National Timber Bridge Design Entry

College & Team Information
College or University:		Student Chapter:
Address:
Phone:	Fax:	E-mail:
Website address:		Faculty Advisor:
Person In Charge of Project:

Team Member	Class	Team Member	Class










Hours spent on project:		Cost of Material ($ Amount)
Student:	Faculty:	Donated:	Purchased:

1. Abstract - (Max 500 word narrative)
	Our bridge was developed through team brainstorming; rigorously testing designs with computer aided analysis, and trail and error tests. The sub-structure of our bridge consists of two parallel arches upon which the deck rests. Our bridge's sub-structure was designed to transfer loads either to the arched Glu-Lams or to our end supports. We determined that using glue- laminated arches would efficiently reduce the deflection of the bridge where the vertical bridge deflection readings will be taken. The arches were designed to transfer the load, from the deck, into a vertical force and a larger horizontal force, thus minimizing deflection in the vertical direction. A larger horizontal force was induced to the arches by calculating a small radius. These horizontal forces are transferred into tension rods secured to each end of the arches. This will restrain the horizontal movement and keep the arches from flattening. Vertical members have been connected from the deck to the arches, which will transfer the forces effectively. We placed the arches directly below the loading points in order to reduce any kind of eccentricities that might cause a greater bridge deflection. This is still within the parameters of the rules as stated; the arches are neither a transverse member nor a deck stiffener. The most serious design challenge came in designing a deck that was stiff enough to prevent deflections in excess of two millimeters. The idea behind stiffening our deck material was to make it continuous. In order to make the deck as continuous as possible while staying within the parameters of the rules we placed hardwood spiral dowels in the ends of our boards in order to get a good connection. This worked in the longitudinal direction and similarly we used a tongue and groove decking material in order to make deck continuous in the transverse direction. We used wood I-beams in order to decrease the deflection under the other areas of the deck. These I-beams are place at their minimum allowable spacing so the deck material will hold the minimum load. The reason we choose to use I-beams instead of a standard 2x material was because the moment of inertia/weight ratio was so much greater for the I-beams than any other joist system. So keeping weight in mind, the moment of inertia was large enough to keep deflection to a minimum in our joist system. The weight of our bridge was a concern of ours. We thought that an arch bridge would be very light weight because we could use less wood than would be used in a conventional truss design. The arches were sized to specific widths in order to get a satisfactory deflection. Each piece of lumber on our bridge has been specifically designed to hold the load it will carry. So, each was piece has been sized and cut to their required dimensions, in order to eliminate any unnecessary weight. On our deck design the I-beams were by far the lightest material that could be used for a joist system. If there is an error in recieving this abstract see faxed hard copy.

2. Deflection Table
Deflection (millimeters - rounded to 2 decimal places)
Loading Inc.	Bridge	Beam L	Beam R	Average (L&R)	Gross Deck	Net Deck
5 kN
10 kN
15 kN
20 kN - 0 min.
20 kN - 15 min.
20 kN - 30 min.
20 kN - 45 min.
20 kN - 60 min.
1) Loading Increments.
2) Bridge - As measured at midspan of the longitudinal beam receiving greatest loading.
3) Beam L - As measured under the longitudinal beam to left of selected deck monitoring point.
4) Beam R - As measured under the longitudinal beam to right of selected deck monitoring point.
5) Average (L&R) - Average of 3 and 4.
6) Gross Deck - As measured under the loading point expected to experience maximum deflection.
7) Net Deck - Column 6 minus column 5.
Deck span (transverse distance between main longitudinal bridge support members measured from inside edge to inside edge) = mm / 100 = mm (max. allowable net deck deflection)

3. Materials List
Material Item	Weight (kg)




















Total Weight (Kg)
Weight Non-wood (Kg)
Percent Non-wood

4. Summary -Describe Bridge and behavior under load - (Max 500 words)
	The physical changes that our bridge underwent were virtually unnoticeable through visual inspection. Dial gauges were used for measuring deflections. From the gauges we were able to tell that the arches were bending at the center and the deck was indeed deflecting. Our bridge experienced a maximum net deck deflection of 1.76 mm. This maximum deflection occurred at the 4 KN load increment. Then subsequently, bridge deck began behaving as a single unit causing the net deflection to occur at a slower rate than when the initial load was applied. At the 12 kN load increment the net bridge deflection was at a minimum value of 1.3 mm. Under the arches the average deflection reached a maximum at 3.9 mm at the 60-minute time mark. Total bridge deflection under the centerline of the arches reached a maximum value of 6.93 mm at the 45-minute mark and remained constant to the 60-minute time mark. There was not any detectable torsion in any members or any noticeable lateral deflections. We did hear a few soft pops from wood as it released energy under loading and members began to settle. Upon inspection there were no visible cracks or other defects, and the bridge appeared sound. We are pleased with the general behavior of our bridge under loading. We are especially pleased to note the favorable performance of the glue-laminated arches. We were concerned about the possibility of de-lamination in the arches under loading. This mode of failure did not occur. If there is error in recieving abstract please see faxed hard copy.

5. Project Drawings and Photos

Longitudinal Cross Section	Tranverse Cross Section	Trimetric View	Project Photo	Team Photo
Click on drawing or photo above for larger view.

6. Component Details
In ten (10) words or less per each component below, describe the bridge:
Stringers/Girders:	Hand made by team members, Glu-Lam arches.
Deck:	2 x 6 tongue and groove fir.
Floor Beams:	Engineered wood I-beams
Suspension:
Unique:	Vinyl curb on deck

Describe preservative treatment for all wood members. Include type and concentrations. Also include a short statement of why this treatment was selected. Did the treatment requirement present any special problems? If yes, provide details

7. Special Considerations