Bridges · Culverts

Box culvert calculator

Single-cell culvert: earth and surcharge loads, corner and mid-span moments.

Standard: Closed rigid frame (slope-deflection) · AS 5100 / AS 1597 concepts

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Input	Value	Unit
Internal width	3	m
Internal height	2.4	m
Slab thickness	0.3	m
Wall thickness	0.25	m
Fill over top	1.5	m
Fill γ	20	kN/m³
Lateral coefficient K0	0.5
Surcharge / dispersed traffic	20	kPa
Water outside	No

Diagram for the worked example

Centre-line frame L = B + tw = 3.25 m, H = H + ts = 2.70 m
Top: γHf + q + slab self-weight; base: (top × L + walls)/L, uniform
Lateral: K0(γz + q), trapezoidal on walls (+ water if selected)
Slope-deflection, I ∝ t³, no sway (symmetric). Trapezoid FEM = aL²/12 + (b − a)L²/30 at the light end, /20 at the heavy end
Service moments: apply AS 5100 / AS 1597 factors, live-load models and dispersion for design.

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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.