Step 1. Preparation of the input data

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The first step is to define the System of Units. This is a very important step for the model. This step has nothing to do with the program itself. Instead, the user has to define the preferred system of units and then all the program data have to be consistent with this system. Then the results will also comply to that system. For details, see System of Units.


We choose a consistent system based on Force. We choose to use:

m for Length (L)

kN for Force (F)

s for Time (T)


The derived units are then the following:

The Acceleration unit is given by: L/T2 (1 Length unit) / (1 time unit)2. In our example: m/s2

The Mass unit is given by: F·T2/L (1 force unit) / (1 acceleration unit). In our example: kN/(m/s2) = Mg = t (IMPORTANT: t has to be used instead of kg!)

The Density unit is given by: F·T2/L4 (1 mass unit) / (1 length unit)3. In our example: t/m3 (IMPORTANT: t/m3 has to be used instead of kg/m3!)

The Stress unit is given by: F/L2 (1 force unit) / (1 length unit)2. In our example: kN/m2


Note: 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.


The Material properties should be given as:

E = 29 GPa = 29000000 kN/m2

d = 2500 kg/m3 = 2.5 t/m3


The Section properties should be given as:

Columns: Square section, 50 cm * 50 cm = 0.50 m * 0.50 m

Beams: Rectangular section, 50 cm * 25 cm = 0.50 m * 0.25 m


The gravity acceleration should be given as g = 9.81 m/s2