SPECIFICITIES OF SEISMIC DESIGN FOR HIGH SPEED RAIL VIADUCTS

Serge MONTENS

SYSTRA

SPECIFICITIES OF RAILWAY BRIDGES

• HIGH LONGITUDINAL PIER STIFFNESS REQUIRED: Rail-structure interaction requirements are

severe: check differential longitudinal displacement under braking-acceleration loads < 5 mm

HIGH PIER STIFFNESS → SHORT VIBRATION PERIOD

→ HIGH SEISMIC ACCELERATION

• RAIL-STRUCTURE INTERACTION ANALYSIS ALLOWS CONSIDERING DISPATCHING OF BRAKING-ACCELERATION LOADS THROUGH THE RAILS

→ LESS CONSERVATIVE DESIGN OF PIER STIFFNESS

→ REDUCTION OF LONGITUDINAL SEISMIC FORCES

• IN HIGH SEISMIC AREAS, RAIL-STRUCTURE INTERACTION ANALYSIS IS REQUIRED IN ORDER TO DESIGN LESS STIFF PIERS, AND OPTIMIZE THE SEISMIC BEHAVIOUR

USE OF LOCK-UP DEVICES (OR SHOCK TRANSMISSION UNITS)

• Lock-up devices could be used to dispatch the loads under earthquake to several piers, but check RSI displacement at SLS (problem of gap when loading lock-up device)

• TRANSVERSE EARTHQUAKE:

- Transverse bearings necessary on abutments

→ R = 1 (response modification factor) for small bridges

- Piers of various heights on long viaducts in valleys → no simultaneous plastic hinging at all piers → R small, often R = 1 to 2

« SERVICE » EARTHQUAKE

• FOR MODERATE EARTHQUAKES, THE TRAIN OPERATION SHOULD RESTART AFTER THE EARTHQUAKE:

→ REDUCED EARTHQUAKE HAS TO BE DEFINED (WITH REDUCED RETURN PERIOD) → THE STRUCTURE HAS TO BE CHECKED FOR THIS REDUCED EARTHQUAKE: NO REINFORCEMENT YIELDING, LIMITED HORIZONTAL DISPLACEMENTS

EXAMPLE OF SHEAR KEYS FOR HSR VIADUCTS

DAMPERS

• DAMPERS CAN BE USED IN ORDER TO DECREASE THE DECK ACCELERATION AND SUBSTRUCTURES SEISMIC FORCES

• THE BRIDGE MUST BE USABLE AFTER « SERVICE » EARTHQUAKE → FUSE ELEMENTS CANNOT BE USED

• THE LONGITUDINAL DISPLACEMENT UNDER « SERVICE » EARTHQUAKE MUST BE LIMITED TO 20mm IN ORDER TO LIMIT RAIL STRESSES

EXAMPLE OF DAMPERS

• A9 VIADUCT ON PERPIGNAN – FIGUERAS HSR LINE: 10 DAMPERS OF 1500 kN

EXAMPLE OF DAMPERS

• VENTABREN VIADUCT ON MEDITERRANEAN HSR LINE

CONCLUSION

• IN HIGH SEISMIC AREAS, RAIL-STRUCTURE INTERACTION ANALYSIS IS REQUIRED IN ORDER TO DESIGN LESS STIFF PIERS, AND OPTIMIZE THE SEISMIC BEHAVIOUR

• GENERALLY R=1 to 2 TRANSVERSELY

• « SERVICE » EARTHQUAKE HAS TO BE DEFINED, AND SPECIFIC CHECKING PERFORMED