A little over 12 months ago CEMEX Rail Solutions were asked by London Underground for a design of concrete bearer for curves of less than 200m radius.
The particular issue with tight curves is that of wheel / rail alignment around the curve. The way to ensure that wheels remain on the track is by use of a check rail next to the running rail; this guides the wheel and keeps it on the rail.
London Underground had designs of 2 base plates, one for the check rail end and one for the running rail on the other end of the bearer but needed to mount it on a concrete bearer. This was not straight forward as there were 2 complications highlighted by a Finite Element Analysis carried out by Durham University.
The method of attaching the base plate to the bearer was via a cast in plastic dowell. This is a known crack inducer in pre-stressed concrete due to tensile forcesset up around the dowell. The dowells on one end need to be in close proximity to mounting positions for 3rd and 4th conductor rail mounting positions.
These conductor rails are bolted on again into a plastic insert (another crack inducer). To overcome these issues we have adopted industry practice from Germany and placed a tight fitting helical reinforcement around the plastic dowells to contain cracks.
The plastic inserts for conductor rail mounting have been replaced by metal inserts. A second finite element analysis by Durham University concluded that these changes had significantly reduced the risk of crack propogation within the unit. A further 2 variants of check rail bearer were designed (short ended at either end) at the same time to allow for drainage catch pits which are sometimes in the way trackside.
Thanks to the contribution of our Operations, Maintenance and Quality Departments the 3 variants went into full production of around 100 units per week at Somercotes in early April and our client is forecasting a positive future demand by end of the year.
A further variant is now being looked at to incorporate standard pandrol fastclip fastenings and inclined concrete; this would be used where the client has noise and vibration issues where a soft undersleeper pad could be used.