Testing and Analyzing File-Folder Bridges

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Testing and AnalyzingFile-Folder Bridges
A Problem-Based Introduction to
Engineering Every bridge begins in the mind of
an engineer
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Our Purpose

• build and test model bridge members
• apply math, science, and computer technology as
  problem-solving tools
• learn how real bridges are designed and built
  and
• learn how real truss bridges work.

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Overview of the Activities

• Activity 1 Test the strength of structural
  members.
• Build specimens for tensile strength testing
• Build specimens of compressive strength testing
• Use graphical techniques to calculate tensile and
  compressive strength of bridge members
• Activity 2 Analyze and evaluate a truss.
• Draw force diagrams for bridge joints
• Calculate internal member forces
• Calculate factors of safety according to building
  codes

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Activity 1 Goals

• Explain what a truss is.
• Identify the major components of a truss bridge.
• Identify the types of truss bridges.
• Explain the following fundamental structural
  engineering concepts force, load, reaction,
  equilibrium, tension, compression, and strength.
• Explain how a truss bridge workshow each
  individual component contributes to the ability
  of the entire structure to carry a load.
• Explain how construction quality affects the
  performance of a structure.

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Component Parts of a Truss BridgeWhat is a Truss?

• A truss is a structure composed of members
  connected together to form a rigid framework.
  Members are the load-carrying components of a
  structure. In most trusses, members are arranged
  in interconnected triangles, as shown below.

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Component Parts of a Truss BridgeWhat is a Truss?

• Because of this configuration, truss members
  carry load primarily in tension and compression.
  Because trusses are very strong for their weight,
  they are often used to span long distances. They
  have been used extensively in bridges since the
  early 19th century however, truss bridges have
  become somewhat less common in recent years.
  Today trusses are often used in the roofs of
  buildings and stadiums, in towers, construction
  cranes, and many similar structures and machines.

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Component Parts - Elevation View
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Component Parts - Isometric View
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Types of Truss Members
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Connecting the Members Pinned and Gusset Plate
Pinned connections were used extensively
throughout the 19th century. Most modern
bridgesincluding the model bridge we will be
building hereuse gusset plate connections.
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The Foundation
Bridges use two different types of foundations.
The ends of a bridge usually rest on abutments,
which serve two functions simultaneouslythey
support the bridge and also hold back the soil
that is filled in behind them. If the bridge
requires additional support in the middle of the
gap, one or more piers are used, as shown below.
Abutments and piers are normally made of concrete.
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Types of Truss Bridges

• If the deck is located at the level of the bottom
  chord, the bridge is called a through truss.
• A pony truss looks just like a through truss,
  except it is not as high and has no lateral
  bracing between the top chords.
• If the deck is located at the level of the top
  chord, the bridge is called a deck truss.

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Through Truss 15th street bridge, Durango,
Colorado
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Pony Truss - East Sweden, Texas- Pony Truss
Bridge over Onion Creek
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Deck Truss - I91 over the Williams River near
Rockingham, Vermont
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15 of the most common truss configurations
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Typical Connections

• The two isometric drawings below are typical
  gusset-plate connections found at the top and
  bottom chords of the main trusses.

These drawings illustrate the types of structural
members used throughout the Grant Road
bridgehollow tubes for the top chords and
verticals doubled bars for the bottom chords and
diagonals. The drawings also show how two gusset
plates are used at each connection to hold all of
the structural members together.
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Schedule of Truss Members

• The Schedule of Truss Members identifies every
  member required to build the bridge. Note that
  each member is identified by the two letters
  corresponding to its endpoints. For example,
  Member AD is a segment of the bottom chord that
  goes from Connection A to Connection D.