Alpaca4d

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Load Pattern ​

A load pattern groups loads and attaches a time series that says how the group varies with time. It is the object the analysis actually applies — loose loads never reach Assemble on their own.

🔧 Grasshopper component ​

Load PatternAlpaca4d ▸ 05_Load
Load Pattern component
UniformExcitation
Inputs
TimeSeriesTimeSeriesConstant, factor 1How the pattern factor evolves with analysis time.
LoadsLoadlistThe loads in this pattern: point, line, surface, gravity.
FactorNumber1Constant scale applied to the whole pattern, on top of the time series.
DofTextXDirection the ground motion acts in.
Attach a Value List for the options: x, y, z (translation along the global axes), xx, yy, zz (rotation about them).
TimeSeriesTimeSeriesThe ground motion, normally acceleration against time.
VelocityNumber0Initial ground velocity, in m/s.
FactorNumber1Constant scale on the excitation — where a record in g gets its 9.81.
Outputs
LoadPatternLoadPatternPattern object, for the LoadPatterns input of Assemble.

A switcher component: pick the unit in the drop-down under it, or right-click it ▸ Units:

  • PlainPattern — static and quasi-static load cases.
  • UniformExcitation — base acceleration applied to every support.

📈 When to use it ​

PlainPattern for everything static: dead, live, snow, wind, imposed. One pattern per load case, so you can scale and combine them independently.

UniformExcitation for a seismic time-history run. It shakes the whole base at once, in one direction, and needs a Transient analysis type with a suitable Integrator — Newmark or CentralDifference.

Do not use UniformExcitation when different supports see different motions — that needs multiple-support excitation, which Alpaca4d does not expose.

💡 Workflow ​

  1. Build the individual loads.
  2. Group them into one or more Load Pattern components, each with its own time series.
  3. Connect the patterns to Assemble.

Keeping loads and patterns separate is what lets the same physical load appear in several cases at different factors.

🔗 Relation to OpenSees
tcl
# PlainPattern
timeSeries ...
pattern Plain $tag $tsTag -fact $factor {
    load    $nodeTag ...
    eleLoad -ele $eleTag ...
}

# UniformExcitation
pattern UniformExcitation $tag $dir -accel $tsTag -vel0 $velocity -fact $factor

$dir is the integer the Dof text maps to: X=1, Y=2, Z=3, XX=4, YY=5, ZZ=6.