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 goal of the bridge team this year was to create a strong yet simple and lightweight bridge that contained as little steel as practical. Optimization of the high tensile strength in steel was emphasized also. It was desired that steel cables would carry a large amount of tensile force, while the majority of the structure maintains stability using the wooden components. This would maximize the effectiveness of both materials. Commercially available ACQ treated southern pine lumber was used for all wood sections. The plan for the bridge was to essentially have a prestressed wooden structure. To do this, a wooden span was created with a deep section in the center. The deeper center section would allow for a larger prestressing eccentricity as well as increasing the moment of inertia significantly in the section with the highest flexural loading. The increased heighth in the center section was accomplished by fixing plywood gussets to the outside of the longitudinal joists. This created a strong, stable, tall mid-section. The deck, composed of 5/4" deck boards, was fixed upon the five joists. The deck panels were interconnected with wood biscuits at the mid-section of each bay to increase load transfer between deck boards. A 5/16" steel cable was run from the top of two joists, which were centered on the load points for the bridge deflection, and under the deep mid-section. This cable was pretensioned using a turnbuckle that was temporarily attached. Once the main cable was tensioned it was secured and the temporary stressing turnbuckle was removed. It was anticipated that the prestressing would be sufficient enough to counter the applied loads.

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 loadings were completed using steel sections combined to acheive exact 5 kN increments. Some increments of the load were applied using 50 pound individual weights. Defelection readings were made with String Potentiometers that were connected to a computer acquisition system. The deflection readings were graphed using an Excel spreadsheet. The loadings went well with no audible "popping" or very extreme deflection changes. However, the unsatisfactory results show that the bridge deflected beyond the maximum allowed deflection. The bridge deflection of 41.66 mm was far beyond the 10mm allowance. The deck deflection slightly exceeded the allowed limit of 3.84 mm, deflecting 4.19 mm. The prestressing cables on the bridge were the main cause of excessive deflection. It is believed that they had not been pretensioned sufficiently to create adequate camber. Without the necessary camber, the bridge was unable to withstand the applied loads without deflecting excessively.

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 girders with large cross-section at center
Deck:	5/4 inch Deck Boards biscuited together
Floor Beams:	2 x 6 and 2 x 4 beams flush with girders
Suspension:
Unique:	5/16 inch prestressing cable on underside of bridge

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
	The treatment for the lumber on UMC�s bridge was all commercially applied. All lumber was treated ACQ that could be purchased at any lumber store. The reason why this was chosen, was because it was readily found and the most practical for this application.

7. Special Considerations
	This bridge was designed to use the lowest amount of lumber possible, but to use as much lumber per unit of steel as possible. This utilizes a renewable resource. The future of this bridge has yet to be decided.