Basics of Bridge Building.

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29 Νοε 2013 (πριν από 4 χρόνια και 1 μήνα)

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Basics of Bridge Building.

The essence of bridge building is design.

1.


What 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.


2.

What does “carry a load’ mean?


To understand load, let’s first review force. Force is simply a push or a pull applied to an object.
It has both magnitude and direction. When a truck crosses a bridge, i
t exerts a force on the
bridge. The magnitude of the force is the weight of the truck and the direction of the force is
downward. Mathematically, this is represented as a vector (a quantity which has both magnitude
and direction). In a picture or diagra
m, it’s usually represented with an arrow and a magnitude in
units of force, such as pounds. Three kinds of forces are loads, reactions and internal member
force. Internal member forces are tension (stretching) or compression (squashing). Therefore,
the

load a bridge can carry must be figured out by finding the internal member force of each part
of the bridge. In other words, how much tension or compression can happen before a part of the
bridge breaks (for instance, a steel bar)?

Compressive strength d
epends on the length, shape and area of cross section, and the

type of

material the item is made out of.

Tensile strength depends on the area of the cross section and the
type of material the item is made out of.


3.

So, how do engineers know a bridge is s
afe to drive on?


Each internal part/subsystem has been tested to see how it reacts to force.
The formula that is
used looks like


Factors of Safety = Strength/Internal Member Force