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)
	Oregon State University's entry in the 1999 National Timber Bridge Competition is a look to the future while still maintaining contact with the past. The bridge design is a combination of the traditional truss with a modern cable-stay design. To minimize total weight while maintaining adequate stiffness, the bridge incorporated glue- laminated beams, carbon fiber reinforcing, wooden I-joists, and traditional sawn members. The design committee presented several options to the bridge group, which were obtained by looking at existing bridges and blending them to create working solutions. The team applied preliminary hand and computer analysis to the proposals to ensure they met contest specifications. To decide on the final bridge design, the participants voted between possibilities that considered uniqueness of design, aesthetics, projected contest performance, and ease of construction. With the finalization of the basic structural form, the exact bridge design could be started. The exact bridge design was an iterative process starting with estimated geometry and preliminary member sizes, later refined by SAP 2000. Each revision was checked by computer and by hand to ensure the bridge met contest requirements. To optimize the stiffness of the bridge, the main load-bearing glue-laminated beams were reinforced with Aramid fibers. Like the the steel in reinforced concrete, these fibers both strengthen and stiffen the composite beam. In this application, these fibers were applied to both the tension and compression zones. The wooden I-joists immediately surrounding the loading points were also re- inforced, but with carbon fibers instead of Aramid. The carbon fibers are stiffer than the Aramid, but harder to obtain. Since the deck deflection requirement was more stringent, the carbon reinforcing fiber went to the deck stiffening I-joists. The initial weight of the bridge was above the competitive level. Several methods were used to reduce the weight. The most effective method was fluting the deck. The weight of the deck was initially equal to the combined total weight of the rest of the bridge, but was reduced 40% by cutting away unnecessary material on the bottom of the decking. Additionally, the reinforcing fibers and glue reduced the necessary member sizes. The 1999 bridge entry from Oregon State Uiversity is a look to the future with its innovative blend of traditional structural systems and modern materials, while still maintaining the look and feel of a traditional wooden truss 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)
	The testing process was conducted in the Forest Research Laboratory on March 11, 1999. A forklift was used to position the concrete panels weighing 720 to 740 lbs beneath a crane. The crane was used to lift the panel and load the deck from the top. The dimensions of the opening above the length of the deck were shorter than the length of the concrete panels. This problem was resolved by lowering each panel at an angle. This allowed one side to enter through the opening until their was enough clearance for the other side to lower down. Additional lead weights were used to meet the required 4kN load for each sequence. This process was repeated five times until 20kN was applied to the deck. Dial gages were placed according to the guidelines and measurements were taken after each loading interval. A crucial structural failure occurred nearly half way through the loading process. As the loads were increased, the decking began to fail in shear. The failure occurred approximately two inches from the edge of the loading block. This failure was the main reason for the non-compliance with the minimum deflection criteria. All loads applied to the failing portions of the deck were no longer able to distribute their load. The failure reduced the moment of inertia in the decking and resulted in a large deflection.

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:	Two glue laminated beams with Kevlar and fiber reinforcing polymers.
Deck:	Nine members of fluted decking, glued to form one system.
Floor Beams:	Seven StrucJoist I-joists.
Suspension:	Eight load transferring cables.
Unique:	Four glue laminated compression struts in truss system.

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
	The most important environmental impact factor considered in the planning stage of the bridge was to minimize waste products during the bridge construction. The goal was achieved and all resources used on the bridge were used efficiently. The model bridge will be donated to the parents of one of our team members. The bridge will be placed in a residential garden setting where its aesthetic beauty can be enjoyed.