Bollman Truss Railroad Bridge

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Bollman Suspension and Trussed Bridge
File:Bollman-bridge-1.jpg
Bollman Bridge with Savage Mill tower in background, 1970
Carries Savage Mill Trail
Crosses Little Patuxent River
Locale Savage, Maryland[1]
Characteristics
Design Bollman Truss[1]
Material cast and wrought Iron[1]
Total length 160 feet (48.8 m)[1]
Longest span 2 × 80 feet (24.4 m)[1]
Number of spans 2[1]
Piers in water 1
Load limit 36 tons (72000 kips)[2]
History
Designer Wendel Bollman[1]
Construction end 1869[1]
Bollman Suspension and Trussed Bridge
Bollman Truss Railroad Bridge is located in Maryland
Bollman Truss Railroad Bridge
Location Savage, Maryland
Coordinates Lua error in package.lua at line 80: module 'strict' not found.
Area 4 acres (1.6 ha)
Built 1869
Architect Bollman, Wendal
Architectural style Other
NRHP Reference # 72000582[3]
Added to NRHP October 18, 1972[3]

The Bollman Truss Railroad Bridge at Savage, Maryland is the sole surviving example of a revolutionary design in the history of American bridge engineering. The 160-foot (48.8 m) double-span truss bridge is one of the oldest standing iron railroad bridges in the United States; currently, however, it is in use carrying the Savage Mill Trail across the Little Patuxent River. It was the first successful all-metal bridge design to be adopted and consistently used on a railroad.[1] The type was named for its inventor, Wendel Bollman, a self-educated Baltimore engineer.

History

File:Bollman-bridge-2.jpg
Paired end posts at mid-span showing connection of diagonal tension members with anchor casting.

The bridge was built for an unknown location on the main line of the Baltimore and Ohio Railroad in 1852, and was moved to its present location, spanning the Little Patuxent River on the spur to the Savage Mill, in 1887. This spur line dates to around 1840 and originally crossed the river on a stone arch bridge; however, due to alterations to the mill in the 1880s and topographical restrictions, a replacement bridge was needed. The bridge remained in service until the mill closed in 1947; switching crews used additional cars in order to avoid crossing the bridge with locomotives, and thus there was never a need for a more substantial structure. A smaller, narrower example was installed adjacent to the railbridge for road traffic, which was torn down after WWI.[4]

File:Bollman Truss Bridge Harpers Ferry.jpg
Bollman Truss Bridge At Harpers Ferry

[5]

It was the first successful all-metal bridge design to be adopted and consistently used on a railroad. The design employs wrought iron tension members and cast iron compression members. It was an improvement over wooden structures, as the independent structural units lessened the possibility of structural failure. Patented on January 6, 1852,[6][7] the company built about a hundred of these bridges through 1873. Their durability and ease of assembly greatly facilitated expansion of American railroads in this period. Bollman's Wells Creek Bridge has also survived, but it employs a different type of truss system.

Description

The Bollman Bridge is a two-span through-truss, resting on granite abutments at each end and a granite pier in the middle of the river. The truss structure is a mixture of wrought and cast iron. The truss configuration is the design patented by Bollman as the "Bollman suspension truss" in 1852. Each span is 79.5 feet (24.2 m) long, 25.5 feet (7.8 m) wide and about 21 feet (6.4 m) tall. The Bollman truss suspends the deck from a network of tension members, while the top chord resists compressive forces. The system is therefore referred to as a suspension truss.[8]

The truss includes decorative elements, such as Doric styled vertical members. The cast iron end towers, which bear transfer the weight of the structure to the abutments and pier, are also detailed. A decorative and protective metal enclosure at the top of the towers was lost to vandalism, but was replaced during the restoration work. Metal strips at each portal read "W. BOLLMAN, PATENTEE", "BALTIMORE, MD.", "BUILT BY B&O R.R. CO.", "1869" AND "RENEWED 1866". Replicas of the original strips were installed during the restoration.[8]

The bridge was brightly painted, using red oxide for the towers and the heavier compression members and an ivory color for the lighter tension members.[8] The bridge was originally painted in a three color scheme, documented in black and white photography, with specific shades unknown.[9]

Restoration

File:AERIAL VIEW OF BRIDGE FROM EAST - Baltimore and Ohio Railroad, Bollman Truss Bridge, Spanning Little Patuxent River, Savage, Howard County, MD HAER MD,14-SAV,1-1.tif
Savage Mill and Bollman Bridge in the 1970s

In 1966 the American Society of Civil Engineers introduced a new program, designating the bridge as the first-ever Historic Civil Engineering Landmark.[10] The bridge was listed on the National Register of Historic Places on December 18, 1972, and was designated a National Historic Landmark on February 16, 2000. The bridge was surveyed for restoration in 1978 by Modjeski and Masters with deterioration of the floor trusses noted. A $214,200 restoration contract was let to Dewey-Jordan of Frederick in September 1982.[9] The bridge was restored by Wallace, Montgomery & Associates, LLP, for the Howard County Department of Recreation and Parks in 1983, and more recently underwent additional preservation work and was rededicated on September 16, 2000. Today it receives regular maintenance as part of Savage Park. Nearby Bollman Bridge Elementary School takes its name from the historic bridge.

  • ExistingBridgeElevation.jpg

    Existing bridge, 1982 (prior to 1983-84 rehabilitation work by WM&A)

  • ExistingBridgeUpperCords.jpg

    Upper cords of the existing structure, 1982

  • ExistingBridgeThruView.jpg

    View through the existing bridge, 1982

  • Elevation of The Bollman Truss following rehabilitation by WM&A, 1984

  • NewBridgePartialElevation.jpg

    Partial elevation, 1984

  • NewBridgePier.jpg

    Pier elevation, 1984

  • NewBridgeLowerCords.jpg

    Lower cords, 1984.

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ US 8624  Suspension bridge
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 8.2 Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ 9.0 9.1 Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Historic plaque placed by the ASCE near the north end of the bridge. Observed April 27, 2007.

External links

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