17-foot Bridge

17-foot Truss Bridge
Built: April 2005

Intro

This bridge was a quick project built for the 2-day TexLUG Spring 2005 Meeting. I had about one week to build this and get it ready for the show.

At the time, the top two longest bridge spans (built by fans of LEGO) made of LEGO parts were:
29.2 feet (8.9 meter) span, a truss bridge at LEGOWORLD 2002 www.brickshelf.com/cgi-bin/gallery.cgi?f=27351
16.9 feet (5.15 meter) span, a truss bridge by Ben and Marco (2001, the Netherlands) news.lugnet.com/trains/?n=14081

When completed, the final length of my bridge measured by TexLUG members was:
Effective span = 17.26 feet (5.26 meters), (center-to-center distance of end supports)
Clear Span = 17.13 feet (5.22 meters), (face-to-face distance of end supports)

Design

I chose to build an arched through-truss bridge for the TexLUG meeting because it would provide a large MOC for our train layout. It always seems to be a crowd-pleaser to show trains traveling over bridges.

I modified my truss spreadsheet to calculate the geometry and size the members. The spreadsheet can be found here: 17_ft_arch.zip (size = 0.11 MB)

I started the design by deciding an overall length for the bridge. Based on the current (at the time of planning) top two longest bridges (see INTRO section above), I guessed that I could beat the 2nd longest but not the longest. I didn't take a proper inventory of my parts- I based my decision on my "feel" of my inventory.

6 photos during
setup (seperate page)

Construction

After the spreadsheet was completed and all the member sizes were established, I started construction by assembling all the individual members. Constructing the bridge was straightfoward: build the members, and then pin them together.

I ran out of time and wasn't able to fully construct the bridge at my house prior to the TexLUG show. I also didn't have enough clear space in my house to set the thing up! With a brand new baby in the house at the time and loads of visitors, space was at a premium :-)

I finished assembly on the individual truss members and also the deck, then took the members (carefully organized and bunched together with labels) to the 2-day TexLUG event for final assembly.

With the help of fellow TexLUG'ers, we set up several long tables end-to-end to create a flat surface for the assembly. I pinned all the truss members together, starting with the deck first and then the main truss members from the midsection outwards. You can see the assembly process in this sequence of photos.

After assembly, I noticed that some of the top members of the truss sagged badly. Since I was assembling this for the first time on location, I brought along a load of spare parts. I made last minute modifications to those sagging members to stiffen and strengthen them.

When the bridge was finally ready, it was already free-spanning its clear distance because of the camber of the deck (the truss members held the deck raised up on a gentle slope from end-to-end). We then pushed the tables out from underneath the bridge, and allowed it to span freely over the floor.

Crash!

We ran trains on the bridge all day long. We even set up a monorail track down the middle. Towards the end of the first day of the show, I guess we got bored and started to make really long trains - long enough to almost span the entire bridge at once. That's when the accident happened.

With a loud plastic-on-tile crash, the bridge suddenly hit the floor. Pieces flew all over the place. Everyone stood still in amazement and disbelief. All I could think was, "oh no, not again!" (recalling the horrible crashed MSG 50 incident).

Upon investigation, we determined that possibly one weakened truss member gave way and then caused the sequential failure of the whole structure. That is the dirty nature of truses if they are built without redundancy. If one member fails, then the entire structure is likely to fail in one catastrophic event.

The group decided that food was more of an issue at the time (or rather, lack of food) so we closed up shop for the day and headed out for dinner. Sometime during the meal, we decided to return and conquer the bridge beast. No one wanted to admit defeat! Besides, we had a whole other day of TexLUG show ahead of us!

With our stomachs full and total sillyness setting in, members of the TexLUG crew got a crash-course on LEGO truss bridge construction. We sorted, repaired, re-built, and re-set-up the bridge that night. It was actually quite fun. We joked, we laughed, we farted around and built the thing all over that evening.

Conclusion

The final day of the TexLUG show went without incident. The bridge held just fine and survived (although we omitted the monorail and restricted the train traffic going over it).

I've smacked my head a few times when looking back on this experience. Basically, I rushed the job and pushed the limits of feasbile size on this project. However, in the end, it was all fun and definitely worth it.

What's Next?

I believe that this type of truss construction can be used to build much longer bridges. With proper planning and definitely some testing (and loads of parts) bridges of 50 feet or more could be possible. I'm not sure if I'll try for a longer bridge in the future, but the thought has crossed my mind :-)

THANKS!

Thanks to everyone in the TexLUG bunch that helped me with this beast. I appreciate your help and participation.

Thanks to Joe Meno of BrickJournal for publishing my article about this bridge in the inaugural issue (No. 1) of the magazine. Joe is a great guy that I've known in the LEGO fan world for a while now. I wish him the best of luck with BrickJournal.

Final Note

I'm sorry that I'm publishing this page 3 years after the bridge was built. Life is busy and time goes by fast :-)

Best regards,
TJ Avery
(Apr. 2008)

Update

As of June 2009, the longest clear spans of LEGO-fan-built bridges made from LEGO parts include*:

45.9 ft (14m) arched through truss bridge: http://news.lugnet.com/loc/au/?n=14617
(note: this 14m bridge was NOT laterally stable and had to be supported along the span)
40.8 ft (12.45m) span: model of the proposed Gibraltar Bridge: www.brickshelf.com/cgi-bin/gallery.cgi?f=150408
29.2 ft (8.9 meter) span: truss bridge at LEGOWORLD 2002 www.brickshelf.com/cgi-bin/gallery.cgi?f=27351 **
23ft (7m) bridge: www.brickshelf.com/cgi-bin/gallery.cgi?f=130662 **
+19.7 ft (+6m) bridge: http://news.lugnet.com/loc/au/?n=14510 **
17.13 ft (5.22m) clear span: my bridge, i.e. the bridge on this page :-)
16.9 feet (5.15 meter) bridge: a truss bridge by Ben and Marco (2001, the Netherlands) news.lugnet.com/trains/?n=14081 **

NOTES:

* I make no claim that this list is final or inclusive. There could possibly be other long bridge spans. Who knows?

** I'm not sure if the length given is the actual "clear span" or total length of the bridge. The "clear span" can be quite different (and shorter) than the total length of the bridge (see the graphic at the top of this page). The clear span is the best measure or indicator of bridge-building ability (well, and strength-to-weight ratio too, but I don't have any of those specs on these bridges).

*** I've heard that the Gibraltar concept bridge and also the 8.9m bridge were made (completely or partially) with parts donated from the LEGO Company. I'm NOT sure if that's true, but I just wanted to note that my bridge was made 100% of my parts - parts that I purchased myself.

Final Note:

If LEGO wishes to "sponsor" me in building a massive bridge, then sure! Send over a truck-load of K8 boxes and I'll build a 100-footer :-))

Thomas J. Avery 2008