Controlling Seismic Risks: Looking at buildings as an example
Although we cannot change seismic hazard, in other words the magnitude and occurrence of earthquakes, we can however increase a structure’s resistance/resilience and so reduce seismic risk through preventive measures.
How structures respond
Buildings do not all respond to earthquakes in the same way and their structural and architectural design influences how they are affected. The structures act as oscillators which amplify or reduce ground movements to varying degrees.
Structure types
In terms of building structures, two main types emerge: portal frame construction with brick infill, and concrete or brick shell construction. In an earthquake, these two types respond differently: portal frame types are flexible and behave with a flexural tendency, whereas concrete or masonry structures are more subject to shear stress, especially in the case of low buildings.
Fragility – evenness
Good architectural design aims for: non-resonance of the structure with the oscillations of the ground, elimination of torsional phenomena, minimising stress concentrations (uneven loads), continuous mass distribution, bracing elements distributed in a way appropriate to mass distribution, etc.
Seismic repair and reinforcement strategies
There are three main operational methods, once the fragility and evenness factors of the building have been dealt with:
- Increasing ductility (for example, carbon fibre jacketing of columns)
- Increasing strength (for example, use of shotcrete)
- Reducing seismic action (for example, Transpec® damper or use of bearing systems to isolate from the ground)
Freyssinet operates in all the following fields:
Seismic safety: a major concern
Robert G., South-East Regional Director in France* presents seismic safety regulations and related issues.
The context:
In the world each year there are over one hundred and fifty earthquakes with magnitudes of 6 or higher (in other words earthquakes that release enough energy to be potentially destructive).
The area of seismic safety is the subject of numerous regulations and obligations the world over. Every natural disaster brings better knowledge of the energies that can be released and sometimes gives rise to changes in “seismic zones”, as was the case with France and the new “zoning” brought in in 2009.
Freyssinet provides an extensive range of solutions to meet seismic safety requirements for both new builds and repair.
What does Freyssinet offer in this area?
We operate in two major fields: new builds and repair of existing buildings.
- In the case of new builds, Freyssinet has developed appropriate seismic safety systems and offers a full range of dedicated products.
• Dampers that absorb seismic energy (TRANSPEC® range)
• Connectors that keep a structure firmly fixed to its foundations during an earthquake (TRANSPEC® Connector)
• Bearing systems (elastic, visco-elastic, pendulum, etc.)
• Shock absorbing cross bracing systems created with hydraulic or seismic safety dampers
• Tuned mass dampers
These various devices can be used alone or in combination to achieve the most effective and most appropriate protection for a particular construction project. Seismic protection is based on three fundamental operational modes which are: isolation, connection and dissipation. Every year numerous structures are built throughout the world incorporating these three protective methods.
In addition, Freyssinet is launching its new ISOSLAB® foundation solution used to isolate a series of buildings or a district and minimise seismic acceleration in traditional construction works. ISOSLAB® is certainly the safest slab foundation solution around, useable in all risk areas (buildings, basements, streets, play areas, etc.) and serving to isolate the general public from the effects of earthquakes.
- In the case of existing buildings, Freyssinet operates at all phases of a project, both pre- and post-quake: diagnosis, studies and works.
Freyssinet’s engineering & design and technical teams help clients make an initial diagnosis before deciding on how to strengthen structures and selecting the desired level of protection. The company can also intervene at the execution stage of the works our clients decide on.
In addition to the techniques described above, Freyssinet carries out seismic protection works based on two major intervention methods:
• Strengthening, consisting in making the structure more resistant, or more ductile (examples of works carried out: buildings, bridges, nuclear plants, etc.)
• Isolation, consisting in cutting into the structure at foundation level and then supporting it in order to insert a series of bearings that may or may not be connected to a damper
Foreva® techniques and solutions, for example underpinning, additional prestressing and carbon fibre reinforcement, are frequently used, effective solutions for achieving compliance with seismic safety regulations and are a major competitive advantage in this market.
*The South-East Region is one of the French regions with the highest earthquake risk levels in the country, 4 out of a possible 5, and is very experienced in handling projects in this field.
Foreva® repair solutions: improve, preserve and secure your structures
The ageing of structures generates a growing need for renovation, heightened by the increasing stringency of regulatory requirements. As an extension of its new-build business, over 30 years Freyssinet has developed expertise and know-how in structural repair with its exclusive solutions marketed under the Foreva® label.
Foreva® is a collection of exclusive solutions using products developed in industrial partnerships and implemented by Freyssinet teams. The Foreva® solutions portfolio covers both structural repair technologies (external prestressing, shotcrete, carbon fibre reinforcement, injection, levelling, etc.) and chemical and electrochemical repair techniques (realkalisation, chloride ion extraction, reinforcement protection, waterproof coatings, cathodic protection, etc.).
Foreva® solutions help extend the service life of structures and have numerous areas of application:
• bridges and civil engineering structures
• buildings
• water civil engineering structures
• industrial structures
• old buildings
• tunnels
For a range of materials:
• concrete
• steel
• wood
• masonry
With Foreva®, Freyssinet puts its know-how at your service and supports you at all stages of your projects, from help with initial diagnosis through to choosing the right solution to execute the works.
New Foreva® solutions are always being developed and the range of products and solutions continues to grow.
Click here to veiw the Foreva® brochure.
Soletanche Freyssinet Group achieves worldwide success
Freyssinet Limited form part of the Soletanche Freyssinet Group, the world leader in specialised civil engineering which brings together an unparalleled array of geotechnical, structural and nuclear engineering capabilities and brands.
Operating throughout the world, our 17,000 employees meet the needs of clients by devising and implementing solutions tailored to the specific features of each project, whatever its complexity and scale, and help boost the performance and durability of each structure.
The Soletanche Freyssinet Group recorded an impressive performance in the second year of its existence, with turnover increasing by 5.1% to 2 billion Euros.
Click here to view the Soletanche Freyssinet Activity Report 2010
Freyssinet Limited work with VINCI Construction UK to win contract
Streatham Hub is a multi-million pound regeneration project by Lambeth Council in partnership with Tesco. The Hub site covers the old ice rink and leisure centre between Streatham High Road and Streatham Station.
The development includes the construction of a replacement sports centre and ice rink, the Tesco store, a bus interchange close to the station, a public square and new homes. The Hub is expected to create around 600 new jobs for Streatham when it opens in 2013.
The project involves an undercroft car park, two storeys of retail store and a transfer structure above that which supports the residential blocks. To one side is the bus interchange, energy centre and service yard all above more undercroft parking. To the other side is a link block and the leisure centre, including the new ice rink and swimming pools.
The total post-tensioned slab area on the project is expected to be 21,250m2.
During the tender stage Freyssinet supported VINCI with value engineering options which assisted in winning VINCI the contract. The majority of these options are now being taken forward into construction as follows:
• The Tescos Store was a 600mm deep cobiax (voided) slab spanning 16×7.5m car park grid. This has been replaced by 2400x550mm deep PT beams and 250mm PT slabs, thus saving 50mm of dig across the 75x75m store footprint.
• The Bus Hub and Service Yard support HA loading and comprised 1600x900mm deep RC beams with 450mm RC slabs. The adopted PT solution has 425mm fl at slabs with 3m2x550mm OA depth drop heads at columns.
• The Link Block contains a 400mm deep PT transfer slab with 1200sq x 550 OA deep column caps at level 1. This carries 5 levels of metsec residential block above. Previously, in RC, this slab was a 600mm deep solid slab.
• The ground level of the Link Block has been post-tensioned too (previously 600mm deep RC cobiax, now 350mm PT flat slab). By post-tensioning isolated beams, previous head room clashes with vehicle ramps below have been solved.
• The Ice Rink slab was designed as PT by Halcrow Yolles from the outset because of the extremely fine deflection control required. It typically consists of 1000x1400mm deep beams and 300mm deep slabs.
Freyssinet Limited was appointed as the specialist PT contractor for this contract in August 2011 and design works have commenced. Construction work will commence in April 2012 and the PT slabs are due to be completed by January 2013.
Streatham Hub, along with Hoe Street and Wade Deacon School are examples of contracts where Freyssinet is supporting VINCI Construction bid teams at tender stage. This synergy between companies is giving them an edge through proposals to use post-tensioning and innovative engineering.
Freyssinet Join Alliance to Revolutionise Offshore Wind
VINCI Construction UK Ltd., and sister VINCI company – Freyssinet International & Cie, have created a joint venture to revolutionise the delivery of offshore wind farms. Developed with support from the Carbon Trust by GBF®, a consortium of Gifford, BMT Nigel Gee, and a specialist arm of Freyssinet – the alliance’s low cost, low risk and low impact approach includes a radical solution for deploying foundations without the need for costly specialist vessels or heavy lifting at sea. The team’s approach also includes a manufacturing process for assembling entire wind-turbine structures onshore before deploying them at sea.
The team’s product comprises a Gravity Based Foundation to be slip formed on land. The tower and turbine will be installed in the construction yard in a continuation of the base production line – economies of scale and a slick methodology will ensure the complete assemblies are produced economically. The completed units will be deployed and installed on the seabed with the assistance of a Transportation & Installation Barge (TIB). The TIB is a low cost, low maintenance dumb barge, built specifically for this process.
Based on UK Government commitments, a six-fold increase in output from wind will be required by 2020. The VINCI Construction UK – Freyssinet JV will construct and deploy the GBF® concept which is set to change the economics of offshore wind farms suitable for gravity bases The JV believes that its methods will enable deployment of turbines in rougher seas and deeper waters than conventional alternatives. A further key advantage is that a completely different supply chain is called upon compared to the better known monopile or jacket solutions.
VINCI Construction UK and Freyssinet International will jointly develop the innovative solution. Close partnerships and collaboration will be critical to the success of the project, and the JV will be working with developers, turbine manufacturers and others, including other companies from the wider VINCI Group to ensure the right arrangements and skills are in place.
There are also considerable environmental benefits to the proposed offshore scheme. The foundations themselves can be made from recycled materials, and the environmental impact throughout the lifecycle of the structures will be minimal. The foundations are designed such as that they can be completely removed at the end of their useful life and hence will have minimal long term impact on the environment once they’ve been decommissioned. While providing local employment opportunities, the projects will also, of course, help the UK to meet its renewable energy targets and deliver sustainable energy in the years ahead.
New Freyssinet Group Branding
Following the worldwide launch of the Freyssinet Group’s new logo and marketing material, Freyssinet Ltd took the opportunity to create a new website and newsletter to promote their activities within the UK.
This will not only allow the Company to keep their existing client base up to date, but also to introduce themselves to new clients, and ensure that both remain well informed of the wide range of products and services that Freyssinet Ltd have to offer.
Whether your project relates to the construction of a new structure or the repair and strengthening of an existing one, throughout the new website there are examples of all of the types of structure that Freyssinet Ltd’s services can be applied to.
Supported by case studies detailing previous projects that have been completed, and brochures providing further detail about their products and services, the new website provides an extensive range of information.
Freyssinet Ltd relocated their Head Office in Telford to a new location last year.
They are now based at:
Innovation House
Euston Way
Town Centre
Telford
TF3 4LT
An internal competition was run to name the new office. The Freyssinet name is synonymous with innovation, which over the years has included the invention and development of post-tensioned reinforcement techniques, the development of TFC (Carbon Fibre Fabric – first developed by Freyssinet in 1996) and the invention of the flat jack, to name but a few.
Freyssinet’s UK branch remains within the Midlands, well placed centrally within the country, with good road links from the M6 and M54.
Associated companies Reinforced Earth Company (RECo) and Corrosion Control Services Ltd (CCSL), also members of the Freyssinet Group, have relocated too, and our factory remains operational from Stafford Park, also within Telford.
Freyssinet Ltd hopes that their new company branding, along with their new office, will allow them to continue to expand and develop their work force, and promote their activities.
New Freyssinet Group Company Brochure
Freyssinet Ltd form part of the Freyssinet Group, a name that is respected worldwide for delivering innovative solutions and pushing the envelope of civil and structural engineering achievement.
Freyssinet brings together an unrivalled set of skills. With its expertise in the design of structures and technologies, the production of materials and equipment and their implementation on site, Freyssinet offers integrated technical solutions in two major fields: construction and structural repair.
Click below to view and download the latest Freyssinet Group brochure
