Shell

A uniform surface pressure on shell elements.

🔧 Grasshopper component

Mesh Load (Alpaca4d) — Alpaca4d ▸ 05_Load, nickname MeshLoad

Inputs

Shell|IdElement or textall shellsThe shell to load, or text naming the shells by ElementId: Slab_1, a wildcard Slab*, an element tag 47, or regex:^Slab.

If left empty the load is applied to every shell element in the model.

ForceVectorPressure px, py, pz in global axes, in kN/m².

Outputs

LoadLoadSurface load, for a Load Pattern.

📈 When to use it

Use it when

• Floor live loads, roof snow, wind pressure on a façade, soil pressure on a retaining wall — anything acting over an area.

Do not use it when

• The pressure varies over the surface. This is uniform per element, so a varying pressure means grouping the mesh faces and applying a different component to each group.
• The action is along a line or at a point → Beam Load or Point Load.

Note

The pressure is not applied along the shell normal. The vector is in global axes, so a downward load on a pitched roof given as 0, 0, -q is a load per square metre of the sloping surface, not of its plan projection. For a snow load defined on plan, scale by cos θ yourself.

Note

ASD Shell makes one element per mesh face. To load a whole slab, give its mesh one ElementId on ASD Shell and type that name into Shell|Id: every face of it is loaded, with one Mesh Load. Each item makes one load, so two names that match the same shell load it twice. A name that matches no shell loads nothing, and Assemble Model warns about it.

The Barrel Vault example puts wind on a curved shell: its arc cut into strips, each facing one way and named on ASD Shell, and one Mesh Load a strip along its normal.

🔗 Relation to OpenSees

There is no OpenSees surface-load command for these elements. Alpaca4d converts the pressure into equivalent nodal loads — the element area divided among its vertices — and writes them inside the enclosing pattern:

load $nodeTag $Fx $Fy $Fz $Mx $My $Mz