Forging new generations of engineers Strength of Shapes Principles of EngineeringTM Lesson 5.1 - Statics Forging new generations of engineers Project Lead The Way, Inc. Copyright 2007

Strength of Shapes

Forces in Tension and Compression A force is a push or pull exerted by one object on another. A tensile force expands or lengthens the object it is acting on. A compressive force compresses or shortens the object it is acting on.

Forces in Tension and Compression The rope is in tension The stand is in compression.

Forces on Shapes Which shapes are strongest? Which deform when in tension? Which deform in compression? It depends on where you hold it and where you push or pull (top, bottom, sides…). Insert pipe cleaners into plastic straws and twist the ends to test different shapes. What happens?

Forces on Shapes Engineers consider shapes under heavy loads when building large structures. Triangles are the only shapes that cannot be deformed without changing the length of one of its sides Arches are strong because the force resulting from a heavy load placed at the top spreads down the sides to the foundation. A group of arches placed around a central point creates a dome, which distributes loads down through curving sides to the foundation.

Triangles Bank of China Tower Eiffel Tower Stansted Airport Centre Pompidou

Iron Bridge at Coalbrookdale Arches San Lorenzo, Florence Musee d'Orsay Roman Colosseum Iron Bridge at Coalbrookdale

Pantheon, Paris - Interior Domes Florence Cathedral Pantheon, Paris - Interior

Applications Psyclone Rollercoaster- triangles in structure US Pavilion at Expo '67 - spherical structure made of triangles Dome tent -poles bent into arches with nylon fabric in tension. Campo Volantin Footbridge - arch with cables in tension