2007 Design Notes

Profile:
There is obviously a big, wide open profile to design in this season. The deck window has been increased to 9" absolute maximum, and the overall height of the bridge can go upwards of 7 feet. So now there are the options: beam, multiple (3 or 4) beam, stacked beam, low profile truss, medium profile truss, or maximum profile truss.

beams:
Maximum depth for a one beam section (if you go "Double Black Diamond" on it) will be about 8 1/8" to be safe. A flat flange, like a square tube, or a bar flange, maybe you can get in the mid-7" range for depth. Is this going to be stiff enough? It just might be, based on the loading and the essentially 19 foot span ( approx. 2 feet shorter than the last two seasons). Always be aware of the killer S1 = 5,6, S2 = 1,2 scenarios, however, because they could quite frankly be worse than last season. 1300 lbs. per grate is not that small.

Multiple Beams
Because of the 1 foot by 1 foot footing box, there is possibility of loading up maybe 2 girders on each side. It's certainly nice for construction to have more liberty in the pier boxes - God knows Davis had some box issues on the construction site in Salt Lake City, like 7 issues.

Stacks:
Well, there is definitely the possibility of stacking a beam system. Either by doing it in a box or girderlike fashion in the 9 inch window, or going deep on the bottom layer of the stack, and then wide/boxy on the top to meet the 3'-9" necessary clearance. The connections can be complicated (see prev. post), so be wary of this design, because fabrication will be paramount more than ever to it's success in efficiency. You could also do a trip stack in the same fashion, but those connections are even more difficult. Big jigs needed. Remember the river too, can you reach 4-1/2 feet easily?

Trusses
If you do a truss you basically want to go as deep as you can, and try to keep the chords down to one piece each. In general, double piece chords aren't that great, because they can hinge/bend at their connection if in compression, unless they're very wide, and bolted/doved thoroughly. The double piece may be good if you intend on going for the full 7' with a pyramid truss or other "simple" truss type structure. The Warren Trusses that have been winning for the past 3 seasons, obviously provide the best structural integrity, but it may need to be skimped down to accommodate for better economy, and the presence of off center loads.

A Word on Loading:
Last season was basically a truck load, with the big weight at the front axle. Now it's more of a tandem load, with two equal, relatively large loads, closer to each other (at worst case scenario). This will alleviate that "arch like" kink at the center of the truss bridge somewhat, but not entirely. The kinks just move closer to the piers a little is all. Double measurement on the "left side" which could very well be the right side, if it's chosen that way. Asymmetry should not be a big design idea for most schools. The span is also about 18" to 24" shorter, and that more than anything, will stiffen up most of the bridges.

Construction Site:
Totally equal (except for the 30' and 15' run). The little barrier in front of the site, is going to make things trickier than last season where there was so much room to run! Now the tippy toes will be out again. The 9 foot river is not to big of a concern except for 4 member/node connections at center span. Reaching for things at 4 1/2 feet is a challenge even on your knees, and there's no room for economical error this year, so choose your profiles wisely and consider their constructability. That is it for now. Design on!!!