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 goal in designing the wooden bridge for the design competition was to maximize stiffness while minimizing weight. An arch design was chosen both for its aesthetic appeal and for the opportunity to optimize weight versus stiffness. The arch structure mimics the shape of the moment diagram thereby providing for an efficient longitudinal structure. The arch structure primarily carried compressive load and needed to be braced against out of plane buckling. For this reason the arch was dropped below the deck at each end and lateral bracing was provided at mid-span. The lateral bracing was provided by extending the transverse stringer beyond the deck and connecting it via a diagonal 2x4 to the top of the arch. The lateral brace cut the effective unbraced length in half, and this increased the buckling strength approximately fourfold. The lateral bracing provided by lowering the arch at the end of the bridge also helped to increase the buckling capacity. Resistance to outward thrust was provided by connecting tensile members from the end of the arch to the center transverse stringer. Half inch all-thread was used as the tension members to create a better connection and to also minimize cost and assembly time. Connections were made by drilling a one-half inch hole through wooden members and attaching a bearing plate and nut. This seemed to be the most time and cost effective connection setup. An attempt was made to utilize 1/8-inch Kevlar rods for the tension members; however, the necessary connections were insufficient to support the load. By using this arch design, it allowed the deck to essentially become a separate structural system. The deck load was transferred to the arch via 1/2-inch all-thread rods. The structural deck system consisted of 5/4 x 6 decking supported by transverse stringers spaced 400 mm o.c. The stringers were hung with joist hangers to a longitudinal girder that was integral with the arch. These factors were considered in the conceptual design of this bridge and allowed it to satisfy the structural objectives quite nicely while adding an aesthetic appeal as well.

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)
	Behavior under Loading The bridge was loaded at two locations. The first loading was positioned at the center of the bridge and was expected to result in maximum arch (bridge) deflection. The second loading was offset 10 mm toward the abutment thereby placing two loads directly between stringers #4 and #5. The second loading was expected to result in maximum stringer (beam) deflection and maximum deck deflection. The maximum measured gross arch deflection of 6.35 mm occurred in the east arch during loading #1. Average maximum arch deflection was 6.13 mm. The measured maximum gross stringer deflection of 8.89 mm occurred at transverse stringer #5 (left beam) during loading #2. In comparison, transverse stringer #4 (right beam) deflected only 6.73 mm during loading #2. Maximum measured deck deflection of 9.19 mm occurred at the point of load application between stringers #4 and #5 during loading #2. Net deck deflection as calculated occurred during loading #2. According to the rules, net deck deflection equals the deck deflection less the average deflection of stringers #4 and #5. Maximum net deck deflection was equal to 9.19 � (8.89 + 6.73)/2 = 1.38 mm. Minor bridge lateral deformation occurred during loading. The east arch buckled slightly inwards (as shown in UW end finished below. jpg), perhaps due to a poor connection/fit in the lateral bracing. The remainder of the bridge elements remained rigid and undistorted, displacing only minimally above the predicted deflection.

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:	Pressure treated 2x6 southern pine
Deck:	Pressure treated 1x6 southern pine planks
Floor Beams:
Suspension:	all-thread attached to arch/abutments with nuts and bearing plates
Unique:	Arch-pressure treated 2x4 sandwiched between pressure treated plywood

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
	Wood Preservation All treated material used in the construction of the bridge were locally available. The arches were constructed of 0.40 pcf alkaline copper quaternary (ACQ) #1 Southern pine 2x4 inner laminations and �� AC plywood outer laminations with 0.60 pcf chromated copper arsenate (CCA) treatment. Transverse stringers were 0.40 pcf ACQ #1 Southern pine 2x6. Two options were considered for the deck surface. The first option considered was locally available southern pine decking with a 0.40 pcf ACQ pressure treatment. The second option considered was a composite panel consisting of rice paper and pheonaulic resin. With the pressure treated wood, local availability and material costs were the major advantages. However, the chemical compound used to treat the wood is a pesticide and as such has environmental and health issues to be considered. The composite material considered was Richlite industrial composite. Being resistant to water, oil and acid there was no concern of material deterioration. Composed of 70% rice paper and 30% pheonaulic resin with sheer and flexural strength greater than wood this seemed an ideal candidate for the deck surface. Additionally the MSDS sheet for this product list no health hazards associated with its use. The final decision on what product to use came down to cost and availability. With a cost nearly 400% greater than the cost of wood, the composite material was rejected.

7. Special Considerations
	Bridge Impact Group Impact- An immensely important aspect of successful design is the ability to collaborate, communicate and concede. Significant difficulties could be avoided if ideas could be freely exchanged, discussed and openly accepted or rejected, but more frequently clashes of intellect occur. Coping with the group dynamic proved to be one of the most challenging aspects of the timber bridge contest; learning to balance multiple personalities and ideas during the design and construction process demonstrated both the teams� weaknesses and strengths. Despite the sometimes overwhelming dissention, our team managed to design, build and present a quality product, a feat only accomplished as the team members combined to strive and commit to a common goal, rather than individual partialities. End of Project Use- The arch bridge is currently displayed outside the University of Wyoming College of Engineering building. The final use and location of the bridge has yet to be decided. Environmental Consideration- Alternative materials were considered for the deck surface, but cost and local unavailability prohibited the use of wood products with preservative treatments other than traditional pressure treatment.