# Units Specification
GSA stores all data in SI unit, but allows the user to specify the units in which his model is defined. These become the base units for working, however these can be changed at any time.
When creating a new model the user’s preferred units are used. These may be changed in the units specification at any time. The units chosen here will be the default units used in GSA, however, local changes of units can be made in individual views.
This can be accessed from the Data explorer, from the 'Model | Data Modules | Specification | Units Specification' menu command, from the General Specification or from the Structure type page of the New Model Wizard. The units specification sets the default units for the model.
In addition the Units dialog is accessible from the Diagram Settings, Contour Settings and Output Settings dialog boxes, and the units button on the Data Options toolbar where there is scope to modify units locally. In this case units which are not relevant are disabled.
# Units
Force
Used for force and force derived units such as moment, etc., but not for stress.
Length – large, small and section
Large length units are used for length and length derived units such as area. Small length units are used for data that are typically small such as displacements and cross-sectional dimensions. Section length units are typically used for cross-sectional properties.
Large length units are also used in units derived from length, such as moment.
Mass
Used for mass and mass derived units such as inertia, etc.
Time
Used for time and time derived units, such as frequency, etc.
Temperature
Used for temperature and temperature derived units such as coefficients of expansion.
Stress
Like displacements, stresses are one of the main results produced by a structural analysis package, so they are assigned their own units distinct from force and length. These units are also used for stress related quantities like the elastic modulus.
Strain
Strain is dimensionless however it is convenient to be able to work with strain units such as με.
Velocity
Used for velocity and velocity derived units.
Acceleration
Sets the acceleration units to be used. Acceleration units are considered as distinct from length and time units. It is common for accelerations to be specified in g so accelerations are given a separate unit.
Energy
Sets the energy units to be used. Energy units are considered as distinct from force and length units.
Angle
It is convenient to be able to choose between degrees and radians for angle measures.
# Reset units
This allow the user to reset the units to
- Preferred – those selected in the Preferred Units accessible from the Miscellaneous Preferences.
- SI – standard SI units.
- kN-m – a more useful set of units for structural analysis based on the SI system of units.
- kip-ft – a set of units based on those commonly used in the USA.
- kip-in – an alternative set of units based on those commonly used in the USA.
# Notes
Other units are derived from these units, so for instance moments are derived from the force and length units giving in the SI units set N m.
Note that data considered to be in units of ‘pressure’ (e.g. Grid Area Load values) are reported in units of Force/Length², not Stress.