AdvancedFrameSettlementIndeterminateServiceability

Support settlement in a frame — stress from movement alone

Nothing extra is loaded — a footing simply ends up 15 mm lower than it started. In an indeterminate frame that alone produces a large share of the bending in the structure, and statics cannot see any of it.

Figure 1.A fixed-base portal whose right-hand footing settles 15 mm.

Given

Span: 6 m
Height: 4 m
: 10 kN/mon the rafter
Settlement: −15 mmright base — DOWN is negative
Bases: fixedthree times indeterminate

Part 1 — A footing that drops 15 mm

Settlement is entered on the support, not as a load.

Build the fixed-base portal exactly as before:

N 0,0 N 0,4 N 6,4 N 6,0 M 1 2 M 2 3 M 4 3 S 1 F S 4 F L 2 -10

Now open the Supports table and give node 4 a vertical settlement of −15 mm. On this site down is negative, so a settling footing is a negative number — the same convention as a gravity load.

Nothing extra has been loaded. A support has simply been told to end up somewhere other than where it started.

Figure 2.The fixed-base portal — with the right-hand footing prescribed to settle 15 mm.

Part 2, step 1 — Stress from movement alone

The indeterminate structure fights back.

Total vertical reaction is still 60 kN — statics does not care that a support moved, because the applied load has not changed.

But the base moment has risen to 21.11 kN·m, against 11.13 kN·m for the identical frame with no settlement. The peak member moment is now 32.44 kN·m against 22.55 kN·m.

A large share of the bending in this frame is being caused by a footing moving 15 mm, with no extra load at all. This is the defining behaviour of an indeterminate structure: it has more restraints than equilibrium needs, so when one of them moves, the structure has to deform to suit — and deformation in a stiff frame means force.

Figure 3.The settled frame: the same 60 kN of load, but substantially more bending — all of it caused by the movement.

✓

Settled vs unsettled, side by side

Verified — hand calculation vs the solver, to round-off

Quantity	By hand	StructureCalcs
Total vertical reaction	wL = 60 kN, unchanged	60 kN
Total horizontal reaction	0	0 kN
Base moment — SETTLED	indeterminate	21.11 kN·m
Base moment — no settlement	indeterminate	11.13 kN·m
Peak member moment — SETTLED	indeterminate	32.44 kN·m
Peak member moment — no settlement	indeterminate	22.55 kN·m

Every value was worked by hand with the classical method, then checked against this site’s solver — the same engine the Try it button opens. This agreement is re-run automatically on every build.

Now make it yours

Open this exact model in the calculator — then change a load, drag a support, and watch every diagram update in real time. The best way to build intuition is to break it and see what happens.

Take it with you

Export this worked example as a PDF, or download it as a .screport and open it in the Report Builder — the model travels inside the file, so you can reconstruct it, re-solve, and build your own report from it.

Want more examples like this?

Tell us what you’d like to see worked next.

Spotted a mistake?

We’d genuinely appreciate your feedback — it helps everyone.