June 22, 2003
June 22, 2003
June 25, 2003
8.379.1 - 8.379.24
Design, Fabrication and Testing of Wooden Trusses for Undergraduate Mechanics
David Hall, Kelly Crittenden College of Engineering and Science, Louisiana Tech University
Abstract The sophomore engineering curriculum at Louisiana Tech University includes a mechanics course that integrates topics from statics and mechanics of materials. This three semester hour course, which is officially listed as 2/3 lecture and 1/3 laboratory, attempts to seamlessly integrate lecture, laboratory, and group problem solving. The laboratory component of the course focuses on the design, fabrication, and testing of a wooden truss made from 3/8 inch and/or ¼ inch wooden dowels supported at the joints by small wooden blocks. The truss span, which ranges from 30 inches to 50 inches, and the loading configuration are varied each term. Three potential modes of failure are evaluated, including dowel fracture due to excessive axial stress, dowel pull-out due to shear failure of the glued joint, and dowel buckling for members in compression. Over the past couple of years, we have developed experiments to quantify the tendency of a given member to fail in each of these three modes. Prior to initiating the truss design, students determine the strength and modulus of the dowels, the shearing strength of the glued joints and the buckling strength of the dowels as a function of length. Armed with this information, student teams evaluate potential truss designs and optimize their chosen configuration to support the maximum load or maximum load divided by truss weight. These trusses, which weigh less than 10 lbs and sometimes support over 3,000 lbs, are built using simple tools and require minimal faculty supervision during construction. This paper will describe all aspects of the project, including truss design rules, the method of fabrication, associated experiments, testing fixtures, testing equipment, and testing procedures.
I. Introduction A constant challenge for engineering educators is to incorporate hands-on laboratory and design projects into their courses that appropriately reinforce engineering fundamentals. Busy instructors are often tempted to resort to a traditional lecture based delivery of course material even when laboratory resources are available. Unfortunately, outstanding projects and laboratory exercises are often dropped from courses due to the added effort required to purchase and prepare laboratory materials, develop assignments, check the testing equipment, answer questions, perform the experiments, and grade the resulting reports. To be sustainable, hands-on laboratory and design projects must be affordable and should seek to minimize the added workload imposed on the faculty and staff.
“Proceedings of the 2003 American Society for Engineering Education Annual Conference and Exposition Copyright © 2003, American Society for Engineering Education”
Hall, D., & Crittenden, K. (2003, June), Design, Fabrication, And Testing Of Wooden Trusses For Undergraduate Mechanics Paper presented at 2003 Annual Conference, Nashville, Tennessee. https://peer.asee.org/11638
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