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)
	The Arched Suspension Bridge Team began with a conceptual design that led to in depth analysis and calculations to determine member sizes, materials, and construction methodology. Ease of construction was a factor in the conceptual phase of the design because the team had very little carpentry experience. Ultimately, the arched suspension bridge was chosen because of its aesthetic elegance and superior performance in making efficient use of material. The resulting arched structure is capable of supporting a 20kN load with only 6.5mm of vertical deflection. Structural analysis software RISA 2-D was used to model the bridge and predict its behavior; hand calculations verified results. The final product is an innovative, practical design of minimal expense and weight that meets the load bearing capacity while maintaining the natural beauty of its dual laminated redwood arches. Construction began with the fabrication of a plywood form for the arches. Four and six foot 1"x6" redwood strips were soaked in water and then steamed to make them flexible enough to bend over the form. The steam box was created from a simple wall paper steamer attached to a 7 foot, 8 in. diameter pvc pipe. Clamps held the bent boards to the form while they dried. Each layer was glued to the layer beneath it and allowed to dry for one day. A total of nine layers comprised each arch. The deck makes use of large, 2"x10" pressure treated douglas fir members to minimize net deck deflection. Calculations showed that only four 2"x4" stringers would be necessary to support the decking if they were securely fastened to make the 2"x4" stringers and 2"x10" decking operate as a single member. This made an extremely efficient use of material. Three 4"x6" floor beams transferred the load from the stringers, through the rods, up to the arches. They were intentionally left unfixed to the stringers so they would settle into position as the load was applied. It was decided that the behavior of the members at the connections was the most difficult to predict and their number was kept to a minimum. In this sense, the bridge reacts as a whole instead of members slipping at the connection points. The success in the performance of the bridge lies in the simplicity of its design and ability to support the 20kN load with a deflection well within the 9.5mm limit, while only requiring 345kg of material. This makes for a very efficient, easily reproduced, yet elegant bridge.

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)
	Four 90x60mm blocks were placed at the location specified by the test setup drawing for the monitoring of the total bridge deflection. On those blocks, we placed two 4x4in wooden members that supported a 4x6in wood beam. On that beam, we aligned a hand jack under a 4x6 column that was connected to a concrete beam of the SFSU science building. Between the jack, that supplied the load to the bridge, and the column, we placed a load cell that was connected to a computer so that we could identify the exact load being placed on the bridge. We placed one gage to monitor the total deflection of the bridge at the location specified by the rules. The gage had an accuracy of 1/100th of an inch. As we applied the loads in the specified amount of time, we saw a linear relationship between the load placed on the bridge and the bridge deflection. The total bridge deflection after an hour of supporting a 20kN load was 6.58mm, which is lower that the maximum 9.5mm specified by the competition. For the Net Deflection, we had to test on one of the inner, middle panels due to constraints in the room and position of the test column that was connected to the building concrete beam. Our faculty advisers, Dr. Norman Owen and Prof. Mutlu Ozer, accepted that we test there because our transversal length was exactly the same as on the panel we were required to test and monitor. Because the 2x10 deck members are running directly transversally, our advisers determined that one would get a very similar net deflection on the panel with the longest longitudinal span and on the panel we monitored the deflection on. With this setup, we placed three gages, that had accuracies of 1/100th of an inch, at the locations specified by the competition. Gage 2 was directly in the center of the panel, gages 3 and 4 were both positioned in the middle of the stringer of the long span. The relationship between the deflection and the load being applied to the bridge was close to a linear relationship again. Out of a possible 4.6mm of net deck deflection, we monitored a deflection of 1.76mm after an hour of applying 20kN on the bridge.

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:	Four 2x4 pt douglas fir spliced at every floor beam
Deck:	Sixteen 2x10 pt douglas fir
Floor Beams:	Three 6 ft. 4x6 pt douglas fir
Suspension:	Six 5/8 in. diameter, 3 ft length threaded steel rods
Unique:	Two glue laminated redwood arches. 6ft inner radius w/ nine 1x6 in. layers each

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
	For the deck members, Douglas fir pressure treated with the industry standard concentration of alkaline copper quaternary was chosen to prevent mold and insect deterioration for a lifespan of 25-30 years. For the arches, redwood was chosen for its flexibility, as well as its naturally rot and insect resistant tannins, also giving a lifespan of 25-30 years.

7. Special Considerations
	Quotes from the team: Fabian: "Eight different backgrounds and ethnicities, ranging from Russian to Bolivian, all coming together and facing the ups and downs of designing, scheduling, and building for half a year. Resulting in a beautiful bridge and 7 life-long friends for me." Greg: "There is a big difference between designing something on paper and actually building it into something tangible." Lewis: "We learned about teamwork and how to depend on each other." Mikhail: "The project allowed us to implement theoretical knowledge obtained in the course of studies while enhancing our hands-on experience. At the same time it stimulated our self esteem as we handled the responsibility of representing our school in a competition of National level." Jose: "This project was so beneficial for me and my teammates since we had the opportunity and learned how to work together as a team in order to make this project a real success!"