Structures & Buckling Developed by: Lane Azure Bob Pieri Chad Ulven

What causes structures to buckle? What is Buckling? Buckling – Buckling is the instability of a long slender member subjected to an axial load, leading to an out-of-plane, sudden failure. What causes structures to buckle?

Reasons Structures Buckle Off-axial loading Improper design Local material yielding Corrosion Dramatic environmental events Impact events

Calculation of Critical Load Pcr = Critical Load E = Modulus of Elasticity L = Column Length I = Area Moment of Inertia

Terminology Modulus of Elasticity (E) - The mathematical description of an object or substance's tendency to be deformed elastically (i.e., non-permanently) when a force is applied to it. Area Moment of Inertia (I) - A property of a cross section that can be used to predict the resistance of beams to bending and deflection, around an axis that lies in the cross-sectional plane. Modulus of Elasticity (E) - The mathematical description of an object or substance's tendency to be deformed elastically (i.e., non-permanently) when a force is applied to it.

Activity 1: Preparation of a Structurally Sound Tower Summary Students will build their own towers using some of the techniques they have learned. The materials will consist of balsa wood and glue. General guidelines are provided, but the students will have a lot of freedom with their design to encourage them to implement what they have learned about structural engineering. Engineering Connection Students are placed in the role of structural engineers for balsa wood towers in this activity.

Activity 1: Preparation of a Structurally Sound Tower Requirements Sheet materials should not be used to gain height. They should be limited for use as the base, weight platform (apex), and to reinforce the rod structure (gussets). The base of tower is limited to 8 inch by 8 inch. The minimum height of tower is 15 inches. The maximum height of tower is 48 inches. The amount of glue sticks that can be used is limited to two (2).

Activity 1: Preparation of a Structurally Sound Tower Procedure Divide students into groups of 3-4. Allow 15 – 30 minutes to research on the internet possible ideas for strongest structural designs. Ask each group to sketch their tower design on butcher paper. It is important to realize there is a limited supply of balsa sticks, so make sure your design is well thought out. Decide how high each group plans on building their structure. Make sure you have enough material in your kit to build your tower. You may have to decrease sacrifice dimensions in order to make sure the structural integrity of your tower is at its best. Distribute supplies, and instruct students on safety techniques. Instruct students on how to properly cut and glue two pieces of balsa wood together. Ask groups to build the towers on their own.

Activity 1: Preparation of a Structurally Sound Tower Evaluation When you look around, do other groups’ projects look like they may last under stress better than yours? (Which group’s tower do you think will hold the most weight?) What is the height of your completed structure? (Put your answers in inches.) Test each tower to see how much it weighs, and how heavy a load it can handle. In order to test the load, place your tower into the test frame provided. Then, use masses to carefully place a load on top.

WHO WON??? Competition Score Team 1 Team 2 Team 3 Team 4 Team 5 Average

Activity 2: Building a Paper Bridge Summary Students will build paper bridges to emphasize the concept of area moment of inertia (I) and its importance on design of load bearing structures. Engineering Connection Students are placed in the role of design engineers for enhancing stiffness of structures in this activity. Materials 3 sheets of 8.5” x 11” copy or printing paper Glue gun Scissors Wood blocks or books to hold your structure Pennies (supplied by your teacher) for weights Other sources of weights (preferably of uniform size) An electronic weight scale

+ Sandwich Structure Face Core Sandwich Structure Face Sheet CORE Sandwich composites are modeled as I-beams, in which the face sheets act as the I-beam flange, and the core material acts as the beam's shear web. This allows sandwich composite structures to offer high stiffness to weight ratios

Activity 2: Building a Paper Bridge Procedure / Evaluation Make two stacks of books of equal height. Place them 6 inches apart. Make a bridge by putting a sheet of paper across the books. Put some pennies on the bridge. How many pennies can the bridge support before it falls down? What happens if the pennies are in the center of the bridge or spread across the bridge? How can you make the bridge stronger? Do it! Test your bridge again by adding pennies one at a time. How many pennies can your bridge support? How can you change the design of your bridge to support more pennies?

What Did You Learn? Which shapes/structures seem to be the strongest while using the least material? Why? If you were going to tell someone how to build a strong and light tower, what would you tell them?