GGU-SLAB: "Single springs" menu item
Beside beam elements, individual system nodes can also be assigned single springs. The application of single springs may be required if you need to investigate a slab, for example, resting on only slightly load-bearing ground and which is therefore supported in various locations by piles.
After clicking a node, a dialog box opens for defining the magnitude of the single spring in kN/m. Input ≤ 0.0 delete an existing spring.
The size of the single spring is acquired from the resistance-settlement diagram to DIN 4014, for example. For instance, if a pile displays a settlement of s = 0.95 cm with a bearing capacity of P = 1340 kN, the single spring size CB is calculated from:
CB = P/s = 1340/0.0095 = 141,000.0 kN/m
If you also need to take the axial stiffness of the pile into consideration the spring constant of the pile CP must be determined from:
CP = E · A/L
E = Young's modulus of pile
A = cross-sectional area of pile
L = length of pile
Example:
E = 30,000,000 kN/m² (concrete)
A = 0.20 m²
L = 12.0 m
Giving
CP = 30,000,000 · 0.20/12.0 = 500,000.0 kN/m
The size of the single spring (overall spring constant) C is acquired from:
1/C = 1/CB + 1/CP
1/C = 1/141,000 + 1/500,000 = 9.0922 · 10-6
C = 109,984 kN/m