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 bridge design concept was based on an arch with a suspended deck design. The arch is a classic structural member that OSU wanted to attempt to utilize. The parabolic nature of the arch allows the member to be in pure compression if properly constructed. Furthermore, the arch is very aesthetically pleasing and provides a rigid design that is easy on the eyes. Here in Columbus the University has a famous suspended deck bridge known as the Lane avenue cable stay bridge. In appreciation and admiration of the Lane avenue bridge we also wanted to achieve a suspended deck for our timber bridge. All thread members were selected to be the tie rods which would hold up the transverse members that were to support the deck. Considering the rods would be in pure tension they could be made slender and strong, further adding to the pleasing look. All thread rods were chosen to optimize stiffness versus cables because of a cables potential to stretch. Additionally, the post tensioning rods were used as additional reinforcement which would be light weight. The arches that were constructed did not perform as calculated. Not enough laminate was used and the joints were not staggered for the individual half inch plywood that comprises the arch. These factors led to a poor performing arch. . Post tensioning rods were added to prevent the feet from spreading. More support was needed so 5/4” by 6” beams were laminated together to give more deck support and take some of the weight off of the arches. We are pleased with our results of having a bridge that meet deflection criteria.

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)
	Under loading conditions the bridge performed well. There was little to no noise during the final test loading. The deck did not bow enough to be visibly noticeable unless one put their eyes right on the plane of the deck. Furthermore, the post tensioning system did not neck nor did the hooks experience much spreading. Calculations showed that the 5/16” all thread could hold enough weight to support the test load. We were unsure if the beveled washers would properly transfer the load to pure lateral forces. If the washers did not translate the load properly the shear forces would sever our all thread rods. Fortunately the washer assembly held as planned. The post tensioning system produced an interesting resonant frequency within the bridge, vibrations could be felt for several seconds after people jumped up and down on the deck. The addition of the 4500 pound test load eliminated any vibrations in the system. The arch had a very slow rebound time after the test. When initially unloaded the dial gauges only returned to .19 inches. Overall we are happy with the bridges performance during loading and feel it will do very well in the life after competition.

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:	Made of 4 pieces of 5/4 X 6” which have been laminated and screwed. Max member length: 9’10”.
Deck:	The top is made of 2 X 4” which are 8’ long and have staggered joints. The bottom is squares of ¾” plywood.
Floor Beams:	Floor beams are made of 4 X 4” which are 4’10” long.
Suspension:	Suspension members which hang the deck are 5/16” 30ksi all thread rods with a beveled washer assembly.
Unique:	A Post tension system is made of 3/8” all thread rods with turnbuckles and eye 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
	All wood came treated ACQ as purchased from the manufacturer.

7. Special Considerations
	This project has been a tremendous learning experience for all group members. There were many challenges and failures along the way. Initially the bridge was deflecting more than allowed. A post tensioning system and then a floor beam system was attached made the final weight of around 1250 lbs. Environmental impact was not heavily considered on this project given the utility of project experience for all parties involved. It is good to provide the Engineers to be with excellent project experience. This will most definitely have a positive environmental impact for our future projects in which we will be able to respond more knowledgeable and more efficiently. The bridge will most likely be given to a school or public works project similar to the location of all previous bridges.