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 2001 United States Military Academy's Timber Bridge was focused on an inexpensive yet practical design that could be assembled rapidly. Based on recent events in Bosnia and Kosovo, we wanted to focus on a design that could be readily applied in a field environment. The ability to build bridges to span the many rivers in the European countryside has proven to be a challenge to today's Army. Recent reports from field units 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 and this project would prove to be an invaluable experience. Based on this real life scenario, we decided to limit our materials (primarily 2x4 and 2x6 lumber) and equipment to those we would find on a standard Army deployment, with speed of construction as a high priority. We based our design on the historic Bailey Bridges used during WWII and in Vietnam. The Bailey Bridge is made up of a series of trusses and is well known for its strength, relative light weight, and the speed with which it can be assembled. The bridge we designed consisted of three, floor type joists. Each truss was made from No. 1, 2x4 treated Southern Yellow Pine (SYP) with nail plates attached at the joints. Each truss has a set of four diagonal members in a reverse "V" orientation. The diagonal members were kept between 45 and 60 degrees to ensure optimality. The two outer trusses are identical. In order to meet the deflection criteria, the center truss had to have its top and bottom chord doubled in thickness. The deck was constructed from No. 1, 2x6 treated SYP. We cut shiplap joints in each piece and then glued the edges together. The decking was then attached to the three floor trusses with stainless steel wood screws. This overlapping technique would ensure that no single deck plank would individually bear the load and simulate a diaphragm performance. Once the decking was attached, No. 1, 2x4 treated SYP curbing was attached. Finally, two sets of No. 1, 2x4 treated SYP bracing was attached to the bottom chords of the trusses, approximately three feet from each end. This would prevent any lateral torsional buckling. The goals of practicality and speed of construction were achieved on our design. Each of the three trusses could easily be carried by two people (soldiers). Moreover, the decking once cut to size, went on quickly with the use of a portable electric drill.

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 10 mm as recorded at the midspan of the longitudinal beam receiving the greatest loading. Additionally, the deck deflection had to be less than 1.4 mm = (deck span/400). Deflections were taken by gauges that were 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 four steel beams. We received permission from Mr. Bennie Hutchens to begin with a 10 kN load with subsequent loads of 5 kN and 5 kN. The 10 kN load was composed of 40 cases of copying paper stacked on a pallet. The pallet was then lifted onto the bridge by a forklift. The 5 kN loads were made up of cases of copying paper and steel 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 5.53 mm for the bridge and 0.53 mm for the deck. Both of these deflections were well below the maximum values of 10 mm and 1.4 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:	2x4 SYP open-web floor joist with nail plates
Deck:	2x6 SYP with shiplap joints glued at 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
	Our bridge design consisted of wood members that were all treated lumber, either 2x4 or 2x6. Post treatments proved to be too hazardous with all the required facilities and safety precautions necessary to meet the competition criteria. More importantly, post treatments would not be an option on an Army deployment to a foreign country.

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