Civil Engineering Reference
In-Depth Information
(a)
Timber track tie in stone ballast
Concrete deck
Drain
(b)
hrough girder
Knee brace
Steel plate deck
Timber tie
Stone ballast
Floorbeam
FIGURE 3.14
(a) Ballasted deck plate girder (BDPG) span. (b) Ballasted through plate girder
(BTPG) span.
devices and grouting after installation.AREMA (2008) recommends a minimum deck
thickness of 1/2 and 6 in. for steel plate and concrete slab decks, respectively.
Ballasteddecksgenerallyrequirelessmaintenanceandareoftenusedduetocurved
track geometry or when the bridge crosses over a roadway or sensitive waterway.
Ballasted deck structures allow for easier track elevation changes, but drainage must
be carefully considered. Drainage of the deck is often accomplished by sloping the
deck surface to scuppers or through drains. In some cases, the through drains are
connected to conduits to carry water to the ends of spans. In particular, deck drainage
at the ends of spans using expansion plates under the ballast between decks must
be carefully considered. Most railroads have standards for minimum ballast depth
and waterproofing requirements.AREMA (2008, Chapter 8) contains information on
recommended deck waterproofing systems.
3.3.2.1.4 Direct Fixation Decks
Tracks may be fastened directly to the deck or superstructure where live loads are
light and dynamic forces effectively damped. Direct fixation decks are most often
used in passenger rail service with rails firmly fastened to steel or concrete decks.
