Abaqus Earthquake Analysis
After analysis, run *FREQUENCY extraction on deformed configuration to monitor period elongation – a key indicator of structural softening.
Ignoring SSI often underestimates periods and overestimates base shear. In Abaqus:
Step 1: Build the FE model
Step 2: Perform eigenvalue extraction
*STEP, NAME=Eigen, PERTURBATION
*FREQUENCY, EIGENSOLVER=LANCZOS, NORMALIZATION=MASS
20
*END STEP
Step 3: Apply gravity load (static step)
*STEP, NAME=Gravity, NLGEOM=YES
*STATIC
0.01, 1.0
*DLOAD
ALL_ELEMS, GRAV, 9.81, 0., -1., 0.
*END STEP
Step 4: Seismic time history step
*STEP, NAME=Earthquake, NLGEOM=YES, INC=10000
*DYNAMIC, HHT-ALPHA=-0.05
0.01, 30.0, 1e-7, 0.01
*BOUNDARY, TYPE=ACCELERATION, LOAD CASE=1
BASE_NODE, 1, 1, 9.81
*AMPLITUDE, NAME=ACC_X, INPUT=eq_x.txt
*DAMPING, ALPHA=0.12, BETA=0.002
*END STEP
Structures experience gravity before an earthquake. Use two steps: abaqus earthquake analysis
For Abaqus/Standard (Implicit):
*STEP, INC=1000, NLGEOM=YES
*DYNAMIC, DIRECT, HAFTOL=1e6
0.01, 30.0, 1e-6, 0.01
For Abaqus/Explicit:
*STEP
*DYNAMIC, EXPLICIT
, 30.0
The time step is automatically computed from smallest element size and wave speed. Use *FIXED MASS SCALING carefully to increase step size without compromising inertial effects. Critical response quantities:
A 60-second earthquake record in Abaqus/Explicit can require billions of increments. Mitigate with:
For implicit analysis, use iterative solvers (*SOLVER, TYPE=ITERATIVE) which are 2-5× faster for large models.
Key output requests:
*OUTPUT, FIELD, VARIABLE=PRESELECT
*NODE OUTPUT
U, V, A, RF
*ELEMENT OUTPUT
S, E, DAMAGEC (for CDP), PEEQ
*ENERGY OUTPUT
ALLKE, ALLIE, ALLVD
Critical response quantities:
