Design a building with a shear wall core

Most mid- and high-rise buildings are held up sideways by a concrete core — the walls around the lifts and stairs. The core is a stiff, hollow tube that takes almost all the wind and earthquake load, so the rest of the frame only has to carry gravity. This tutorial uses the Shear wall core template: a perimeter frame of beams and columns around a central core whose walls are analysed as plates.

#How a core building works

Two systems share the work:

• Gravity: the floors span to the beams and secondary beams, and the beams to the columns — and, along the core faces, straight onto the core walls (the template puts no beams there; the walls carry the floor edge).
• Lateral: the floors act as stiff horizontal diaphragms that collect wind or earthquake forces at every level and deliver them to the core. The core then works as a vertical cantilever fixed at its base, bending like a tall I- or box-beam. The walls parallel to the load act as webs (shear), the walls across it as flanges (bending).

Because the core is so much stiffer than the frame, it attracts most of the lateral load automatically — the 3D analysis shares it by stiffness. You can see this in the results: the core wall stresses are large, the frame column moments small.

#Step 1 — Pick the template

1. In the gallery choose Buildings › Shear wall core.
2. The default is 5 × 3 bays of 7.5 m and 10 storeys, in concrete with fixed bases. The core occupies the middle bay (left of middle when the count is even).

#Step 2 — Set the size

Parameter	Section	Default	Range
Bays in X	Plan	5	3–9
Bay width X	Plan	7.5 m	5–10 m
Bays in Y	Plan	3	3–7
Bay width Y	Plan	7.5 m	5–10 m
Storeys	Height	10	2–25
Storey height	Height	3.5 m	2.8–5 m

The core is always one bay by one bay, so its size follows the bay widths: 7.5 × 7.5 m by default. One secondary beam runs through each X bay. The core walls are one plate per face per storey, fixed along their base by a line support.

#Step 3 — Materials, sections and wall thickness

1. Pick the Design code and concrete Grade.
2. Sections for three groups: Columns (perimeter and interior), Beams, and Core corner columns — the columns at the four core corners, embedded in the walls.
3. Under Slabs and walls, set Floor slabs, Roof slab and Walls and plates (the core walls, default 300 mm).

#Step 4 — Supports and loads

1. Bases fixed. Pad footings are sized under the columns; the core walls stand on line supports and get no pad footing — size the core raft or pile cap separately (see the raft foundation tutorial).
2. Set the Floor use, Finishes and services and Wind speed.
3. Switch on Earthquake and set the Structural system to Walls or core. The behaviour factor (q, R, Rd·Ro or μ/Sp depending on the code) is shown under it. Enter the site hazard and soil class — see response spectrum analysis.

#Step 5 — Analyse

Press Run analysis (F5). With earthquake on, Struxt3D first finds the vibration modes, then combines them by CQC in X and Y. Check:

1. Vibration modes: the results summary gives the First period and the mass captured in X · Y. For a 10-storey core building the first period is typically 0.8–1.5 s. Animate the first modes: they should be sway in X, sway in Y and twist. If twist comes first, the core is too small or too eccentric for the plan.
2. Displacement under Wind +X and Wind +Y: the core bends as a cantilever, so drift grows towards the top. Rule of thumb: total wind sway around height/500.
3. Moment and Axial in the frame columns: under lateral load they should be small compared with the core — confirmation that the core takes the sway.

#Step 6 — Design the walls, beams and columns

1. Press Run design (F6). Beams and columns are designed as reinforced concrete members; floor slabs get reinforcement and punching checks; and every core wall is designed as a pier at the base of each storey for its axial force, in-plane moment and shear.
2. Open the Shear walls table (Full interface): each wall's reinforcement, whether it needs boundary elements at the ends, the forces Pu, M3 and V2, the governing check and its ratio. Seismic pier forces are combined mode by mode before CQC, so the moment is not lost to the signless combination.
3. Show Reinforcement bars to see the wall bars in 3D, the beam stirrups and the column ties.
4. Select a wall and open its own Calculation report to get the storey-by-storey pier calculation.

The theory behind the wall checks is in Shear wall design.

#Typical problems and fixes

• Base walls fail in flexure or need boundary elements everywhere. The core is slender. Thicken the walls, increase the concrete grade or — in the real project — enlarge the core.
• Torsional first mode. A single central core gives little torsional stiffness to a long plan. Keep the plan compact (fewer bays in X) or add perimeter bracing or walls.
• Mass participation under 90 %. The warning names the mass captured. Tall cores with heavy floors may need more modes; read the warning before trusting the base shear.
• Core corner columns attract large forces. They are embedded in the walls and move with them. They are kept in their own group so their size does not drive the other columns.

#Rules of thumb

• A core on its own suits buildings to roughly 20–30 storeys; taller ones usually need outriggers or a stiff perimeter frame as well.
• Wall thickness ≥ storey height / 16 to / 20, and 200 mm minimum.
• A core is most efficient when it is central: off-centre cores cause twist.
• Height-to-width ratio of the core much over 10 makes the walls slender; consider outriggers or a perimeter frame that shares the load.