Milan Branch of the Iowa Interstate RR

Lattice truss bridge spans

Below is a picture of two scale cardboard mockups showing the lattice truss bridges which will span the Rock River.

Lattice truss bridges are not modeled very often, even though there are many examples of that type of bridge throughout the country.

The photo also shows the location of a speaker which will be embedded into a small river island and will play moving water and bird sounds. Attached is a small snippet of the sound which will loop once installed.

 

A friend, Clark C., is helping me create the custom bridge spans with his expertise using lasers. He first mocked up a schematic for each of the different lattice configurations based on an Illustrator file I sent him (below). The spans have several distinct horizontal lattice designs which include angle iron and I-beams in two different crisscrossing reinforcing lattice patterns. In addition, those designs alternate between the inside and outside of the main truss. This creates a very interesting and somewhat complex fabrication challenge.

We will be developing the depth of each side span in “layers” similar to 3D printing. This will allow the unique open areas (see image below) between the main lattice members to be rendered accurately. At least, that’s the idea. 🙂

Clark mocked up a test section to see how the laser would render a portion of the truss and supporting lattice.

Below is what the computer rendering looks like. Each tone represents a different depth of cut, and the laser can be sped up (more intense ablation) or slowed down (multiple passes for better detail) to achieve different quality levels.

By their design nature, turn-of-the-century lattice truss bridges are delicate looking which makes them unique but also challenging to construct. We’re hopeful that the “layered” approach will allow those delicate cross members to be modeled faithfully without the potential for bending or warping along their length.

Clark discovered that the laser cuts did warp the material as shown below. But by applying oven heat to slightly ease the material and then applying weights as it cooled resulted in flat, uniform pieces.

Below you can see some of the cross members attached to the main truss and weathered for effect.

Clark will be creating some additional cuts to see if the material can be thinned down even more. So far, it looks very promising for these unique spans. Stay tuned!

 

Categories: Planning, Scenery

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5 Comments

  1. Dear Scott,
    Strongly reccomend trying, if at all possible, to get a pair of speakers into the scene. With appropriate _scale_ sound design, a pair of speakers can permit startling positioning of various noisemakers within the scene, and an all-encompassing ambience (think of it like aural weathering) which can be used to position aural point-sources _beyond_ the speaker locations…
    Looks like it’s shaping up to be a gorgeous scene… 🙂
    Happy Modelling,
    Aim to Improve,
    Prof Klyzlr
    PS what do you intend to use as the audio source?

    • Thanks, Prof.

      Are you saying include more speakers to make the sound envelope the scene better? I’ll be using ISE’s soundboard (out of production).

      Sound is a .wav file from FreeSound.

  2. What kind of material is being used for the bridge spans?

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