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)
	In the Spring semester of 2008, the students of UT Martin designed a timber bridge. The main focus of this bridge was to minimize deflection, but not a great amount of attention was given to the reduction of weight. The thought behind this was that the structural integrity of the bridge was of greater importance than the weight. Initially, the decision was made to construct the beams out of laminated wood. Gluing the lumber together to make a laminated beam made a very stiff beam. The thought was that this would minimize deflection because of the extra stiffness. Though, not a great deal of effort was given in reducing the weight, the beam was constructed of smaller lumber as we progressed toward the center of the beam in its construction. It had 2X10’s on the top and bottom and progressively decreased in size until the center of the beam where it was constructed of 2X4’s. This along with the 1/6th of an inch planeing greatly reduced the weight when compared to the weight of the beam if it was constructed of only 2X10’s. This was a negligible sacrifice in the structures strength in an effort to reduce the weight. The deck was 5 foot wide and contructed of 2X8’s with a 2X4 curb on each side. It set atop the beams which were space 2.5 feet from center to center. Due to the inability to weigh the bridge as a whole, each component was weighed individually. This was accomplished by the use of two bathroom scales with each value read added together.The end result was a moderately light beam with an abundance of strength and stiffness. The data was taken and intial and final gage readings were recorded. The end reading was subtracted off of the total bridge deflection and then recorded in the table below. The beams deflections after loading were minimal.

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)
	As seen by the test results, the deflection of the beam was well within the 10 millimeter restriction. We were very pleased to see such a small number, although it was slightly higher than the theoretical deflection that was calculated. As seen by the data listed above, the final deck deflection was 0.4978 mm. As time passed the bridge deck experienced a non-linear amount of creep. In the 15 minute interval between the 30 minute and 45 minute time slots, the deck experienced a creep of about 56 hundredths, while the creep in the other 15 minute intervals was substantially less. The reason anomaly is unknown. The amount of deflection with every 5 KN weight increase is substantially more. As seen by the deck it would deflect about 1 unit for every 5KN increase in load. The bridge never once showed any visual signs of strain. It seemed to support the weight effortlessly.

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:	N/A
Deck:	2x8 deck with 2x4 curb screwed to beams
Floor Beams:	glue laminated beams made of 2x4s, 2x6s, 2x8s, & 2x10s
Suspension:	N/A
Unique:	N/A

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 preservative used on the bridge was Lowe’s top choice Southern Pine pressure treated lumber. We have found that the most common method used is a combination of a vacuum and pressure treatment. This method substantially increases the wood life 5 to 10 fold in instances where it may be exposed to the elements.

7. Special Considerations
	This bridge was a good experience for the students who were fortunate enough to have some involvement in its design and creation. Hopefully all involved have learned from their mistakes along with their triumphs enabling the next bridge to be even more of a success along with helping in our professional lives. The team is not really sure of what is planned for this bridge.