Chapter 6

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25 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Chapter 6

Designing Structural Systems

Terminology

Structure


a body that will resist external
forces without changing its shape, except
for that due to the elasticity of the material.

Structural systems


systems in the natural
and technological world that provide a
means of stability and foundation for
mobility.

Natural Structures

Human Body

Beehives

Snail shells

Spider Webs

Ant Colonies (hills)

Termite trails

Technological Structures

Bridges

Homes

Skyscrapers

Domes

Roads

Phones

Computer Cases

System Failures

Planned Obsolescence


the name given to
the concept of planning the failure of a
technological product after a certain amount
of use.

Durable goods


products that are intended
to last more than three years.

Non
-
durable goods
-

products that are
designed to not last more than three years.

Failures (cont.)

Safety Factor
-

determines how much a
product or an element within a product is
overbuilt.

Forces on structures

Static Loads


loads at rest.

Dynamic Loads


forces in motion.

Internal forces


the molecular makeup of a
material to counter external forces.

External forces
-

loads that are applied to
an object in question.

Equilibrium


when internal and external
forces are equal.

Stress and strain

Stress


the strength of a material (when an object
will fail or break).

Strain


the change in shape of a material caused
by compression or tension forces (how far the
material stretches under a load).

Young’s Modulus of elasticity
-

the measure of
stress and strain of a material.

Elastic stage


point 0 to A where a material will
change shape, but return to normal.

Plastic stage
-

point B, where a material will remain in
its strained shape and not return to normal.

Breaking point


point C, where a material fails or
breaks.



The Five Common Forces

Compression


The inward forces on an object
(pressing down or in).

Tension


the outward forces on an object (the
pulling apart of something).

Bending


when the forces are acting across the
entire material (both compression and tension).

Shear


forces acting in opposite directions but in
the same plane

Torsion


forces that try to twist a material apart.

Structural Components

Beams


Horizontal members that are designed to
resist compression and bending forces. (fig. 6
-
20)
pg 125.

Trusses and Girders


complex beam designs.

Struts


components that resist compression (piers
and columns)

Ties


components that resist tension (cables or
rigid steel elements).

Fasteners


Mechanical: rivets, bolts, screws and
nails; chemical: welds and glues



Calculating Loads

Physical Models

Mathematical models

Computer models

Vector Analysis

Graphical Analysis

Bow’s Notation

Why is all this Important?