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6. Structural elements

Talking book

In this unit, we have seen different types of structural elements. Now, let's look at the most important ones according to their function.

6.1. Columns, pillars and pilasters

Talking book

These are vertical elements that support the weight of the structure on top of them and transfer it to a lower level or to the foundations.

They resist compression stress and, depending on the historical period, are made of stone, reinforced concrete or metal.

Pillars are round or rectangular.
Columns are cylindrical and usually have a decorative as well as structural function.
Pilasters are columns or pillars which are part of the wall.

6.2. Beams, joists and lintels

Talking book

These are linear horizontal elements that keep a space between two supports.

Beams sit on pillars and transfer the weight of the slabs or the roof.
Joists are smaller beams within slabs that carry the load to the beams.
Lintels are used to create open spaces between columns for openings, windows or doors in walls. They were also called architraves in classical architecture.

These elements bear bending stress and nowadays they are made of steel or reinforced concrete. Remember that concrete resists compression and the steel rebar framework resists traction.

In ancient times, when stone was the most common construction material, lintels could not be very long, so the openings they made were very small.

Conjunction so to express reason for something

...resist compression stress and so are usually made of materials like stone

6.3. Arches and vaults

Talking book

These are two –or three– dimensional curved elements, which are used to cover the space between two walls or columns. The pieces in them resist compression stress and so are usually made of materials like stone.

Arches are built using a temporary structure called a centring, which holds the pieces (the arch stone) that form the arch in construction. When the top piece, called the key stone, is in place the arch can stay in position on its own. This means that it is self-supporting and it requires no mortar or cement.
Here are some types of arches:
Vaults are built by using a series of arches in a line (a barrel vault) or intersecting arches (a rib vault).

6.4. Buttresses and flying buttresses

Talking book

These are used to hold up the loads of arches and vaults.

A buttress can be part of a wall and is used to reinforce the wall and transfer the loads from the vaults to the ground.
A flying buttress is an exterior arch which bears lateral loads from the vaults to the buttresses, which is the vertical element which holds them up.

Nowadays we use reinforced concrete as well as stone.

6.5. Load-bearing walls and retaining walls

Talking book

These are vertical elements that transfer loads to the ground.

Load-bearing walls bear compression stress and can be built with materials like stone, bricks and adobe.
Retaining walls bear bending stress because of the force that the earth puts on them. They must be built with reinforced concrete or with a large amount of material.

6.6. Concrete slabs

Talking book

These are horizontal elements working in two directions. They transfer the loads that the rest of the structure bears and they resist bending stress. They are made up of:

Joists: carry the weight of the slabs to the beams.
Blocks: fills the space between the joists. They are hollow elements that help to make the slabs lighter.
Reinforced concrete surface: makes the slabs even.

6.7. Footings, plinths, shallow foundations and piles

Talking book

The purpose of these elements is to distribute the load of the structure, building or bridge so that it does not sink. These elements together are called the foundations. There are different types:

A footing is a type of platform at the base of a structure that holds the weight of the rest of the structure.
Plinths are rectangular blocks of concrete under columns.
Shallow foundations are made of concrete that sit on the ground and are used to distribute loads. They are usually used for soft ground.
Piles are columns driven deep into unstable ground or clay, so that they rest in firmer soil.

6.8. Suspenders and tension rods

Talking book

Structural elements are classified by the following functions:

Resisting compression stress: pillars, columns and pilasters.
Creating a space between horizontal elements: beams, joists and lintels.
Filling the space between two walls or columns with a curved element: arches and vaults.
Holding up the loads of arches and vaults: buttresses and flying buttresses.
Transferring loads to the ground: load-bearing walls or retaining walls.
Transferring the loads from slabs: joists, blocks and reinforced concrete surfaces.
Distributing loads in the ground: footings, plinths, shallow foundations and piles.
Resisting traction stress: suspenders and bracing.

These are linear elements, normally steel cables, whose function is to resist traction stress. They are used in suspended constructions and in bracing.

Activity 33
Where is the centring of the arch in construction in the picture?

Activity 34
What types of arches can you see on the front of this building?

Activity 35
Select the correct statement regarding the types of stress a structure bears.

Activity 36
Using the development plan of an arch stone you can see, build an arch using five pieces. Put it together horizontally on a piece of cardboard. Raise it carefully and check that it stays up by itself without any glue.

Activity 37
In the photo, we can see the formwork of the main beams of a concrete slab. Find the start rebars of the pillar, the rebars of the beams, the temporary jack posts and the safety net. Match to make sentences.

Activity 38
Identify the structural elements. Match the material used in each part of the structure with the types of stress each part bears.