Design and auto-sizing

Run design analyses the model and then checks every part of it against your design code: members, slabs and plates, shear walls, pad footings, composite beams and steel connections. With auto-sizing on, it also chooses the lightest member sections that pass and thickens slabs that fail. The result is a model coloured by utilization — the ratio of what an element must resist to what it can — where anything over 1.00 fails.

#Running the design

• Press F6 anywhere in the app.
• Click Run design on the results summary after an analysis.
• In the Full interface, choose Design › Run design (Design again once designed), or the button at the foot of the design settings.

You do not need to run the analysis first: Run design always analyses the current model. The progress card names each stage — Designing members, Sizing members (pass 2), Checking every member, Designing slabs, walls and footings, Thickening slabs, Designing the concrete, Designing connections — and a message reports the outcome: Design done. Everything passes. or how many members and other checks fail, shown in red.

#What is checked

Element	Checks
Steel members	Axial, bending, shear and their interaction, flexural buckling, lateral-torsional buckling, deflection
Concrete beams and columns	Longitudinal bars and links for bending, axial force and shear, column slenderness and biaxial bending, deflection
Timber members	Bending, compression with buckling, shear, deflection
Cables	Tension
Slabs and plates	Bar meshes and extra bars in both directions, shear, punching at columns, deflection
Shear walls	Pier bars, shear, boundary elements at the base of each wall
Pad footings	Size for the allowable bearing, then bending, one-way and punching shear, and the bars
Composite beams	Steel beams under the slab: studs, construction stage and composite stage (unshored), and walking vibration
Steel connections	Base plates, end plates, fin plates, gussets and splices: bolts, welds, plates and anchors

Each check follows the code you chose in the Materials step, with its clause shown beside the result. The element design tutorials explain the checks in detail: steel beams, concrete beams, steel columns, concrete columns, slabs, shear walls, footings, composite beams, connections and timber.

#Auto-sizing

With Size members for me (Materials step) or Size members automatically (Design menu or settings) on, the design runs in passes. In each pass every group gets the lightest section in its list that passes all strength checks and keeps the deflection under D + L within the limit, and the model is analysed again with the new sections, because stiffer members attract more force. When the sections stop changing, every member is checked in full.

• Sizing is per group: all members in a group share the section the worst member needs. To size one member differently, move it to its own group.
• The sections chosen are kept in the project. The results summary lists them under Sized for you (for example Beams: IPE 300 → IPE 360).
• Ctrl+Z undoes the whole run, sections included.

With Thicken slabs that fail also on, slabs and plates that fail are made thicker step by step, up to twice their starting thickness. A thicker slab is kept only if it helps.

With auto-sizing off, the sections and thicknesses are checked exactly as you set them.

#Design settings

In the Full interface, Design › Design settings… opens every design option in the Properties panel. Most can also be switched in the Design menu.

Group	Setting	Default
Code	The design code (also sets the combinations, grades and sections)	From the Materials step
Members	Size members automatically	On
Members	Deflection span / — the limit under D + L, 100 to 1000	250
Connections	Steel connections (steel members only)	On
Slabs and walls	Slabs and plates · Thicken slabs that fail · Shear walls	On
Foundations	Pad footings, with Bearing (kPa) and Base depth (m)	On, 200 kPa, 1.0 m
Composite floors	Composite beams · Floor vibration	On

Changing a design setting keeps the analysis and drops only the design results, so the next design is quick. Changing the code clears the analysis too, because the loads change. In the Simple interface, auto-sizing is in the Materials step and pad footings in Supports & loads; the others keep their defaults.

#Reading the design

#Utilization colours

After a design the view shows Utilization: each member coloured from low to high, with values over 1.00 in red. A member is coloured segment by segment, so you can see where along it the ratio peaks. A member that fails a check that applies to it as a whole — buckling, say — is red along its length.

#The member inspector

Click a member to see its utilization as a number and a bar, whether it passes, which check governs and in which combination, the five highest checks with their ratios, the clause, its deflection as a share of the limit, the connections at its ends and, for beams under a slab, its composite design. The Calculation report button writes its full calculation — see Calculation reports.

#Footings

Designed footings appear as concrete blocks under the supports, red if they fail. Click one to see its plan size, thickness, bars, cover, the largest soil pressure against the allowable, the governing check and a Footing report button.

#Design tables

The Full interface adds a table for each kind of element designed:

Tab	One row per	Main columns
Design	Member	Section, governing check, clause, combination, ratio, deflection, status
Connections	Connection	Joint, member, type, description, ratio, governing check
Slabs & plates	Panel	Reinforcement in x and y (B bottom, T top), extra bars, ratio, punching, deflection
Shear walls	Wall	Reinforcement, boundary elements, Pu, M3, V2, ratio
Footings	Support	L × B, h, bars, largest pressure, ratio
Composite beams	Beam	Studs, degree of composite action, ratio; floor vibration in the note

Failing rows are marked. Click a row to select the element, and export any table as CSV.

#When something fails

• With auto-sizing on, a failing member usually means even the largest section in its list is not enough. Shorten the span, add a column or bracing, change the material or grade, or split the group.
• Slab punching failures name the column node; thicken the slab or add a drop panel by hand.
• A footing that cannot meet the soil checks says a pad footing does not suit that support.
• The Full interface's Messages tab and the report's Notes list what could not be designed and why.

Struxt3D gives a sound first design, not a final one. Read Accuracy, assumptions and limitations before relying on it.