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)
	Ohio University's 2006 Timber Bridge submission consisted of a truss bridge, composed of standard dimensional lumber with screwed, plywood connections. Several designs were considered before choosing the traditional truss. Team members were asked to develop preliminary designs that met the design criteria, then they were reviewed at the next meeting. A traditional truss bridge was chosen for aesthetics, practicality, and constructability. Before a structural analysis was performed, team members discussed the expected load paths and stress distributions through the structure. Through experience, it was predicted that commercially available, dimensional treated lumber would be sufficient for all members in the bridge. A model was then created in SAP 2000 to determine the strength demands. Material properties were assumed, then updated later when preliminary design calculations were performed. Aside from the deck, most of the truss members were Southern Pine No. 2 2x4s, and a few longer compression chords were SP No.2 2x6s. A list of members can be seen in the schematic drawings. Strength calculations were done per the 2005 National Wood Design Specifications, using the Allowable Stress Design method. Screwed plywood connections were used instead of steel gusset plates since team members had experience in designing dowel-type connections, and unit strengths of gusset plates were undeterminable without testing. Treated 1/2 inch plywood plates were cut to fit the connecting members, and then adhered on both sides of the members with construction adhesive and screwed with 2 1/2 inch wood screws. The deck members were designed for bending. The bridge was divided into 4 spans along its length, each 1 m long. An analysis was conducted checking the demands for all combinations of 2m-2m spans and 1m-3m spans, since no member was allowed to be longer than 3m in the structure. 2m spans, from the end of the bridge to the center, were chosen since the lowest moment demand was determined from this configuration. The members were designed to be Southern Pine No. 1 2x12s, and were governed by bending strength. It is noted that when the lumber for the bridge was donated, only No.2s were supplied, which did not provide sufficient strength.

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)
	During the process of loading the bridge, the only members that displayed any significant deflection were the 2 x 12 deck members. These members were loaded in flexure, and failed by splitting along their length before the ultimate loading was reached. This failure occurred between 15 and 20 kN. This failure was somewhat expected, as the decking members used were of a slightly lower grade than had been specified during the design, but were still used due to the fact that they were the only members of appropriate size that were locally available, and the team could not afford time for the right grade to be ordered. Southern Pine No. 1 was specified, but Southern Pine No. 2 was used. There were five LVDTs used to measure deflections at different locations on the bridge. Gauges were placed at the center of the outer supporting beams of the bridge. Three LVDTs were also placed along the centerline of one of the deck members being loaded. One of these deck member gauge was placed directly under the loading point. The exact locations of these LVDTs can be seen in the load setup drawings. The locations were marked A, B, C, D and E. The loading was applied by means of a hydraulic jack. The jack was propped against the bottom of a steel loading frame that was attached to a strong floor. This jack was made to bear on a system of steel I-shapes that sat on top of the bridge. It seems that if the decking members had not failed, the bridge would have been quite efficient at supporting the load. All LVDTs attached to members that did not fail showed that the deflections were linear, and rather of small magnitude.

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:	4 Pressure Treated Southern Pine No. 2-2 x 4 girders
Deck:	10 Pressure Treated Southern Pine No. 2-2 x 12 deck pieces
Floor Beams:	6 Pressure Treated Southern Pine No. 2-2 x 4 beams
Suspension:	Not Applicable
Unique:	Pressure Treated Southern Pine No. 2 truss chords: 12 -2 x 6 and 33-2 x 4

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
	ACQ (alkaline copper quaternary) preservative treatment was chosen for all wood members. The concentration of this treatment was 2.5. This treatment was chosen because it was the only locally available choice. ACQ is also an environmentally friendly method of preservative treatment. The treatment requirement did not present any problems to the design project.

7. Special Considerations
	As of right now, there is no future use plan for the model bridge.