TheBridgeEng

Abutment — first sizing

Abutment sizer — spread footing

First sizing of a cantilever abutment on a spread footing. Set the superstructure reactions, height, abutment length and soil — the tool proposes footing dimensions that pass the classic stability checks (bearing, middle-third, sliding FS 1.5, overturning FS 2.0, Rankine earth pressure), and estimates the main reinforcement. Planning-level screening; wing walls, seismic and detailed RC checks belong to final design.

The tool grows the footing in 0.25 m steps until every stability check passes.

Section — to scale, with loads, bearing pressure & main bars

Proposed footing — width B

—m

Bearing q_max / q_a—

Eccentricity e / (B/6)—

middle third

Sliding — required 1.5 / FS—

FS ≥ 1.5

Overturning — required 2.0 / FS—

FS ≥ 2.0

Main reinforcement PRELIMINARY

Stem — rear vertical—

Toe — bottom transverse—

Heel — top transverse—

Dead-load reaction (total)8000kN

20001600030000

Live-load reaction (total)2000kN

0500010000

Abutment height H8.0m

4812

Footing base to top of backfill / backwall.

Abutment length W12m

81420

Out-of-plane length; loads are spread over W (per-metre strip design).

Foundation soil

γ kN/m³

φ deg

q_a kPa

μ base

Dense sand / gravel: γ 19, φ 35°, q_a 400 kPa, μ 0.55. Backfill assumed same γ/φ.

Your footing width B5.0m

2.57.2512

Toe stays B/3; stem & footing thickness follow the H-based rules.

Step	Quantity	Value	Note

Field notes — what to watch for

Sliding governs more abutments than overturning — if the base is short on friction, a shear key is cheaper than a longer heel. The soil parameters move the answer far more than any structural choice: φ of 30° versus 34° changes the pressure by a fifth. Spend your effort on the geotech report, not the concrete.

Inputs are saved on this device · reset to defaults