BS 1 - BS 6
RS 12 - RS 42
KK 1 - KK 3
SA 16 - SA 25
ASQ 12 - ASQ 20
VA 1
BS-spherical node

DESIGN FOR BS-SPHERICAL NODES

The design for the BS-spherical node is usually done with a Finite-Element-Program (FEM).

Example for the desing of a BS-spherical node type KK3 for the “Riesenbühlturm”.

Outer shell diameter              =   400 mm
Shell thickness                      =   25mm
Material                                =   GS 52     ( cast-iron 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 FEM-shell.
In the pole range of the FEM-shell, the finite elements have an unfavorable length ratio (higher
than 1.5 : 1). Calculation results with a load entry in poles of the FEM-shell would be too inaccurate!

In order to guarantee the stability of the FEM-shell and in order to level the inaccuracies of idealization the FEM-shell is supported at any node with the following stiffness factors:

deflection stiffness in x-, y- and z-axis             =    100 kN/m

rotation stiffness around x-, y- and z-axis        =    100 kN*m/rad

At the places of the member connections the drill holes were simulated (here rectangular) in the FEM-model. The selected element-length should take regard to the diameter of the drill holes. The stiffening around the hole edges by the steel-tubes (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 BS-bowl washers. Alternative every member load can be simulated by a corresponding number of single loads into the element nodes around the holes.

[Finite-Element-Model]

All possible load combinations were calculated. The loads to the FE-shell 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 Finite-Element-Program determines small supporting-force components. If the supporting-force 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 stress-peaks with stress-relocation because of plastication of the ductile material
GS-52, the ultimate bearing-capacity is even higher.

[Tested BS-spherical node (Fu = 522 kN)]

e-M@il: info@bertsche-system.de