Table of Contents

• Content Standards

• Lesson Title

• Objectives

• Guiding Questions

• Materials

• Activities

• References

•Handouts Title Page

Forces and Loads

Loads

Static Loads

Dynamic Loads

Live Loads

Dead Loads

Tension

Compression

Tension and Compression (Images)

Shear

Shear (Image)

Torsion

Torsion (Images)

Standards

Standards for Technology EducationConstruction SystemsWVEIS 2424

Standard 7: Forces and Loads (2424.S.7)Students will identify and examine the forces and loads acting upon structural elements.

Forces and Loads ObjectivesStudents will:

2424.7.1Differentiate between the forces that act on structures (tension, compression, shear, and torsion), and determine which forces are present in various structural elements. 2424.7.2Differentiate between static, continuous dynamic, and impact dynamic loads, and give examples of each.

Forces and Loads

George Washington Bridge, NYC

Lesson Title

Objectives

After performing several small activities and studying with the handouts the students will be able to distinguish between different forces that are present in various structural elements and will have basic knowledge of different loads that act on structures.

Guiding Questions

• Which forces have you already heard of?

• Where do loads on structures come from?

• Why is it important that Engineers understand the basic principles of physics?

• Can you think of a simple, every day example where we can find tension and compression?

• Do you know of any structures that have collapsed?

Materials

• Rubber band for each student• Marshmallow for each student

• Handouts – (alternatively the applicable slides can be presented

in form of a PowerPoint presentation)

Activities

• Tension: – Students are to link their hands together and pull.

They will feel tension.

– Let students stretch a rubber band. They see tension in action. The rubber stretches, and the band gets longer. It's in tension.

• Compression:– Have students put their hands together and push

hard. They will feel tension

– Give each student a marshmallow to put on the table in front of them. As they push it down with their hand, the marshmallow gets shorter because it is in compression.

References

– http://www.adl.gatech.edu/classes/dci/structur/dci08.html

– http://www.answers.com/topic/shear-stress?cat=technology

– http://www-geology.ucdavis.edu/~GEL1/W03_verosub/G1Hwebsite/buildinggroup/Andrews/challenges.html

– http://www.enm.bris.ac.uk/research/nonlinear/tacoma/tacoma.html

Forces and LoadsForces and Loads

George Washington Bridge, NYC

Forces and Loads

• Forces that act on structures are called loads• Loads on structures come from three main

sources:– Structure weight– Occupants or users– Natural elements

Loads

• Two main categories:

– Static Loads• The effect of the load on a structure

– Dynamic Loads• The permanence of the load

Static Loads

– Static loads change slowly or are motionless

– Static loads can include:

• The weight of the structure• The weight of its occupants• Any furniture or machinery

Dynamic Loads

• Change rapidly or move unpredictably

• Dynamic loads can include:– Wind– Waves– Earthquakes– Traffic over a bridge

Live Loads

• Anything not permanently attached to the structure

• Can be moved or changed over time

• Live loads from natural elements:– Snow, Winds, earthquakes, water

• Live occupant loads:– People, Furniture, Machines

Dead Loads

• Weight of the structure itself

• Includes all structural elements and components, such as

– Roof– Walls– Floors– Foundation

TENSION- The Pulling Force

• Stretches materials apart

• Look for materials in tension in:– Rope and suspension bridges– Telephone wires– Tents– Steel cables supporting a full elevator

COMPRESSION - The Pushing Force

• Compression pushes materials

• Look for materials in compression in:– Pyramids– Telephone poles– Arch bridges

Tension and Compression

SHEAR – The Sliding Force

• Shear causes parts of a material to slide past one another in opposite directions

A road destroyed by shear

TORSION – The Twisting Force

• Torsion is the force that twists a material

Tacoma, Washington, 1940

Torsion movement, twisting motion