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Ross Crawford / projects / shb / detail | |
Rosco’s LugNet Page These pages are no longer updated. You can view my LEGO related pages here. All images hosted by Brickshelf L.L.C. but who knows how long that will last.
Building the Studley Harbour bridge
Detail General Information OK. The bridge obviously is based (fairly heavily) on the Sydney Harbour Bridge. It’s not quite the right shape, and the pylons aren’t quite as big as they should be, but it’s pretty close, given the limitations of LEGO bricks, and my LEGO budget 8?) It’s about 1:140, so it’s nowhere near minifig scale. No, I don’t plan to do a minifig scale version - that would require the main span to be over 12m, and I doubt if that could be done in LEGO. It’s only plastic, after all! At 49m, the Sydney Harbour Bridge is the widest long-span bridge in the world. When building commenced, it was going to be the longest arch span, but the murkans grabbed that title by finishing the Bayonne bridge first. Did they build the Bayonne bridge just to grab the record? Some interesting points:
Anyway, it wasn’t until West Virginia’s New River Gorge bridge was opened in 1977 that the record was beaten. These remain the three longest arch spans in the world. Design This is the first project for which I’ve done significant design before building started. The design involved some building & testing, of course, but the arch & pylons were basically designed before I lifted a brick. The pylons were designed around the availability of grey bricks & slopes. They are mostly 1 stud thick, but are surprisingly solid. The sloped sections help, the worst part are the end walls which are 50 studs wide and 40 bricks high. They have extra ribs inside to help stiffen them. The hinges were tricky to design. I wanted them to appear to be attached to the 45 degree slope, as the real ones are. But they had to be able to take the load that the arch puts on them. Using the bent technic beams was the best way I could find to acheive this. Unfortunately, I couldn’t come up with a neat way to have macaroni bricks below the hinges (as in the real bridge), so the hinge bearings are fixed to the abutments. The arch is a fairly simple design - obviously the join points needed to be held by pins or axles to get the small angles. I thought the load on these joints would be too great for pins, and likely to cause failure, or at least distortion, so I compromised. Each segment of two side-by-side beams is held together by multiple pins, but the joins between sections are held together by #8 axles. Having solved the easy design problem, I spent most of the design time on working out the lengths of all the beams required to get the correct shape. All 28 segments in the real bridge are the same width horizontally. I wanted to mimic this as close as possible, but because the smallest resolution I could get (with sufficient strength) was 1/2 stud, corresponding to about 1/2 metre, it wasn’t going to be possible to get them exact. So I compromised again, and made all the segments of the top chord the same length. So having decided that, I needed to work out the required lengths for the bottom chord segments, and the vertical & diagonal braces, to make the correct shape. Again, the limited resolution proved to be my enemy. In the end, I decided that, because the bottom chord takes most of the weight, it should be a “good shape” - in this case it’s close to parabolic. I then experimented to get the shape of the top chord as close as I could to the real thing. The hardest part is near the centre, where the distance between the chords changes by less than a metre between adjacent segments. You may say “so what, you’ve got resolution to 1/2 metre”, but the main problem is the lengths of the chord segments, which change by much less than 1/2 metre between segments. Anyway, with much fiddling & experimenting, I came up with something close. The segments aren’t quite equal widths, as mentioned; some of the “vertical” braces aren’t quite; and the shape of the top chord isn’t quite right - the sections either side of centre diverge a little too quickly from the bottom chord. But all in all, I was pretty happy with the design. Construction The abutments are mostly hidden, but are technic beams & plates. I used bent technic beams to attach the hinge pins. The main objective was to make it look like the hinge was attached to the sloping abutment somehow, like the real bridge. I’m pretty happy with the result! Note that the 4 hinges carry the entire weight of the arch span. The pylons are built almost exclusively with grey 1xN bricks, and 2xN slopes. There’s obviously some arches near the deck, too. The pylons serve no structural purpose, other than to provide a little extra stability (due to their weight) at the ends. On the real bridge, the granite is just facing - the pylons are actually steel & concrete inside. I didn’t have enough LEGO “Steel” to do this 8?( They are 30x54 studs at the base, reducing to 20x50 studs at road level. Note also that they’re shorter than designed - the thinner section (museum level) should be about 4 bricks higher, and maybe another brick higher in the top section. I added a cut-away section to one pylon after they were finished. It houses the bridge museum, which is in the south-east pylon of the real bridge. As it’s less than 1/3 minifig scale, there’s not much space in there for much interesting stuff. The arch consists of technic beams, stuck together using friction pins to make longer beams, then connected using #8 axles at all the joints. The main support points are 2x2 round bricks, which mate with macaroni bricks on the ends of the arch. This is probably over-kill, but I just wanted to model the real construction as close as I could. Note that there were minor changes made in the lengths of beams from my original design, but overall I followed it pretty closely. The two sides are held together by horizontal perpendicular beams top & bottom. There are also diagonal beams on top, which minimise twisting. These aren’t very strong - they’re only attached by a hinge plate at either end, and by a 1x8 plate at the centre. Note also that they’re not exactly a 5x12x13 triangle - because the hinges at each end are on opposite sides, the hypotenuse is slightly more than 13 units (26 studs). Where the beams cross at the centre, they actually put some lateral pressure on one another, making the whole assembly quite rigid, but only in the horizontal plane - they can’t take much weight. The arch is fairly solid, but it still needs a method of holding the ends at the appropriate distance, to stop it spreading apart at the bottom! I was originally going to use string, but subsequently decided to use baseplates - 28 of them! They’re held together with various random blue plates I had lying around. Because of this, the deck doesn’t need to take any tension at all, and is actually not continuous (see below). But it does complicate transport a bit (see further below!). The bottom chord takes most of the weight - during assembly, the bottom chord can actually take the entire weight of the arch with no problems. The top chord mainly serves to hold the shape of the bottom chord. The hangers are fairly simple. They’re just beams held together with plates. A horizontal beam spans between pairs of hangers at the bottom. The deck rests on these horizontal beams. They consist of two rows of 2xN plates joined with 2x4 bricks, but their studs face towards the bridge centre. Some of them have special lugs sticking up, which hold the deck in the correct (lateral) position. The hangers are attached to the bottom of the arch using pairs of 1x4 liftarms. I did it this way mainly for looks - the hangers on the real bridge are attached with structures that look a little like this. However, it also means the hangers can be easily folded out of the way for transport. The deck is built from grey 6x8, 6x6, 4x8 & 4x6 plates, held together with technic beams and 1xN plates (underneath). There’s actually 3 separate decks, the wide one in the middle (24 studs), and 2 narrow “outrigger” ones - one on either side (4 studs each). Their construction is similar, so I’ll only discuss the main deck. It’s built in 4 sections. Two sections are attached to the pylons at each end, and go to about the second hanger. The other two sections go from there to near the centre of the bridge on either side. They come together in “toothed” joins - they’re not actually connected. This allows for expansion / contraction of the deck (negligible on my version, but I wanted it to be like the real thing!) There’s also 1xN plates along the bottom outside edges of the decks - this just made it look nicer by making sure the top plates joined nicely at the edges. During construction, I came across this strange little LEGO anomoly. I thought it was gonna work out OK, but the curve was just too much, so I ended up using technic beams at every second joint, which made the deck much more flexible, and reduced the curve to a usable amount. I only did this on the main deck - the outriggers were OK. Dimensions Here’s a comparison of some of the dimensions with the real bridge:
Transport The arch can be broken in half lengthwise for transporting. Each half is about 2m long, and can be carried relatively easily by 1 person. The hangers can safely be left attached to the arch for transport, though some are often removed anyway - see “Assembly” below. As mentioned above, the deck is in manageable sections anyway. The pylons are a nice size, and can be carried fairly easily. The hardest parts to transport are probably the baseplates! These are held together with plates, and lifting them up as a whole unit is impossible. I usually just separate them into individual baseplates for transport. Assembly It’s actually fairly easy to assemble. The most important task is to decide exactly where you want it before starting to assemble - it’s pretty much impossible to move it afterwards! It needs a space of 16 x 2 baseplates, or about 4 x 0.5 metres. First, you lay down the baseplates, and attach the pylons at the end. Because one pylon has the museum in it, you’ll need to decide which end you want that. The next step depends on whether or not you have helpers. If not, you’ll need some kind of stand, of appropriate dimensions - about 95cm high, at least 50cm long & about 30cm wide. If it’s height-adjustable, that’s a bonus too! Ive found the best candidate is the humble ironing board! Set the stand at the centre of the baseplates (ironing board is really good here, as it means the legs aren’t actually on the baseplates 8?), and grab the half-arch with the centre beams on it. Remove the centre and second hangers, and any more which may conflict with the stand (not necessary if you have helpers, but makes it easier to insert the deck later). Place the big end carefully on the hinges, and rest the little end on your stand (If you have helpers, just get one of them to hold it!). Take the other half-arch, remove hangers as necessary, rest the big end on the other hinges, and the little end on your stand (or a second helper if available). Optimally, it should rest close to the other half already there. If not, adjust the height of your stand! Now comes the tricky bit - you need to join the halves (obviously). You’ll need the 4 #10 axles and 4 bushes supplied. Take 2 of the axles, and adjust the height at the centre until the holes in the bottom chord match. But don’t be too hasty! The diagonal beams attached to the second half-arch also have a hole at the end which must co-incide at the same point! This is where having the height easily adjustable becomes really handy! Once you’ve got all these at the right spot (both sides!), insert one of the axles in each side. Note that it may require some light force, as the main chord beam meats the join section at a slight angle. Secure the axles with bushes. The stand (or helpers) can now be removed, however like safety belts on planes, I’d recommend you leave it (them) there until the top chord is attached. This is similar to the bottom chord. You just line up the holes, and insert the remaining 2 axles. Note that this may require lowering of the arch slightly (compressing the bottom chord). Secure the axles with bushes, and voila! the hard part is done! If you’ve got this far, all that remains now is the deck. I usually put the main deck in first, but you’re free to do it how you want. The end sections (shortest) are most easily inserted from behind the pylons, however if you’ve placed it close to a wall, this may not be possible. The toothless end is attached to the beams protruding from the pylons, so make sure you get it the right way ‘round. Inserting the centre sections is a bit trickier, but not much. I’ve found it’s easiest to insert them from the centre (which is why I recommend removing the 3 centre hangers). Slide the first one in carefully, with the black plates towards the centre of the bridge. I’ve found it’s better to insert it further than it needs to go, resting it on top of the end section. This gives you more space to insert the last section. After inserting the last section (with black plates towards centre as before), locate it properly on the hangers with locating lugs, then move the other centre section into place, and locate it properly, too. Now it’s a simple matter to place the outrigger decks - they’re much the same, attached to the pylons at the end, and with locating lugs to position them properly. Finally, attach the supplied flags & antennae to the top of the arch (anywhere you like, but the centre is probably best 8?) and your bridge is ready to carry traffic! Photography All the pictures were photographed in my kitchen, with my Kodak DC3400 digital camera.
Site last modified November 4, 2004 Home
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