Educator: Mondlane.J

Topic : structures

Subject: technology Compiled by Mondlane.J

structuresBy 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.

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.

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.

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.

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.

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.

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.

Activity 2

1. Write down the forces that acting on structures and explain and write one example to each forces.

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.

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