Abstract
The growing need for sustainable production of electricity highlights the importance and the necessity of having higher number and more effective offshore wind towers. The rapid growth of offshore wind towers is estimated to produce 4% of electricity demands in Europe by the end of 2020. The research described in this paper is part of a project dedicated for the development of innovative structural system using advanced materials for lightweight and durable offshore towers. Specifically, it discusses the nonlinear finite element modelling of the connection between representative prefabricated rings of offshore wind tower made by steel fibre reinforced concrete (SFRC), and prestressed by a hybrid system of carbon fibre reinforced polymers (CFRP) bars and steel strands. This connection is assured by post-tension high steel strength cables and concrete-concrete shear friction width an idealized geometric configuration of the faces in contact. The model takes into account the loads from the rotor, wind and water currents, by considering the critical loading conditions for the safety verifications of serviceability and ultimate limit states. The material nonlinear analyses are carried out with FEMIX V4.0 software, considering a 3D constitutive model capable of simulating the relevant nonlinear features of the SFRC, and interface finite elements for modelling the shear friction of the concrete-concrete surfaces in contact. The parametric analyses involve the influence on the relevant results of the SFRC fracture parameters, pre-stress level of the reinforcements, shape of interlock mechanism, friction angle and interface cohesion.
Highlights
The developing need of energy production is draining the natural resources like oil, natural gas, coal etc., at a more rapid rate than ever
Each ring is prestressed with 16 carbon fibre reinforced polymer (CFRP) bars of 30 mm diameter placed in the centre of the steel fibre reinforced concrete (SFRC) wall (Fig. 3b)
Parametric studies are performed to assess the influence of the connection between the rings on the following aspects: a) SFRC fracture parameters, which are dependent on the fibre orientation; b) Pre‐stress level in the steel and CFRP reinforcement; c) Shape of concrete‐concrete interlock mechanism; d) Friction angle of the concrete‐concrete contact conditions; e) Cohesion of the concrete‐concrete contact conditions
Summary
The developing need of energy production is draining the natural resources like oil, natural gas, coal etc., at a more rapid rate than ever. The main scope of this paper is to perform material nonlinear analysis of the connection between two representative steel fibre reinforced concrete (SFRC) prefabricated rings (of thin wall and variable diameter) of the structural system developed in the scope of the research project. The loads considered consist of forces acting on top of the structure due to wind passing throughout the rotor, wind pressure on the tower structure, waves slamming the tower, and loads produced by water currents on the tower structure (see Fig. 2). Each ring is prestressed with 16 carbon fibre reinforced polymer (CFRP) bars of 30 mm diameter placed in the centre of the SFRC wall (Fig. 3b). An additional linear layer of SFRC (1 m thick) is modelled (Fig. 3b) to avoid the development of unrealistic stress fields and severe cracking on the SFRC rings, where the real tower equivalent loads are applied (top of ring 2). The interface elements are assigned the following properties: slip at the end of the linear bond‐slip relationship is 0.5 mm (S0), slip at the peak bond stress is 2.5 mm (Sm), material cohesion of 1 MPa, friction angle as 37 , parameter defining pre‐peak bond stress‐slip relation is 1=1, parameter defining post‐ peak bond stress‐slip relation 2=1 and a normal stiffness (Kn) of 2.0 107 N/mm
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