Development of a simple prediction model for slab

Development of a simple prediction model for slab track vibration using field measurements Steve Barlow Pandrol Asia-Pacific

Scope of study n n n 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 (2)

Plinth track

RHEDA track

J-slab

Precast FST slab track

Embedded Rail

What are we trying to achieve with slab track? n n Reduce the space taken by trackform, particularly in tunnels Reduce maintenance liabilities Keep costs down Reduce the track stiffness

PART 2 Low stiffness rail fasteners

Reducing track stiffness – why? n n 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 n n n Rail foot fastened by steel spring clips Vertical stiffness limited by rail roll (typically 15 to 20 k. N/mm static) Typically 2. 5 mm maximum vertical deflection

Conventional resilient baseplate with spring clips

Low stiffness baseplate n n Supports and clamps rail by the web Low vertical stiffness (typically 3 to 5 k. N/mm static) Vertical rail deflection up to 6 mm typical Straight swap for existing baseplate in most cases

Low stiffness baseplate clamping rail by the web

PART 3 Description of field measurement locations

Location 1 n n n Hong Kong MTRC Plain slab at grade Installed January 2002 Straight swap for existing soft fasteners 7. 4 d. B insertion loss measured on slab

Location 2 n n n Hong Kong Airport Railway Viaduct on 300 metre radius curve Fitted January 2004 Retrofit to replace existing ‘soft’ baseplate 8. 2 d. B insertion loss and 5 d. B(A) less secondary noise beneath viaduct

Location 3 n n n London Underground – Victoria Line Retrofit to slab track Castin sleeper version Operational since March 2000 Gives 16. 2 d. B insertion loss on slab More than 125 MGT traffic since operations began

Location 4 n n Madrid Metro Line 11 Installed August 2001 Replacement of existing stiff fastener on booted block 23. 1 d. B insertion loss recorded on slab

Location 5 n n n Guangzhou Metro China, Line 1 Installed 2005 345 m radius curve and tangent Retrofit for stiff fastener 11. 5 d. B insertion loss on slab

PART 4 Swapping over baseplates

Swapping over baseplates n n Raise rail temporarily Remove old baseplate Use other rail as datum Position new baseplate

Swapping over baseplates n n n Low stiffness baseplates positioned Clamping tool used to fasten rail Once alignment is set, start work on other rail

Swapping over baseplates n n Both rails clamped and aligned Take ‘after’ vibration recordings immediately

PART 5 Taking vibration readings

Measuring vibration n n 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 n n n 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 n n n 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 (Ks 1) k. N/mm 21 21 133 130 52. 1 Static secant stiffness after (Ks 2) k. N/mm 4 4 5. 1 4 4 5. 25 26. 1 32. 5 13. 0 7. 4 8. 2 23. 1 11. 5 Stiffness change (Ks 1/Ks 2) Insertion loss (total vibration) (d. B) 16. 2

~15 d. B insertion loss change per tenfold static stiffness change

END Steve Barlow Pandrol Asia-Pacific scb@pandrolasia. com