
Simple models and open codes make our ideas clearer.
This code conduct timestepping analysis of nonlinear lumped mass cantilevers by the unconditionally stable Newmarkbeta method (average acceleration method).
It is a lite version only for educatinoal purpose. PDelta effect is not included and only two simple hysteresis models are provided.
UHYST01 is the bilinear elasticperfectly plastic model and
UHYST02 is the peakoriented bilinear model, known as Clough model.
To use it, please download and complie the following Fortran code NLMDOF.for.
Source code: MDOF.zip
Two another files, defining the structural model and the ground motion input, need to be prepared and put into the same directory with the program. An example input file is provided as below with comments.

NDOF: 3 /number of DOFs
ksai: 0.05 /damping ratio
Hyst: UHYST02 /hysteresis model: UHYST01 or UHYST02
Mas1: 1000 /mass of each DOF (ton)
Mas2: 1000
Mas3: 1000
Spr1: 2.2e6 2.646e7 0.05 /Spring properties
Spr2: 2.2e6 1.205e7 0.05
Spr3: 2.2e6 0.323e7 0.05

The 3 properties of a spring are:
Initial stiffness(N/mm) Yield strength (N) Post yield stiffness ratio
Number of lines defining the masses and the spring properties must correspond to NDOF.
Example input: Input (included in MDOF.zip)
The ground motion data needs to be put into the PEER/NGA format, where the first 4 lines defines the head information, and each data line after the head contains 5 samples of ground acceleration. See below for an example:
Example earthquake ground motion: ElCentroNS.at2 (included in MDOF.zip)
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