10' Arch Bridge

overall view

angled view

Super Chief crossing

Tony's Allegheny

at the show

inside view

side view

Arched Through-Truss Bridge

This is an arched through-truss bridge. It's not modeled after any specific bridge in real life.

Model Specs and Facts:
Build time: approx. 5 weeks
Date of completion: 6-July-2009
Total bridge length = 129.1 inches = 3.28 m
Free span length = 125.3 inches = 3.18 m
Total width = 33 studs
Deck width = 24 studs
Made of 100% LEGO pieces, and no glue was used

This was a quick design and build to generate a large model for TexLUG's public display at the Mall of the Mainland's model train show in Texas City, Texas (July 11, 2009).

truss design

deck & hanger design

Planning the Model

The design, in concept, was very much the same as previous truss bridges that I have built. The process started by using my bridge design spreadsheet to size the members. I modified my sheet slightly to fit this particular truss shape and number of sections.

Spreadsheet used for the design: bridge_10ft.xls (0.3 MB)

I know this description is incredibly short, but the process is fairly easy and straightforward.

test assembly at home

close up of joint

abutment columns

stacked & packed
for the show

Building the Model & Setting Up

I estimate I probably spent 40-50 hours total building this model over a period of about 5 weeks.

I decided to beef up some of the truss members and make them 2-studs wide instead of one. I also built an X-pattern cross bracing instead of just a single diagonal member. I took my time and made sure that all the lateral members were stout and firmly connected. The resulting model was very strong. I didn't perform any load tests, but I think it was probably the strongest truss bridge that I've built yet (considering its length and weight).

I did goof up when building it. I originally had the deck width set too small to accomodate TexLUG's trains. In particular, Tony Sava's Allegheny model requires about 12 studs clearance. After I had finished most of the truss and lateral frames, I had to re-size and widen the whole thing. (and still it wasn't wide enough! It accomodated the Allegheny, but wouldn't tolerate two trains running past each other at the same time.)

I built a set of paired columns to support each end of the bridge. The construction of these columns used all LEGO parts, and they were made of box-sections with plating over the surface. The photo to the left shows the inside beams before the plate was attached.

I broke the truss into 4 major sections. These were then paired together to form two modules for transport.

The model's debut was at TexLUG's public display at the Mall of the Mainland's model train show in Texas City, Texas (July 11, 2009).

My photos from the event.
Tony's photos

Thomas J. Avery 2010