Students conduct several simple lab activities to learn about the five fundamental load types that can act on structures: tension, compression, shear, bending, and torsion. In this activity, students play the role of molecules in a beam subject to various loading schemes.

Engineers must consider many forces when planning and designing materials and structures, including tension, compression, shear, bending and torsion. bending bond compression elastic force inelastic load molecule shear tension torsion Identify the five fundamental loads: compression, tension, shear, bending, and torsion. Explain what is meant by something being elastic and non-elastic (inelastic). Describe characteristics of molecular bonds. Just a class of students! Have you ever seen a collapsed building or a collapsed bridge? What happened? Why did it fail? Materials and structures can sometimes fail when subjected to large enough loads. Each different type of load can cause its own type of failure. Stresses, fatigue, and failure can sometimes be seen with the naked eye on the surface of the member or structure. However, the movement of tiny individual molecules is where the real failure begins. The ability of an object to return quickly to its original shape and size after being bent, stretched, or squashed. A break, split, or crack in an object or a material. The inability of an object to return quickly to its original shape and size after being bent, stretched, or squashed. For this activity, each person represents a molecule of steel inside a steel bar and their arms represent the internal bonding forces that hold molecules together. A molecule is the smallest piece of steel that can exist with the chemical and physical properties of steel - billions of molecules link together in lines to make a piece of steel. Form two lines of 10 people each, lining up side by side, facing each other (see Figure 1). These two lines represent a structural element. Each person must use his/her left hand to hold hands with the person whom they are facing in the other line. Then, each person locks his/her right arm around the arm of the person on his/her right. Four other students act as an applied load. Position one student at each end of both lines, and have them pull with equal force (if possible). Have the students pay attention to what they are feeling while the molecules are being pushed and pulled. Next, form the same lines again, but have the four people applying the loads push equally on each line end. The job of the molecules is to try to maintain their original formation, like a solid, non-elastic object. What type of load did you model this time? What did it feel like to be a molecule inside the material? Now have the "applied load" students pull one line of molecules to the left, and the other line of molecules to the right (as shown in Figure 2). Group discussion questions are embedded in the Procedure section. Describe the fundamental loads and the effect each load (of force) has on a structure or structural member (or component). Give real life examples of tension, compression, shear, bending, and torsion. Evaluate students for participation in group discussions and answering questions.