3. structures
By the end of this module you will able to:
Identify different types of structures
Explain why the designs changes over the years.
Explain why structures sometimes fail.
Explain what civil engineers do.
Describe different types of forces that act on structures.
Explain how to strengthen beam.
Explain how to join solid structures.
Explain what is the stability is and how an object can be made
stable.
Explain how the centre of gravity influences the object stability.
Design and make a model arch bridge.
4. Different types of structures
A shell structures holds and protects a load that is
inside it. A shopping bag holds shopping inside it,
packaging or container.
Some structures are solid, like the walls dams or
building, some statues, and platform of railway.
Natural structures such as spider web supports
the spider and its prey.
Artificial structure are humans have made, like
buildings, machines and furniture.
5. Structures failure
Structural failure occurs because of poor design,
fatigue or failure of the materials or joints.
There are two forces that act on structure
Dynamic forces
Static forces
Dynamic forces are forces that move around and
do not always act on the same part of the
structure.e.g weight of person moving around chair.
Static forces are forces do not move and are due
to structure own weight or the load that it supports.
6. Continue…
Structural failure occurs when the materials that have been used to build
the structure are not strong enough to withstand the forces acting on
them. what would happen in each of the following cases?
A building contractor uses inferior materials to save money. the bridge
collapses while the workers are still working on it.
A suburbs is build downstream of a huge dam wall. The wall has slowly
begun to crack, but nobody has noticed.
Structural failure may also occurs when the joints are not strong enough.
What would happen in the following cases?
A temporary stage ,which has been built for the inauguration of a new
president or performance of famous pop group, collapses during the
function.
A soccer stadium collapses during an international match.
7. Discuss examples of structural
failure
1. Name examples of accidents that
were caused by structural failure.
2. Explain the consequences of each of
these failures.
8. What engineering design do
A civil engineer specializes in the design of structures like houses and
buildings roads and bridges, dams, water reservoirs and pipelines. He
or she ensures that the builders, electricians and plumbers meet all the
requirements to prevent structural failure.
An architect or engineer must take the following factors into account
when designing a structure: the selection of suitable materials, the
properties of materials , method of construction, cost of the materials
and the availability of the materials.
9. Different types forces acting
on structures
Force that cause parts of structure to stretch are called tensile
forces.
Forces that squash or compress parts of a structures are called
compression forces, example the weight of roof of house wall.
Bending forces make parts of structure bend, for example a builder
standing on scaffolding plank will cause plank to bend slightly.
Forces that twist parts of structure are called torsile forces.
example when you turn a key in lock or turn door knob , you are using
torsile forces.
Shearing forces causes two parts of object to slide over each other,
example the weight of the gate pulls it away from the post it is hanging
on.
10. Activity 2
1. Write down the forces that acting on
structures and explain and write one
example to each forces.
11. Strengthening beam
Originally all beams were made of solid materials . This made them
heavy and expensive.
Engineers prefer beams that are strong enough to do the job, but
weight as little as possible. This gives them a better strength to weight
ratio. engineers changed the cross-section of beams to achieve a goal.
Now they use beams that are shaped in round and square tubing, angle
girders and I-girders.
Angle girders are beams that have shaped like a capital L
I- girders are beams that are shaped like a capital I
Square tubing beams are beams that look like a hollow square
from each end.
12. Stability
If you bumped against the table A in the illustration below , the table
might move slightly , but it would not fall over. If you bumped against
the table B not fall over easily is stable structures. A structure that fall
over easily is unstable. Why are some structures stable and others
unstable?
B
A
