CRM Engineering

Offshore wind turbine foundations are designed to owner and jurisdictional specified codes. Typically, North Sea installations would follow Offshore Standard DNV-OS-J101, Design Of Offshore Wind Turbine Structures. Grouted connections are typically used to connect the pile to the sleeve in mono-pile and other constructions.

Section 9 of DNV-OS-J101 covers the design requirements for grouted connections. For computation of the behavior of the grouted connection for the limit states, a detailed analysis of the grouted joint is necessary. For such tasks we use the Abaqus finite element analysis program with the concrete damaged plasticity model.

A representative material definition would be:

*Material, name=grout
*Density
2440.,
*Elastic
5.5e+10, 0.19
*Concrete Damaged Plasticity
15., 0.1, 1.16, 0.67, 0.
*Concrete Compression Hardening
8.42e+07, 0.
1.173e+08, 0.0004
1.274e+08, 0.0008
1.3e+08, 0.0035
5.98e+07, 0.005
1.2e+07, 0.01
*Concrete Tension Stiffening
7e+06, 0.
4.5e+06, 0.0003
3.1e+06, 0.0005
2.1e+06, 0.0008
500000., 0.1
*Concrete Tension Damage
0., 0.
0.8, 0.005
0.9, 0.008
0.99, 0.1

Components of this material model:

• The compressive non-linearity starts well before the compressive ultimate strength
• The *Concrete Tension Stiffening option defines the behavior of the grout in tension
• The *Concrete Tension Damage option defines the amount of damage from tensile strains. This is analagous to the cracking in the grout.

DNV-OS-J101 mandates that the analyses model the contact between the grout and the streel structure and that the analyses be carried out with and without friction for structures without shear keys. Since the grout is expected to crack in tension, an implicit solution such as is used in Abaqus Standard may not be possible due to the highly discontinuous nature of unreinforced concrete (grout) cracking. In these cases, we simulate the structure using Abaqus Explicit, a finite-difference dynamics code.