be, in situations like these, to have a building with a mass of water at such high altitudes.
The effects of the earthquake on the water: it sloshing
The water movement during seismic eventslike those that occurred on March 28, is identified with the technical term of sloshing. This physical phenomenon represents nothing else than the movement of the mass of water inside a container When excited by movements of the container itself which contains it. In fact, the mass of water would like to inertia maintain its initial positionbut he must adapt to the movement of his container: this is established thus exchange of forces between the fluid and the walls that contain it, resulting in a complex regime of hydraulic pressure of the fluid itself which can be identified as:
- a component convective, that is, the one that actually undergoes the Sloshing motion;
- a component impulsive, That is, the one that moves in unison with the container.
The effects of sloshing on the structures
We must first distinguish two types of effects:
- What happens locally on the walls that make up the fluid container;
- What happens globally to the structure seen in its entirety, up to the foundations.
As we said, the water movement generates a new pressure regimetherefore changes the forces that urge the walls of the container, aggravating them during the seismic motion in a few time. This means that, when a swimming pool is made at high altitude, it will be necessary to take these effects into account, as the structure – during its movement generated by the earthquake – can excite in turn the water and therefore generate a stress regime that affects the sizing of the container.
However, it must also be considered that this same movement causes the birth of a new strength than globally urges the structuretendentially with the opposite direction to that present due to the earthquake: this force – which contributes globally to the balance of the system – can act beneficially against the resistence and of the stability of the structure, allowing the building + swimming pool to contrast in a tendentially better the soliciting seismic actions.
So does it mean that it is thanks to these touched pools that these buildings have not collapsed?
Of course not, a touch swimming pool It is not designed/made to structurally participate in dynamic balance In the event of an earthquake, it is not something that has taken into account in the design phase directly. This is because it tends to system intrinsically has many uncertainties that could make their effectiveness falter. For example, if this were the case it would also like to say that the swimming pool itself could never be emptied, because – emphasizing – it is as if we were removing a beam or a pillar from the structure!
Rather, it will have been necessary, in the project phase, to take into account the local effects first discussed, to obtain a sufficiently rigid and resistant container even in extreme conditions such as these.
The use of liquid dampers tuneds
The concept we have first exposed can be engineeredtherefore used in a rational way to control the structural response during the vibrations of a structure. In this case, we talk about Tld (Tuned Liquid Dampers). The operating mechanism is in all respects similar to that of granted massessuch as the one present within the Taipei 101, only that in this case it is the water to be “granted“, so that it is its own movement that ensures the right energy dissipation at the entrance. An example of this application is the Comcast Centera skyscraper from Philadelphia which contains in one room 1 100 m3 water who avoid the same to demonstrate strong oscillations under the actions of the wind. The wave motion is in this case controlled and the mass of water cannot disperse a grain, How can it happen in the touch swimming pools at altitude. The same quantity of water is not introduced casually, but engineered for Ensure the desired dampening structural effect.
