To design a safer building Lesson 2.3 Failure Analysis To design a safer building Lesson 2.3

Structural engineers Analyze, design, plan, and research structural components and systems to achieve design goals and ensure the safety and comfort of users or occupants. Make sure that the building or bridges does not collapse. Build and test scale models

Failure Analysis Involves building a scale model and Testing it with various loads to see how strong it is and where it breaks, or “fails.” The goal of this process is to identify weak aspects of a design and possible failure sites, so that the design can be strengthened before construction starts.

Design challenge This is a team activity in which you and your teammates will go through the engineering design process to design and build a tower, and analyze how it failed.

1. Define the problem Problem Statement Design and build a prototype of the tallest tower that supports the largest load, with the least cost. Test the prototype and identify the weak points and types of failure. Write a report, describing what you accomplished and what you learned.

Criteria A successful tower design will Be at least two feet high Support a live load of at least a 500ml- bottle of water Be free standing Have a 3”x3” platform to place a load

Constraints The materials used for construction of the prototype are limited to Notebook paper Straws Masking tape Paperclips

2. Research the problems Think about the forces that will act on your tower. When a load is applied, the tower will act as a system to support the load. But different components of the system will be subject to different forces.

Tension A stretching force that happens when you pull the ends of an object apart.

Compression Compression: a squeezing force that happens when you push the ends of an object together

Tension + Compression = bending

3. Develop Possible Solutions Sketch two to three different ideas. Think about the following: Which materials are strongest for use in tension or compression? How can these materials be shaped so they will be stronger? How can the materials be fastened so the joints are strong? What design elements will make the tower tall and stable? What design elements will hold up heavy live loads? What design elements will make it an attractive structure?

4. Choose the best solution Complete the Pugh chart Strength Height Least expensive Sketch the design

5. Create a Prototype Price Discuss what you need 1 notebook paper: $1000 Masking tape, per inch: $600 A straw: $900 A paper clip: $750 Discuss what you need

COMPETE!! Height Strength Cost-effective 4 points for the tallest tower 3 points for second, 2 points for third, 1 point for fourth. Strength 5 points for fully-supported tower 3 points for partially-supported tower Cost-effective 4 points for the cheapest tower (3, 2, 1)

Test and Evaluate Does it Meet the Criteria? Measure the height Calculate the final cost Test for weight.

Failure Analysis Next, you will analyze how and why the building fails and how it can be improved. Carefully add weight little by little until the tower just begins to fail. Record the maximum weight. Identify weak points of the building Identify which forces below cause failure.

Basics of Failure Analysis Has 4 main areas. Failure modes Suddenly or gradually? Failure site Where in the object failure occurred Failure mechanism What physically happened in the failure Root cause The aspect of design, defect, or load that lead to the failure.

Terms of Failure Analysis Elastic Deformation Material returns to its original shape Elastic Limit The material does not return to its original shape any longer. Plastic deformation begins Plastic Deformation The material does not return to its original shape any longer. Failure Point The material breaks

4 Types of Materials Elastic materials Plastic materials Brittle materials Malleable material

Elastic materials Change their shape when under a load, but return to their original shape when the load is removed. Example Rubber, A diving board, Anything else?

Plastic materials Also change their shape but remain permanently deformed Example Melted plastic, plastic bag, anything else?

Brittle materials Break or crumble rather than deform under a load Example Concrete, brick, anything else?

Malleable materials Can easily be shaped by hammering or rolling, and keep their new shape. Some materials can be made more malleable by heating. Example Aluminum foil, copper, anything else?

More types of forces Torsion: Twisting force Shear: It occurs when part of an object is pushed on way and another par of the object is pushed in the opposite direction

Safety Analysis 𝑆 𝑓 = 𝑀𝑎𝑥 𝑙𝑜𝑎𝑑 𝑀𝑎𝑥 𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝑙𝑜𝑎𝑑 (1 𝑙) Buildings, bridges, and other structures are always designed to support more than the maximum weight expected. Find the safety factor ( 𝑆 𝑓 ) for your tower with the formula below. 𝑆 𝑓 = 𝑀𝑎𝑥 𝑙𝑜𝑎𝑑 𝑀𝑎𝑥 𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝑙𝑜𝑎𝑑 (1 𝑙)

Benefit/ Cost Analysis In order to compare different designs, engineers sometimes calculate the “Benefit/Cost Ratio”. Find the Benefit/Cost Ratio = 𝐻𝑒𝑖𝑔ℎ𝑡 𝑓𝑡. 𝑀𝑎𝑥 𝑙𝑜𝑎𝑑 𝑙𝑏 𝑇𝑜𝑡𝑎𝑙 𝑐𝑜𝑠𝑡 $

Communicate Write a report of your tower project. Picture of Failure Analysis Sketch your tower before it fell, labeling the various components of the tower and why they are there. With a colored pen or pencil, identify each of the weak points in the design, writing in the type of the force that caused the failure.

Report should include Why is your tower a good design? Did it meet the criteria and constraints of the problem? How safe is this design? What are the weakest points under extreme live loads? What is the benefit cost ratio of your design?

Redesign If you design and build the tower one more time, how would you redesign the tower so it is taller, stronger, or less expensive?