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
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