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 designing this bridge it was our goal to build a practical, yet strong bridge. It was our intention to use easily accessible materials and built it using simple tools. It was kept simple to allow for easy field erection. We used treated southern yellow pine available at any lumberyard. At first, 2” x 2” members were to be used. However, these members weren’t sufficient enough in width for our fasteners. It was imperative that there was at least double the thickness of the ½” bolt on either side of the fastener. Due to these criteria, 2” x 4” members had to be used to allow for the 1” clearance on either side of the fastener. Also, an end distance of 2” for compression members and 3.5” for tension members were needed. We used ½” threaded rod with fender washers and nuts on either side of each joint as a fastener. Along the bottom of the bridge, under the deck, there are ½” diameter continuous threaded rods of the same size spanning the width of the bridge, except the two off center joints in the middle, which are simply bolt joints like in the super structure. These were used because the rods are excellent in tension strength, which is needed on the bottom of the bridge. Again, each side has nuts and fender washers on either side of the bottom chords and center support. The super structure above the deck was designed to stiffen and strengthen the bridge. However, it is extremely over designed due to the increase from 2” x 2” to 2” x 4” members. There is a center member under the deck. It was designed to be a queen post truss, using ½” rod for the inside member. 2” x 4” beams were used to span the top of the bridge to keep the side trusses plumb. 5/4” x 6” decking planks were used for the deck. Rather than inserting many joists or center members a tongue and groove joint was added to strengthen the deck and minimize weight and deflection. The brid

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 bridge itself was very stiff under loading. The side truss closest to the loading, which was Beam Left, deflected only 4.90 mm. The bridge was preloaded with 3700 lbs three days before final testing. During this preloading there were some creaks heard, but no loud cracks. The bridge did have some creep at first due to settling of bolts and joints. This was expected. The loading was done with a hydraulic testing machine capable of 100,000 lbs. We used a 5000lb load cell to measure the load. The bridge was too large for the machine, so it was set up directly next to it. We used an I beam connected to the machine that hung over to our load points. On the bridge we used two 6 x 6 wood posts laid flat to connect two loading points and placed a third on top perpendicular to the two below to transfer the load. The load cell was placed in the center of the third 6 x 6. Great care was taken to ensure even distribution of load. The weight of the 6 x 6 posts was taken in to account in the loading weight. The LVDTs were calibrated before any weight was applied to the bridge itself. The load points had to be moved transversely to one side to get them in the mid-span of our longitudinal beams. Our deck deflection was required to be 1.9 mm according to L/400. Our max net deck deflection was 4.75mm. The deck was designed to hold the load , but was not stiff. Once the full load was applied, our deflection was 4.47 mm on the truss closest to the load points. The deflection of the mid point of the center longitudinal beam was 18.99 mm at full load. At each fifteen-minute interval, there was some creep. The deflection slowly increased throughout the hour. The final deflection of the truss closest to the load points was 4.90 mm. So there was a .15 mm creep in the truss during the one hour. We didn’t expect much creep during hour. The total average bridge deflection was 12.59 mm after the one hour. This bridge was designed for easy construction

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:	Two side trusses pinned with 1/2" dia. rod
Deck:	5/4" T&G decking
Floor Beams:	N.A.
Suspension:	N.A.
Unique:	Queen post truss for a center member

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
	Due to cost and time constraints, we opted to utilize .40 retention C.C.A. treated southern yellow pine.

7. Special Considerations