Steel construction. Solutions for the renewable energy and offshore sectors. published by energyengineering magazine

Transcription

1 Steel construction Solutions for the renewable energy and offshore sectors published by energyengineering magazine SCI-Energy-Supplement.indd 1 25/10/ :00:22

2 Introduction SCI is a world leader in technology development and innovation. Here is a brief introduction to the company World Leader The Steel Construction Institute (SCI) is the leading independent provider of technical expertise and disseminator of best practice to the steel construction sector. Working in partnership with clients, members and industry peers, SCI helps build businesses and provide competitive advantage through the commercial application of its knowledge. SCI has been at the forefront of steel and composite design innovations for the last 25 years. These forms of construction are highly appropriate and ideally suited to the energy sector. SCI assists clients to meet their business needs by providing essential technical support to their activities. As such, SCI is increasingly being engaged at the product concept stage and its involvement continues through the design, testing and evaluation phases, to the production of technical literature and supporting software. Regulatory changes and technical improvements to products and services all signal an increased need for independent authoritative endorsement. SCI provides unbiased, third party assessment and certification for steel construction products and systems. SCI can offer highly specialised skills developed during 25 years of experience in various sectors. Those skills are readily transferable to the renewable energy and offshore wind sectors. SCI can find solutions to meet extremely demanding situations that offer better design quality and buildability. Membership Advisory Support Technical Information Courses Technical Information Design Guidance Code Drafting Product Technical Literature Construction Solutions Sustainability Product Development Research and Engineering Communications Technology Engineering Software On-line Information Systems Online Training Assessment SCI Assessed Q-Mark CE Marking SCI s business areas Specialist sectors such as offshore and nuclear need to comply with a range of performance and safety requirements. Companies who are increasingly active in the renewable energy sector, or facing these types of specialist construction challenges, can benefit from SCI s wealth of experience. A key strength of SCI, is the ability to commercially apply this technical knowledge.

3 Interview Construction Technologies Dr Bassam Burgan, SCI Director, who has responsibility for the development of SCI s renewable energy and offshore services talks to Robert Gerald Since the Steel Construction Institute s (SCI) formation in 1986, the organisation has played a leading role in technical innovation and development of industry standards and guidance, helping the construction sector achieve a world leading market share for steel. Over the last 20 years, SCI has proved it has a great deal to offer the renewable energy market; its credentials include wide ranging quality engineering expertise and breaking new ground with innovative concepts. SCI works with clients in new areas to meet the needs of a diverse construction industry and believes that steel has a key part in the delivery of economic solutions for renewable energy generation. The institute was formed in response to steel s growing popularity as a structural material in the early 1980s. This was driven by a series of economic and technological factors, says Dr Bassam Burgan, SCI Director. The industry quickly recognised that maintaining and enhancing this position depended upon the creation of a body of knowledge to ensure the most effective use of steel in construction. SCI was established in May 1986 with the purpose of achieving this objective. From those beginnings, the SCI has evolved to take on increasingly diverse and challenging applications of steel, with its work on the use of steel in the offshore sector beginning with a major joint industry project addressing the analysis and economic design of jacket structures for offshore installations in the North Sea. Following the Piper Alpha disaster in 1987, SCI led a series of joint industry projects that addressed the design issues arising out of that accident. This led to publication of the Interim Guidance Notes for the Design and Protection of Topside Structures, which became the industry standard guidance in 1992, says Dr Burgan. The work also led to the establishment of the Fire and Blast Information Group, which continues to this day to develop specialist design guidance and update the oil and gas sector on key fire and explosion safety issues. SCI has also been at the forefront of double skin composite construction technology which is highly relevant to the renewable and offshore sectors. SCI has carried out research and development into double skin steel composite construction for the last 20 years. We have looked at a variety of challenging application environments, Dr Burgan explains. We are perfectly placed to deliver this technology which is ideal for meeting operating environments in the offshore wind sector. SCI s interest in this area and the subsequent development of double skin composite construction started in 1990, sparked off by work undertaken on the Conway river tunnel and the challenges arising from this. In 1990, SCI won EC funding for a project to research and develop this form of construction. Most pertinent to the offshore wind energy sector was SCI s further research between on this form of construction under fatigue loading conditions. We believe that double skin composite construction has a big part to play in the delivery of economic foundations for large offshore wind turbines adds Dr Burgan. Its modular construction means it delivers cost, programme and safety benefits. The offsite and modular nature aids the construction process - heavy foundations necessary for offshore structures can be pre-fabricated in a factory and then floated and sunk into position in one section.

4 Many of SCI s skills are transferable to the renewable energy sector, where there is not always a precedent for designing or constructing due to the pioneering nature of this work. When clients are designing new foundation systems or products for incorporation into such systems, SCI can undertake all the work that underpins the development such as testing, analysis and bespoke software services. This really helps clients gain confidence and market acceptability for the new concept or product, says Dr Burgan. We can also undertake independent assessment, accrediting products and systems which helps gain market acceptance - a real asset when breaking new ground. With CE marking likely to be compulsory by 2012, SCI has seen SCI-Energy-Supplement.indd 4 significant uptake of SCI Assessed, an independant assessment service leading to the award of the SCI Assessed quality mark. A new and evolving sector, such as renewable energy, can hugely benefit by having new concepts and products supported in this way. SCI also helps with design outside the design codes. Since the offshore renewable energy sector is new and at the sharp edge of innovation there are often gaps in codified design methods. We can support designers by applying fundamental engineering principles, Dr Burgan explains. We can also develop bespoke design and guidance so that innovation in this vital area isn t hampered by a lack of codified design methods. In addition, our sustainability credentials span a very broad spectrum. We offer life cycle assessment and carbon foot printing services that are as applicable and relevant to the renewable energy sector as they have been in the building sector. Steel has become the main construction material in the renewable energy sector, in a variety of construction forms. With ongoing research and development, steel based concepts can meet the most stringent performance requirements required demanded by this sector. 25/10/ :00:24

5 Study Tidal Barrage SCI looks at the use of steel construction in tidal barrages The Steel Construction Institute (SCI) undertook an investigation into the use of steel construction in tidal barrages. A large part of the work was to develop designs in steel for the components of a barrage, and to cost typical barrages. It allowed the potential for steel to be investigated for a range of likely barrage configurations and sizes. Additionally, the work included the study of established offshore techniques perfected on North Sea structures in such areas as piled foundations, modular construction, grouting and sealing methods, and installation aspects. SCI was able to bring together, in one project, the in-house capabilities of its offshore and onshore departments to optimise the use of steel for tidal barrages. This was a unique combination of civil, marine and offshore technologies. The initial barrage component designs were performed for caissons, foundations, turbine draught tubes, gates, bridges, cranes and modules. The design of each considered several construction methods such as ship type fabrication comprising multi-stringer stiffened plate, thicker plate with few stiffeners, and composite steel/concrete/steel construction. Each type of construction was costed depending on whether existing construction facilities could cope with the required amount of fabrication, or whether purpose built yards were necessary. The generic design and associated cost data were assembled into sets of curves showing the variation of cost with the design parameters. As work progressed on the designs, it became apparent that an automated design routine was essential to enable the great number of variables to be considered. As well as variations in environmental parameters such as tide range, water depth and wave height, there were also design variables such as wall thickness, stiffener spacing, yield strength and many more. Variations in overall size, shape and ballast arrangements for providing suitable factors of safety at construction and working stages were considered in arriving at the optimum design. The next stage of the work was to optimise construction techniques for typical barrages and arrive at overall costs. These bench-mark barrages were Padstow, Mersey and Severn, representing small medium and large barrages. This project was extremely informative in developing optimum construction techniques. It would be possible to extend the design method to give a probability distribution of the complete structure cost depending on the variation of many smaller components. This would also enable the most significant component costs to be identified, in order to aid design optimisation.

6 Concepts SCI discusses new concepts for offshore wind turbine foundations Foundations Concepts for offshore wind structures Current designs of offshore wind turbines in relatively shallow water are based on extensions of the monopile system that is used in onshore wind towers. The next generation of offshore wind towers is in deeper water, and will require a step change in construction to reduce the rising cost of offshore wind energy generation. The construction cost of recent offshore wind projects is as high as 3 million per MW of installed turbine power output or typically in the range of 8 to 12 million per offshore tower, foundation and its electrical installation. New concepts have been proposed by SCI. These are based on various forms of pre-fabricated double skin foundations. They use prefabricated caissons or gravity bases for deeper water around the UK, which has one of the best wind resources in the World. The concepts utilise double skin structural forms suited to water depths between 20 and 40 m. 0.7 m Double skin cone concept 4 m m Three prefabricated double skin concepts are suggested for the gravity base: A double skin base and cone solution, suitable for water depths of up to 25 m. A multiple caisson solution in which the caissons are placed around the base of a conventional tower. This solution is suitable for water depths of 20 to 40 m. A segmental caisson solution in which the four segments are placed around the tower and connected together, suitable for water depths of around 30 m. Double skin cone concept The sub-sea structure comprises three distinct parts: A double skin concrete filled base that is square in shape and can have additional steel skirts to prevent scour Barge A plate steel cone that is welded to the top plate of the base. A lower part of the tower that is connected to the cone and to the upper tower at approximately 5 m above sea level. The prefabricated base, cone and lower part of the tower are floated into position. In operating conditions, the base is designed so that it is not subject to tension as a result of over turning effects and the bearing pressure is within the design limits for the sub-sea foundations of that particular location. Multiple caisson solution The individual caissons are 12 to 15 m diameter and a group of three or four caissons forms the base to the tower. The caissons are prefabricated as double skin units and floated into position. Because

7 they are relatively small in size, the wall thickness of the caissons may be in the region of 300 mm. The caissons are floated in-line with articulated connections and are placed around the tower. Their open tops are filled with a heavy ballast material and they descend at a controlled rate. In their final position, cables are wrapped around the caissons to bring them together and they are clamped by jacking in position around the base of the tower. The outward jacking forces are resisted by the shear forces in connecting bolts between the caissons. This system has the advantage that the size of the caissons can be adjusted to the water depth and 4-6 m m m a) Plan form b ) Side view Segmental caisson concept Grout filling Segmental caisson Tied connection 0.3 m m m Multiple caisson solution necessary foundation conditions. Also, there is economy in scale in the manufacture of the caissons. Skirts can be pre-attached to the base of the caissons. Segmental caisson concept The segmental caisson concept is an adaptation of the circular 0.2 m Grouted filling Heavy fill 5 m m m Bi-steel caisson 2 m 13 m diameter 0.5 m 1 m 0.5 m m caisson idea except that the four segments form a circle around the tower. The disadvantage is that the caissons are not circular which means they are not so resistant to hydrodynamic forces during installation and so they are not as large as the circular caissons. Their advantage is that they form a stronger assembly in the final condition, which makes them suitable for water depths of around 30 m. Again, the caissons are floated in-line with articulated connections and are placed around the tower. Their open tops are filled with a heavy ballast allowing them to descend at a controlled rate, similar to the circular caisson concept discussed earlier. Benefits of double skin composite construction: Steel plate Eliminates the need for formwork More structurally efficient and lighter than reinforced concrete High ductility and impact resistance Steel plate Stud connectors Concrete The steel plates act as an impermeable membrane Faster construction: prefabricated modular units Clean finish

8 TM Are you Getting the best From steel? Is steel a significant material in your renewable energy solution? Would you like to explore how steel could be used more efficiently? Would your product or concept benefit from research and development or independant assessment? Yes/no Yes/no Yes/no SCI is the leading, independent provider of technical expertise and disseminator of best practice to the steel construction sector. We are committed to offering and promoting sustainable and environmentally responsible solutions. SCI has a proven track record in bringing new innovations to the construction sector (we completed our first renewable energy project in 1990) and is a world leader in the development of double skin composite design. We are working with organisations throughout the world to help them get the most out of steel. SCI services to the renewable energy sector include: Steel material expertise Research and development Project management and IT Funding Network FE analysis Joint/connection design Material durability Best practice design and dissemination Leading experts in Eurocodes 3 and 4 Lab testing Verification of data and processes Validation of data and processes Project management experts Communication and dissemination solutions Bespoke design software solutions Knowledge of UK government and EU funding mechanisms Collaborative research programmes Conduit to 650 members We would be delighted to discuss our service offerings with you and explore how we may be able to add value to your renewable energy solutions. Join the SCI group Follow SCI on Twitter If you would like to find out more about the SCI please contact Melissa Barber or Sandi Gentle. Tel: or visit our website at