Archived Construction Sector News - 2008
Taylor Woodrow Construction and The Boots Building, Nottingham, UK
In partnership with Taylor Woodrow Construction, one of the UK’s largest civil engineering contractors, ACG designed a customised composite strengthening solution to enhance the original flexural capacity of compound shaped steel beams. The Boots Building in Nottingham, England was strengthened using an LTM®20 series epoxy carbon prepreg system.
The capability of LTM®20 series to cure at temperatures as low as 28°C (82°F) was specified to eliminate the need for complicated heating systems. The material provided a natural tack when laminating that enabled fibres to maintain the correct orientation. This ensured that flexural, shear and torsional load design requirements were achieved.
Utilising a standard vacuum bag consolidation, the mechanical properties of the laminate yielded a high fibre volume fraction and low void content, necessary to transmit loads effectively.
This Boots Building project demonstrated that a prepreg route for structural strengthening provided a reliable and cost effective solution. Alternative approaches would have necessitated the removal and replacement of the original beams, a costly, and time-consuming process that would have closed one of Nottingham’s main thoroughfares for several days.
The ACG repair was completed within two days and with no disruption to the public and at a fraction of the cost.
Winner of Quality in Construction & Building Manager of the Year Research and Development Awards, 2002-2003
In-situ Repair of Mackintosh Building - Manchester, UK
A project at the Mackintosh Building Manchester, demonstrated the in-situ repair and reinforcement of cast iron columns to facilitate a change in use. The repair and strengthening with prepreg materials was shown to be commercially and technically viable when compared to more traditional methods.
A carbon and glass fibre composite over-wrap method using ACG’s VTM®260 series prepregs was selected for this project. With its extended out-life and low curing temperature of 65°C (149°F) this prepreg system was easy to handle and required only simple equipment to achieve the necessary vacuum and cure temperature.
The glass fabric provided adhesion to, and insulation between, the column and the carbon reinforcement; thus resisting further corrosion while providing additional strengthening and creating a final surface for any subsequent over-coating. In addition, a VTM®260 series adhesive was pre-laminated to the cast iron to ensure effective bonding.
Initially the columns were stripped of fixtures and paint coatings then grit blasted, solvent washed and made good. The over-wrapping was applied in the vertical direction interspersed with glass fabric prepreg to a total of 8 plies of carbon. The completed laminate was then consolidated using proprietary shrink tape and vacuum bag materials. Two vacuum de-bulks were required and cure was brought about using tenting and blown hot air.
This project showed the prepreg route is a reliable and cost effective route for in-situ structural repair and strengthening and can be accomplished in short time-scale.
Miscellaneous Applications
Other structural repair and strengthening techniques are well developed, and ACG’s design, engineering and material package can support a wide range of applications, for example:
Plate bonding
Pre-formed composite plates can be used for surface bonding to concrete or steel structures to increase flexural capacity and reduce deflections.
Beam and column wrapping
Fabric reinforcements impregnated with epoxy resin can be used to increase axial capability of column or increase shear capacity of beams.
Preformed composite shells
Tailor made in a factory- controlled environment and bonded around columns on-site for confinement solutions.
Preformed shear straps
Bonded to sides and soffits of beams to form external straps.
NSM Composite rods and strips
New technique of Near Surface Mount (NSM) where reinforcement is set into grooves cut into concrete substrate.
ACG wins JEC 2005 Construction Category Award
Advanced Composites Group won the JEC 2005 Construction Category Award at the JEC Composites Show in Paris, France, for groundbreaking design and development of the technology for advanced composite bridge construction. The design was the result of the search for more efficient construction methods and was designed and built in partnership with NECSO Entrecanales Cubiertas (Madrid) one of Europe’s leading construction companies.
Civil engineers traditionally use the ‘composite’ properties of concrete and steel when designing bridge structures, but for the first time ever, ACG assisted NECSO in producing a 46m beam element utilising carbon fibre prepreg technology. The reinforcing fibres and polymer matrix in this design provide all the structural strength of the element. NECSO selected ACG’s prepreg technology to ensure that actual laminate properties were as close to design predications as possible and that necessary quality control was maintained from material specification through to component manufacture.
One of the main benefits of constructing the bridge in this innovative way is the reduction of time for which the road passing underneath the bridge needed to remain closed. The expense was significantly lower in terms of crane/haulage/manpower costs. The bridge went up in two days compared with forty days, the expected standard for a 150ft bridge. Due to the low weight to high stiffness ratio of the beams, entire units were delivered to site, where they were jointed into three 46m long elements and located onto the pre-cast concrete support columns in a single crane lift operation.
The beams were manufactured by NECSO utilising high strength uni-directional and bi-axial carbon fibres, pre-impregnated with ACG’s VTM®260 series epoxy resin, specified as the viscosity and tack profile is particularly suited to full impregnation of the fibres using only vacuum pressure and low temperature curing. NECSO validated the design by testing a full-scale 13m beam to design limit load at ELSA laboratories at JRC, Italy.
Test results indicated that an ultimate load at failure of the beam was in excess of 100 ton, providing a structural safety margin of 3.4 times the maximum limit load of an equivalent pre-cast concrete beam, with a deflection in service figure of 1/500. Each beam element, including the non-load bearing in-situ cast concrete deck, weighed approximately 15% of the total weight of a traditional reinforced concrete beam.
After location of the beam elements, the concrete deck road surface was cast in-situ and the beam elements anchored to the abutment. NECSO have installed load cells to ensure that adequate data of the in-service structural performance of the bridge can be monitored. The works were undertaken by NECSO under a commercial contract supported by Spanish Ministries (Infrastructures & Public Works and Science & Technology), demonstrating not only the technical performance but also the commercial competitiveness of building bridge structures with ACG’s carbon fibre prepreg technology.