Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Transverse Beams
• Dead Load
– Steel Deck and Beam – 490 lb/ft3
– Rails - 490 lb/ft3
– Ballast – 120 lb/ft3
– Ties – 60 lb/ft3
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Steel Deck and Beam
• Selected Beam W12x136
– 136 lb/ft (AISC Code)
• Deck
– 1/2 inch thickness minimum (AREMA Code)
• ½ in x 1 ft / 12 in x 2 ft x 490 lb/ft3 = 40.83 lb/ft
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Rails
• Spacing (AREMA Code)
– 56.5 in
• Locations of loads
(centerline of tracks =
centerline of bridge)
– 18 ft – 56.5 in x 1 ft / 12 in =
13.29 ft
– 13.29 ft / 2 = 6.65 ft (location
of one track)
– 6.65 ft + 56.5 in x 1 ft / 12 in =
11.35 ft (location of the other
track)
• 136 lb/yd (AREMA Code)
– 136 lb/yd x 1yd / 3 ft x 2 ft =
90.667 lb
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE
Taylor Van Vliet
Tom Wiest DESIGN
Ballast
• Minimum ballast depth = 6 inches below tie.
(AREMA Code)
– Minimum ballast cover of tie = 4 inches (AREMA Code)
• Total of 10 inches ballast
– Disregard the 1.75 ft3 the tie takes up and the change in
depth in the shoulders of ballast
• 10 in x 1 ft / 12 in x 2 ft x 120 lb/ft = 200 lb/ft
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Ties
• Use largest tie – 9 ft x 7
in x 9 in
– 7 in x 9 in x 1 ft2 / 144 in2
x 60 lb / ft3 = 26.25 lb/ft
• Find location of loads
– 18 ft – 9 ft = 9 ft
– 9 ft / 2 = 4.5 ft (Starts at
4.5 ft)
– 4.5 ft + 9 ft = 13.5 ft
(Ends at 13.5 ft)
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Live Loads
• Live load applied to transverse beams (AREMA
Code)
– Maximum axle weight = 80,000 lb
– Minimum axle spacing = 5 ft
– Transverse spacing = 2 ft
– Total 1.15AD/S
• 1.15 x 80,000 lb x 2 ft / 5 ft = 36,800 lb
– Applied at the top of each rail
• 36,800 lb / 2 = 18,400 lb
• We know locations (6.65 ft and 11.35 ft)
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Impact Load
• Percentage of live load applied
– Rocking, other forces
– Length = 18 ft
– Total 40 – 3L2 / 1600
• 40 – 3 x 182 / 1600 = 39.39%
• .3939 x 36,800 lb x .9 (ballast) = 13046 lb
– Applied at the top of each rail
• 13046 lb / 2 = 6522 lb
• We know locations (6.65 ft and 11.35 ft)
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Wind Load on Train
• 300 lb/ft at 8 ft height
– 300 lb/ft x 2 ft = 600 lb
– 600 lb x 8 ft = 4800 lb – ft
– 4800 lb-ft
ft / (56.5 in x 1 ft / 12 in) = 1020 lb (on one rail)
– -1020 lb on the other rail
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Total Loading
• Dead Load
– Uniform Loads
• 136 lb/ft + 41 lb/ft + 200 lb/ft + 26 lb/ft (from 4.5 ft to 13.5 ft) = 403
lb/ft
– Close enough to 400 lb/ft
– Point Loads
• 90 lb at 6.65 ft and 11.35 ft
• Live Load
– Point Loads
• 18,400 lb + 6523 lb +/- 1020 lb = 25943 lb
– Close enough to 25943 lb at 6.65 ft and 11.35 ft
Spring Quarter 2009
Josh Harmon
IDS Project:
Troy Sampson
David Swartz
Zeb Toman
RAILROAD BRIDGE DESIGN
Taylor Van Vliet
Tom Wiest
Sizing the Transverse Beam
• Find max moment based on load
case
– 188,000 lb-ft
• Choose strength of steel to be used
– 70 ksi
– FOS adjustment = 70 ksi x 0.55 =
38.5 ksi (AREMA Code)
• Calculate section modulus
– 38.5 ksi = 188 k –ft / S
– S = 58.6 in3
• W12x136 has S = 64.2 in3
• Check deflection
– 0.2 in < 18 ft x 12 in/ft * 1/360
Spring Quarter 2009
Josh Harmon
Troy Sampson IDS Project:
David Swartz
Zeb Toman
Taylor Van Vliet
Tom Wiest
RAILROAD BRIDGE DESIGN
Replacement
Technologies
Self-propelled modular transporters
(SPMT’s) could allow for the bridge to be
replaced in one piece.
The bridge is assembled somewhere near
the existing bridge. The existing bridge is
lifted and set down somewhere for
demolition. Finally, the new bridge is set in
place.
The current method used in most bridge
replacement projects is to have lane
closures while work is done overhead. A
bridge could take several months to
construct.
The use of SPMT’s allow for the bridge to
be replaced with road closures lasting for
only a few days.
