Concrete towers for onshore and offshore wind farms : conceptual design studies

CONTENTS PROFILES OF THE CONCRETE CENTRE AND GIFFORD PREFACE 1 INTRODUCTION 1.1 Background 1.2 Looking to the future 1.3 The role of concrete 1.4 Current applications of concrete in the wind energy sector 1.5 Background design considerations 1.6 Towards more competitive concrete design solutions 1.7 Aim of this document 2 DESIGN PHILOSOPHY 2.1 General approach and configuration 2.2 Design for construction 2.3 Design concepts 3 DESIGN 3.1 Indicative designs 3.2 Foundations 3.3 Tower elements 3.3.1 Base zone 3.3.2 Middle zone 3.3.3 Upper zone 3.4 Prestressing of the tower 3.5 Thin walled shell units 3.6 Joints 3.7 Construction sequence 3.8 In-situ slipform construction 3.9 Cranage and lifting 3.10 Structural analysis 4 QUANTITIES AND COSTS 5 CONCLUSIONS 6 FIGURES PAGE iii STUDY OF CONCRETE TOWERS FOR OFFSHORE WIND FARMS 7 DESIGN PHILOSOPHY 7.1 Design drivers and approach 7.2 Design scenarios and criteria 8 DESIGN 8.1 Tower configuration 8.2 Pylon 8.3 Foundation and substructure 8.4 Structural design methodology 8.5 Commentary on life cycle issues 8.6 Description of outline designs 8.6.1 Continuous taper design 8.6.2 Necked stem design 8.6.3 Concrete pylon with concrete gravity foundation 8.6.4 Concrete pylon on steel monopile 8.7 Pylon fabrication and erection 8.7.1 Precast concrete method 8.7.2 Slipforming the tower 8.7.3 Prestressing techniques and details 8.7.4 Ancillary details 8.7.5 Formwork for precast units 8.7.6 Joint details 8.8 Construction and installation of the foundation and tower 8.8.1 Current installation methods for steel towers 8.8.2 Installation of gravity foundations 8.8.3 Alternative proposals for caisson and tower construction and installation 8.9 Versatility of the concrete tower concept 8.10 Standardisation of pylon geometry 8.11 Prototype and demonstration designs 9 QUANTITIES AND COSTS 10 COMPARISON OF STEEL AND CONCRETE TOWERS 10.1 Comparision of the dynamics of steel and concrete towers 10.2 Comparision table of offshore tower structures’ characteristics 11 CONCLUSIONS 12 FIGURES 13 GENERAL CONCLUSIONS 14 REFERENCES A1 APPENDIX A Embodied CO2 estimates for wind towers The relative merits and viability of concrete and steel for the wind industry, with practical methods and conceptual configurations for on- and offshore facilities, design philosophies, and construction practices for concrete wind towers; considering fabrication, transportation, installation, maintenance, decommissioning, removal and disposal