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 concept for the 2003 United States Military Academy's Timber Bridge focused on an inexpensive yet practical design that could be assembled rapidly. Based on recent operations in environments such as Afghanistan and Iraq, we wanted to focus on a design that could be readily applied in a field environment. The last two operations have emphasized speed to increase the lethality and power of the U.S. Armed Forces and to decrease the duration of hostilities. The ability to surpass obstacles such as ravines or rivers constrains the speeds of the Army and Marine Corps. Recent reports have stated that this lack of mobility has hindered our ability to move troops and supplies throughout the countryside and has impacted the mission. As soon-to-be Army officers, we could easily see ourselves in such a situation for which project would prove to be an invaluable experience. Based on this real life scenario, we decided to limit the complexity of our design to achieve one that is easily constructible yet strong. Our materials consisted primarily of 2x12 LVL and 2x8 dimensioned lumber, attached together with wood glue, nail plates, and 2 1/2" #8 deck screws. The bridge we designed consisted of five I-beams. We chose this design to utilize the moment of inertia to keep deflection minimized.Each I-beam was made from treated Laminated Veneer Lumber with nail plates attached at the joints. The deck was constructed from No. 1, 2x8 treated SYP. We cut shiplap joints in each piece and then screwed the edges together and into the compressive flange of the I-beams. This overlapping technique ensured that no single deck plank would bear the entire load and that our deck would act as a rigid diaphragm. Once the decking was attached, No. 1, 2x4 treated SYP curbing was attached. We achieved our goal of practicality with our design. The beams were easy to mass produce, and they were easy to set into place. The end result is a bridge that is strong, easy to fabricate, and transportable in compact pieces that can be rapidly assembled at the work site.

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 competition dictated that the bridge must be able to carry a 20 kN load for one hour and deflect no more than 9.5 mm as recorded at the midspan of the longitudinal beam receiving the greatest loading. Additionally, the deck deflection had to be less than 2.54 mm = (deck span/100). We measured deflections with gauges that we carefully placed in the four required locations. Each dial gauge was scaled to 1/100th of a millimeter. The 20 kN load was achieved using cases of copying paper and three fiberglass steel beams. The 5 kN load increments were composed of 20 cases of copying paper and were lifted manually. The load was on a single pallet that rested upon 2 sheets of plywood. The plywood sat on top of the three beams that ran across two wooden boards, which crossed the 4 load points. The 5 kN loads were made up of cases of copying paper and fiberglass beams put on by hand. The bridge behaved in the manner we expected. With the addition of each load and time interval, the bridge's deflection increased. At the end of one hour, our deflections were 3.06 mm for the bridge and 0.11 mm for the deck. Both of these deflections were well below the maximum values of 9.5 mm and 2.54 mm respectively.

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:	LVL I-beams, 12" top flange, 12" web, 6" bottom flange
Deck:	2x8 SYP with shiplap joints screwed along overlapping edges
Floor Beams:
Suspension:
Unique:

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
	All timber members were preservative treated and pressure impregnated with CCA in accordance with ASTM D1760 at Hoover Treated Wood Products, Inc., who donated the material to our team. After treatment, the lumber was kiln-dried to a 19% or less moisture content. This treatment minimized the moisture, thus reducing the weight of the bridge. The treatment occurred in the factory which had the proper equipment and safeguards.

7. Special Considerations
	This project has been a tremendous learning experience. We would like to thank our sponsors: PDJ Components, Inc. and Hoover Treated Wood Products for donating the bridge material. This project has definitely fostered excellent community relations, which we plan on continuing in the subsequent years. This year's bridge will most likely be placed on one of the many walking trails found throughout West Point.