LEGO enthusiasts all have built all sorts of bridges from their bricks. Be it a suspension, truss, cable stay or cantilever for all sorts of purposes. My own bridge creation goal was an arched one.
Arched bridges are not an entirely new experience for me but those built in the past of LEGO bricks did have problems. Part supplies were very low and that meant cutbacks in load handling properties and achieving the desired form (shorter height and length). Often, the arch would be thin in both depth and width. Poorly drawn sketches were all that was used to give me ideas of form.
Well, that changed with the creation of Study 5 and its larger sibling Study 10. Before laying down the first brick, vast amounts of time went into good old fashion drafting on velum, no CAD here. Although precise stud and brick values were not used I got by letting one stud = 2/10 inch and the same 2/10 inch value for a brick. "But studs and bricks are not 1:1." you might say. Well, that is something I just let slide.
Now here's where instinct gets into the act. A question I'm often asked is "Was a formula used to make the curve's form?" and the answer is no. My first experience making an arch was not using LEGO as my medium but sand and that was done 20 years ago! I came up with a method of layering wet sand to produce a large rectangle and when it reached that right height and water concentration, I would start trimming off excess sand using my hands or a stick. The curve itself just meant getting to that stage during the trimming process that I felt looked "just right".
That same instinct went into creating the arch on paper for the LEGO version but this time with scales on X axis and Y axis on velum and only the right (or left) half of the arch to be drawn (thanks to symmetry). The parameters (how many studs and bricks) was still a matter of instinct. Very light sketches of the curve were drawn on the velum and left to "ferment", so to speak. The sketch would be placed out of view for several days (3-5) then looked at and I'd decide go ahead and make changes to the sketch or just leave it be for a few more days. This stage took at least 3 weeks before I was able to say it was "just right".
When the top and bottom of each curve of the arch was "just right" the partitioning stage was next. Partitioning is essentionally taking a curve and breaking it down into a series of rectangles (or similar) that can be any length but all must have a uniform width/depth value. The rectangles can rest just above the curve or just below. I let the brick height serve as the value all the rectangles would have in common and let the stud length be variable. The rectangles would have to fit between the upper and lower curves. Only in very select locations would I let a rectangle go outside the curve's bounds (instincts again). When the partition was done, I carefully erased the upper and lower curves and break the rectangles into recognized lengths of brick and made sure the bricks set above or below would have some form of step pattern to provide good hold.
From here on things get easy. The bed of the roadway uses a ladder frame construction that uses bricks very efficiently and makes a good, strong form. How long the "rungs" of the ladder travel would be my means to determine how wide the arch would be. To provide a good, solid means of preventing the road from buckling, a large support column was placed in the space between the bottom of the upper curve and the roadway. The lower portion of the arch that forms a trapezoid like shape and a separate wide anchoring foundation are both constructed near solid and are quite heavy to provide plenty of stability. The rest, 1x1 columns between upper curve and roadway for example, just served as decoration.
Sorry, I don't keep plans. Instead I take pictures in uncompressed format (TIFF then, now RAW) and use them as reference. I don't use brickshelf anymore but you can find pictures of a follow-up to Study 5 called Study 23 on Flickr. Look me up using my MOCpages name and look for my MidSummer Study folder. HTH
Very good. My previous experiences with LEGO arches are that 1. borrowing that many bricks from my friends is hard, and B.They often fall. You might want to try building something in the style of Gustav Eiffel.