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)
	Assembly of the double arch sections began with construction of two sets of glue-lam templates. The arches were built up with ten layers of 1x3 Douglas fir trim board fixed to the templates in successive 6-ft. lengths. The strips were fastened and brushed with wood glue before the next layer was applied. Once dry, the surface fasteners were removed and the arches were planed to a uniform width of 2 1/4 inches. Incised, pressure treated 2x2 Douglas fir was used for the truss cross members. Two longitudinal support members were glue-lams constructed with four layers of spliced Douglas fir 2x4’s fastened to the arch sections with 1/2 x 5-inch carriage bolts. Nine transverse girders were constructed by sandwiching 6-inch strips of 3/4-inch plywood between two pieces of pressure treated Douglas fir 2x6. The resulting beams provided greater stiffness to carry the load at the decks weakest center points. Two 2x4 cross braces were attached to the top portion of the arch sections to prevent torsion during loading. Four locations along the inside top edge of each arch section were selected as application points for Strong Tie all-thread hanger assemblies.Eight sections of 1/2-inch zinc coated all-thread were fastened vertically from the arch sections through the centerline of the longitudinal support members. Once in place, the rods were tensioned to provide maximum additional deck support.The deck itself is built from two layers of 3/4- inch tongue and groove sub-flooring assembled from eight individual sections. Two coats of Monochem Epoxy Reinforced Paint were applied to the deck surface to provide a weatherproof, durable coating that is specifically designed to withstand repetitive traffic. The epoxy material seals the surface of the deck (including seems), and forms a rubberized, non-skid surface. The treatment is commercially available and is relatively inexpensive. All wood members except trim board used in arch glue-lams were commercially CCA pressure treated to AWPA standards. The arch sections were treated post assembly with Copper 8-quinolinolate solution. Additional protection was achieved for the entire bridge structure with the application of exterior grade water base primer and two coats of water base enamel.The pressure treatment and copper 8 preservative, plus the exterior grade paint should provide superior protection from sun, rain, and infestation.

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)
	Bridge deflection measurements were obtained using four sets of Laterally Variable Dimensional Transducers (LVDTs), positioned at the specified positions, Deck Right, Deck Left, Deck Center, and Deck (underneath). LVDT sensor numbers 17, 18, 19, and 20 correspond to specified positions as follows: Sensor No.17 = “Bridge Right” Sensor No.18 = “Bridge Left” Sensor No.19 = “Deck” Sensor No.20 = “Bridge” The area predicted to experience the greatest deflection was between the centerline (longitudinally) of the deck and the inside right side edge of the deck, in line transversely with the specified loading points. An LVDT was placed on the underside of the deck directly below predicted area of maximum deflection. Several additional photographs showing LVDT placements were taken to ensure adequate documentation of deflection monitoring positions. Load Testing began at 3:00 P.M. on Wednesday, April 10, 2002. The loads were gradually applied from 0 kN to 20 kN in approximately 8 minutes. All deck deflection measurements increased at an approximately proportional rate. Deflection measurements at Bridge Left, (No.18) and Bridge Right (No.17) were nearly equal throughout loading, as predicted. Once the 20 kN maximum load was reached, the loading was stabilized and monitored for one full hour. All deflection and load readings were monitored and recorded at the specified intervals between 3:00 P.M. and approximately 4:09 P.M. The understructure tie-rods and transverse cross bracing successfully prevented torsion in the upper arch sections. The bridge structure remained square throughout the loading process. Except for a few creaks and pops, no deformation in the bridge was detected. No bridge deflection was apparent anywhere to the naked eye at any time during loading. Overall, the loading and testing of the bridge was pretty uneventful. The bridge performed very well and the deflection results were close to our expectations.

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:	3/4" plywood, sandwiched between 2 pieces of pressure treated 2x6.
Deck:	Two layers of 3/4" plywood treated with epoxy reinforced paint.
Floor Beams:	Glu-lam consisting of 4 layers of spliced, pressure treated 2x4s.
Suspension:	Glu-lam, 10 layers 1x3 DF base strips, treated with copper 8-quinolinolate.
Unique:	1/2 inch rods hung from arches, connected to longitudinal beams.

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
	Arch sections were treated with copper 8-quinolinolate @ .25%. All other wood members wre purchased in CCA incised and pressure treated condition. It would have been nice if the base strips used for the arch sections were available in pre-pressure treated condition.

7. Special Considerations
	A plan to construct a painting and treatment tent was devised from the beginning. Safe, approved materials were used during construction and the laboratory and surrounding area were protected during treatment. The bridge is to be sold to one of our team members. He will be giving it to his folks for use on their ranch property.