All of it to BS 8110-1:1997, as used in Nigerian practice, with BS 8666 for bar bending schedules and BS 6399-1 for imposed-load reduction. Each member below can be run on its own, or as part of a whole-building takedown or column grid.
Slabs
One-way & two-way solid · BS 8110 Table 3.14
Solid slabs spanning one way or two, with the moment coefficients taken from the code for the panel's edge conditions and aspect ratio. One-way slabs are designed per metre width, and the sheet says so.
Checks
- Thickness against the minimum
- Cover against the minimum for the exposure
- Flexural steel, short and long span, support and midspan
- Shear stress v against vc
- Deflection: actual span/d against the allowable, with the tension-steel modification factor
Beams
Flexure, shear links & deflection · cl 3.4
Singly and doubly reinforced rectangular sections, with shear links sized and spaced from the code's tables. Continuous beams can take the Table 3.5 coefficients — and the engine checks that the table is allowed to be used at all before it does.
Checks
- K against K' = 0.156, so compression steel is added rather than assumed away
- Steel area within 4% bh, and above the minimum
- Shear stress against 0.8√fcu, capped at 5 N/mm²
- Link spacing against 0.75d
- Deflection by span/d
- Table 3.5's own validity: Qk <= Gk, and three or more spans
That last one matters. The coefficients are only valid inside those limits, and outside them the engine fails loudly rather than returning a number that looks fine.
Columns
Short & slender, uniaxial & biaxial · cl 3.8
Short columns take the code's simplified equations 38 and 39. Slender columns are designed to cl 3.8.3 with the additional moment Madd, and the section's own moment–axial capacity is solved by strain compatibility rather than read off a chart. Being slender is reported as a classification, not as a failure — it decides which route the design takes.
Checks
- Least dimension against the minimum
- Slenderness, and lo against 60 × the smaller side
- Steel between 0.4% and 6%
- Axial capacity N with the steel provided
- Moment capacity at the design axial load
Corner columns of a moment frame are designed biaxially to cl 3.8.4.5: they are end columns of frames in both directions, so they carry the other direction's moment alongside the governing one. Whenever a column carries real moments, equations 38 and 39 are bypassed — they assume there are none.
Pad footings
Bearing, bending & punching shear
Sized on the allowable bearing pressure you give it, then designed for the cantilever moment and both shear cases.
Checks
- Bearing pressure against the allowable
- K against 0.156
- Shear stress v against vc at the critical section
- Punching: stress on the 1.5d perimeter
- Punching: stress at the column face
Strip footings
Under load-bearing blockwork · per metre run
For walls rather than columns, designed per metre run. Where the projection falls inside a 45-degree load dispersion, nominal steel governs the transverse bending, and the sheet states which case it is in.
Checks
- Bearing pressure against the allowable
- Projection against the 45-degree dispersion
- K against 0.156, and shear v against vc
- Transverse and minimum steel
Raft foundations
Solid raft, when pad footings run out of room
A raft is an inverted slab: it spans between columns with the ground pushing up, so the span steel goes in the top face and the steel over the columns goes in the bottom. Every raft sheet shouts that, because getting it upside down on site is serious.
Checks
- Bearing pressure against the allowable
- The raft stays in contact with the ground — no uplift at a corner under wind
- K against 0.156, in both directions
- Shear v against vc, and punching at the 1.5d perimeter and the column face
- Minimum steel
Settlement is not calculated, and the sheet says so. When a raft cannot carry the building, that is where the engine stops — there is no pile module, because piling needs a soil model this app does not have.
Staircases
Flight as a one-way slab · per metre width
The flight is designed as a one-way spanning slab, per metre of width, with the waist, going, rise and landings taken into the loading.
Checks
- K against 0.156
- Shear v against vc
- Deflection by span/d, with the modification factor
- Main and distribution steel
Lintels
Over door & window openings
Reinforced concrete lintels over openings, carrying the wall above and anything bearing on it, with hanger bars in the top face.
Checks
- K against 0.156
- Shear against 0.8√fcu, capped at 5 N/mm²
- Deflection by span/d
Wind & stability
Storey shears, overturning, drift & plan torsion
A standalone module, and a path the takedown and column grid can both use. It works out the wind pressure on the building, splits the storey shears into the frames or walls resisting them, and carries the result through to overturning and sway.
Checks
- Restoring moment against overturning
- In-plane shear stress in a wall against 0.8√fcu
- Flexural steel against the minimum
- Sway against h/500
- The stability index, so a first-order design says whether it is still valid
Accidental plan torsion — an eccentricity of 5% of the plan width — always applies, and amplifies the outermost frame or wall. Wind is evaluated in both directions and the worse governs. The wind speed you enter is used as given, as an effective gust speed at roof level that must already include terrain and height — only an altitude factor is applied on top of it. There is no Nigerian wind map built in. It also needs the same plan at every level: a building that steps in is refused for wind rather than approximated. See what it will not do.
Layouts, floors and setbacks
The whole building, not a typical member of it
A takedown or a column grid designs the building the plan describes, and the plan does not have to be a rectangular array. Columns can be taken out where there is a stairwell or an open bay, added where the plan has one off the grid, and moved; bays can be different widths in both directions. Every column is then designed on the tributary it actually carries — half the distance to the nearest standing column each way — rather than on one worst-case spacing.
The grid also designs every slab panel between adjacent setting-out lines and every beam span between adjacent columns, for each suspended floor and for the roof. The typical slab and typical beam are still worked as well, because those are the calculation an engineer checks by hand.
Buildings that step in
A column can stop below the top of the building, so a first floor can set back off the ground floor and a penthouse off that. Each floor is accumulated against the tributary the storey framing it gives, so the columns holding a setback up are designed for the larger share they really take, and the bill is counted level by level.
What it refuses
- A beam line whose spans differ by more than 15 %, or a beam shorter than twice its own effective depth. BS 8110's moment coefficients need roughly equal spans and its beam clauses do not cover deep beams, so those lines come back FAIL with the reason rather than a confident answer — and the plan editor says so while the drawing is still on screen
- A column stopping while the floor above still spans over it — that is a transfer beam, and there is no transfer element here
- Wind on a stepped building: the lateral method has one plan extent and one set of frames, so a setback is gravity-only, up to 3 suspended floors
- Fewer than four columns on any storey, or a column no beam reaches
- Bays outside 0.5 to 15 m, or more than ten bays either way. A shorter bay is a deep beam — a beam whose clear span is under twice its depth — and BS 8110 has no rules for one, so a column tapped closer than that to a setting-out line goes on the line
All of that is checked while the plan is still on screen, naming each column by its grid reference. See the plan underlay tutorial.
Fire resistance & robustness ties
Reported on every building
Neither of these falls out of a structural calculation, so both are explicit rather than implied. Fire cover and minimum dimensions are tabulated for dense concrete fully exposed, and every sheet using them says to confirm the real requirement — it depends on occupancy, aggregate and how many faces are exposed, none of which the app knows.
Robustness ties are reported, never detailed: the sheet tells you the tie forces the code requires and leaves the detailing to you, and says as much.
Design one now
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Read next
- How it works — what a calc sheet contains, and what comes out of it
- What Structura will not do — the exclusions, and why each one is there
- Worked examples — slabs, beams, columns, footings, stairs and takedowns done by hand, step by step
- Rebar weight chart — mass per metre, steel areas by spacing, bars per tonne
- Cover, grades and mixes — durability and fire cover, and what a site mix gives