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)
	This MSU bridge began as a class project in CE 4653/6653, Timber Design, Fall Semester 2003. The team leader, who spent countless hours on the bridge project, is Erin Robinson. The team selected a tied-timber-arch bridge, with the arch supporting full-length side beams (cut to permitted length, and glued/bolted to form full length ). The beam/arch assembly was analyzed extensively using RISA 3D to optimize the size of the members. It was found that main side beams of approximately 3"x8" size and arches of approximately 3" deep by 4" wide (tied together by verticals)would result in deflections of the main beams of approximately 0.1" The two arches were fabricated by the students. Each arch was laminated from 4" x 1/2" nominal lumber ("lamina" ). A plywood template form was built, with wood stops that formed the arc of the arch. The wood lamina pieces were bent to form the arch curve, and glued and bolted to form a 4-lamina glued-laminated arch. The lamina were clamped while the glue dried, and bolted at approximately 18" inch intervals. When the arches dried and were removed from the forms, they held their curved shape. Once the bridge was assembled, steel cable was laced between the main side beams and the arch. The cables were connected to eye-bolts in the arch, and eye-lag screws in the side beams. However, during the first load test,the cable clamps slipped to the point that no load was transferred to the arch. The side beams were not designed to carry the entire weight. The main side-beam beam splices (bolted/glued connections)distorted excessively. As a result of this test, the bridge was re-designed with a retrofit that consisted of two steel tees whose webs served as tension side plates for the main beams. The tee flange on one side served as a saddle to support the side beam. Three 3/8" steel rods on each side of the bridge replaced the cable between the archs and the side beams to replace the cables. Holes were drilled in the outside flange of the tee, through which were place the rods. Levelling nuts at the top and bottom of the rods were used to remove any initial slack in the rods. A description of the bridge construction and testing apparatus is being forwarded (MSUnotes.doc) as part of the submission package package.

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 retrofitted bridge was successfull loaded to 5,000 pounds with no visible damage. The deflections that were recorded were checked with a frame analysis computer program to verify that they were in reasonable ranges. During the initial test, the test loads were places on wood blocks approximately 2" x 2" x "2. The team leader selected these blocks because she felt they were required in the test specification. The blocks supported steel grate, on which the load was placed. The blocks proved to be unstable and did not adequately support the grate, which bent badly under load and toppled some of the load onto the plywood deck. The faculty advisor felt strongly that this loading arrangement was unsafe, and directed that steel bearing pads replace the wood blocks. Two longitudinal planks were placed under the blocks for stability. The planks were counted as part of the bridge weight. Steel spreader beams spanned the pads transversely, and a double-thick steel grate spanned the spreader beams longitudinally. The load was placed on the grate, and was monitored closely throughout the second load test for stability. The bridge behaved as predicted by the computer models.

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:	Stringers - 2-1x8 in two parallel rows Transverse beams - 2x6 at ends and load points
Deck:	3/8" plywood
Floor Beams:	Main side beams: 2 - 1x8 bolted/glued
Suspension:	Glued/bolted 4-lam circular archs fabricated by students
Unique:	Steel tees used as splice plates and saddles 5/8" steel threaded 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 lumber was pressure treated. Plywood was exterior.

7. Special Considerations
	The re-design as a result of the first load test using steel tees for tension splices and saddles, suspended from 5/8" rods, was a valuable lesson in retrofitting a timber bridge that may have been damaged by overload or deterioration. The bridge model will be used as an ASCE display during open-house weekends for prospective students at Mississippi State University.