B&M Merrimac St. Bridge in Newburyport MA

[jbvb]

2025: A build thread copied here because RR-Line is gone
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25-Apr-2010: Between the Newburyport, MA station and the bank of the Merrimac river, the B&M passed over Merrimac St. on a through girder bridge. Unused by trains since 1965, it's a rail trail now.



This is the easterly abutment, with the US 1 overpass in the background. Span is probably about 50 feet.



The underside shows a few peculiarities: The abutments were clearly built for an earlier span. And though the bridge isn't skewed, the floor beams don't line up with each other.

I need a selectively-compressed model good enough to be within 18" of the layout edge. I'm not sure this is really going to be a "craftsman" build, but several RR-Line regulars said "separate thread" so here I go.

My knee is not up to climbing around bridge structures, so I relied on Paul Mallery's bridge book for many dimensions. I'm not building with a contest in mind anyway, I just want it to suggest the prototype and not scare the engineers (bridge, not locomotive).

I had some MicroEngineering 30' deck girder bridge parts around, so I scaled the width of the road down to about 25'. The prototype designers weren't worried about clearance underneath, so the rails sit much higher relative to the side girders than commercially available model bridges. This meant I could space the tracks about 14' apart and not worry about making clearance for the center girder.



I only had two and a half girders, but I couldn't have used a third intact one anyway; The middle girder is enough deeper than the two sides that I really wanted to model it.

Per Mallery and my photos, floor beams in the 25-30" range were reasonable, and the LHS had Evergreen 5/16" I-beam. I notched the ends so the beams wouldn't protrude outside the ends of the girders.

[jbvb]

I fitted the cross beams above the angle at the bottom of the girders. This will leave the Code 83 railheads a few scale inches below the side girders. I glued the cross beams to the girders with solvent cement.



Then I squared it up and left it to dry while I went down to dinner.

26-Apr-2010: Sorry about the focus - I've just been picking up my camera and shooting as I built.

This is what I did about the 'half' girder I had for the middle position:



I cut it in half and spliced the halves together, then notched it to fit over thefloorbeams. I used Methyl Ethyl Ketone to glue it in place (my standard liquid 'solvent cement' for styrene). But I'm not being too delicate here - I did the splice with "model airplane" tube cement because I wanted a strong joint without a lot of fiddly filing.



The ME bridge track I had is right for this deck, so I'm not hand-laying it. This test-fit shows that I can't get away with just pronouncing it finished at this point - the missing parts are too visible.

I added stringers using Evergreen 1/8" I-beam. If I'd had 3/16", I'd have used that instead. I cut them with my Chopper and assembled them with tube cement because the joints won't be visible. I worked from below with the track in place to get the right spacing below the tops of the floor beams.

I used .040 x .188 strip to fill in below the partial center girder. Then I made a bottom piece for the center girder out of .040 x .125 and .040 x .188 styrene strips (it's going to be dark under there). I notched it for the floor beams so it fit against the filler strips.

Later this week I'll rough-in the abutments and then I'll know if I have to do the diagonal bracing on the underside.

2-May-2010: I roughed-in the abutments, and decided I had to add diagonal braces. Because they're not very visible, I used Evergreen .060 angle (a bit big) and didn't bother with the attachment flanges; I just glued the ends to the flanges of the floor beams.



'm not going to be able to finish the track till the bridge is permanently mounted, so today I'm building backdrop, to be followed by screen wire for the abutments and retaining walls.

[jbvb]

Meanwhile, here's a picture that tells a story:



The Eastern RR built through Newburyport in 1838, but being a New England seaport, it was already pretty urban. This location worked best, convenient to downtown and minimizing the cost of the river crossing 100 yards east. They took the land they needed, but by the time they double tracked (1880?), property values near the station had risen and they clearly couldn't run roughshod over their abutters:

Vertical stone retaining walls 20' high are not common, but here's an example. If you look close, you'll see this building is in it's own little pocket; The Eastern bought the lot behind it and let the embankment go all the way to the edge of the street. You can't see that beyond *that* lot, there are two more houses in another stone-walled pocket. If I model it all, I'll have to keep a picture handy to show nitpickers...

9-May-2010: First, I painted the abutments and exposed Homasote with black latex paint. Then I cut, formed and stapled scrap aluminum window screen in place to provide support for the stonework and embankment.



In the modern photos, the granite stones look like Rockport (MA) granite. However, in the era I'm modeling they were a uniform sooty black, with very conspicuous light gray mortar lines. I'm using an out-of-production wood flour/glue product called Wood Putty that Savogran used to make. Because of it's glue base, there's no question about new material sticking to old. I've built a number of abutments of this style by first getting the right shape with uncolored wood putty. Then I make a black batch, using masonry color, and apply a fairly thin layer over the whitish base. When the black coat is leather-hard, I carve through it to expose the white in the joints.

I thought of an alternative technique, and decided to try it on a section of wall which is going to be mostly hidden behind Donahue Motors:
I painted it with flat black latex while the wood putty was still damp. I gave the paint an hour to dry and then carved mortar lines with a stainless 'dental style' pick I got from a traveling 'tool guy' at the Springfield show.



t's clear that I need to take care to get the surface of high-visibility areas reasonably smooth before painting, but I think it works. I'll be weathering it too, once the adjoining scenery is installed.

21-Jan-2011: I got the abutments mostly done quite a while back, but I didn't get around to painting the bridge till November, photographing it till December, or posting till now:

[jbvb]

I bent, filed and soldered Code 55 guardrails at the workbench. I applied Weldwood contact cement to the bottom of the running and guard rails and let it dry. I put the bridge in place, got the gauge and alignment right and heated the rails with a soldering gun to fasten everything down on the bridge itself; the ends aren't yet fastened to the 'land' ties.



I couldn't make the guardrails prototype standard length; the bridge must remain removable until scenery is done, so I didn't want long floppy points I'd need to spike down. Also, the curve from the End of Double Track switch is close on the right and using the right length on the left would have looked odd.

Neil M. said:

That's an interesting bridge james.
The unequal plate girders make sense. The central girder carries twice the load of the edge girders. The outer girders carry half the weight of the track and train on either track but the centre girder carries the other half of the weight of both tracks. The easiest way of increasing the load a girder can carry is by increasing the depth of the I section.

I suppose when the line was double tracked the two outer girders were kept but spaced further apart and a new centre girder was added in?
Looking at it with modern eyes it looks like the bridge is asking to get hit by a lorry/truck driver who can see he can get under the outer girders and hasn't noticed the reduced headroom under the centre of the deck!

Bruce asked about the guardrails, Frederic about the bridge track.

22-Jan-2011: Neil, AFAIK double tracking was done in 1880, before the weights of cars and engines started increasing. The current bridge was installed on the 1880 abutments between perhaps 1910 and 1922, when the river bridge was strengthened. By then, a new abutment would probably have used concrete. Road clearance is 18+ feet, much higher than the northeastern norm of 14-15 feet.

Bruce, I used M-E weathered Code 55 I had on hand. Before WWII, the B&M used guardrail point castings. Into the 1960s, they burned a taper on the two rails and bolted them together to form a rougher point. In the 1970s, they just bent the ends inward a foot or so and spiked them in place. I'm (roughly) modeling a cast point here, so I just filed tapers and soldered; I didn't make the
notches you show, though I've seen them on other RRs, probably associated with heavier rail.

Frederic, the bridge track itself is Micro-Engineering Code 83, modified only to re-space the ties over the crossbeams.

2025: the bridge has been in service for 14 years; scenery and a city have grown up around it.  It's in the lower right corner of this:

[ACL1504]

James,

Fantastic job on the Merrimac ST. Bridge. Excellent scratch build and look great.

Tom 

[Philip]

  Nice work!

[jbvb]

Thanks, Tom & Philip.  The rail joiners are still bright in the recent picture because I've kept the bridge removable. I may reconsider when I've finally paved Merrimack St. under it. But I won't do that till Bolles Motors (bottom center) is finished with sidewalks and entrance steps/ramps.