The purpose of this project was to design, fabricate, and load test a 1:10 scale model for a replacement steel bridge. The scale model bridge has a minimum clear span of 18 feet, and will be tested with a randomly placed load of 2500 pounds. Requirements for the bridge as well as scoring criteria were provided by AISC. The scoring of the bridge is based upon deflection, construction time, and weight.
A unique solution using cold-formed, high-strength steel was implemented to minimize the deflection and weight of the bridge. The design was completed using the SAP2000, RISA-3D, and COSMOSWorks software packages. Results from the models were compared to provide independent verification of member forces and deflections. Hand calculations were based upon the AISC Manual of Steel Construction and the AISI Cold-Formed Steel Design Manual.
Fabrication of the bridge was performed in the NAU CEFNS Fabrication and Manufacturing Shop by the team members and volunteers. Load testing was performed at the annual 2009 Pacific Southwest Regional Conference hosted by the University of Hawaii, Manoa.
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This project could not have been either completed or successful with out the help and support of many people, companies, and organizations. For this reason our deepest gratitude goes out to the following:
• Northern Arizona University College of Engineering
Forestry & Natural Sciences.
• Dr. Wilbert Odem, Dr. Joshua Hewes
• CEFNS Manufacturing Shop
• Schuff Steel Company
• Mr. Jay Allen
• Gecko Steel Truss
• Mr. Dennis Smarra
• TOR Engineering
• Mr. Bob Hubbard and Mr. Dave Merrell
• Praxair Welding Supply
• Mr. K. Bryan Noyes
• Prescott Steel and Welding Supply
• Copper State Nut and Bolt Co.
• Danny Harris and Eli Reisner
•
Lastly, we would like to thank the NAU Student Chapter of ASCE and all of our friends and family who supported our efforts.
This year the ASCE Pacific Southwest Regional Student Conference was hosted by the University of Hawaii at Manoa.  This is a three day event where 18 universities compete in several events.  The team
captains are very proud of the results
from this years conference.  This is the
first time in the past several years that
NAU has entered a qualifying bridge. 
Although the bridge did not place very
well in the construction speed category,
the team participated extremely well in
the categories of lightness and stiffness
with 3rd and 4th place, respectively.
Overall the NAU Steel Bridge Team took 7th place out of 18 schools in competition. As a school, NAU took 7th place overall in the PSWRC 2009 Conference.
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EGR Design
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PLAN
PROFILE
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Exaggerated  SAP2000 Lateral-Torsional Frame Buckling
The analysis of the bridge was performed primarily in a simplified RISA-3D model.  79 unique load combinations were applied to the model to determine a full force envelope for all members.  P-δ effects were considered in this model. The force data was output to Microsoft Excel, and summary tables were created for the design of individual members.
A more complex finite element model in SAP2000 was created modeling partial fixities of the end moment
connections, partial fixities of the bracing frame, the proprietary top chord, and the custom tapered
columns. This SAP2000 model was used for verification of the RISA-3D model through member
force matching and for determining the buckling modes. 150 load cases were applied to this
model, using modified stiffnesses from the stressed state of the equivalent static load case
in the buckling load cases to account for P-δ effects on the buckling of the structure.
COSMOSWorks was used in conjunction with the SAP2000 model to determine the partial
fixities of the required moment-resisting connections to increase the accuracy of the model.
The design of the bridge began by investigating a simple beam bridge and 3 different basic truss types: a Pratt truss, a Warren truss, and a bowstring truss. During preliminary analysis, the simple beam and bowstring truss were eliminated for either excessive deflections or fabrication and construction complexity. Through multiple iterations, a combination Pratt and Warren truss was selected to minimize the number of members and connections as well as the inherent stiffness provided.
Each individual member and connection was designed for the maximum compression and tension expected. LRFD design methodology was used, with a 1.2 load factor applied to the 2500 pound loading to be conducted at competition.  An additional accidental eccentricity was applied to compression forces in members to ensure that small variations during fabrication did not cause failure at competition.
20 gage, 45 ksi yield galvanized steel was selected for all tube members while 20 gage, 55 ksi yield galvanized steel was used for the top chord. 14 gage, 36 ksi steel was selected for the connections and columns.