


























DESIGN FOR BSSPHERICAL NODES 



The design for the BSspherical node is usually done with a FiniteElementProgram (FEM). 



Example for the desing of a BSspherical node type KK3 for the “Riesenbühlturm”. 



Outer shell diameter = 400 mm
Shell thickness = 25mm
Material = GS 52 ( castiron according to the German Standard)
System diameter for FEM = 375mm There is no member connection done at the access hole (D = 120mm) and at the hole for removing the cast core (D = 38 mm)
Therefore, these two holes are defined centrically in each case in the poles of the FEMshell. In the pole range of the FEMshell, the finite elements have an unfavorable length ratio (higher
than 1.5 : 1). Calculation results with a load entry in poles of the FEMshell would be too inaccurate! 



In order to guarantee the stability of the FEMshell and in order to level the inaccuracies of idealization the FEMshell is supported at any node with the following stiffness factors:
deflection stiffness in x, y and zaxis = 100 kN/m
rotation stiffness around x, y and zaxis = 100 kN*m/rad 



At the places of the member connections the drill holes were simulated (here rectangular) in the FEMmodel. The selected elementlength should take regard to the diameter of the drill holes. The
stiffening around the hole edges by the steeltubes (welded to the shell) is normally not considered. 



The loads are applied normally to the spherical surface (with preference) as surface loads around the holes. This is justified because of the existence of the BSbowl washers. Alternative every
member load can be simulated by a corresponding number of single loads into the element nodes around the holes. 







[FiniteElementModel] 



All possible load combinations were calculated. The loads to the FEshell are for every load combination with each other in equilibrium (i.e. the sum of the force vectors is the zero vector).
Theoretical all six force components of the above mentioned supporting are zero. Because of the normal inaccuracies of idealization, the FiniteElementProgram determines small supportingforce components. If the
supportingforce components Ax, Ay, Az, Mx, My and Mz are in a no more negligible range, there must be mistakes in the system and / or in the load inputs. 



By absorbation of stresspeaks with stressrelocation because of plastication of the ductile material GS52, the ultimate bearingcapacity is even higher. 






[Tested BSspherical node (Fu = 522 kN)] 



eM@il: info@bertschesystem.de 
