The Bollman Bridge For “G Scale”

The Bollman bridge will be our new project this is a very interesting bridge in Maryland.  We are going to be making the G scale version of the this Bridge;  below you can read a bit about it.  Then I will add pictures of the process of making the replica.

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 double-span truss bridge is one of the oldest standing iron railroad bridges in the United States. It was the first successful all-metal bridge design to be adopted and consistently used on a railroad. The type was named for its inventor, Wendel Bollman, a self-educated Baltimore engineer.

 

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. 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.

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 long, 25.5 feet wide and about 21 feet 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.

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.

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.

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The first thing we did when we started the construction of our bridge was to replicate the decorative elements:  The Doric vertical members and the metal strips for the portals.

To make the metal strips, the front plates were drawn and then cut on a computerized plasma cutting table, then flat bar was attached around the plate to complete the front strip.

Once those two custom components of the bridge were made, we could move on to making each side of the bridge.

After we had two sides for the bridge we started to connect them.

The Finished G scale version is 11 feet – 4 inches long, 13″ tall and 14-1/2″ ID – 18″ OD.,  wide enough for double track.

 

The bridge will get powder coated and after it is installed it will be painted as the original, red with white accents.  It should be a nice bridge to look at.

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