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)
	To start off this project, students split into 5 different areas: design, materials, construction, testing, and quality control. This organization allowed the work to be distributed among team members which increased project efficiency. After looking over the specifications and guidelines, it was decided that the two main priorities was to make this project a learning experience for all members of the team and to have fun. The materials unit started researching different types of decking material could be used and meeting with the staff at the WSU Wood Materials Engineering Laboratory (WMEL) to figure out how to manufacture it. After a team consensus, 4”x6” composite deck boards were chosen which would increase deck stiffness and would give the team experience in wood plastic composites (WPC). The WPC profile included voids that were designed to maximize moment of inertia (and hence stiffness) and the voids helped to reduce the weight. Two glued- laminated beams (glulams) were chosen for the primary supports of the structure. Modulus of elasticity was measured for each piece of constituent lumber, and an E-rated beam layup was accomplished to optimize beam stiffness. This project highlighted two technologies that were developed at WSU – E-rating lumber and WPCs. Two WSU faculty formed the Metriguard Company several decades ago to commercialize MSR lumber grading technology. Similarly, of the $1 billion WPC market in North America, over 40% uses formulations developed at WSU.

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)
	Because this year will be Washington State University’s (WSU) debut in the Timber Bridge Competition, a common theme of displaying the technology and capabilities of WSU was chosen. A WPC deck consisting of 63% 60 mesh pine wood flour, 31% high density polyethylene, 4% Zinc Stearate, and 2% EBS Wax was chosen. The WPC deck board profile is very stiff and minimized net deck deflection and is naturally resistant to biodeterioration. The extrusion process to combine these materials into continuous beams was carried out at the WSU WMEL by students on the bridge team with guidance from WMEL technical staff. To keep within the maximum 25% non-wood requirements, the timber components of the support structure were sized conservatively. A practical design was chosen that would minimize deflection and be easy to construct in the field. The two main longitudinal members are laminated beams made up of 14-2x4s. MOE of each 2x4 was measured using ASTMD198 testing methods. Next, a beam layup was made which placed lower stiffness lumber in the core of the beam and high stiffness boards at the outer laminations of the top and bottom. Each piece of lumber was then cut to shorter lengths with 60 degree scarf joints to maximize adhesion of wood fibers. After each piece was cut and placed in a proper position, the beam was laminated together using 100 parts Cascophen LT-75C and 16 parts Cascoset FM-282C resorcinol adhesive donated by Hexion Specialty Chemicals. Joists spanning between the glulam beams were 2x12 No.1 Douglas fir lumber. The 2x12s were connected to the glulam beams using Simpson Strong Tie U210 joist hangers. 3-1/4” 16d nails were used to fasten the joist hangers to the beams and ¾” nails were used to fasten the 2x12 joist to the joist hangers. The deck was fastened to the 2x12 joist with 5” lag screws. The load testing was conducted at the WMEL using steel test fixtures and a 100kip actuator. String potentiometers (string pots) were used to measure deflections at necessary locations and automated data acquisition system recorded the data at a sampling rate of 5 HZ. Average deflection of the glulam beams reached 1.68mm when 20kN of force was applied after 10.8 minutes of testing. After holding the 20kN load for 45 hour (time max deflection was read), average deflection had reached 1.69mm due to creep of the beam under a constant load. The net deck deflection after loading the beam for 20kN for 1 hour was 0.540mm and increased 0.086mm from the time when the 20kN load was initially reached. The deck panel length was 421.8mm; therefore the net deck deflection was 12.8% of the maximum. The string pot deflection measurement devices were accurate to the 1/1000 of an inch, which is equal to .025mm, and explains the fluctuations in the deflection readings.

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 beams consisting of 14 DFL 2x4s.
Deck:	Composed of 9 WPC beams.
Floor Beams:	Composed of 2x12x56 DFL
Suspension:	NA
Unique:	NA

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
	Since the bridge was built in the Pacific Northwest, there are many differences in wood treatments from the southeastern region of the United States. It is not feasible to have a species such as Southern Pine delivered or purchased, thus limiting the bridge to such wood species as Douglas-Fir Larch or Hem-Fir. The primary species grouping available in the region on eastern Washington that is pressure treated is Hem-Fir. Hem-Fir has much lower strength and stiffness values than Douglas-fir or Southern Pine. In addition, our faculty advisor was concerned about exposing students to planer shavings and sawdust from PPT lumber. After inquiring with the judges, a waiver was granted concerning the use of wood treated to AWPA standards. The WSU bridge team understands the concerns about a bridge possibly being used by the public. As such, our bridge will be surface treated with copper napthenate by a WMEL employee who is a licensed pesticide applicator. Furthermore, the bridge will be displayed in the Civil Engineering Department courtyard and will not be used for any other purpose.

7. Special Considerations
	This project had a significant positive impact on all members of the team. The hands-on experience associated with this project provided team members with experience with what happens after the design process and will be a great supplement to the wood engineering design and composites courses taught at WSU. Knowledge of non-traditional wood-plastic composites was also gained at will be valuable for team members after graduation. Working with staff at the WSU WMEL gave students experience in interacting with professionals which will prove useful in the careers. Students also gained hands-on experience on conducting full-scale structural tests and following appropriate ASTM standards. Lastly, students learned that not everything in the theoretical design process will go according to plans, and creative improvisation is needed to drive a project to completion. This required students to function as a team, respecting divergent opinions and ideas. Also, the WSU Timber Bridge team would like to thank Dr. Donald A. Bender, the WSU Wood Materials & Engineering Laboratory and Hexion Specialty Chemicals for their significant contributions to this project.