Section 14 - Satsop River Bridge - Part 1

Its time to layout the Satsop River section. The layout design given and druthers of this section is identified in Station 14 Satsop River.

Layout Design Elements

The Satsop River section adjoins the Basalt Sand and Gravel section to the north and the Polson Canyon section to the south. This section has of eight layout design elements: (from backdrop to fascia):

1. A darkened cloudy sky suggesting inclement weather is approaching. 
2. A mid distant tree line and visible riverbank.
3. A shallow river with significant sand and gravel on the river bottom and sides.
4. A 5 bent wood trestle and a wood abutment. 
5. Two 16 panel plate girder bridges
6. Two 10 panel plate girder bridges
7. 4 unique piers 
8. A concrete abutment for one of the 16 panel bridges.

Section Construction

See the WWSL section construction reference page for the construction technique. 

As this section is a river scene I have modified the construction technique. Instead of using the two 1x3 girders on the bottom of the section, I need a solid bottom on the section for the riverbed. The 1x3 girders are replaced by a 2 foot by 8 foot piece of plywood 3/4 inches thick. The two ends of the section are cut out to permit attachment of the section electrical connectors and section interface bolts. 

 The remainder of the section is built per WWSL construction standards.

ROW Design Considerations 

The most critical design considerations on this section is the length of the bridge. With only 96 inches of linear space to model two curved legs, two river banks and and 5 bridges, something has to be compressed. 

First I looked at the two curved legs. At Basalt, the 26 inch radius curve needs to connect to a tangent track located 10 inches from the front fascia. That means that 16 inches of space is needed on this section for the north wye design element. At Polson Canyon, the 26 inch radius curve needs to connect to a tangent track located 16 inches from the front fascia. This means that 10 inches of space is needed on this section for the south main line and the abandoned spur track. A total of approximately 26 inches is needed for the curved main line components. That leaves us with 70 inches of tangent mainline track for the five bridges. See Satsop River Bridge N5 for the baseline construction details.

4. The timber trestle is a six pile per bent design. I pulled up a construction diagram of a timber trestle built by the Southern Pacific.  That diagram has each bent a distance of 15 feet apart. In HO scale that's a bit less than 2 inches per bent. Five bents and a wood abutment is about 10 inches. See Satsop River Bridge N5 (Timber Pile Trestle) and Satsop River Bridge N5 (Wood Bulkhead) for construction details.

5. I am planning to kitbatch the plate girder bridges. The Atlas Thru Plate Girder Bridge has been produced in two types: 1) ten steel plate panels equally spaced, and 2) 10 steel plates of different widths. I will use two of the equally spaced 10 panel bridges to represent the 16 panel bridges. This is a 38% selective compression of the bridge scene. Total length of those two bridges will be 18 inches.

6. Using the selective compression percentage above, I will need to add (rounded up) 4 panels to each of two additional 10 panel bridges to represent the 20 (modeled 14) paneled panel plate girder bridges. Total length of those two bridges will be 25 inches. 

See Satsop River Bridge N5 (Deck Plate Girder Bridge) for construction details.

7. There are 4 interesting piers to be constructed. Three are wood pile bents, one is a steel pile bent. They will be scratch built.

See Satsop River Bridge N5 (Steel Pier) and Satsop River Bridge N5 (Pile Piers 2-4)  for construction details.

8. The concrete abutment will have to be designed to reflect the dimensions of the embankment constructed. See Satsop River Bridge N5 (Concrete Abutment) for construction details.

Adding all those bridge lengths gets me to about 53 (18+25+10) inches, with a leeway of about 17 inches for 'off the bridge tangent track' leading into the curves at each end. 

Laying out the Structures 

I used a pair of 3 foot yard sticks to determine the anticipated length of the bridge complex (53 inches) and for initial siting of the river banks and the bulkhead, piers and concrete abutment.

There is a section maintainers tool shed, a bridge tie pile and a rail car shed for a bridge inspection car. I built structure footprints for each of them for conformation of siting those structures.

Laying out Right of Way

I am not going to go into great detail about putting down the roadbed lines. See the Right of Way Reference Page  for the details if you haven't had the fun to do it before. 

Essentially you're going to follow this process: 

1. Lay out the main line. I centered it at the 12 inch line.
   
2. Lay out the transition template line.
   
3. Lay out the main line curves. 
   
4. Lay out the bridge template, the length of the bridge and adjust as necessary.
5. Lay out the south embankment leading to the bridges. 
6. Locate the abutments and piers (to include heights).
7. Lay out the sloped river bank on the north side of the river.
   

Because this section ties into both the Section 15 - Basalt and the Section 13 - Polson Canyon, some layout of those sections will need to be done at the same time, primarily the main line locator at Basalt (10 inches from the fascia) and the northernmost Polson Canyon curve (16 inches from the fascia).  .

1st (Northern) Division is

• The WWSL 1st Division is designated Class B main line. See 4.2.11.2  Modeling Technique for Medium Profile Roadway for details. 

Right of Way Drainage.   

There are no unusual requirements for drainage.

Track Details.

The main line will require unique Catenary pole placement at pier locations. See 7.1 Cantenary Systems Overview for details.

See 4.2.3 Laying Straight Track and 4.2.4 Laying Curve Track for construction details.

In the next blog (Section 14 - Satsop River Bridge Module - Part 2) I will discuss the Scenery Design Considerations.