Structural Engineering Fundamentals: Types and Conditions

Fundamentals of Structural Engineering

A structure is the set of elements in a body designed to resist the forces (loads) acting upon it, fulfilling three essential conditions:

1. Stability: Remaining upright and preventing overturning.
2. Resistance: Withstanding loads without breaking.
3. Rigidity: Minimizing deformation under load.

Understanding Loads

The forces acting on a structure are known as loads. These loads are typically classified as either permanent (dead loads) or variable (live loads).

Classification of Structures

Structures are generally categorized into four main types:

• Massive Structures: Characterized by their large volume and weight (e.g., pyramids, stone benches).
• Vaulted Structures: Utilize arches and vaults to distribute forces (e.g., stone bridges, cathedrals, arches).
• Frame or Lattice Structures (Entramadas): Composed of interconnected linear elements, common in modern buildings (e.g., blocks of flats).
• Suspended Structures: Structures where the main load-bearing elements are tension members (e.g., suspension bridges).

Key Structural Elements

Common elements found in frame and lattice structures include:

• Trusses (Cerchas)
• Joists (Viguetas)
• Beams (Vigas)
• Pillars (Pilares) and Columns (Columnas)
• Foundations (Cimientos)

Defining Structural Conditions

• Stability: The ability to remain in a vertical position and prevent overturning.
• Resistance: The capacity to support loads without failure or breaking.
• Rigidity: The property of deforming as little as possible under stress.

Behavior of Articulated Shapes

The stability of structures often depends on how their joints handle forces:

• Articulated Triangle: This shape is inherently rigid. It does not deform laterally because the applied force is concentrated and distributed efficiently through the members.
• Articulated Quadrilateral (Square): This shape is unstable and easily deforms (collapses) under lateral load.
• Articulated Quadrilateral with a Diagonal Bar: Adding a rigid diagonal bar triangulates the shape, preventing deformation and making the structure stable.
• Articulated Quadrilateral with a Diagonal Rope: A rope (tension member) only resists pulling. If the load causes compression on the rope's side, that side deforms, while the side where the rope is in tension remains stable.

Action and Reaction Forces

Consider pushing a tree: it typically remains stationary because its roots are firmly held by the earth. The force exerted by the earth counteracts our applied force. When we push the tree (action), the tree responds against us with an identical and opposite force (reaction).

Everyday Structural Examples

• Pen Structure: Includes the cylinder or prism that holds the ink tube.
• Plastic Cup Structure: Encompasses the entire object, including the ridges and the edge, providing rigidity.
• Camera Structure: Consists of the outer case designed to hold and protect its different internal components.
• Table Structure: Composed of the legs and the board, working together to support weight.

Structural Analysis Prompts

Exercise 1: Dam Structure Analysis

Illustrate the structure of a dam, detailing all the forces (loads) acting upon it.

Exercise 2: Classification

List five examples of natural structures and five examples of artificial structures.

Examples of Structures

Natural Structures:

• Shells
• Trees
• Skeletons
• Nests
• Rabbits (referring to their biological structure)

Artificial Structures:

• Bridges
• Viaducts
• Overpasses
• Trestles
• Drain conduits under embankments

Visualizing Structural Types

The following image illustrates the differences between the main structural classifications: Massive, Vaulted, Lattice, and Suspended structures.