Concrete Bridge-Abutment Interface

Model Railroader General Discussion (Model Railroader)
1

I’m relatively familiar with how bridges mount on their abutments, with their shoes and whatnot, for a variety of bridges. However, one type of bridge has me stumped.

I plan on using one of these http://rixproducts.com/6280103.htm to cross a creek. There’s not a whole lot of bridges of this type in my area, as best I can tell, so I can’t go snooping around for eyes on one. How would the beams mount on the abutment? Would it be the same for those outside beams, given that they have a different shape?

Also, what’s the longest such a bridge could run, unsupported? I’d rather not have a pier in the middle of my creek, if I can avoid it, and would prefer to narrow the creek rather than interrupt it.

2

Helllo all,

The bridge abutment for this model would be a standard highway over pass interface.

Unless you live where there are no concrete bridges over highways I’m sure there are some in your areas that you could examine.

Just like any other bridge to abutment interface remeber that the bridge sits ontop of the abutment not against it.

For the bridge to abutment interface most use a noched interface that allows some expansion of the bridge from weight and heat or cold.

Most of the time this expansion joint will be covered with metal plates or mesh at each end and sometimes in the span itself.

The bridge then sits in the noch in the abutment for the roadway to be level.

Hope this helps.

3

In the US there is a quasi-governmental agency call AASHTO that governs all things regarding highway and transportation engineering design and construction. It is a national agency that’s been around since about 1920 and every state DOT adheres to it. Any quick internet search should turn up a mountain of information, including thousands of photos.

The beams supporting your bridge look (kinda) like standard pre-stressed concrete AASHTO I-beams. For that style of beam there are six types. Those particular ones look like Type I and are good for up to about 120 feet. Type VI beams are similar (but quite a bit larger) and might go up to about 200 feet. For anything longer, the designer would probably go to a different style, such as concrete box girder or something.

4

I hadn’t actually thought to look up the AASHTO. I knew it was the sort of bridge that was very popular in the WPA days. Curiously, almost every bridge in my area is steel. Most of Northern Virginia’s infrastructure is very, very new. If I was back in PA, there’d have been plenty of them around.

5

I would think the concrete beams rest on the abutment as with any bridge. There is proably some form of sliding joint to allow for expansion/contraction. A rule of thumb for span is 20:1 so measure the depth of the beams and multiply by 20. If you don’t want a pier in the middle could you put them at the 1/4 and 3/4 points of the span?

Bill

6

Not having built the kit I can’t answer how the abutments work, but I think I can help with the question about spans.

What is the total span that the bridge needs to cross?

The bridge kit will build a 150’ (20") bridge. Assuming that the bridge is divided into three spans with two piers, and based on a 120’ maximum span for the center section of the bridge, you could have up to 16.5" between piers. That should be plenty to model a creek without a pier mid-stream.

I’m assuming that the piers can be placed where ever needed.

Dave

7

Hello all,

I Googled Highway Bridge Abutments and under the Images for Highway Abutments I found many photographic and schematic examples of what you are looking for.

Hope this helps.