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 main objective of our design was to make an innovative, streamline, and very efficient bridge. We decided on a timber-concrete composite. Going in we knew we would be disqualified from the best overall design due to the fact that more than 25% of our design’s total weight is not wood, however, we wanted to concentrate on winning most innovative design, and place in practicality, support structure, aesthetics and deflection. Our design is such that it should distribute load across its surface evenly as the entire system acts as a single girder. The bottom half of the bridge is made up of a glulam slab lain on its side. The glulam measures 4’6” x 13’2”, and is composed of laminated, SPF No. 2 - 2 x 10, ripped to ~4 3/8” thickness, all of which is glued together with Resorcinol adhesive. This is then covered by the top half, which consists of a concrete (Approx. 150#/cu. Ft), deck ~2 3/4” (this is an average; the deck is 2 1/2” at each and, rises to 3” in the middle to facilitate water drainage, not for structural purposes). The concrete is embedded with steel mesh and rebar to resist cracking and tensile stresses. The glulam is connected to the deck with 3 evenly spaced rigid steel connectors, which are epoxied into the glulam and protrude through the vapor barrier and into the concrete ~2”.By using the composite, we can incorporate much smaller timbers because we utilize the benefits of each substance; concrete is excellent in compression, and wood is excellent in tension. Since the bottom half of a traditional beam in bending experiences tension - and the top, compression - by forming a continuous joint with a rigid steel connection, we can achieve a very efficient system. To analyze our design we used a program developed by engineers, who are experts in the field of wood-concrete composites. This program consists of an Excel spreadsheet, which allows us to alter the weight, density, and thickness of the concrete, and the type and size of the timbers. After all factors are entered, it yields the total overall deflection, and the shear and tension ratios for the composite. With our current design we hypothesize that we can achieve a 4.04 mm overall deflection under combined full dead and live load conditions. All of our strength ratios are below ˝ of their total capacity, ľ of the concrete is in pure compression, and most of the wood is acting in tension. The amount of concrete in tension is compensated by the rebar and steel mesh embedded within it. Should we increase the amount of concrete by an inch or two, the concrete would move more into compression, and the timber completely into tension, which would make for a much stiffer design. We opted not to do this in order to make the bridge as streamline as possible. The 2x4 curb is pressure treated, but the glulam is not, as the deck acts as a drip edge.

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 Bridge yielded unexpected results during loading. Deflection was regular while the bridge was being loaded (as it reached 2.71 mm) during the next 40 minutes when the deflection should have crept up, it crept down. This could be because of the weather conditions. The bridge was loaded wet, as the hour went by it dried, the weight of the water could have added slight deflection. As the water evaporated the bridge deflection decreased. NOTE: The spike in deflection seen on the graph upon loading to 20kn is extraneous. It was caused when the lifting forks, used to load the bridge, accidentally slammed down on the bridge deck. Please see the Deflection VS Time graph submitted via email to bennie.hutchins@ms.usda.gov

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:
Deck:	3 ˝ in. thick concrete slab connected to wood gluelam beam
Floor Beams:	Full width, full length glulam tension member laminated with resorcinol adhesive.
Suspension:
Unique:	Y Connectors Expanded steel vertically fixed into gluelam beam, poured into concrete

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 2x4 curb is preservative treated, but the glulam is not, as the deck acts as a drip edge which will protect it.

7. Special Considerations
	The technology of designing and building is evolving. We here at the University of Massachusetts, Amherst have designed an innovative bridge that is a different technology from anything we have ever learned. What we have created is an extremely strong and rigid bridge that could work in multiple applications. This design has taught us to be more aware of how to combine wood with other building materials – using their strengths and weaknesses and how the resulting composite can perform in certain situations. We also contributed to service learning with this bridge, in that we as students volunteered our own time to provide a community with a useful bridge that will eventually be used in a park. This technology will become more popular in the future. The National Timber Bridge Competition was a great learning experience for all of us here.