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 first step in the timber bridge design competition was to decide on a bridge type. After class discussion, we eliminated truss and kingpin designs because of weight and aesthetics. We then decided on an arch bridge because it would provide a great deal of strength for the amount of material, plus we wanted to take on the challenge of constructing an arch. The deck of the bridge consists of tongue and groove 1x4, screwed down to transverse beams. The 1x4 was the lightest wood product that had not been processed. Due to the processed wood criteria, all other options were eliminated. Between the transverse beams and the deck were fiberglass strips, approximately 5cm (2") wide and no longer than 1.4m long. These were added to prevent deck deflection by adding strength in the tension zone. The load on the deck was supported by transverse beams, which were 2x5 LVL's that were cut from 2x10 LVL's. Sizing of the members was done by checking beams of standard dimensions and load, then scaling down to the size and load for the bridge. Steel rods were tied into each transverse beam (except the middle member), which transferred load directly into the arch. Rods were decided on over cables in order to prevent the large initial deformation of cables. The transverse beams are also tied into longitudinal beams. The longitudinal beams took little to no load since the transverse beams tied straight into the arch. Because of this, the longitudinal beams were cut into sections, eliminating the need to run the beams along the entire length of the bridge. This provides a large reduction in weight. The majority of the load was taken by the arch. In order to maximize stiffness, we decided to use LVL's for the arch members. Due to constructiondifficulty in forming an arch, we decided to use several straight members to create an arch. The LVL's were then placed in between sheets of plywood for added stiffness and aesthetic purposes. To prevent the ends of the arch from kicking out, we added a steel rod that runs along the length of the bridge. The rod runs through the bottom of the arch members, and were tightened to add stiffness to the arch. The ends of the arch are tied into two more transverse beams, located at each end of the bridge. Bracing along the top of the bridge will prevent buckling of the tops of the arch members.

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 final testing of the bridge was performed on March 18, 1999. The design, construction, and testing of bridge were performed by the Timber Design (CE 437/537) class at Ohio University (Winter Quarter), acting in conjunction with the local chapter of ASCE. The loading was performed by piling several pre-weighed bags of gravel symmetrically on a loading platform, which rested on the bearing blocks. In order to measure deflection accurately, various Linear Variable Displacement Transformers (LVDT's) were used. These LVDT's have an accuracy of 0.00127mm(0.00005"). A MEGA DEC loaded with a TCS program was used to record voltage changes, which were then converted to metric deflections. The deflections recorded from the data acquisition system and the four LVDT's have been previously recorded in Table 2. As loading began, two steel I-beams were placed on the bearing blocks and a plywood platform was constructed. Bags of aggregate were weighed and placed symmetrically on the platform. This method continued used until the entire required weight rested on the bridge. Data was recorded at the required loading and time intervals. With the entire load in place, several observations were made. The arches performed perfectly. The joints of the LVL's did not match up with the joints of the plywood, which allowed the load to easily transfer through the arches. The rods were tightened according to specifications in order to create a light camber in the deck. The threaded rods transferred the load from the transverse beams to the arches. No cracking was heard and no buckling occurred. The threaded rods as the bases of the arches ensured the arches did not kick out. The main problem with the design dealt with the deck. In anattempt to form a composite deck, fiberglass was used with the 1x4 decking. The deck had no difficulty supporting the weight. However, at the load points, deflection was noticeable. A depression was formed beneath the loading block at each loading point due to the load. It was observed that the deflection of the deck seemed to follow a nonlinear path during loading, while the longitudinal beams followed a fairly linear path. It was also noticed that when the load was removed, the deck has a permanent deflection of 0.75mm. (This movement also took into account the relative displacement of the longitudinal beams.) Due to the short ten week quarter provided to the class, not enough research and testing time was available to alter the design one 1x4 decking was chosen. As an attempt to strengthen the deck, the fiberglass was used to stiffen the deck and better transfer the load through the deck. As an alternative, a thicker deck material such as 2x6 (possibly lap jointed), or a better composite material, could have been utilized.

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:	1.75 x 4.75in. LVL sections connected by hangers and rods.
Deck:	Tongue and groove 1x4, with fiberglass strips underneath.
Floor Beams:	1.75 x 4.75in. LVL in 1.4 meter sections.
Suspension:	0.25 inch threaded rod connected to arch and stringers.
Unique:	Arch made out of 1.75 x 5.50in. LVL and 0.25in. plywood.

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

7. Special Considerations