City Bridge – Pt X

Web Stiffeners – Redux
GirderDim8I’ve finally arrived back at the web stiffeners and with all the dimensional changes .. and that I since then I have learned more about how they were constructed I will remake them. Here are the dimensions I will be working with:

  • 1.250″ – This is the height of the web plate
  • 1.258″ – The main angles are set .004″ away from the edge of the web plate on top and bottom. In ‘real life’ this was about 1/8″ to allow for irregularities of thew web plate so there would be no interference between the web plate edges and the Flange Plates.
  • 1.222″ – Inside measurement to the angles.
  • 0.082″ – length of inner face of angle.
  • 0.018″ – Thickness of angle wall
Some Measurements
StiffenerSpacingWith the prints in my grubby paws it is time to start assembling the thing. What to my shock .. I only had two splice plates printed! Oh woe is me! I swear. My OCPD makes me want to order another two. Common sense says they will never be seen so .. who cares.In the meanwhile .. some dimension ..
Rivets and sizeing
stacked_1600When I took a good look at the splice-plate and stiffeners I had printed .. I had a sinking sensation. The rivets on the splice-plates being much smaller then those on the stiffeners. I looked again .. and .. knew I had messed up somewhere in my measurements. Yup.I went back to my Sketchup drawings and .. sigh. The smaller rivets on the splice-plate are 3/4″ diameter while the ones on the stiffeners are 1.4″. What happened? Well … to cut to the chase .. I was working in Pmm (Pseudo MM) but made the rivets .750 .. dang it! That’s like one of those super-hero women doing back-flips to avoid the gunfire of the villain .. I was doing backflips between Full Size, 1:48 and my Pseudo MM .. and got confused and ran my head into a virtual wall.
an Epiphany of sorts
I looked at this for a bit and then vaguely remembered something I had read – and found this. In “The Practical Design of Plate Girder Bridges” by Harold Hughes Bird published 1920 on page 84 it says .. “it would be better both for designers and manufactureres is, say, the nominal diameter of the rivet represented the diameter of the hole, i.e. a 7/8″ diameter rivet represented the diameter of the hole, i.e. a 7/8″ diameter rivets means a 27/32″ diameter rivet with a 7/8″ diameter hole.” .. ah ha! Says I. That means the splice plate is the actual rivet size (3/4″) without a head. What about the 1.4″ dia rivets (heads) I have on the stiffeners?
They are HOW big?
renderedI found a description of various rivets in a book titled “Steam-boiler Construction: A Practical Handbook for Engineers, Boiler-makers …” by Walter S. Shutton, from 1898 where the head dia is shown to be 1.5 to 1.6 x the dia of the rivet.Ok. So .. fora 7/8″ dia rivet then the head would be 1.3125 to 1.4 inches.

Horray! That means the rivets in the stiffeners are 7/8″ rivets with 1.4″ dia heads. Cool. The splice plate? I can work with that. I had thought about simply leaving off the splice plate on the sides of the bridge that can’t be seen .. but .. I can re-work the design for the 1.4″ heads .. or .. see if I can ‘cap’ the splice-plate rivets with Micro-Mark resin rivets. In any case .. these can be the side not seen .. probably .. maybe.
—–
In the end .. I simply re-worked the splice plate using the 1.4″ rivet heads. I duped the thing and connected the two pieces with short sprues so the mesh would meet the minimum requirement for printing FUD (minimum size of object being 0.5×0.5×0.5 cm). The new splice-plates are to the left here – as rendered in Kerkythea

Realistic look at rivets
StiffCUwPennyThose close-ups showing the ‘warts’ on the print are not really fair .. that’s not what the eye sees. Here’s a better look .. pulled back with a penny to show size. While the current 3D printing I can get from FUD isn’t the best .. it will do for now I think.
Assembly
gluing_1Starting to assemble everything. The flange web is .040″ styrene (actually this is made up from two pieces of 0.020″ styrene sandwiched with the splices offset to get the length I needed). That’s quite a bit thicker then it would be in ‘real life’ .. where it would be 5/8″ or so – but since it won’t be seen that thickness helps quite a bit in the model. The main angles .100″ styrene. Here I’m gluing in lengths of strip styrene for the diagonal brackets.
diagonals_gluingNext, I’m creating diagonals using .080 in. angle. The additional diagonal(s) needed to form the structural “X” will follow. What I’ll do is glue a bracket assembly to the center on the initial diagonal as a place to intersect the “X”.
pp9


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