A Hands-on Project for a Wood Structures Course

The material behavior of wood used in structural applications is a complicated topic. The strength values differ in each direction and for each type of loading as opposed to the relatively simple yield and fracture strengths of steel, or the trusty compressive strength of concrete. Professors at two universities have implemented a hands-on project in the Structural Wood Design course at their respective universities with the objective of stimulating critical thinking in relation to the behavior of wood structural members. Teams of four to five students are given a list of available wood members to choose from including dimension lumber, plywood, OSB, and sets of nails and wood screws. The teams are then tasked with building beams using their chosen members to span a given distance and fit within designated height parameters. Once the beams are constructed, they are load tested using a hydraulic ram. The team whose beam has the highest capacity to weight ratio receives a bonus on the assignment. Each group submits a report outlining their thought process for design, experience in construction and testing, and the lessons learned. The project not only stimulates critical thinking about wood behavior, but requires careful planning ahead to meet the design goals with different possible combinations of members. It also provides hands-on experience hammering in nails and installing screws, something which many students have never experienced. The students are able to see different wood failure types first-hand, which provides a visual and memorable reference point for in-class discussion. Direct assessment of student performance is made using the structural capacity to weight ratio of the resulting beams. Indirect assessments are made using a survey administered through Google Forms. Student performance was assessed at each individual university and performance is compared between the two distinct groups of students. Student comments provided in the assessment survey indicate that the students perceive the project as providing valuable practical experience and a useful contribution to their learning in the course. Introduction Wood products are used for approximately 90% of residential construction and 11% of nonresidential structures in the United States [1], yet studies have shown that only just more than 50% of civil engineering programs offer a course in wood design [2]. Design of wood residential structures to withstand major wind events, such as hurricanes and tornados has been discussed more frequently in recent years [e.g. 3, 4] and cross-laminated timber has great potential for larger structures in the future [5]. Engineers with a strong background in wood design are a valuable asset to the wood construction industry. Structural behavior of wood can be a difficult topic for students to grasp due to its anisotropic material behavior. This behavior contrasts with the relatively simple descriptions of steel and concrete material properties used for designing structures. The strength of wood varies in each direction and the number of failure mechanisms can confuse students compared to the trusty yield strength of steel and compressive strength of concrete. Wood design requires consideration of as many as six different strength properties, all with adjustment factors for different conditions. University students are often exposed to projects that use wood on a small scale to illustrate the principles of mechanics or the basic design process [e.g. 6, 7]. However, even by their senior year, many civil engineering and architectural engineering students have never observed, much less participated in actual construction of full sized structures, whether wood or otherwise. Laboratory projects that require the students to build their own specimens and test them provide the students with not only a visual example of material and structural behavior, but a valuable glimpse into the requirements for construction. A perspective into the difficulties of actually building something the students draw on paper is valuable to their learning how to produce a design that can be easily built. It also provides an opportunity to observe the effects of construction errors on overall performance. Project Description A very similar project was utilized in the Wood Structures course at both the University of Oklahoma (OU) and Mississippi State University (MSU). The University of Oklahoma is a public research university located in the suburban city of Norman, OK, with a population of approximately 118,000 and part of the Oklahoma City Metro area with a population in excess of 1 million. Mississippi State University is a land-grant university in a rural area near Starkville, MS, a town with a population of approximately 24,000. The locations and history of the universities attract somewhat different demographics, but the two universities are in states with similar characteristics, are both public universities, and have similar sized civil engineering departments with 436 undergraduate students at MSU [8] and 417 at OU in Fall 2016. The purpose of presenting the project as performed at the two universities is to illustrate how a similar project can be integrated in slightly different course contexts and adapted to the available resources, student populations, and other constraints. Both assignments had very similar objectives, methods, and assessment. The Structural Design – Wood course at OU is a required course in the architectural engineering program and is a professional elective in the civil engineering undergraduate and graduate programs. The course typically has between 30 and 45 students, approximately 30% of whom are architectural engineering students, 50% civil engineering students, and 20% civil engineering graduate students. All students in the class were required to complete the project. The Wood Structures course at MSU is an elective in the civil engineering program, and all students in the class were civil engineering majors. There were 43 students in the class, a combination of undergraduates and graduate students. The undergraduates were required to do the wood beam project, while three of the graduate students chose to join them (in addition to a different project they were asked to do). The Structural Design – Wood course has been taught every year at OU for many years, but Fall 2016 was the first time Wood Structures was taught at MSU in more than ten years. The project described in this paper was first successfully utilized at OU in Fall 2015, but the results described are primarily derived from the experiences of Fall 2016. The overall goal of the project was for the students to work as a team to design, build, and test a composite wood beam using materials provided by the instructor. The OU project had two iterations, one at the beginning of the semester to provide an introduction to wood behavior and one at the end of the semester to allow the students to use what they had learned in the course in their decision making. It also had a number of constraints whereas the MSU project gave students more open ended design options. The OU project (assignment details provided in Appendix A) had the following requirements: The beams must be 8 ft (96 in.) long Groups were provided with four wood components and a bag of screws or nails. The components available were 2x4, 2x6, 2x8, 16 in. wide pieces of 5/8 in. plywood, and 16 in. wide pieces of 7/16 in. OSB. Groups must use at least three of the provided wood components. Span length of 90 in. The early semester iteration required the students to “draft” fantasy football style from a limited number of each of the allowable pieces while the second iteration gave the students free reign to choose any of the listed components. The numbers available in the draft were ten 2x4, four 2x6, four 2x8, eight 16 in. wide pieces of 5/8 in. plywood, six 16 in. wide pieces of 7/16 in. OSB sheathing, four bags of thirty 10d common nails, and four bags of thirty #9 x 3 in. wood screws. The number of screws or nails in each bag was increased from thirty to fifty for the late semester iteration. The draft format of the project forced the students to plan ahead as to what materials they could potentially have to work with and consider multiple options. Students were provided with very little information on behavior and design prior to the early semester iteration in order to foster their full creativity. Most teams were not able to obtain their first choice of members in the draft, which forced them to consider an unexpected change. The MSU project (assignment details provided in Appendix B) had the following requirements: Beams must be exactly 12 ft (144 in.) in length. The maximum width and depth was 6 in. and 12 in. Span length of 11.5 ft (138 in.) Connections can be made with nails, screws, bolts, and glue. The beams constructed at both universities were tested using hydraulic actuators and deflection was measured at specific points during testing. A single point load at mid-span was used at OU and third point loading was used at MSU. Both projects required the teams to submit a brief report summarizing: materials and design process, what the team learned through the process, and design details in the form of drawings of the beam. The common performance metric used for the projects at both OU and MSU was the maximum load to weight ratio, which provided an indication of material efficiency. The students at both universities were also required to take a survey after the project, administered using Google Forms [9] to assess their perception of the impact of the project on their learning in the course. Results The designs produced by the students were varied, but followed a number of similar patterns. For the early semester iteration at OU, many students constructed T-beams or I-beams based on their experience in steel and concrete courses. The variation in construction types a