2012 COMPETITION RULES AND INSTRUCTIONS
The competition will consist of the construction and testing of a model timber bridge on the home site of each team.
The competition is open to all student chapters of American Society of Civil Engineers and Forest Products Society in the United States and Canada. Joint (ASCE/FPS) and multiple entries from one school will be accepted.
Each contestant (team) will be required to design, build and test a bridge constructed from wood structural members. The wood used in this project must be from a commercially available species. Be sure to check out our list of more than two dozen links to wood products design data, technical values, specifications, treatment information, supplies, etc. on the main page for the Competition. Contestants may use donated materials and/or services, however, donated services may not include any form of fabrication or preparation of composite bridge members.
One of the new Scoring Criteria for 2012 is “Durability” (see Awards: Performance Awards, below). The treatment of wood members is not a requirement, but contestants must fully address why treatment was not selected and how their bridge will perform in a real-life situation in their locale, considering moisture, temperature and other factors that impact the durability of bridge members. Some locations with low moisture and cold temperatures may not require treatment to AWPA Standards in order to achieve adequate performance throughout the bridge’s expected life. In fact, some teams may find it hard to secure bridge materials within their area that are treated. This change is being implemented to facilitate their entry in this Competition.
This change is not intended to approve wholesale abandonment of the merits of proper treatment of wood members. Teams that do not address this durability and treatment issue adequately will receive low scores from judges in this area. Contestants are strongly reminded that most Competition bridges find an after-life following the Competition testing (trail bridges, etc.). Use of untreated bridges in areas that require treatment will not only negatively impact Judges’ decision, but will also tend to eventually contribute to a negative opinion toward wood as a competitive construction material when these bridges begin to fail, short of their design life. Another factor is the obvious safety issue.
Contestants should consider, where applicable, treating all wood members to AWPA standards. Retention levels for bridge members not in contact with the ground (deck, rails, upper trusses, etc.) may meet "above ground use" standards. Retention levels for bridge members to be in direct contact with the ground should meet “ground contact” standards. See www.awpa.com for details on ordering publications and standards or go to Western Wood Preservers Institute then select preservative type for standards tables.
Since all the most common procedures for meeting AWPA standards require pre-treatment in a pressurized environment to attain adequate retention levels, the treatment type and process should be part of the bridge design process, rather than a post-treatment alternative. There are plenty of safe treatment materials available, so student safety should be considered, but not prohibitive.
Likewise, the life expectancy of all metal fasteners, cables, plates and other non-wood components should be considered for all bridges, since all bridges are assumed to have a “life after competition”. These factors should be considered in your discussion of "Bridge Durability" in the Online Entry.
Design Span: 4.0 meters from center line to center line of supports. The maximum length of an individual piece in any member shall not exceed 3.2 meters. There is no length limitation on built-up and laminated members provided that the individual pieces, including plywood, used in making the member do not exceed the specified maximum length. Maximum width of supporting base plates is 60 mm. There is no length constraint on cables, straps, rods or other tensioning devices.
Horizontal Clearance: 1.3m inside curb to inside curb.
Special Consideration for Varying Bridge Length and Width: Since most Competition bridges are placed into a real-life use situation following the Competition and since some of these real-life situations may require a bridge of different length and/or width than that specified in Competition Rules, contestants will be allowed to increase (but not decrease) the specified bridge Design Span (4.0 meters) by up to 50% (to maximum of 6.0 meters) and/or also to increase the specified deck Horizontal Clearance (1.3 meters) by up to 50% (to maximum of 1.95 meters). Remember than the maximum allowed deflection for each parameter remains at "BRIDGE SPAN divided by 400" and "DECK SPAN divided by 100". All bridges will then be scored in the Bridge Weight criteria by weight per square meter (Bridge Design Span X Horizontal Clearance).
Vertical Clearance: 2.5 meters from deck surface (overhead clearance).
Depth of Understructure: Maximum of 500 mm at center-span and 1000 mm at support base measured from top surface of deck to lowest point of support structure.
Test Load: 20 kN for 1 hour. (See test setup for location of loading blocks.)
Load Application and Deflection Measurements: The load will be applied in 4 equal increments of 5 kN each, with the full load of 20 kN being achieved in not less than 5 minutes or more than 20 minutes. Deflection readings will be recorded at each 5kN load increment. Then, four deflection readings shall be recorded at 15-minute intervals during the 1-hour full-load duration.
Maximum Vertical Bridge Deflection: Maximum allowed bridge deflection is Design Span divided by 400, as recorded at midspan of the longitudinal beam receiving the greatest loading. Subtraction from deflection due to compression of supports will not be allowed. If two or more longitudinal beams are predicted to receive equal loading, select only one to monitor, or monitor all such beams and submit average deflection (contestant's choice).
Maximum Vertical Net Deck Deflection: Maximum allowed net deck deflection is Deck span divided by 100, with deck span being measured as the shortest side of the largest “deck panel” formed by 2 longitudinal members and 2 transverse members, if applicable. "Deck panel" is defined as any area of clear-span deck bordered (i.e. defined) by the 2 nearest longitudinal bridge support members and the 2 nearest transverse support members, if applicable. In other words, deck span is the distance between points monitored by the 2 gauges at points 3 and 4 below. However, note that deck span is actually measured from inside structural member to inside structural member. If largest deck panel is a cantilevered section of the bridge, then one side is defined by the curb.
Gross deck deflection shall be measured under the centroid of the loading point placed where the deck is calculated to experience maximum deflection under full loading if the 4-point was moved anywhere on the deck. This point should be the same as the center of the largest “deck panel” described above. The selected loading point must be at the deck’s weakest point. It must be halfway between any transverse members such as floor beams, deck stiffeners, cross-bracings, diaphragms, etc. that make contact with the deck’s underneath surface. It must also be halfway between any adjacent longitudinal support members.
Net deck deflection shall be determined by subtracting the average of the deflections recorded in the 2 bridge structural members forming the longer side of the largest bridge “deck panel” as recorded at midpoint of the longest sides of the “deck panel” and as measured by gauges at points 3 and 4 below. See “Test Setup” sketch for details on placement of the 4 loading points, size of bearing plates, etc.
Note that more than one loading setup may be required to properly measure both bridge deflection and deck deflection at their weakest points, i.e. at points of expected maximum deflection. Some designs may, however, allow for one loading setup to monitor both defections. If needed, the 4-point loading setup may be moved as a unit transversely only to monitor Maximum Vertical Bridge Deflection, but it may be moved as a unit both transversely and longitudinally to monitor Maximum Vertical Deck Deflection, thus placing any one of the four loading points over the center of the largest “deck panel".
Drawings must clearly document location of load points. Location of all monitoring gauges for each loading set-up must also be shown as follows:
Note that distance between point 3 and point 4 is Deck Span. Net Deck Deflection is deflection measured at point 2 subtracted by the average of the two deflections measured at points 3 and 4. Failure of drawings to clearly document location of below 4 gauge points and the location of the 4 loading points (at one or both setups as applicable) will result in disqualification. Disqualification may also occur if photos “c” and “d” below (See Documentation) contradict drawings.
Bridge Deck: The bridge deck does not have to be wood, but note 25% by weight nonwood restriction on total bridge weight. Any material can be used as long as: it is designed to effectively transfer loads at all locations on its surface to the support structure, is not an open grid, can be treated to withstand weather-related deterioration, can withstand repetitive traffic loading and wear, and is capable of supporting the complete 4-load combination moved anywhere on the deck surface. In other words, it must work in real-life application! The maximum length per piece limit (3.2 meters) still applies to deck materials. The deck must be uniform in thickness, material, etc. throughout (i.e. “beefed up” deck in the area of the load point selected for gauging deck deflection will cause disqualification).
Prestressing: Prestressing will be allowed provided it is done 48 hours before testing.
Bridge Weight: Bridge must be weighed before testing and must include all bridge parts forming a part of the bridge as a structural system. Note that total non-wood components cannot exceed 25% of total bridge weight.
Curb: The curb does not need to resist a force but must be connected to the bridge. The curb may be a part of arch or truss members. Curb material must meet same requirements as Deck except for load-bearing, but can be a load-bearing member. It must have a minimum size of 40 mm x 80 mm (2 x 4).
Contestants will be required to submit by email:
Following materials should be mailed to reach Competition coordinators by deadline:
A technical report must be submitted online via Internet using templates provided (Online Entry) and will include:
A panel of three independent judges not affiliated with any contestant institutions will select the winners. Entries that do not meet all rules and performance criteria will be disqualified for consideration for Performance and Best Design Award but will be eligible to compete for Special Awards. No single entry shall be eligible to receive more than three (3) awards.AWARDS:
Deadline for online entry http://southwest.msrcd.org/timberbridge and receipt of mailed materials is April 13, 2012. Mail to SW Mississippi RC&D, P. O. Box 3670, Brookhaven, MS 39603. Enclose following information with mailed material:
Student Chapter name, address, phone, fax, e-mail. Be sure address is a permanent department mailing address; will be used for mailing awards check.
All materials received by RC&D will become the property of RC&D.
Winners will be announced online by May 1, 2012. In addition, the full entries of all participants will be released online and available for all contestants as well as any Internet user to review. Each can learn from the successes and failures of others! The results will also be publicized through various publications.
Submit questions by e-mail to Bennie Hutchins, or phone 601-748-2622. Check Q & A/Updates regularly for valuable competition updates, rules clarifications, etc.