Method of Joints: Theory and Practice of Designing, Building, and Testing Trusses

Abstract

The authors of this article, like many of us, are proponents of engineering education but are also proponents of shop skills, craftsmanship, technological literacy, and the tacit knowledge and skills developed through applying sound theories during practical hands-on learning. The authors believe that engineering is an important aspect of our discipline, but so are the application of thinking, tool skills, measurement, geometric construction, manufacturing, instrumentation, testing and analysis, mathematical and scientific theories, and many other hands-on, minds-on skillsets that all need to maintain association with our discipline. As the authors are proponents for engineering education that is done well, they have provided an explanation of truss design using the Method of Joints that combines the application of practical hands-on learning with sound mathematical and scientific theory. The Method of Joints is a static principle stating that all joints in a truss must be in equilibrium. This means that forces on truss members of each joint must combine at the joint to equal zero for all joints. The Method of Joints will allow students to design trusses to meet specified criteria using mathematical models. The process of designing a truss to meet specific requirements involves students applying the Method of Joints to create and apply computational models. In the activity students will be able to design and predict the amount of weight causing truss failure, then test their truss to validate their predictions’ accuracy. If students minimize possible errors by building their trusses exactly as designed and calculated, most trusses will fail within 5% of the calculated amount. In two previous articles, component force systems were covered to help with the understanding of forces systems involved in truss design and the Method of Sections was also presented as another method for solving for forces in a truss (Huges & Merrill, ITEEA 2020, pp. 16-22). For a more thorough understanding of truss design, it is recommended that the reader review these two previous articles

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