Principles of Structural Mechanics and Applied Forces

Fundamental Concepts of Forces and Structures

A force is anything that can deform a body (static effect) or change its state of movement or rest (dynamic effect).

Examples of Forces

• Gravity: Pulls us towards the Earth and gives us weight.
• The force of the wind.
• Mechanical forces that move machines.
• Pressures of gases in closed containers.
• The force created by the effects of heat.

A structure is the set of elements in a body that are intended to resist the effects of the forces that act on it. A structure prevents a body from breaking or becoming too deformed.

Loads and Internal Stresses

The forces that act on a structure are called loads.

Types of Loads

• Fixed or Permanent Loads: Do not vary over time.
• Variable Loads: Are occasional and changeable.

Loads act on the bodies, causing internal tensions, which vary depending on how they are applied and the specific shape of the objects. This internal tension is called stress. It happens to all bodies subjected to the application of one or more forces.

Types of Stresses

These stresses describe how forces attempt to deform the object they are acting upon:

• Traction: Forces try to stretch the object.
• Compression: Forces try to flatten or compress a body.
• Bending: This stress acts on elements that are supported at their extremities and have a weight applied to them.
• Torsion: Forces try to twist a body.
• Shear or Cutting: The forces act like two scissor blades: they are very close together, moving in opposite directions, as they try to cut an object.

Essential Structural Conditions

• Stability: The capacity of a structure to remain upright and not tip over.
• Resistance: The capacity of a structure to bear the tensions that it is subjected to without breaking.
• Rigidity.

Classification of Artificial Structures

Massive and Lintelled Structures

The first human-made structures were carved from rock or were built by stacking rock or other materials, leaving little space between them.

Vaulted Structures

The arch was invented later, and vaults enabled builders to cover larger spaces and increase the size of the openings in the built structure. A vault is made from a number of arches placed side by side, with the spaces between them filled in.

Lattice Structures

These are built from cement or steel bars that are joined to form a rigid grid. Key components include floor slabs, beams, and foundations (footings, slabs, piles).

Triangulated Structures

These structures are used horizontally to cover large spans and are divided into trusses and triangulated beams. Trusses are normally used in roofs because the slope created is perfect for laying tiles so that the rain runs off it.

Suspended Structures

This type of structure is hung from cables, called tie rods.

Pneumatic Structures

These are light and can easily be dismantled.

Rolled and Plate Structures

Are made from thin sheets of metal, plastic, or composite materials. They are very resistant because they can bend.

Geodesic Structures

These three-dimensional triangulated structures combine the properties of vaults and bar structures.