4.1. Types of structures.

What types of bridges do you know? Order them from ancient times to the present day. What differences do you see between them? 

Over time, human beings have improved their ability to build structures. At the beginning they needed a lot of material for their construction, but advances in the knowledge of the structures and their operation, together with the appearance of new materials, allowed to create lighter and resistant structures. 

Mass or massive structures

At first, the structures were made by concentrating a lot of material, leaving hardly any gaps, placing blocks of stone or clay on top of each other (as in the pyramids) or digging in the rock. Greek temples of stone and wood, stone blocks of pyramids are some examples.

These type of structures are solid, heavy and very sturdy structures. Examples including walls, dams, etc.

Vaulted structures 

The vaulted structures are formed by arches and vaults and are based on the use of cut stones and placed in such a way that only the compression effort that is well supported by the stone appears in them. The Romans employed the semi-circular arch in the construction of bridges: semi-sterily covered aqueducts, and the barrel vault and dome. Semispherical to cover basilicas and pantheons. Later, pointed arches and cross vaults of different styles were used in the construction of mosques and cathedrals. Today they are still used in emblematic buildings. 

Truss or triangulated structures 

They are formed by bars, usually metal or wood. They are lightweight and sturdy. Triangulation makes the structure non-deformable, which is a good solution for the construction of bridges (triangulated beams), covered with large lights (trusses) and vertical structures, such as towers and scaffolding. 

The discovery of steel and its application to this type of structures allowed great works, such as the Eiffel Tower. 

Suspended  or hanging structures 

These are held in place by cables and suspenders attached to study supports. Examples include suspension bridges, tents, marquees, etc.

Cables are used to build them, from which the structure hangs and which are called suspenders. When they can be adjusted, stretching them more or less, they are called tensioners. The cables only resist traction efforts, but they have the advantage of being able to adapt their shape to the loads they receive at all times and being extremely light. 

Braces are used to hold bridges, tents, antennas and towers.  There is a wide variety of hanging structures that can cover large spaces, such as stadiums or pavilions, without using intermediate pillars. 

Frame structures

These structures are formed by vertical and horizontal elements: columns and beams that act as supporting elements. One example might be the structure of a building.

Concrete was a breakthrough in construction as it can take any shape. Thanks to its properties it has a good resistance to compression, and in addition, the steel bars that form its armature withstand tensile stresses. 

Shell or laminar structures 

They consist of thin sheets of metal, plastic or composite materials, such as reinforced concrete. They owe their resistance to the curvature or folds. The curvature makes the sheets resist tensile and compressive stresses on their surface. 

The folds and ribs give precise rigidity to the areas where they are located. Thus, for example, the rim of a plastic cup prevents it from deforming when we drink, and the stretch marks presented in the grip area make it more resistant to compression in that area.