How An Outrigger Works

Abstract

This is an in-class activity where students volunteers, with the use of ski poles, help to demonstrate how an outrigger bracing works on a tall building structure.

Learning Objectives

After this activity, students should be able to:

  • Understand how forces act on structures
  • Understand how outriggers aid in allowing the surrounding structure to resist these forces

Background

Use the First Wisconsin Bank by Fazlur Khan as the model for showing this new form developed for skyscrapers which we will see is called an outrigger.

building

In the center of the building there is a core, typically made of concrete walls surrounding elevator shafts. This core is connection to the outside columns through outriggers (There are also a belt trusses that connect vertical columns horizontally).

demonstration

Compare with flying buttresses in tall cathedrals: respond to thrust of pointed arches but also act like an outrigger system to resist wind loads.

building

Materials List

  • 2 student volunteers
  • a pair of ski poles

Procedure

For this demonstration, two students are asked to first revisit the wind/tower demonstration from The Eiffel Tower lecture to show how wind forces act upon a tall structure.

Again, one student represents the tower structure and the other: the wind.Then have them repeat the demonstration with the "tower" student bracing with the use of the sky poles and have them compare the difference. The difference in support should help the students to visualize how the outriggers absorbs the additional load on a building.

demonstration

From the lecture: The Gothic Cathedral and the Skyscraper

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