Think of structural design as creating the skeleton for a building or a bridge. It’s the invisible framework that holds everything together, ensuring a structure can stand up to all the forces it will face during its lifetime. The main goals are simple but critical: to create something that is strong, stable, and durable.

Every part of a structure, from the tallest skyscraper to the smallest house, has a job to do. That job is to carry loads safely from the top of the structure all the way down to the ground. This path the forces travel is called a load path, and designing it correctly is the core of structural engineering.

A load is any force that pushes or pulls on a structure. Structural design starts with identifying every possible load a structure might encounter. We can group these into a few main categories.

Next are the temporary, movable forces.

Finally, we have forces from the world around us.

Once engineers understand the loads, they choose materials to resist them. The choice depends on the material's strength, cost, and durability. The three most common structural materials each have their own strengths.

Steel is incredibly strong for its weight. It's great at resisting both tension (pulling forces) and compression (pushing forces). You'll see it in skyscrapers, long-span bridges, and industrial buildings.

Concrete is fantastic under compression but weak under tension. That's why it's almost always reinforced with steel bars (rebar), creating a powerful composite material. It's versatile, durable, and used in everything from foundations to high-rises.

Wood is a lightweight and easy-to-work-with material. It's commonly used in residential construction for frames, floors, and roofs. Modern engineered wood products have made it even stronger and more reliable.

A structure must be stable. This means it needs to be in a state of equilibrium. In simple terms, equilibrium means all the forces acting on a structure are balanced. The downward pull of gravity (from dead and live loads) must be perfectly opposed by the upward push from the ground.

Imagine a simple beam resting on two supports. The weight of the beam and any load on top of it pushes down. The supports push up with an equal and opposite force. If they didn't, the beam would either fall through the floor or fly up into the air. Neither is very good for a building.

This principle applies to the entire structure. Every piece must be in equilibrium, transferring its load to another piece, until all the forces are safely delivered to the foundation. This balance is what keeps our buildings standing strong.