Construction
Getting load safely into the ground.
Construction assembles materials into structures. Every structural decision answers one question: how does load travel from where it is applied down into the ground without any member failing on the way?
Types of load
- Dead load — the permanent weight of the structure itself.
- Live load — occupants, furniture, snow; variable and movable.
- Lateral load — wind and earthquake, acting sideways.
- Dynamic load — moving or impact loads, which can far exceed their static equivalent.
Structural systems
Load-bearing walls carry load continuously along their length — simple, but openings weaken them and the plan is fixed. Post and beam concentrates load into columns, freeing the walls to be non-structural, which is what allows large windows and flexible interiors. Frame construction extends this into a three-dimensional cage and is how tall buildings are built.
Materials in compression and tension
| Material | Strong in | Weak in |
|---|---|---|
| Stone, brick, concrete | Compression | Tension |
| Steel | Both | Buckles when slender; loses strength in fire |
| Timber | Both, along the grain | Across the grain; moisture, fire |
Reinforced concrete exists precisely because concrete is weak in tension and steel is not. Steel bars are placed where the tension occurs, and the two materials happen to expand at almost the same rate with temperature — without that coincidence the combination would not work.