Civil Engineering Reference
In-Depth Information
TABLE 4.1
Dead Loads on Steel Railway Bridges
Item
Dead Load
Track (rails and fastenings)
200 lb/ft
490 lb/ft
3
Steel
150 lb/ft
3
Reinforced and prestressed concrete
145 lb/ft
3
Plain (unreinforced) concrete
35-60 lb/ft
3
Timber
120 lb/ft
3
Sand and gravel, compacted (railroad ballast)
100 lb/ft
3
Sand and gravel, loose
15 lb/ft
2
Permanent formwork (including concrete in valleys)
10 lb/ft
2
Waterproofing on decks
Source:
From American Railway Engineering and Maintenance-of-Way Association
(AREMA), 2008,
Manual for Railway Engineering
, Chapter 15. Lanham, MD.
With permission.
refinement in multibeam spans where exterior beams may be subjected to a greater
proportion of any superimposed dead load.
At the commencement of design, dead load must be estimated from experience or
review of similar superstructure designs.This estimated design load must be reviewed
against the actual dead load calculated after final design of the superstructure. Small
differences between the estimated and actual dead load are not important, provided
the dead load is a reasonably small component of the total design load. Steel railway
bridge engineers will often include an allowance of 10-15% of estimated steel super-
structure weight to account for bolts, gusset plates, stiffeners, and other appurtenant
steel components. Dead loads typically used for ordinary steel railway bridge design
are shown in
Table 4.1.
Temporary construction dead loads and the transfer of dead load during shored
or unshored construction of steel and concrete composite deck spans should also be
considered during design (see Chapter 7).
4.3 RAILWAY LIVE LOADS
Railroad locomotives and equipment (box and flat cars, commodity gondolas, and
hopper and tank cars) vary greatly with respect to weight, number of axles, and axle
spacing.
Modern freight locomotives have two three-axle sets with a spacing between axles
of between 6.42 and 6.83 ft, and a spacing between axle sets (commonly refereed
to as “truck spacing”) of between 45.62 and 54.63 ft. These modern generation
locomotives weigh up to 435,000 lb. There are, however, many four- and six-axle
locomotives of weight between about 250,000 and 400,000 lb, and with lengths
between 50 and 80 ft operating on the railroad infrastructure.
Axle spacing is typically 5-5.83 ft for NorthAmerican four-axle freight car equip-
ment. Truck spacing may vary from 17 to 66 ft (Dick, 2002). Gross car weights up to
