System of Units
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EngiLab Beam.2D has no default system of units. This is not a limitation of the program, but a deliberate choice in order for the program to work globally, no matter what system of units is used. This way there is no limitation in the system of units that can be used. Any consistent system of units can be used.
Before starting to define any model, you need to decide which system of units you will use. All input data must be specified in consistent units. As a result, the analysis results will also comply to that system. The important point about using consistent units is the necessity to stick with units that work correctly together - not to mix units that do not have a correct relationship with each other.
In order to define a consistent system of units, you have to define first the primary (basic) units and then the derived units which are dependent on the primary units. We propose two different approaches for defining a consistent system of units, as described in detail below:
A. Consistent system of units based on Force
Define the three primary (basic) units for Force (F), Length (L), Time (T). For example you can choose to use kN, m, s (sec). The derived units are then the following:
* The mass unit (in our example 1 t) is the mass that accelerates by the acceleration unit rate (in our example 1 m/s2) when the unit force (in our example 1 kN) is exerted on it.
B. Consistent system of units based on Mass
Define the three primary (basic) units for Mass (M), Length (L), Time (T). For example you can choose to use kg, m, s (sec). The derived units are then the following:
* The force unit (in our example 1 N) is the force required to accelerate the unit mass (in our example 1 kg) at the acceleration unit rate (in our example 1 m/s2).
Common consistent systems of units
Some common systems of consistent units are shown in the table below.
As points of reference, the mass density of steel, the Young's Modulus of steel and the standard earth gravitational acceleration are given in each system in the table below.
•1 t (tonne) = 103 kg = 1 Mg. It is a mass that accelerates by 1 m/s2 when a force of 1 kN is exerted on it.
•1 slug = 1 lbf·s2/in. It is a mass that accelerates by 1 ft/s2 when a force of 1 pound-force (lbf) is exerted on it.
•1 MPa = 1 MN/m2 = 1 N/mm2
The user chooses to use the MTS system, a common choice for structural engineering applications:
EngiLab Beam.2D data have to be given as shown below:
The results will also comply to that system, thus they will be given as:
* Rotations are ALWAYS given in RADIANS.
Note: In the above example, if one wants to apply self-weight to the structure, he can add the standard earth gravitational acceleration at the -y direction: ay = -9.80665