Life Cycle Assessment of Tall Onshore Hybrid Steel Wind Turbine Towers

Increasing needs for taller wind turbines with bigger capacities, intended for places with high wind velocities or at higher altitudes, have led to new technologies in the wind energy industry. A recently introduced structural system for onshore wind turbine towers is the hybrid steel tower. Comprehension of the environmental response of this hybrid steel structural system is warranted. Even though life cycle assessments (LCAs) for conventional wind turbine tubular towers exist, the environmental performance of this new hybrid structure has not been reported. The present paper examines the LCA of 185 m tall hybrid towers. Considerations made for the LCA procedure are meticulously described, including particular attention at the erection and transportation stage. The highest environmental impacts arise during the manufacturing stage followed by the erection stage. The tower is the component with the largest carbon emissions and energy requirements. The obtained LCA footprints of hybrid towers are also compared to the literature data on conventional towers, resulting in similar environmental impacts

On the structural response of a tall hybrid onshore wind turbine tower

Given the increasing demand for taller structures in wind energy applications and the accompanying need for a better understanding of their structural response, the present study performs aeroelastic analysis on a novel wind turbine structure and discusses the obtained results. The response of a hybrid onshore wind turbine tower consisting of a 60 m lattice structure and a 60 m tapered tubular structure, with a 5 MW class AII turbine, is investigated. From the Design Load Cases (DLC) established in IEC64100-1 standard, focus is set on DLC 1.1 and DLC 1.3 which correspond to power production conditions and embody the requirements for loads resulting from atmospheric turbulence during normal and extreme operating conditions respectively. DLC 6.1 which refers to standstill or idling conditions under extreme wind model is also studied. In order to account for the interaction between elastic, viscous and inertial forces of the structure and the external aerodynamic forces, ashes, an integrated analysis software, is used. After developing the wind turbine tower model and generating the turbulence models, 600 seconds simulations are performed. The wind flow is assumed to be parallel to the hub axis. For DLC 1.1 and DLC 1.3, parametric studies with the wind speed ranging from 3 to 25 m/s, with an incremental step of 1 m/s, are executed. In DLC 6.1, the blades are feathered and the wind speed is rapidly increased to 42.5 m/s. Time histories of the elemental forces and the nodal displacements are extracted in critical positions of both the lattice and the tubular part. The mean values of the output data are evaluated and plotted against the wind speed. Conclusions regarding the influence of the wind speed on the induced tower behaviour are drawn

Flexural Buckling of Concrete-Filled Aluminium Alloy CHS Columns: Numerical Modelling and Design

The current study deals with numerical modelling and design framework of concrete-filled aluminium alloy columns with circular hollow sections (CHSs) under pin-ended boundary conditions. The examined aluminium alloy is 6082-T6, and the concrete infill has cylinder compressive strength of 30 MPa. Finite element modelling was employed to simulate the investigated columns. Reported test data were used to verify the developed finite element models. Material and geometrical nonlinearities were considered during the analyses. Parametric analyses have been executed to generate structural performance results over a wide range of member slendernesses for a stocky and a slender cross section. The obtained load-mid-height lateral displacement curves were discussed. The ultimate capacities predicted by numerical analyses were utilised to assess the design strengths predicted using combined formulae of EN 1994-1-1 and EN 1999-1-1 and design criteria proposed by Zhou and Young for the plastic resistance of concrete-filled aluminium alloy CHSs combined with flexural buckling strength predictions suggested by EN 1999-1-1. It was shown that the latter provides more accurate and consistent design strength predictions

Testing, numerical simulation and design of prestressed high strength steel arched trusses

The structural behaviour of prestressed high strength steel arched trusses is studied in this paper through experimentation and numerical modelling. Four 11 m span prestressed arched trusses fabricated from S460 hot finished square hollow section members were loaded vertically to failure. Three of the tested trusses were prestressed to different levels by means of a 7-wire strand cable housed within the bottom chord, while the fourth truss contained no cable and served as a control specimen. Each truss was loaded at five points coinciding with joint locations along its span, and the recorded load-deformation responses at each loading point are presented. Inclusion and prestressing of the cable was shown to delay yielding of the bottom chord and enhance the load carrying capacity of the trusses, which ultimately failed by either in-plane or out-of-plane buckling of the top chord. For the tested trusses, around 40% increases in structural resistance were achieved through the addition of the cable, though the self-weight was increased by only approximately 3%. In parallel with the experimental programme, a finite element model was developed and validated against the test results. Upon successful replication of the experimentally observed structural response of the trusses, parametric studies were conducted to investigate the effect of key parameters such as prestress level, material grade and the top chord cross-section on the overall structural response. Based on both the experimental and numerical results, design recommendations in the form of simple design checks to be performed for such systems are provided

A NUMERICAL STUDY OF PRESTRESSED HIGH STRENGTH STEEL TUBULAR MEMBERS

The structural behavior of prestressed high strength steel (HSS) tubular members is investigated through the execution of advanced finite element modeling. Numerical models are developed and validated against published experimental data on HSS tubular members subjected to different levels of initial prestress and loaded either in tension or compression. The effect of the presence or absence of grouting on the strength and ductility of the members is also considered. To numerically replicate the structural response recorded in the tests, some key modeling features including the employed numerical solver, the adopted material models and the element types warrant careful consideration. Upon developing of the finite element models, the numerically generated ultimate loads, the corresponding failure modes and the full load-deformation curves are compared to the experimental ones, indicating a successful validation. As anticipated, prestressing enhances the load-bearing capacity for the tensile members, whereas it is detrimental for the compressive ones. A series of parametric studies is performed to assess the influence of key factors on the structural response of prestressed HSS members and the obtained results are discussed. Design guidance for tensile and compressive prestressed tubular members is also provided

Aluminium alloy channel columns: Testing, numerical modelling and design

Aluminium alloys can be employed in a wide range of structural applications offering high strength-to-weight ratio, whilst they can easily be extruded in various shapes. Channel (C-) sections have been increasingly employed as compression members, such as wall studs and chord members of roof trusses in framed residential and commercial buildings. However, relevant studies on their compressive behaviour are quite limited and thus a greater emphasis should be placed on providing a deeper understanding. Towards this direction, this paper examines the structural performance of C-sections under axial compression. An experimental and numerical investigation was performed on 6082-T6 heat-treated aluminium alloy C-section columns. In total, 6 fix-ended stub column tests were executed to examine the cross-sectional compressive behaviour, whilst 8 pin-ended column tests were conducted to study their minor-axis flexural buckling behaviour. The obtained experimental results were utilised to validate the developed finite element models. Subsequently, extensive parametric studies were carried out to generate additional performance data over a broad range of cross-sectional aspect ratios, and cross-sectional and member slendernesses. Both the experimentally and numerically obtained ultimate strengths are utilised to assess the accuracy of Eurocode 9 design provisions, including the flexural buckling curve. On the basis of the experimental and numerical results, a new flexural buckling curve is proposed improving the design accuracy. The applicability of the Direct Strength Method on the design of aluminium alloy C-sections subjected to axial compression is also evaluated resulting in the most accurate and consistent design strength predictions

Plastic design of hot-finished high strength steel continuous beams

High strength steels (HSS) are increasingly used in structural engineering applications owing to their high strength to weight ratio. Due to the inferior ductility and strain-hardening characteristics of HSS and the lack of relevant structural performance data, plastic design is currently not permitted for HSS indeterminate structures. To this end, the present paper aims to generate structural performance data and to assess the applicability of plastic design to hot-finished HSS continuous beams. Upon a summary of previously drawn conclusions regarding the applicability of European design provisions to S460 and S690 hot-finished square and rectangular hollow sections, a gap on the response and design of indeterminate structures is identified. Validated numerical models of two-span HSS continuous beams are subsequently used for the generation of a wide range of structural performance data by developing a broad parametric studies numerical program. The effect of key parameters such as the cross-section slenderness, the cross-section aspect ratio and the steel grade on the structural response of continuous beams is assessed. The obtained results are discussed and the possibility of plastic design for high strength steel indeterminate structures is evaluated, whilst reliability of the elastic and plastic design methods is also verified according to Annex D of EN 1990

Compressive behaviour of high-strength steel cross-sections

The recent increase in the use of high-strength steels (HSSs) in modern engineering practice necessitates a deeper understanding of their structural response. Given that HSS design specifications are largely based on a limited number of test data and assumed analogies with mild steel, their applicability to HSS sections needs to be assessed. In the work reported in this paper, finite-element models were developed and validated against experimental data of hot-finished S460 and S690 grade steel stub columns. Parametric studies were conducted to generate a large volume of structural performance data over a wide range of cross-section slenderness values and aspect ratios. On the basis of the results, the suitability of the Eurocode 3 (EC3) class 3 slenderness limit and the effective width equations for HSS sections were assessed. Aiming to account for element interaction effects, which are not considered in EC3, an effective cross-section method applicable to HSS slender sections was developed. Finally, the continuous-strength method was extended to stocky S460 sections, for which overly conservative strength predictions were observed. The reliability of the proposed design methods was verified according to annex D of the Eurocode structural design basis (EN 1990)

Numerical Modelling and Design of Aluminium Alloy Angles under Uniform Compression

Research studies have been reported on aluminium alloy tubular and doubly symmetric open cross-sections, whilst studies on angle cross-sections remain limited. This paper presents a comprehensive numerical study on the response of aluminium alloy angle stub columns. Finite element models are developed following a series of modelling assumptions. Geometrically and materially nonlinear analyses with imperfections included are executed, and the obtained results are validated against experimental data available in the literature. Subsequently, a parametric study is carried out to investigate the local buckling behaviour of aluminium alloy angles. For this purpose, a broad range of cross-sectional aspect ratios, slenderness and two types of structural aluminium alloys are considered. Their effect on the cross-sectional behaviour and strength is discussed. Moreover, the numerically obtained ultimate strengths together with literature test data are utilised to assess the applicability of the European design standards, the American Aluminium Design Manual and the Continuous Strength Method to aluminium alloy angles. The suitability of the Direct Strength Method is also evaluated and a modified method is proposed to improve the accuracy of the strength predictions

Testing, numerical simulation and design of prestressed high strength steel arched trusses

The research leading to these results has received funding from the Research Fund for Coal and Steel (RFCS) under grant agreement No. RFSR CT 2012-00028