Sliding Liquid Surface in Earthquake Isolation Bearing
SLIDING LIQUID SURFACE IN EARTHQUAKE ISOLATION BEARING
In absence of an earthquake, the building transmits a part of the vertical static load to the single bearing, where the internal liquid is stressed to centred compression, due to the presence of an hinge, located to the base of each pillar. The incompressibility of the liquid and the hermetic seal of the device – which contains the liquid – guarantee a reaction of the bearing in accordance with the conditions of equilibrium and stability. During an earthquake, the foundation-soil complex horizontally moves in any direction sliding without friction – due to the presence of the liquid – with respect to a central body, which leans on the liquid.
This body, in turn, moves in opposed direction to the motion due to a system of pulleys and to an inextensible cable, sliding on the liquid surface with respect to the foundation-soil complex and involving in the motion the above building too, without so transmitting it earthquake energy, because the friction force between the building and the bearing - in correspondence of the liquid surface of sliding – is almost zero, in conformity with the equilibrium condition to the horizontal translation. The displacement of the foundation-soil complex in any direction occurs according to the vector sum of the components X and Y of the motion, thanks to the presence of devices with ball bearings. The earthquake isolation system, which uses the above bearing, presents the following characteristics:
•the device, containing the liquid surface of sliding , must be with hermetic seal both in the state of quiet and in the state of motion of the soil;
•during an earthquake, the seismic energy in the building is practically zero, due to the almost total absence of internal friction in the liquid, which guarantees a very good possibility of the building sliding with respect to the foundation-soil complex;
•the system is independent from the earthquake frequency, due to the total absence of building vibration natural frequency;
•the economical competitiveness with all systems with total or partial absorbition of earthquake energy is very high;
•the phycho-physical discomfort in the inhabitants, due to the small horizontal translation of the building during an earthquake, is negligible.