Structural Engineering & Statics
where the load goes
Concept

Effective depth — where it appears

The distance from a concrete section's compression face to the centroid of its tension reinforcement, which is the lever arm every check divides by. Nearly every quantity in a concrete section is proportional to it or to its square, which is why it is the dimension worth arguing over and the cover is the dimension that erodes it.

Named by 3 essays across 3 fields — each of them below, with the objects they name alongside it.

2d = 450column7.2 m bayperimeter u₁ = 4427 mmshear to carry V = 604 kNv = 0.606 against 0.658 N/mm²92% of the resistance used

A check made on a perimeter, not on a section

Every shear check in this collection is made on a plane cut through a member. A slab sitting on a column has no such plane, because the shear leaves in every direction at once — so the check is made on a closed line, and a line grows with the column while the load grows with the square of the bay.

internal-forces · punching shear water table39.2 kN/m² upward, everywhereweight 18.7 MN6 muplift 23.54 MN · weight 18.72 MNfactor against flotation 0.80no strength appears anywhere in that ratio

A basement is a boat

Every load in this collection presses down and is resisted by strength. Hydrostatic uplift presses up, is resisted by weight, and does not care what is built on it — so the check contains no material property at all. It is a ratio of two weights, and one of them is water.

equilibrium · uplift x = 2341800 mm² of steel, n = 15b = 30015.4 N/mm²541 kN in the steelz = 462C = T = 541 kN · C·z = 250.0 kNm = the applied momentcracked I 3809×10⁶ mm⁴ against uncracked 6673×10⁶ — 43% of the stiffness gone

Where the steel is, not how much of it

A section in bending resists a moment with a couple, and a couple is a force times a distance. The force is bought — it is an area of steel at a stress. The distance is free, decided by where the bars were put, and it is the variable almost nobody optimises because it does not appear on an order.

sections · lever arm

Named alongside it

The objects these essays reach for when they reach for this one.

Control perimeterEquilibriumPunching shearAggregate interlockBallastBondBuoyancyClamping forceColumn headCoverCracked sectionDrainage

All concepts