Steve Barlow Pandrol Asia-Pacific Development of a simple prediction model for slab track vibration using field measurements Steve Barlow Pandrol Asia-Pacific
Scope of study Consider only concrete slab track. Consider only vibration, not noise. Consider only the vibration measured on slab adjacent to rail fastener. Do not consider vibration transmission through or from structure Hence, only concerned with the performance of the fastener itself.
PART 1 What is Slab Track?
Cast-in baseplates
Pre-cast block track
Embedded sleeper (1)
Embedded sleeper (1)
Embedded sleeper (2)
Embedded sleeper (2)
Plinth track
RHEDA track
J-slab
Precast FST slab track
Embedded Rail
What are we trying to achieve with slab track? Reduce the space taken by trackform, particularly in tunnels Reduce maintenance liabilities Keep costs down Reduce the track stiffness
Low stiffness rail fasteners PART 2 Low stiffness rail fasteners
Reducing track stiffness – why? Want to reduce ground borne vibration (a.k.a.structural noise) Theory tells us to either: 1. Increase mass (e.g. FST) 2. Reduce track stiffness
Options for lowering slab track stiffness
Conventional baseplate Rail foot fastened by steel spring clips Vertical stiffness limited by rail roll (typically 15 to 20kN/mm static) Typically 2.5mm maximum vertical deflection
Conventional resilient baseplate with spring clips
Low stiffness baseplate Supports and clamps rail by the web Low vertical stiffness (typically 3 to 5kN/mm static) Vertical rail deflection up to 6mm typical Straight swap for existing baseplate in most cases
Low stiffness baseplate clamping rail by the web
Description of field measurement locations PART 3 Description of field measurement locations
Location 1 Hong Kong MTRC Plain slab at grade Installed January 2002 Straight swap for existing soft fasteners 7.4dB insertion loss measured on slab
Location 2 Hong Kong Airport Railway Viaduct on 300 metre radius curve Fitted January 2004 Retrofit to replace existing ‘soft’ baseplate 8.2dB insertion loss and 5dB(A) less secondary noise beneath viaduct
Location 3 London Underground – Victoria Line Retrofit to slab track Cast-in sleeper version Operational since March 2000 Gives 16.2 dB insertion loss on slab More than 125MGT traffic since operations began
Location 4 Madrid Metro Line 11 Installed August 2001 Replacement of existing stiff fastener on booted block 23.1dB insertion loss recorded on slab
Location 5 Guangzhou Metro China, Line 1 Installed 2005 345m radius curve and tangent Retrofit for stiff fastener 11.5dB insertion loss on slab
Swapping over baseplates PART 4 Swapping over baseplates
Swapping over baseplates Raise rail temporarily Remove old baseplate Use other rail as datum Position new baseplate
Swapping over baseplates Low stiffness baseplates positioned Clamping tool used to fasten rail Once alignment is set, start work on other rail
Swapping over baseplates Both rails clamped and aligned Take ‘after’ vibration recordings immediately
Taking vibration readings PART 5 Taking vibration readings
Measuring vibration Multiple train passes for each case Train speed constant Time lapse between before and after measurements minimised Same recording and reporting method used in all cases
Taking slab vibration readings Accelerometers screwed to steel plates, bonded to slab Positioned close to rail foot at mid-span where possible Data recorded and processed in the same way every time
Factors affecting vibration results Rail condition and geometry Wheel condition Train speed Local conditions Track structure
PART 6 Vibration results
Change in static stiffness of rail fastener Units Location reference 1 2 3 4 5 Static secant stiffness before (Ks1) kN/mm 21 133 130 52.1 Static secant stiffness after (Ks2) 5.1 Stiffness change (Ks1/Ks2) 5.25 26.1 32.5 13.0 Insertion loss (total vibration) (dB) 7.4 8.2 16.2 23.1 11.5
~15dB insertion loss change per tenfold static stiffness change
Steve Barlow Pandrol Asia-Pacific scb@pandrolasia.com END Steve Barlow Pandrol Asia-Pacific scb@pandrolasia.com