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 2002 Rose-Hulman Timber Bridge Team started the bridge design knowing that the bridge was going to be used by one of the team member’s parents after completion, so craftsmanship and appearance were as important as the structural integrity of the bridge. The timber bridge was based on an arch-supported suspension bridge that could be built out of pressure-treated materials available at a local lumber company. The arches were constructed by the bridge team out of surface planed treated spruce 1”x4”s laminated with HB Fuller glue. The arches were bent dry around a plywood form and clamped and glued in single layers, eliminating almost all spring-back when the arches were removed from the forms. Once the arches were laminated, they were again run through a planer to clean the glued edges. The girders were doubled up yellow pine 2” x 8”s hung from the arches with galvanized 5/8” diameter rods. The chords of the arches were built up from 2”x6”s and 2”x4”s, with a planed 5/8” spruce board acted as a spacer between them where the threaded rods went through. The tension connections between the chords and the arches are the most interesting part of the bridge design. A method that originated in fixing timber-framed structures, a threaded rod was run through the joint, which intersected two pieces of pipe with threaded rod connectors welded into the center. These pieces of pipe bear their load on the chord while there is as steel bearing plate on the other end of the arch. This method was used because it allowed us to the natural tensile strength of the wood rather than a full length tension rod, and it eliminated any gusset plate at the arch/chord connection interface. This allows for minimal amounts of steel to be visible when viewing the bridge from the longitudinal direction. Pipes and threaded rods were used in place of solid steel bars because of the lighter weight. It also is much easier to manufacture in the machine shop because no tapping was required. The transverse joists consisted of yellow pine 2”x4”s notched into the 2”x8” girders. The decking was made from 2” tongue and groove boards laid at a 45° angle so that it would cross more support pieces. The decking was held in place using 3” stainless steel screws. All other steel on the bridge was either galvanized, or primed and painted after machining to prevent corrosion. The curb then consisted of 2”x4”s placed along the top of the chords to cover the edges of the decking. At the ends, the arch itself was used as part of the curb.

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 load points of the deck were shifted slightly as a 4-point until to ensure that a load point was centered between the longitudinal and transverse joists. The final use of the bridge dictated that girders be equally spaced under the arch portion of the bridge, which required that the load points be shifted slightly to get the maximum deck deflection. The load of 20 kN was applied by stacking a load of CMU blocks on top of the bridge, which were weighed immediately before the testing began. The bridge was loaded in 5 kN increments, and the deflection was measured for each loading condition. After 20 kNs had been loaded, deflections were then measured every 15 minutes until an hour elapsed. The bridge deflected the most during the loading stages, and then slightly more deflection occurred with time. Deflections were measured at the midpoint of the left chord, under the load point, and on the left and right chords even with the load points. The right chord experienced the most deflection under the load, possible because the tension connectors were not completely bearing until the load was applied. Once the load was added, the right chord acted in a similar fashion as the left. If the bridge was reloaded a second time, the deflections would have been considerably less, since the bridge stopped rebounded when about half of the bridge was unloaded, indicating that there were some loose joints that tightened up in the loading.

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:	Doubled up 2x8 SYP glued and screwed together
Deck:	2x6 SPF T&G flooring placed at 45º angle
Floor Beams:	2x4 SYP noteched into girders
Suspension:	Arch laminated from 1x4 SPF
Unique:	Tension devices negated gusset plates or long rods

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 was .40 CCA treated lumber

7. Special Considerations
	The bridge is to be used by one of the team member's father, so the final usage was taken into account during design, especially aesthetics and symmetry. Steel was painted, galvanized, or made from stainless steel. There are noo visible gusset plates from the side, and it is strong enough for a riding lawn-mower to cross, which ensures that it will be useful after we used it.