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Lattice Girder Deck Truss Bridge - Kit bashing


zr2498
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The plan:

To add a single span, lattice girder deck truss bridge to left side of the stone viaduct as seen towards the back in the photo below. The stone viaduct was constructed using the 'Townstreet' range. The pier and abutments are kit bashed, again using the Townstreet castings.

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The deck truss bridge will be based on the marvelous Findhorn viaduct. Unfortunately there is only space for one span - it will be 530mm long.

 

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I will try to use as many components as possible from a bridge kit produced by CVMW, plus various bridge girder components that the same company supply separately.

No doubt there will be a great deal of additional styrene profile, and perhaps some details etches to add as I go along.

A picture of a finished bridge kit below is very much different to the deck truss bridge, but some components, especially for the deck can be readily adapted.

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The exact detail of the Findhorn viaduct cannot easily be copied. Even if I were to get construction drawings, I would need to start from scratch with photoetch design. So being pragmatic, I guess as long as the bridge is of the same proportion, has a similar basic layout and elements of the Findhorn viaduct, I will be satisfied.

One big change though, will be to convert the bridge to double track (to suit my layout). The other requirement is to ensure that the bridge looks British rather than American (as intended for the CVMW kit). The deck will be plated and ballasted unlike the open deck, and lets face it the bridge will end up looking completely different with the truss underneath.

Planning and construction has started and I will give an update on progress later this week.

Dave

 

 

 

 

Edited by zr2498
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Below is the basic frame layout of the truss sections. There will be 4 frames (2 per track).

The number of sections per frame has been reduced from 8 (Findhorn) to 6. By scaling from coach lengths, the bridge span and depth could be estimated, but it will be reduced to 6 sections to align with the pitch of the cross bearers and stringers supplied with the CVMW kit deck arrangement.

 

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Starting with the deck:

Initially, parts are used from the Central Valley Model Works bridge kit

 

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These will include the cross bearers, splice/joiners and stringer plates.

Unlike the kit instructions, in the case of a deck truss bridge, the splice joiners will be flush with the bottom of the cross bearers as both the cross bearers and the stringer will rest on the truss framework.

 

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The assembly is connected (glued) at the pins of the stringers and the holes of the splice joiners only at this stage.

This will allow squaring of the deck to be done after further parts have been added.

 

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The assembly is 6 sections long instead of the 8 of the Parker truss. The end plates for the deck were subsequently replaced with cross bearers as per the mid sections. This will enable the fixing of the outer part of the deck plate and the handrails to be the same over the entire length (as on the Findhorn).

The splice joiners at the ends were trimmed to give just a small extension on the outside of the cross bearer.

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The deck assembly has been taken as far as possible for now, as I'm waiting for some styrene profiles to make rail bearers, intermediate cross bearers and supports / stiffeners for the deck plate.

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Next will be preparation of parts for the truss frames.

 

 

 

Edited by zr2498
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The truss framework:

The construction of the basic elements of the Findhorn viaduct girders are varied and complex.

a) The outer beams are plates with attached angle making outward facing flanges. These are either plated, left open with internal gusset strengtheners or laced.

b) The diagonals mostly have inward facing channel sections, with lacing joining the flanges. What is rather strange is that some of the diagonals have different designs which vary as you move between the ends and the centre of each span. Double laced, single laced and simple straps are evident.

The photo below might give some impression.

 

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The bridge kit girder components consist of outward facing channel sections connected by full plates, gusset plates or by lacing.

So, some more compromise. A design will be needed to get as close as possible to the prototype.

 

First, the box section girders on the outer part of each frame.

Lower and upper beams

The closest copy is to use the gusseted girders with 'open' design at the lower beam, and closed (outer side fully plated) for the upper beam.

 

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The end (vertical) beams can be constructed very close to the Findhorn original using

 

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Just managed to spot the end verticals on this photo.

 

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Each of the girder sections is supplied on the sprue in two halves which have to be joined and then cut to length at the optimum position.

To estimate the number needed a few assembled girders are lined up against the original template (6 out of 8 spacings are used for the new bridge).

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The two diagonals will meet at the lower beam. Note that there are no verticals in the centre portion of the new truss arrangement.

 

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One gusset plate will removed to allow the diagonals to enter the beam.

 

Method for joining and aligning top and bottom gusset plates

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Drill bit size No 26 (9/64")

 

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Cleaning up following adhesive (showing the 3 types of girders)

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I reckon 2 pints of outer beams cleaned and ready for cutting after a new template is produced

 

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Next, to prepare the diagonals

Dave

 

 

 

 

Edited by zr2498
One photo removed and detail added
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