Design a multi-storey frame building

The multi-storey frame is the classic building structure: columns on a rectangular grid, beams on every grid line at every floor, and floor slabs spanning between them. This tutorial walks through the Multi-storey frame template in Struxt3D — from choosing the grid to a designed, auto-sized frame with a calculation report — and explains what to look for at each step.

#How a moment frame carries load

Gravity load follows a simple path: the floor slab carries the occupants and finishes to the secondary beams and the beams on the grid lines, the beams carry it to the columns, and the columns carry it down to the foundations. Each element only has to be strong enough for what arrives from the element above it in the chain.

Sideways load — wind and earthquake — is the harder part. Without bracing, the frame resists sway only through rigid beam-to-column joints: the beams and columns bend together, like a table whose legs are welded to the top. This is a moment frame. It gives open, unobstructed bays, but it is flexible, so sway (drift) and column bending often govern the design rather than the floor loads.

If the sway is too large you have two options: bigger members, or bracing. The template can add X-braced bays on each face (under More options), which turns those bays into stiff vertical trusses that take most of the sideways load. See Supports, joints and member end releases for how joint fixity changes the behaviour.

#Step 1 — Pick the template

1. Open the app. The first step, Template, shows the gallery. Filter by Buildings and choose Multi-storey frame — or use the Open the template button above.
2. The 3D model appears at once with the default 4 × 3 bays and 5 storeys. You land on the Size step.

#Step 2 — Set the size

Every value can be typed or nudged with − and +. The model rebuilds as you go.

Parameter	Section	Default	Range
Bays in X	Plan	4	1–10
Bay width X	Plan	6 m	3–12 m
Bays in Y	Plan	3	1–6
Bay width Y	Plan	5 m	3–12 m
Storeys	Height	5	1–25
Storey height	Height	3.5 m	2.5–6 m
Secondary beams per bay	More options	1	0–3
Braced bays per face	More options	0	0–2

Secondary beams run parallel to Y inside each X bay and halve (or third, or quarter) the slab span. Braced bays per face = 1 braces the middle bay of each face; 2 braces the two end bays. Cladding panels on the four faces are added automatically — they carry no load themselves but collect wind and pass it to the beams and columns around them.

#Step 3 — Materials and sections

1. Choose the Design code: Eurocode, AISC / ACI, KDS, CSA, NSCP 2015 or AS/NZS. The code sets the grades, the load combinations, the live loads and the wind and seismic rules. See the design code tutorials.
2. Pick the Material. The template starts in steel; switch to concrete for an RC frame or timber for glulam. Then choose the Grade.
3. Under Sections, each member group — Columns, Beams, Secondary beams and (if used) Bracing — has a section list. The defaults are reasonable starting sizes.
4. Under Slabs and walls, set the thickness of the Floor slabs (default 200 mm) and the Roof slab (default 150 mm). They are analysed as plates and add their self-weight.
5. Leave Size members for me on if you want Struxt3D to find the lightest passing sections during design.

#Step 4 — Supports and loads

1. Bases: Fixed (the default for this template) or Pinned. Pinned bases make the frame much more flexible sideways — the columns then bend in single curvature over the ground storey.
2. Foundations: switch on Pad footings to size a footing under every column, and set the Allowable bearing and the Depth of the base.
3. Floor use: Office, Residential, Retail or Storage. The live load in kN/m² comes from the chosen code and is shown on each button.
4. Finishes and services (default 1.5 kN/m²) is added to the dead load on every floor.
5. Wind is on by default and acts in ±X and ±Y on the cladding (pressure on the windward face, suction on the leeward face). Set the Wind speed for your site — see Wind loads.
6. Switch on Earthquake for a response-spectrum analysis and pick the Structural system: Ductile moment frame for this template, or Braced frame if you added bracing.
7. Use Show on the model to view each load case before you run.

Self-weight and the code's load combinations are added for you; the panel tells you how many strength combinations there are.

#Step 5 — Run the analysis and read the results

Press Run analysis (or F5). The workspace switches to results. For a frame, check these in order:

1. Displacement under the service combination (D + L): the largest vertical deflection is usually at mid-span of an edge beam. Use Animate to see how the frame moves.
2. Pick a wind case (Wind +X) and look at the sway at the top. A common target is height/300 to height/500 under service wind — 17.5 m / 400 ≈ 44 mm for the default 5 storeys. This is a rule of thumb: check your code's serviceability limits.
3. Moment under the Envelope: beam moments should be hogging at the columns and sagging at mid-span; columns at the base carry the largest wind and seismic moments.
4. Axial: the ground-storey interior columns carry the most. The Load on the supports figure in the results summary should be close to (floor area × storeys × (dead + live)) — a quick hand check.
5. With earthquake on, open Vibration modes: the first period of a 5-storey steel frame is typically 0.6–1.0 s. The summary shows the mass captured in X and Y — codes ask for 90 %.

More on this in Reading results and Viewing results.

#Step 6 — Design and auto-size

1. Press Run design (F6). Every member is checked to the code — strength, buckling, lateral-torsional buckling and deflection (span/250 by default). In steel, end plates, fin plates and base plates are designed too; with concrete the beams and columns get reinforcement; floor slabs are reinforced and footings sized if switched on.
2. With auto-sizing on, the summary lists Sized for you: each group's section before and after.
3. Show Utilization: blue is lightly used, red is at or over 1.0. Click the worst member (the Highest utilization link) to see which check governs and under which combination.
4. Open the Calculation report for the whole model, or select a member and use its own report. Shop drawings produces erection plans, connection details and, for concrete, reinforcement drawings.

Auto-sizing picks one section per group, so every beam takes the size the worst beam needs. Lightly loaded secondary beams already have their own group; a member's Group can be changed in its properties. See Design and auto-sizing.

#Typical problems and fixes

• Columns governed by sway, not by axial load. Add Braced bays per face, fix the bases, or accept heavier columns. Bracing usually saves the most steel.
• Edge beams fail in deflection. They carry cladding and the slab edge. Increase the beam section or reduce Bay width X.
• Too few modes reach 90 % mass. The results show a warning; the response is still computed from the modes found. Tall, irregular frames need more modes — see Response spectrum analysis.
• Weak-axis bending. The template's columns are not rotated, so frame action in one direction bends the columns about their minor axis. Check Minor moment and, if it governs, use a section that is stiff both ways (a tube or box in steel, a square column in concrete) or set the columns' Rotation in the Full interface properties.

#Rules of thumb

Use these only to sanity-check the first sizes; the code checks decide.

• Steel floor beams: depth ≈ span / 20 (secondary) to span / 15 (primary).
• Concrete beams: depth ≈ span / 12 to span / 15; columns at least 300 mm, often 400–600 mm for 5+ storeys.
• Ground-storey interior column load ≈ tributary area × storeys × 10–15 kPa (factored).
• Moment frames are economic to about 10–15 storeys; above that, bracing or a shear wall core takes over.