Buildings and Structures 1

Elements of Structure and Causes of Collapse

Aim

To provide students with information to allow them to deal with incidents involving buildings and structures safely and effectively.

Learning Outcomes

At the end of the session students will be able to:

• State the main elements of a structure

• Describe the principal causes of collapse

• Recognise the common signs of collapse.

Elements of structure(1)

• Any member forming part of the structural frame of a building

• Any beam or column not being a member forming part of a roof structure only

• An external wall

• A separating wall.

Elements of structure(2)

• Compartment wall

• Structure enclosing a protected shaft

• Load bearing wall or load bearing part of a wall

• A gallery.

Types of load

The function of each element of a structure in most buildings is to carry loads placed upon them, these loads are principally;

• ‘Dead’ load

• ‘Imposed’ load

• ‘Wind’ load.

Dead load

• The weight of all parts of the building

itself that is imposed on the

elements. These are constant.

Imposed load

• Consists of people, furniture, machinery

etc, normally found in the building when

it is occupied.

Wind load

• The load due to the effects of wind

pressure or suction.

Collapse of buildings

• During firefighting operations the risk of collapse must always be considered and watched for

• The principal causes of collapse are;

Overloading

Expansion.

Collapse of buildings

Overloading(1)

• Heavy machinery on upper floors can pose a danger in the event of walls or supports becoming weakened, water deployed in these areas should be removed as soon as possible.

Collapse of buildings

Overloading(2)

• Another consideration is the weight of the water applied to floors. The existing ‘Imposed’ load coupled with the additional weight of water which may weigh several tonnes may load the structure beyond its capacity.

Collapse of buildings

Expansion(1)

• Occurs in two ways either involving the contents of a building or involving the structure of the building itself.

Collapse of buildings

Expansion(2)

• Water directed on absorbent materials causes the material to expand which can exert pressure to walls, ceilings and floors. Examples of such materials are;

• Tea, hops, wool, jute, paper, wood and pulp.

Collapse of buildings

Expansion(3)

Other expansion hazards include;

• ‘Curtain’ walls expanding, displacing glass panes or facing panels

• Expansion of steel joists pushing walls out of perpendicular

• Heating of one side of wall only.

Common signs of collapse

• Cracked or dropped arches over doors, windows or other openings

• Spalling of stonework, falling of cornices

• Sagging floors or beams, or gaps between floors and walls

• Displacement of steel or cast iron pillars supporting joists or beams.

Signs of collapse.

Column buckling

Bulging wallDropped arch

Floor sagging and pulling out wall

Displaced column

Cracks in wall

Confirmation Assessments will be based on this lesson and the corresponding study note

Learning outcomes

• The main elements of a structure

• The principal causes of collapse

• The common signs of collapse.

THE END