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 Clarkson University Team utilized an innovative internal cable truss system to achieve extraordinary strength in timber bridge construction. The internal truss system is the basis of the bridge’s main span girders. The girder cross-section allows for two 9.525mm steel cables to be run in between its three webs. Through the use of these internal tensioning cables, girder pretension was possible, resulting in increased stiffness and a minimal bridge deflection of 6.71mm (.264 in). This stiffness was also seen in the test section analyzed earlier this year. The enclosed cable truss system allows for an aesthetically pleasing appearance, without limiting clearances above or below the bridge deck. High strength eyebolts permit the adjustment of both tension forces and cable angle which were optimized by the team. Eyebolts were reinforced using aluminum bearing plates, eliminating any punching shear effects. Rabbit joints were used to connect the girder’s top and bottom flanges to the webs, resulting in a simple yet strong connection under tension and compression. The longitudinal joints were connected using half-lap joints to maximize surface contact area for adhesives and fastening. The team opted not to use any materials that are engineered such as plywood, gluelam, or pressure treated wood.Rather than utilizing “engineered” lumber, which is often costly and difficult to obtain in areas such as Potsdam, NY, common cost effective materials were used. All wood elements for instance are commercially available white spruce. The stringers consist of two nominal 2x4’s accompanied by a deck surface of longitudinally placed 2X10’s. The deck boards are spaced slightly apart to allow for drainage; in addition the curb is elevated to allow any debris to leave the deck surface. The stringers and deck element’s straightforward design allowed for rapid construction. A deck wider than the minimum competition requirement was chosen in order to permit all- terrain vehicle traffic at the Colonial Village Fun Park (CVFP)in Potsdam, NY. By setting the main girders inside from the edge of the deck surface the transverse span of the stringer was able to be minimized allowing the load to be transferred more efficiently. 88.9mm galvanized screws were utilized to increase gripping and durability for deck attachment. All wood was treated with Wolman RainCoat Deep Penetrating Water-Repellent, applied on all surfaces and analyzed for significant absorption. For additional protection of the bridge, CVFP staff will apply their own paint to match the scheme of the park on an as-needed basis.

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 Clarkson University Timber Bridge performed exceptionally under loading. No visible inelastic deformations were observed and no noticeable cracking occurred. This was verified in that both the trial test girder, which was analyzed in early February, as well as the final design, rebounded completely after removal of the applied load. The measured deflections were relatively small and within the specified limitations.The testing apparatus was a typical load frame and hydraulic load cell. The load was distributed to the four load point system using three steel W-section beams. 50.8mm (2 inch) cylindrical steel roller supports were utilized in order to fulfill the loading regulations. In compliance with the 2004 competition rules, the load was applied in four equal increments of 5kn each with the total of 20kn being reached within the 5-20 minute allowed time frame. Deflections were measured using dial gages at the specified points. Readings were taken at each load application and at 15 minute intervals over the full 60 minute load duration. The actuator was maintained at 20kn for the entire load period.The overall net deck deflection was measured to be 2.64mm and the overall bridge deflection was 6.71mm measured from the mid point of the left girder section. The bridge seemed to stiffen after approximately fifteen minutes of full loading; then after, only small deformations were observed. The post-tensioning/internal truss system utilized in the main girders performed extremely well in stiffening the members and eliminated excess stress on the wood elements. This was determined through analysis of the test section results and implementation into the final 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:	Two joined 2x4s / Triple web post-tensioned box beam
Deck:	2x10 treated white spruce deck panels
Floor Beams:	N/A
Suspension:	Dual cable post-tensioned truss suspension system within girders
Unique:	Aluminum plates prevented punching shear of post-tensioning bolts

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
	Wolman RainCoat water repellent preservative was used in the treatment of all wood. It®s a deep penetrating liquid that provides resistivity to rain and dew. Additionally, several coats of paint will be added to exposed areas by the future owner. The product was chosen over pressure-treated wood, due to the reduction in weight and cost.

7. Special Considerations
	When designing the bridge special considerations for environmental impacts were taken into account. This was done so that any future use of the bridge would provide for enjoyable recreational use, while minimizing adverse environmental effects. Some of the special considerations include: utilization of every board and hardware, so as to reduce excess amounts being discarded to a landfill, using galvanized metal so that rust was not induced, and treating the bridge with wood treatment preservative so all wood is preserved. Each of these considerations were utilized because they not only reduced short and long term costs, but also helped meet the requirements of the bridge without compromising its strength properties. Upon completion of the loading test, the bridge will be used at the Colonial Village Fun Park in Potsdam, NY. There, it will be used as a walking and ATV bridge as a means of crossing a small brook. This will provide the recreational facility with not only a functional bridge, but also an aesthetic accessory to its surroundings.