Structural Principles and Building Stability
Structural Principles and Building Stability tests how loads travel, how forces act and why buildings do not overturn or deflect excessively. Expect dead and live loads, tension, compression, shear, bending, moments and triangulation.
Core rules
- Dead load is self-weight; live load is occupants, furniture, snow or wind.
- Tension pulls, compression pushes, shear slides, and bending combines tension and compression across a section.
- Moment = force × perpendicular distance; units are kNm.
- Triangulation gives stiffness because a triangle cannot change shape without a member changing length.
- Stability needs load paths to foundations, bracing and adequate bearing.
Worked example
A simply supported beam spans 4.0 m and carries a 10 kN point load at midspan. By symmetry, each reaction is 10/2 = 5 kN. Maximum bending moment for a central point load is WL/4 = (10 × 4.0)/4 = 10 kNm. The reasoning is: first find reactions from vertical equilibrium, then use the standard midspan moment expression. Do not report 10 kN as a moment; the unit is kNm.
Traps
- Mixing force (kN) and moment (kNm).
- Forgetting self-weight or a second load case.
- Assuming triangulation removes the need for foundations or bracing.
- Using span in millimetres in a formula expecting metres.
Sketch the load path and state the units.