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 team, this year, looked at ways we could innovatively use alternative materials to help stiffen our bridge. We wanted to design a bridge that was not only stiff, but easily and systematically constructible, while keeping weight down. The design this year consisted of a 5 I-beam design with the top flange being the deck. The web of the I-beam consisted of a 0.5 inch sheet of plywood. The flanges of the I-beams consisted of 1 x 4’s laminated on their strong axis. The total depth of the structure was near allowable capacity at 495 mm, this provided a larger moment of inertia and helped to stiffen the overall structure. 5/8 inch B-7 Grade Steel All-Thread was placed transversely through the laminated deck to help stiffen the members and reduce the deck deflection. Fiberglass composite tape was rolled out along the underside of the deck to help stiffen the structure, while keeping weight down. Instead of using a thick sheet of plywood for the web, vertical stiffeners were placed to help distribute shear and bending stresses throughout the beams. Through hours of hand calculations and with help from structural analysis programs like RISA, it was determined that the bridge would deflect below detection sensitivity under a load of 20kN. Although this turned out to not be the case however the structure is still amazingly rigid.

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 web of the I-beam was a 0.5 inch thick sheet of plywood. Because we could not have a piece longer than 3 meters, we used another two sheets of plywood to connect the two pieces of plywood in the middle. This served two purposes: it connected the two pieces of plywood and also provided a build up on the web for purposes of moment resistance. Because the web was only 0.5 inches thick (1.5 inches in the middle) vertical 2 x 4 web stiffeners were placed to prevent the web from buckling and to help with the influence of shear loads on the web. The deck / top flange consisted of laminated 1 x 4 lumber pieces that were systematically cut to ensure a speedy fabrication in addition to spreading joint placements as evenly as possible. The laminate 1 x 4s were laminated in 4 sections of 7, and 4 sections of 8. 2 sets of 3 laminates were also fabricated to create the cantilevered overhangs. 3 inch torque screws were placed every 10 inches alternating sides so that the end product had a screw every 5 inches. Once the laminates were glued together holes were marked and drilled using a 3/4 inch, 18 inch long wood auger bit. These holes were drilled in order to place 5/8 inch diameter grade B7 steel all-thread transversely through the laminated sections of wood. The drilled holes were placed slightly lower than the neutral axis so that the steel would be placed in a tension stress zone. The laminated 1 x 4s were glued and screwed to the individual plywood webs to create 5 individual T-beams. These T-beams were then glued and clamped together. Once this was completed the bridge was flipped over using a crane. Bearing plates 5 inch x 5 inch x 1/4 inch made of plywood were placed on each end of each beam. Equal spacing between I-beams was important. Therefore, 0.5 inch plywood sheets were attached to the bottom of the bridge. Plywood was placed at the ends and the middle of the structure. To help with tension in the deck and to function as an extra means for connecting the T-beams, fiberglass composite weave was laid out in two 6 inch strips between the webs running longitudinally with the underside of the deck. Curbs (2 x 8s) were attached to the sides of the cantilevered edges. These were placed on edge rather than using the usual 2 x 4 curbs. This decreased the width of the bridge and kept the adequate curb clear-span in addition to helping reduce the overall weight of the structure. Before testing, it was thought that the bridge webs may buckle slightly, but this did not occur under full loading of the bridge. During loading, the bridge made no audible noises and no noticeable deflections were noted in the deck deflection until 15kN was placed on the second test set-up. Overall the bridge performed exceedingly well and was extremely rigid.

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:	Laminated T-beams consisting of 1x4 flanges with plywood webs.
Deck:	Laminated 1x4 positioned on strong axis, deck functions as flange.
Floor Beams:	N/A
Suspension:	N/A
Unique:	Fiberglass composite on underside of deck, all-thread transversely through deck.

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 used was #2 Southern Yellow Pine. All 1 x 4s were CCA (Chromated Copper Arsenate) treated lumber. 2 x 8 curbs were ACQ (Alkaline Copper Quartenary) treated lumber. The majority of 2 x 4 vertical stiffeners were ACQ Prowood treated. The lumber was all donated, thus the type of treatment for the wood was not selected by us. The treatment of the wood presented no problems, proper precautions were observed in the handling of the wood. Minwax was used as a sealant to prevent water damage, and increase service life.

7. Special Considerations
	The project was very beneficial for the entire team. Design meetings were held for an hour every week for 4 months. A design was selected, plans were made, and the bridge was fabricated in a two month time frame. Every member had a hand in the entire bridge process from start to finish. The bridge is scheduled to be auctioned by the University this May.