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 specific report is to demonstrate how the timber bridge was designed, within the restrictions set by the competition specifications. Before the designing process began, the team intended to design and build a bridge that would depict characteristics of the bridge both functionally and aesthetically. The first type of design that came to mind was a three-pinned glulaminate arch. After days of debating the pros and cons of a three-pinned glulaminate arch, the team decided to go with that particular bridge as the primary design. Three-pinned glulaminate arches are used quite frequently in timber bridge design, especially in the Black Hills. Not only does it serve its purpose as a super-structure, it looks environmentally friendly to its surrounding area. Being within the vicinity of these beautiful structures motivated the team to design this type of aesthetically, appealing bridge. The structural analysis program used for this design was RAM Advanse. Not only did RAM Advanse give the team an understanding of how the bridge would perform under loading, it determined maximum deflections throughout the bridge, as well as maximum shear and bending moments along every member distributed by the 20 KN load.As the project progressed, the team designed an efficient mold to match the size of the arch. Eight ½” x 3 ½“pieces of plywood were glued together to form the shape needed for the arch. The components of the glue are Cascophen G-1131A and Cascoset Regular B. Cascophen G-1131A is an alcohol-water, adhesive solution of a partially condensed resin. Cascoset Regular B is a tan powder formulated from paraformaldehyde and serves as a mixing component with the G-1131A. Obviously, deflection was the main priority when it came to designing the bridge. Three-pinned arch bridges are commonly used because minimal deck deflection occurs when tension cables are attached from the arch to the deck surface. To minimize deflection, eight ready rod cables were fastened from the arches to two girders located beneath the deck running perpendicular to the deck. The design included that the deck panels were to run longitudinal to the curb, not transversely. Since the deck was designed based on the longitudinal direction of the deck, a nominal thickness of 2” was used. To strengthen the deck furthermore, the deck panels were connected together by 3/8” diameter wooden dowels every 30-mm. The worst case deck deflection was recorded at the mid-span of the longest deck panel.

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 design of the three-pinned glulaminate arch portrays minimal deflection in the three-dimensional analysis. With the expectations of performing under a 20 KN load, the bridge met all deflection specifications under the design criteria. The timber bridge was tested at two locations. The first four-point test was positioned at the center of the deck. The team was interested to see how the deck would perform with a load of 20 KN placed directly at the center of the bridge. The second four-point test, where the actual deflections were recorded, was positioned at the center of the longest longitudinal deck panel. Based on equations of equilibrium, this is where the worst case deflection would occur. The deflections for the competition were recorded at this location. The rules state that the maximum vertical bridge deflection can not exceed 9.5-mm. Using multiple dial gages that were setup at specified locations, the maximum vertical bridge deflection measured 6.25-mm, which is considerably less than the maximum deflection of 9.5-mm. The maximum vertical net deck deflection suggests that it can not surpass deck span divided by 100. The deck span in the design came out to be 1760-mm. The maximum vertical net deck deflection measured 5.87-mm, which is substantially less than 17.60-mm. Under loading conditions, the bridge exhibited minor deflections due to the strength of the ready rod cables attached from the arch to the girders beneath the deck. The cables stiffened the deck, which prevented any extensive deflection from occurring. Throughout the loading process, the measured deflections increased as predicted and remained under the maximum allowable deflection at each location.Originally, bolt shear was a minor concern in the pin connections. Once shear bolt capacity was determined, shear was not an issue at the connections. The shear capacity came out to be approximately 45-KN (4590 Kg), which is much greater than the total load of 20-KN (2040 Kg). Another concern in our design was how the eight pieces of glued plywood would react under loading conditions. Initially, the glulaminate arches were not going to be treated due to the fact that the team did not know how the arches would perform during testing. After careful thinking, the arches were taken to Wheeler Consolidated for treatment. The team was a little hesitant when the arches returned from the treatment plant, but the treatment had no effect on the arches and the arches performed great. Overall, the design met all expectations from the analysis calculations to the final day it was tested.

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:	Transverse wood specimen located beneath the deck
Deck:	Longitudinal wood specimen ( thickness of 2 inches)
Floor Beams:
Suspension:	Tension cable that strengthens the deck (attaches arch to girder)
Unique:	Glulaminate Arch - Six foot radius arch made of eight plywood pieces

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
	In western South Dakota we have ponderosa pine that is harvested in the local area. This lumber is available and treated with Creosote and Copper Naphthnate in most lumber yards. The local lumber yards have “S.P.S” which stands for spruce pine fur so you never know what species you will receive and it is not available in rough cut full dimension lumber. It is available in green treatment. Wheeler Lumber in Whitewood, SD has Douglas fur in rough cut full dimension lumber and they treat with Copper Naphthnate. Douglas Fur has better strength properties than ponderosa pine so it allowed less material to carry the loads that the competition requires. We also wanted a treatment that would last and was safe to handle. The green treatment from lumber yards is not good in wet areas that a bridge will be in and tends to leach into the ground. Creosote treatment is an EPA controlled pesticide and has several conditions on disposal and is not safe to handle. Creosote will handle wet conditions but will leach into soil and water for many years. Copper Naphthnate is not controlled by the EPA and is much safer to handle. Copper Naphthnate does not leach into soil or water and can safely be applied by hand on any cut ends or holes that are drilled. We had an easy decision in picking Douglas Fur with Copper Naphthnate Treatment.

7. Special Considerations
	After the bridge was designed and built, the team felt that the “Timber Bridge Competition” experience was beneficial as the team moves forward to becoming engineers in the near future. This project prepared the team for real-world design applications and are now ready to take on any challenges that lie before them in the engineering field. This type of project brings out skills that the team thought you never had and tests your ability to perform at a high level in engineering design. The team will take advantage of what they learned from this project and use it in the future. The team has not picked a permanent location for the bridge but have narrowed the selection down to 2 sites. The first location would be on the beautiful campus of South Dakota School of Mines located near the Civil Engineering Building. By having the bridge on display, the team hopes to encourage future Civil Engineering students, preferably freshman and sophomores, to partake in the “Timber Bridge Competition” for their senior design project. Another location would be to have it displayed in Pierre, SD at a children’s center. This decision will take place before May 5th, 2009.