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 Student Chapter of the Forest Products Society of the University of Arkansas at Little Rock designed, constructed, and tested this timber bridge during the Spring Semester of 2007. The Construction Management Program at UALR purchased all materials and sponsored the FPS Student Chapter's effort to construct the bridge. The bridge team members, consisting of UALR Construction Management students, have all had experience in the various phases of timber design and construction as part of their academic studies. All of the design, construction, and testing of the timber bridge was accomplished by the bridge team students with advice from departmental faculty members. The timber bridge was constructed primarily of 2-inch treated pine, with ľ” treated plywood, screws, and loc-tite glue. Initially, the bridge design team tested a trapezoidal shaped beam, which measured 15” in depth, and acceptable results were recorded with the test beam. One critical design consideration involved the selection of the best location for the joints in each of the beam members. Joints were necessary for all long members since none of the members could be full length. The placements of the joints were located to maximize material lap and the joint separation, in accordance with the rule constraints. Another design consideration involved the selection of the wood members. When selecting the wood members the team decided to construct the bridge with high quality treated lumber as to minimize knots/irregularities and to maximize overall member strength. With the test beam yielding satisfactory results in deflection performance, the team proceeded to build the second beam to the same specifications. The bridge design utilized two beams constructed as built-up Trapezoidal-Beams with 2x12’s for the top members, 2x6's for the bottom members, and two layers of ľ” treated plywood on each side. The deck was constructed of 2x4’s, stood on edge, so as to achieve minimal deflection. In doing so, the bridge did not need any lateral deck supports thereby eliminating additional weight. All deck members where screwed down to the beams and also to each adjacent deck member. There are three transverse braces located at quarter points connecting the beams to ensure no lateral movement in the bridges beams. After all deck members were in place, 2x8 trim was placed around the entire deck to create a clean look to the bridge. The final pieces of lumber were used to construct 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)
	UALR’s bridge entry was constructed of solid two inch treated pine and ľ” treated plywood, 10X3” deck screws, and Loc-tite construction adhesive. The bridge utilizes two trapezoidal beams that are approximately 15” tall and 12” X 5” top and bottom, respectively. A test beam was built, and following testing and analysis, the team decided on a design trade-off that added some weight, but eliminated the need for any additional deck support framing. Once the deck was attached, 2 X 6 and 2 X 8 bands were attached at its perimeter. The 20 kn load was applied as required by the rules with a hydraulic jack fitted with a three inch pressure gauge. As the load was applied, the recorded deflections were uniform throughout the entire process. Since both beams were expected to have the same load applied, the team decided to monitor one beam, at its midpoint, for deflection. This was our first experience with the Loc-tite adhesive product, which is recommended for use with treated lumber, and the team was very pleased with its performance. The deck deflection was monitored with two gauges located under the beams and in line with the gauge that positioned under the center of the selected deck span. The adjusted readings showed a deck deflection of .86 mm, which was 12% of the maximum allowed deflection. The bridge team recognized that the deck design would add weight, which would be offset, somewhat, by not requiring support structure beyond the two main beams. However, this design allowed the team construct a bridge that was different, in many ways, from our past entries.

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:	N/A
Deck:	Treated 2x4, applied on edge with transverse placement
Floor Beams:	Two built-up trapezoidal beams, approx. 12"x5"x15"
Suspension:	N/A
Unique:	N/A

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
	The team used ACQ treated lumber for the beam. ACQ is an Alkaline Copper Quaternary treatment. The reason for the use of this lumber is because the lumberyard only had 2x8’s, 2x10’s, 2x12’s and ľ” plywood in ACQ. For the deck we used a new type of treatment that is called Smart Sense MicroPro. The local lumberyard that we got the material from is starting to phase in this type of treated lumber. Smart Sense has a preservative retention of .25(pcf) for general use above ground which includes decking, joist, beams and sills. Smart Sense pressure treated wood offers corrosion characteristics similar to that of CCA pressure treated wood or untreated wood. Smart Sense is fresher and brighter with a more modern appearance, plus offers the option of MicroShades "in-solution" redwood red/brown or cedar-honey/brown color pigments. The new MicroPro copper preservative system is the only new exterior wood preservative system that is EPA approved, at the appropriate retention level, for Above Ground, Ground Contact and Fresh Water applications for Southern Yellow Pine and South American Pines. Another reason for the use of Smart Sense is that it has a lifetime warranty for above ground general use.

7. Special Considerations
	UALR’s 2006 entry is scheduled to be set up adjacent to new structural steel connection display, and will focus attention on structural wood connections. This years entry will be offered to UALR’s physical plant, and it could find a home on a small creek that winds its way through the Northwest corner of the campus. This project was an enjoyable and informative experience for the entire bridge team, and we would like to thank everyone that has a part in making this competition possible.