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 bridge is a half-through arch bridge made up of two arches and a deck. The curved, tapered arches consisted of a built up “I” shaped cross section consisting of a web made of three laminates of 3/8”(10m) plywood and a top and bottom flange each made up of three 3/8” (10mm) by 3.5” (90mm) laminates glued in place using WEST MARINE SYSTEM Epoxy. The arches are based on catenary curves and were pattern plotted at full size scale and cut out of plywood. The flange laminates were made by re-sawing and surfacing 2x4's x 10ft into 10mm x 90mm x 2.0 meters. We then glued these 'laminates', cutting end-to-end miter joints and gluing with Epoxy, forming (12qty) 6.0+-meter long laminates. These laminates were then cut and re-glued with offsets at approximate 2/3m intervals so that the joints would be evenly distributed through the length of the arches. The laminates were glued to the arches using Epoxy and clamps. Holes were drilled through the central vertical axis of the arch at three evenly spaced intervals between the arch-to-sub-deck connections. Through these holes 5/16” (8.5mm) threaded rod was hung by washers and nuts and wood blocks to support the transverse 4x6 (100mm x 150mm) beams. The rods are tensioned by tightening the nuts and double nuts are used to prevent the nuts from slipping. These transverse members in turn help support the sub-deck at intervals between the arch-to-sub-deck connections. The sub-deck is made up of five 3.8m 2x6 longitudinal joists connected at the end by a 2x6 nailer. The joists are made up of 2.0 m 2x6s which are glued up, end to end, 8/1 rise/run miter joint similar to the arch laminates. The joists are connected to the transverse nailers by commercial corner brackets on the ends, commercial cross brackets at the 4x6s and commercial joist hangers in the center. The arches are connected to the deck framework with 2 qty 6” x 5/16” galvanized carriage bolts at each arch-to-sub-deck connection. The decking is made up of 2 x 4's milled into ship-lap boards laid transversely across the longitudinal members and connected with deck screws. Various bracing members under the sub-deck are in place to prevent the arches from racking or bending-in towards each other. The curbs are placed, as required, 1400mm apart, and are under the arches.

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 deflection of the bridge was measured using four Dial Indicator deflection meters reading in thousandths of an inch. Because of the design of our bridge, we had to set up two different load configurations. For the first load configuration, for bridge deflection, we set the deflection meter under the midpoint of the center transverse 4x6 girder (which was expected to experience the greatest deflection.) We also placed deflection meters on the longitudinal beam on both sides of the girder. When loaded, the bridge deflected incrementally under incremental weight, but the deflection increased only slightly over the span of an hour. We noticed that unlike last year our arches did not lean inward, probably due to the fact that our suspension cables went directly through the center on the arch instead of hanging off the side like last year. The Second configuration required that one of the load points be place on the centroid of one of the four identical deck spans. Since the transverse girder prevented access to the direct centroid we placed them as close as possible to the centroid of the deck span. We chose one of the inner two spans as we expected the deck displacement to be greater in the center of the bridge than near the sides and also because the span was slightly wider. When loaded, the deck also experienced an incremental deflection on both the beams and the gross deflection meters, but again only slightly over the next hour. The net deflection also increased somewhat incrementally.

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:	3qty 4x6 transverse members supported by suspension rods from arches
Deck:	2x4s milled into ship lap joints and transversing longintudinal beams and attached to sub-deck by deck screws
Floor Beams:	3.8 m 2x6 beams joined end to end with 1/8 rise/run miter joint glued with West System Marine epoxy
Suspension:	5/16" threaded steel rods fastened above arch and below girders with double nuts and washers
Unique:	Curved tapered arches with “I” section made from plywood laminated web and laminated flanges

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 wood was southern yellow pine treated with chromated copper arsenate in accordance to AWPA standards of .25 for "above ground use". This material was chosen because it was affordable and/or donated.

7. Special Considerations
	As a team we have reinforced classroom concepts, notably the affect that moment of inertia can have on a beams deflection. We also learned that tongue and groove joints will distribute loads in both longitudinal directions as compared to ship lap joints that only distribute loads in one direction. We plan to raffle the bridge off to our ASCE professional chapter in order to raise money for 2005