Nonlinear Finite-Element analysis of a large offshore concrete structure
Autor: Joël Arnet
Sprache: Englisch
Kurzfassung
The mechanically consistent constitutive laws of reinforced concrete developed at the ETH Zürich such as the cracked membrane model is limited in its application to the use for distinct structural elements such as membranes, plates or beam elements. This thesis aims to utilise these laws in a nonlinear Finite-Element analysis for a large prestressed concrete offshore structure subjected to a lateral iceberg impact load. Furthermore, the goal is to identify the benefits and limitations of the nonlinear analysis procedure. The constitutive laws are implemented in the user-defined material model called CMM-Usermat in the software ANSYS Mechanical APDL. The modelling of the structure consists of a linear and nonlinear part. The former is used to calculate the reinforcement contents required for the nonlinear analysis, employing the Sandwich model with taking into account the increase in prestressing force and adaptable cover thicknesses. The analysis is performed based on the internal forces, the stresses and strains consisting of the steel stresses at the crack, the concrete principal stresses, the crack orientations and the principal strains as well as a cross-section analysis. These are generated from the manual post-processing of the result data. Thereby, it could be identified that the offshore structure is dominated by a compression membrane state, where the iceberg impact load only has a local effect, showing little cracking and low reinforcement stressing. The nonlinear Finite-Element analysis using the CMM-Usermat allows an actual insight of material capacity utilisation and the effective cracked stiffness of the structure. Despite its complex and time-consuming implementation, the interpretation of the cracked membrane model result variables permits for the engineer a better understanding and traceability of the global structural behaviour of large structures.
