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 2007-2008 MU Timber Bridge Team worked tirelessly this year at producing a wooden bridge that will rival the best in the country. Our goals were to design for extremely small deflections, while reducing as much weight as possible without compromising strength. The underlying concept in this design is that “the glue is stronger than the wood,” thus the greater the number of glue seams, the greater the laminate strength. However, our confidence in the above stated theory was shaken by the high moisture content of the donated lumber. The largest construction obstacle was that high moisture levels from the treated lumber slowed drying time for the water based glue. This obstacle was overcome by cutting the 3/8” slats and allowing them to dry, thereby reducing timber drying time by 75%. With smaller pieces, surface area is increased and the distance moisture must travel from the centroid to the nearest surface is reduced. The Golden Bridge design is a product of MU Civil engineers’ esteemed efforts. It incorporates a large portion of each team member’s engineering education. The parallel axis theorem was instrumental in the design of the I-beams. Maximum height (0.5m) was selected and repeated calculations were performed using minimal cross-sectional areas. Deflection equations for 4 point loading and deck deflection were performed until desired results were obtained. Shear and moment influence lines were used for selecting all joint locations. Lateral-torsional buckling, web local buckling and flange local buckling were evaluated. A RISA model was used to check hand calculations. Weight was reduced with triangular cut-outs in the webs and diaphragms. Routered edges on the Warren truss (attached to web), curbs and diaphragms decreased weight while enhancing aesthetics. The cut-outs, routered edges, planning and sanding reduced bridge weight by 12% (compared to original weight calculations). In consideration of the Golden Bridge design attributes, such as vertical bridge deflection and net deck deflection, the following assumption was made by 2007 national champion, Oklahoma State: “our bridge acts as a single composite member and does not have a deck that is separate from the main beams or girders. As such, one could assume that the deck deflection is the actual bridge deflection.” This assumption is applicable to the Golden Bridge design as confirmed by Competition Coordinator, Bennie Hutchins. Furthermore, to abide by contest rules, a second loading set up was performed at the center of the largest deck panel to measure deck deflection. Unfortunately, representative data could not be obtained without compromising the structural integrity of the Golden Bridge, i.e., cutting large holes through the tension flanges to insert deflection gauges. Due to the anisotropic behavior of timber, and the engineered performance of the Golden Bridge, it is reasonable to assume that the deck deflection is a function of the bridge deflection. Based on this assumption, the deck span is 4000 mm, the allowable deck deflection is 4000/100 = 40 mm and the net deck deflection (percent of allowable) is 1.69/40 = 4.2%.

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 Golden Bridge design entails five laminated I-beams assembled side-by-side. The top and bottom flanges are biscuited to the adjacent I-beams to the extent that the I-beams become box beams. The diagonal bracing attached to each web provides a Warren truss rigidity. A 1-1/4” laminated deck was glued and screwed to the top of the five I-beams to distribute the load transversely. Laminated vertical curbs were attached to the longitudinal edges of both the top flange and deck. This provided greater moment resistance, minimum bridge width (1.3 m inside curb to inside curb) and aesthetical appeal. The Golden Bridge acts as a single structural element due to the composite action between tension and compression surfaces. During loading, the Golden Bridge performed exceptionally well. No audible sounds were detected from the bridge, no creaking, popping, or cracking. Deflections were so small that even with a taut string aligned with the bottom edge, no visible deflections could be detected. To begin bridge construction, a rigid 16’x3’ lamination table was assembled. The table enabled the production of two straight full-length laminated boards each day. The laminate boards used for the flanges, deck, and curbs, consisted of 3/8” thick rips out of 1-1/2”treated southern pine lumber. All end joints were cut on a 45º angle to maximize surface area contact, thus maximizing joint strength. Great care was taken to stagger each joint so they did not line up transversely, thus providing adequate development length. For the flanges and curbs, the maximum slat length was 9’-6” and the minimum was 0’-8”. Much waste was conserved with utilization of small scraps, however greater work efficiency was obtained in the deck boards by gluing 14’ rips and cutting them down to 54” later. Once the lamination phase was complete, the boards were planed 1/8” on each side, providing uniform thickness, reduced weight and smooth surfaces. The laminates were then jointed and ripped, to make longitudinal edges parallel. The flanges were cut on the centerline with a dado blade 1/2” deep, 7/8” wide. The webs consisted of two sheets of 1/2” plywood glued under great pressure (12 kip). After careful examination of the moment and shear influence lines, the joint layout was determined. Each joint was cut on a double 45º (cut 45º in 2 planes) to maximize surface area contact, each web has a joint in the center and one that is 4’ on each side symmetrically. This puts only one joint in the maximum moment region and all three out of the maximum shear region. The webs and flanges were bonded together and strengthened with a web-flange connection piece. The dimensions of this piece were determined with the following considerations: the parallel-axis theorem, web development length and torsional resistance. The stain and polyurethane were selected not only for their weather resistance attributes, but also for the way light is reflected from its perfected surfaces. The Golden Bridge has a rhythm and a sense of order that brings about a wholeness and unity of the structure.

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:	Laminate composite I-beams with warren truss stiffeners.
Deck:	Laminates oriented to distribute load transversly.
Floor Beams:	N/A
Suspension:	N/A
Unique:	Routered edges, triangular cut-outs in web/diaphragms reduce weight.

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
	Treated #2 southern yellow pine. ACQ (alkaline copper quaternary) and Pro-Wood ACQ treatments were both used in fabrication. Poly-Urethane finish/stain was applied to provide water resistance and prolong the service life of the bridge.

7. Special Considerations
	Through teamwork, we were able to divide and conquer, producing two extremely rigid structures. Of the twelve initial members, four had participated on the Timber Bridge Team last year, and a majority of the team members this year are seniors. All members participated in design weekly, this reinforced classroom concepts for older members and introduced advanced concepts to younger members. Design began with researching a broad range of good bridges, particularly the ones which did well in past competitions. We invited faculty to meetings to provide their insight. Ideas merged from each and every possible resource we could obtain. The team devised a method of qualitatively comparing design alternatives and eventually narrowed two dozen designs down to two: design number 2 and design number 6. Material waste was minimized, sawdust was recycled and CCA lumber was not used, to mitigate environmental impact. Our MU Timber Bridge Team maintained team spirit, direction and motivation throughout the design-build process, under the leadership of our bridge president, Adam Kral and Vice president, Joshua Long. The Golden Bridge will be on display on campus at Engineering East until notified otherwise.