nl-2011-08-ponder

A deck plate girder bridge with steel trestle legs. Note that the ends of the metal legs rest on concrete blocks and that the far right end of the brodge itself falls on a concrete abutment as the track reaches more level ground.

Things to Ponder When You're Planning Your Model Railroad Layout . .

Bridges – Further Considerations

by Raymond G. Potter

Having thought out and chosen the bridges for your layout, be aware that bridges do not exist in a vacuum. Some modelers make the mistake of tossing a bridge into position and throwing scenery or structures around them with no consideration to the elements that make a bridge part of its environment. The components around bridges that support them or attach to them can be just as important as the bridges themselves and are a big part of selling the reality of the bridge. These components include abutments and piers, both of which are important elements in holding up the bridge. Additionally, further variety can be given to a region if a large bridge span is subdivided into smaller discrete bridges, sometimes of varying types.

A deck plate girder bridge with steel trestle legs. Note that the ends of the metal legs rest on concrete blocks and that the far right end of the brodge itself falls on a concrete abutment as the track reaches more level ground.

A deck plate girder bridge with steel trestle legs. Note that the ends of the metal legs rest on concrete blocks and that the far right end of the bridge itself falls on a concrete abutment as the track reaches more level ground.

A big mistake some less experienced modelers might make is putting in a bridge without addressing how it is supported. A bridge will not just rest its end on a grassy hillside. Bridges usually have concrete or stone supports that hold up each end called abutments. Abutments have a real world importance in stabilizing the ends of the bridge. They can also add visual interest to your bridge if they are nice sculpts or castings and they are painted and weathered properly. Choosing the right abutment can have a big impact on how well your bridge blends in with its surroundings. Abutments can be poured concrete or stone and there are a variety of unusual shapes from simple rectangular blocks to fancy stepped affairs. A few bridge kits include abutments, but in most cases you will buy them separately as resin or plastic castings. For unique or custom bridges, or those where there the tracks below have clearance issues, you might have to create your own abutments by bashing several commercially available parts together or building one out of wood covered with some kind of texturing. Stone or concrete viaducts are usually built straight into the hillsides they approach so they are both bridge and abutment combined; these structures would not end in a separate abutment. .

These complex looking abutments and piers suppoting the foreground bridges are made of stacked stips of PVC sheet and wood with good weathering applied.

These complex looking abutments and piers suppoting the foreground bridges are made of stacked stips of PVC sheet and wood with good weathering applied.

This stone viaduct blends into the hillside. No additional abutments or piers are needed.

This stone viaduct blends into the hillside. No additional abutments or piers are needed.

Some bridges are divided into smaller segments; this is especially true of bridges on curves. In the real world, the place where the two bridges meet does not float in air. There would be a vertical column there to hold up the transition point. This column is called a pier. Piers can come in as great a variety of shapes and textures just as do abutments. Well chosen piers will usually match the general style of the bridge’s abutments or of the bridge itself. A metal bridge will have support piers made from metal or concrete. Metal legged piers still usually end in concrete pads on the ground. These would look odd on a wooden bridge where stone or wood would be more appropriate. Consideration must be given when building bridge piers as to whether the piers will interfere with tracks running below the bridge. Most important, piers must be strong enough to support the bridges themselves as well as heaviest load expected to run across them.

Finally, there is no hard and fast rule that says only one type of bridge can be used to span an area. Clever bridge modelers will sometimes combine two or more similar types of bridges to cover a broader span. Usually this would mean two different types of metal bridges, like a truss and a plate-girder, or two different types of wood bridges, like a trestle and a wooden truss. It is generally not realistic to have a wooden bridge join a metal bridge, though there are always the occasional exceptions. Look for examples in the real world where several types of spans are joined together to cross a bay or a river. .

The legs on this multi-section deck plate girder bridge needed special consideration to clear the swing-out of locomotives and long cars traveling on the curved track below.

The legs on this multi-section deck plate girder bridge needed special consideration to clear the swing-out of locomotives and long cars traveling on the curved track below.

Well chosen and well designed bridges and their supporting elements add a lot to a layout. They help set the tone for grungy industrial areas, rural country forests, and arid deserts. The choice you make for bridges on your layout will influence whatever you plan to run on or around them. Forethought will help avoid problems resulting from poor clearance or inappropriate thematic choices, and sound construction will prevent mishaps. Good judgment and an eye for detail will make sure that bridge is realistically supported and integrated into its environment. Not every bridge is right for every location, so research is essential to your choice, whether that means asking a knowledgeable friend or surfing the internet to find what you need. Good bridges attract attention, as do bad ones. When all is said and done, visitors to your layout will stop and stare in admiration at your nicely chosen, properly constructed, and realistically painted and weathered bridges.

You don't see extensive bridges running through the center of cities too often, but this replica of Cleveland's Veteran's Memorial Bridge is a nice example.

You don’t see extensive bridges running through the center of cities too often, but this replica of Cleveland’s Veteran’s Memorial Bridge is a nice example.

 


from the August, 2011 SMARTT Newsletter

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