The Inspection of fifty (50) viscous dampers located in the steel roof of main terminal building of Athens Int’l Airport has been accomplished by HiSCS Inspectors.
Viscous dampers are considered anti-seismic hydraulic devices which through hydraulic operation (network of special oil inside internal chambers and orifices in the body of the device) can absorb (consume) kinetic energy, which is produced during the movement of the structure under dynamic actions (earthquake).
The service movements of the structure (temperature effects-contractions/expansions etc.) are taking place with zero reaction of the damper (very low velocity of damper’s piston movement).
The constitutive law of hydraulic damper is exponential, following the formula:
FD = C · Vα (MN)
Where:
C = unit constant [MN x (s/m)α],
V= the velocity of the superstructure (m/s) and
α = an appropriate exponent usually between 0.10 and 0.50.
The exponent α, if it is not specifically defined in the design stage, can be chosen by the manufacturer considering the following criteria:
– the device will not develop resistance to very slow movements of the superstructure (e.g. thermal contractions etc.)
– the device will be activated very quickly in dynamic movements.
The composition of the viscous liquid (oil) and the design details of the device are the know-how of the manufacturer.
The dampers were manufactured in 1998 having the following characteristics:
– Maximum design axial load: 50 KN
– Maximum axial load capacity: 1.5 X 50 KN = 75 KN
– Maximum piston movement speed: 0.6m/sec
– Maximum piston extension/compression capability: ±125mm
– Exponent α ~ 0.5 KN/[m/sec] with damping constant C = 64.5
– Nominal axial length (neutral position) from stud to stud: 1230mm
In total 50 devices are placed in several locations of the steel roof of MTB.
Considering their age, i.e., 25 years old, a regime of routine inspection has been established to verify serviceability and proper function.
The inspection works took place during midnight hours to keep the least annoyance to the passengers. An electrical driven basket lift has been used to reach the roof where dampers were installed.
All dampers have been checked and measurements about their function (residual movement capacity, leakage phenomena, rotation etc.) have been recorded.
A special inspection software has been used so as to speed-up the site works to a minimum possible.
Dampers are designed and inspected following EN-15129-7 (Anti-seismic devices-velocity dependent devices).
