The maintenance and repair works of 128 viscous dampers located in the Athens Metro – Line 1, in Maroussi station bridge has been awarded by HiSCS.

Viscous dampers are considered anti-seismic devices which through hydraulic operation (network of special oil inside internal chambers and orifices in the main body of the devices) can absorb (consume) kinetic energy, which is produced during the movement of the structure under dynamic actions (earthquakes).

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 constitutional law of hydraulic damper is exponential, following the formula:

F_D = C · V^α (MN)

Where:

C = unit constant [MN x (s/m)^α],

V= the velocity of the superstructure (m/s) and

α = an appropriate exponent α ~ 0.15 KN/[m/sec] with damping constant C = 30.53

The dampers were manufactured and installed in 2004 having the following characteristics:

– Maximum design axial load: 75 KN

– Maximum piston movement speed: 400mm/sec

– Maximum piston extension/compression capability: ±55mm

– Nominal axial length (neutral position) from pin to pin: 570mm

The maintenance works follow the proposed remedial works as specified in the inspection report (inspection of dampers took place in 2023).

More precisely:

• Cleaning and painting of dampers main body and anchor plates.
• Cold galvanization and tightening check of mechanical anchoring elements (nuts and bolts).
• Replacement of worn bellows (covering and protecting the rod piston from dust and filths).
• Repair of misaligned anchor plates of dampers with the superstructure and substructure.
• Check of internal oil filling/pressure to verify their efficiency and if necessary, refilling.
• Installation of protective galvanized steel cages against birds and animals (to avoid nests and birds’ droppings in direct contact with the dampers steel parts)

Works will be accomplished by a team of 2 technicians under the supervision of HiSCS Engineers, within a period of 2-3 months avoiding any disturbance to the passengers and operation of the Metro station. A movable working platform will be used to access the dampers and perform all needed works, such as disassembly, cleaning, painting, check of oil internal filling status, assembly, and installation of protective cages).

Maintenance and retrofitting following the inspection report recommendations and proposals, builds a strong regime in public structures by prolonging their service life and keeping their effectiveness against daily service and earthquakes in a high level of efficiency.