OpenSees Example 3. Cantilever Column with units

Introduction

The principal features of this example is the introduction of units and the separation of the model-building and the analysis portions of the input file. For demonstration purposes, this example visits the 2D cantilever column, again.

Input

Static Pushover

Files

Ex3.Canti2D.InelasticFiberSection.Push.tcl

Dynamic EQ Ground Motion

Files

Ex3.Canti2D.InelasticFiberSection.EQ.tcl
BM68elc.acc (ground-motion file)

Run

To run Static Pushover analysis:

source Ex3.Canti2D.InelasticFiberSection.Push.tcl

To run EQ ground-motion analysis (BM68elc.acc needs to be downloaded into the same directory):

source Ex3.Canti2D.InelasticFiberSection.EQ.tcl

Notes

This example is the first to follow most of the recommended techniques in building an input file:

Model and analysis parameters are defined as variables
The basic units, used to define Force, Length and Time need to be independent.
Units need to be used consistently throughout the input file, otherwise some arguments will not scale properly
The model-building files and the analysis files are separated. The same analysis file can be used on different model-building files (elastic or inelastic elements).
This example does not, however, take advantage of previously-defined Tcl procedures and scripts, as will Example 4.

In OpenSees/Tcl, units are simply defined as variables that become scaling factors. This technique allows the user to input variables with different types of units, not just the ones chosen for output. For example, section widths can be defined in inches, while element length can be defined in feet.

For example, with the following commands used in setting some of the units:
set in 1.; # define basic units -- output units
set kip 1.; # define basic units -- output units
set sec 1.; # define basic units -- output units
# -------
set ft [expr 12.*$in]; # define engineering units
set ksi [expr $kip/pow($in,2)];
</blockquote>
When the user says:
set HCol [expr 3*$in];
set LCol [expr 30*$ft];
</blockquote>
Tcl multiplies 30 by 12 to give the column length in inches. By scaling the input, all input processed by OpenSees is in the basic units, as is the output.
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