We choose the ductile iron because its mush safer because ductile martial gave people who maintained the stair warning before it fractures and also,
Moreover, we design our stair can resisted until 250 Kg but the average will be 80 kg.
So we have sixteen stairs in the all process in the same time and maximum weight resenting will be 25 kg. In conclusion in every cylinder can resisted maximum weight 39249kg.

Mesh Information

property	Value	Units
Elastic Modulus	1.2e+011	N/m^2
Poisons Ratio	0.31	N/A
Shear Modulus	7.7e+010	N/m^2
Density	7100	kg/m^3
Tensile Strength	861695000	N/m^2
Compressive Strength in X		N/m^2
Yield Strength	551485000	N/m^2
Thermal Expansion Coefficient	1.1e-005	/K
Thermal Conductivity	75	W/(m·K)
Specific Heat	450	J/(kg·K)
Material Damping Ratio		N/A