Failure AnalysisTo design a safer building

Lesson 2.3

Structural engineersO Analyze, design, plan, and

research structural components and systems to achieve design goals and ensure the safety and comfort of users or occupants.

O Make sure that the building or bridges does not collapse.

O 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

OThis 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 StatementO Design and build a prototype of the

tallest tower that supports the largest load, with the least cost.

O Test the prototype and identify the weak points and types of failure.

O Write a report, describing what you accomplished and what you learned.

Criteria

A successful tower design willO Be at least two feet highO Support a live load of at least a

500ml- bottle of waterO Be free standingO Have a 3”x3” platform to place a

load

Constraints

The materials used for construction of the prototype are limited toO Notebook paperO StrawsO Masking tape O Paperclips

2. Research the problems

O 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.

TensionO A stretching force that happens

when you pull the ends of an object apart.

CompressionO 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:O Which materials are strongest for use in tension or

compression?O How can these materials be shaped so they will be

stronger?O How can the materials be fastened so the joints are

strong?What design elements will make the tower tall and stable?

O What design elements will hold up heavy live loads?O What design elements will make it an attractive

structure?

4. Choose the best solution

O Complete the Pugh chartO StrengthO HeightO Least expensive

O Sketch the design

5. Create a PrototypeO Price

O 1 notebook paper: $1000O Masking tape, per inch: $600O A straw: $900O A paper clip: $750

O Discuss what you need

COMPETE!!O Height

O 4 points for the tallest tower O 3 points for second, 2 points for third, 1 point

for fourth.O Strength

O 5 points for fully-supported towerO 3 points for partially-supported tower

O Cost-effectiveO 4 points for the cheapest tower (3, 2, 1)O 3 points for second, 2 points for third, 1 point

for fourth.

Test and Evaluate

Does it Meet the Criteria?O Measure the heightO Calculate the final costO Test for weight.

Failure Analysis

Next, you will analyze how and why the building fails and how it can be improved.O Carefully add weight little by little

until the tower just begins to fail.O Record the maximum weight.O Identify weak points of the buildingO Identify which forces below cause

failure.

Basics of Failure Analysis

Has 4 main areas.O Failure modes

O Suddenly or gradually?O Failure site

O Where in the object failure occurredO Failure mechanism

O What physically happened in the failureO Root cause

O The aspect of design, defect, or load that lead to the failure.

Terms of Failure Analysis

O Elastic DeformationO Material returns to its original shape

O Elastic LimitO The material does not return to its original

shape any longer. Plastic deformation beginsO Plastic Deformation

O The material does not return to its original shape any longer.

O Failure PointO The material breaks

4 Types of MaterialsO Elastic materialsO Plastic materialsO Brittle materialsO Malleable material

Elastic materialsO Change their shape when under a

load, but return to their original shape when the load is removed.

O ExampleO Rubber, A diving board, Anything

else?

Plastic materialsO Also change their shape but remain

permanently deformedO Example

O Melted plastic, plastic bag, anything else?

Brittle materialsO Break or crumble rather than deform

under a loadO Example

O Concrete, brick, anything else?

Malleable materialsO Can easily be shaped by hammering

or rolling, and keep their new shape. Some materials can be made more malleable by heating.

O ExampleO Aluminum foil, copper, anything else?

More types of forcesO Torsion: Twisting forceO 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 AnalysisO Buildings, bridges, and other

structures are always designed to support more than the maximum weight expected. Find the safety factor ( for your tower with the formula below.

Benefit/ Cost AnalysisO In order to compare different

designs, engineers sometimes calculate the “Benefit/Cost Ratio”.

O Find the Benefit/Cost Ratio

Communicate

Write a report of your tower project.O Picture of Failure Analysis

O Sketch your tower before it fell, labeling the various components of the tower and why they are there.

O 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 includeO Why is your tower a good design?O Did it meet the criteria and

constraints of the problem?O How safe is this design?O What are the weakest points under

extreme live loads?What is the benefit cost ratio of your design?

RedesignO If you design and build the tower one

more time, how would you redesign the tower so it is taller, stronger, or less expensive?