Galglass are design and build specialists for concrete and steel storage tanks. As the market leading specialist contractor in the design and construction of cylindrical post-tensioned (PT) in-situ reinforced concrete sludge digester tanks in the UK, Galglass first appointed Freyssinet by as their post tensioning partner on the design and construction of 3No. 18m dia. x 15m high tanks at Ringsend sewage treatment works in Dublin in 2000/01. Freyssinet were initially selected by Galglass as their partner because of their unrivalled reputation, expertise and experience in the post tensioning sector, with the relationship also bringing commercial and quality advantages.
Since then, the partnership has grown from strength-to-strength. With the latest round of water industry investment programmes coinciding with increased emphasis on renewable energy, which can be generated using methane gas (a natural by-product of the sludge digestion process), Galglass has seen the demand for digester tanks increase dramatically since 2009. To date Freyssinet have supplied and installed post tensioning systems at four Galglass project sites in the UK and Ireland: • Ringsend WwTW Tank 4, Dublin, 2009 • Afan Sludge Digester Tank, Port Talbot, 2010 • Five Fords WwTW, Wrexham, 2011 • Howdon Digester Tanks, Newcastle, 2011
Historically, tanks of this type were designed and constructed traditionally with very thick and heavily reinforced concrete wall sections. Even then, tanks designed and constructed in this way would frequently suffer wall cracking and leakage, leading to a reduced operational life and client dissatisfaction; in addition, construction of such tanks was costly and slow, and the carbon footprint of structures of this type was very large. The key benefit of the innovative Galglass Post Tensioning approach to digester design is that it ensures that the tank walls are maintained in permanent horizontal compression under all load cases and for the whole design life (typically 40 – 60 years) of the structure, thereby guaranteeing leak-free construction. The use of post tensioning also allows much more economical wall thicknesses and reinforcement quantities, so that costs and build times are significantly reduced and the associated carbon footprint is dramatically lowered.
Freyssinet’s in-house design team consists of suitably qualified experienced engineers and technical personnel with many years of experience in post-tensioned tank design and construction. They are responsible for: 1. Deciding on the suitable post-tensioning system to suit to the range of stress resultants provided by Galglass analysis 2. Estimation of post tensioning losses for the selected post tensioning system 3. Calculation of required number of tendons 4. Providing effective tendon layouts that can easily be adopted on site 5. Providing technical assistance during the design development and construction All in all, the partnership with Freyssinet presents Galglass with a “win/win” situation in promoting its market-leading PT digester product – Galglass Engineering Director Lindsay Powell says: “The credibility that the Freyssinet name and reputation brings to our highly successful PT digester system is clearly recognised by ourselves and our clients. The quality and high performance levels of the finished product speak for themselves, and it is reassuring to know that we can rely on the skills, experience and technical/site services support offered by Freyssinet for projects of this type. The highly successful track record of the partnership and the corresponding high levels of customer satisfaction are a credit to both Galglass and Freyssinet, and with a number of high-profile digester projects currently ongoing and more in the pipeline, it is a partnership which we feel will continue grow and develop in the future to the continued benefit of both parties”.
Freyssinet and Galglass are currently in negotiations for further works at Blackburn Meadows WwTW, Sheffield, Woodhouse Mill WwTW, Sheffield and Bellozanne WwTW, Jersey.