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 primary concept that drove San Francisco State University's 2002 entry into the Tenth National Timber Bridge Design Competition was to construct a bridge that was not only sturdy but beautiful as well. Largely inspired by a new steel arch pedestrian and cyclists crossing in Berkeley, CA, our team came up with the idea to utilize built-up overhead laminated arches that would span the required distance as specified in the contest criteria. This design provided us with the strength and beauty we desired. Not only would the arches distribute the load more evenly across the span, they would be an eye pleaser as well. The 3'' x 3'' arches consisted of four layers that were fabricated by using 3/4'' marine plywood which were then laminated into smooth curves. The lamination process of attaching one layer to another was made quick and easy thanks to our use of "gorilla" glue, which is by far better than epoxy glue. It is important to note that midway through our project, our team made a decision to alter the design of the hangers for the arches from wood to 1/4'' threaded metal rod hangers. We believed that this would increase the rigidity of the bridge while at the same time keeping the use of materials and the weight of the bridge to a minimum. In order to connect the arches to the bridge we chipped a 1 1/2'' x 1 1/2'' space out of each corner of the supports. After placing the ends of the arches into these spaces (filled with "gorilla" glue) they were secured by screws drilled straight into the supports. In addition, strong tie connectors at the corner of each connection were utilized. In order to keep within the member length guidelines of the contest we constructed each longitudinal beam by connecting two pieces using a splice connection. It will be noted that these connections were glued and bolted. The transverse beams setup consisted of 11 beams that were attached to the longitudinal beams wit Among the eleven beams there were three 4"x4" and eight 2"x4" beams. There is one 4x4 at each end and one in the center of the span. No.1 air dry Douglas Fir was used for the deck beams. It was chosen for its low moisture content, which provided maximum strength and minimal shrinkage.The design of our project accomplished using computer modeling (RISA) as well as hand calculations to determine the deflections and stresses that it would be subjected under load. Since the member is structually indeterminate, computer modeling proved to be the most efficient method of analysis with the hand calculations being used to verify the resulsts.

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 performance requirements for the competition dictated that the bridge must be able to carry minimum of 20KN, approximately 4500 lbs, for one hour and deflect no more than 9mm recorded at the mid- span of the longitudinal beam receiving the greatest loading. And the deck deflection was required to be no more than 3.5mm = ( deckspan/400) during the loading. Each dial gauge was zeroed before the readings and deflections were taken by gauge readings that were carefully placed in the five required locations. The 20KN load was distributed to the point loads by means of a system of three I- beams that were placed on four 60mm by 90 mm ( 60mm x 90mm) wooden blocks where the point loads are located. The loads were applied with hydraulic pressure in four increments of 5KN up to the required 20KN. The loads were applied to the Left side of the bridge which was 76mm (3inches) from the inside curve of the left beam. Therefore; the left beam was carrying the greatest loads and indicated that the deflections on the left beam was more than the right beam. Generally, the bridge behaved in the manner we expected. With the addition of each load and time interval, the bridge's deflection increased. At the end of one hour, the maximum deflection was 2.15mm for the bridge and 1.10mm for the deck. Both of these deflections were well below the maximum values of 9mm and 3.5mm respectively.

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:	None used
Deck:	very strong
Floor Beams:	IT was very strong
Suspension:	1/4" all treaded rod was made the deflection minimal and the bridge attractive
Unique:

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 treatment we used was from the marine resin supplier . With the application of the outside finish. Because , we been advised from that this treatment has been used for a long time.

7. Special Considerations
	Our basic consideration was designing a bridge which would have long endurance and withstand elements. Wood is economical and beneficial for the majority of people, especially for those who live in third world countries who do not have the technology to produce other substitute materials. And it is easy to construct and maintain Wood. It can be used for many small rivers and over passes that can be accessed for small villages and communities.