An CFRP fabrics as internal reinforcement in concrete beams

This paper presents preliminary results of an experimental programme that investigated mechanical properties of a balanced-symmetric CFRP fabric laminate. Although FRP fabrics have potential to be formed into efficient reinforcement systems that can enable the development of innovative low embodied energy concrete structures, very little research on applications of FRP fabrics has been reported in the literature. In accordance with the classical laminate theory, in a balanced-symmetric laminate there is no coupling between in-plane deformation and curvature, nor between in-plane normal loading and shear deformation. As a result of the choice of lay-up arrangement the flexural reinforcement systems in concrete beams can be designed by considering the conventional section equilibrium analysi

Surface and subsurface structural response on the City of London cable tunnels project

This paper presents surface and subsurface ground and structural response to the excavation of an urban cable tunnel within London clay and the Lambeth Group strata. Project specific tunnelling volume losses were estimated and found to be dependent on face advance and geology. The presence of adjacent buildings reduced predicted ‘greenfield’ settlements. The tunnel passed below a continuous section comprising basements, box rail tunnels and other structures. These structures generally responded at the level of their foundations. The presence of a pile group through which the tunnel passed only reduced surface settlement by ~50%. Passing below two existing segmentally-lined LUL tunnels these responded immediately and as predicted, although with somewhat increased trough widths indicating a stiffening effect. A multi-span bridge directly above the LUL tunnels on deep pier foundations, part of the Holborn Viaduct, settled more slowly and twice as much as anticipated. A possible general effect of tunnelling on heavily loaded foundations including end-bearing piles is discussed

Behaviour of long structures in response to tunnelling

This paper presents observations of the response of long structures when exposed to tunnelling activities in London Clay. The type of structures varied from a 100 years old masonry arch tunnel to a more modern reinforced concrete frame structure. The common property shared by these structures is that they are long in comparison to the depth beneath them of the tunnels being constructed. Numerical analyses have also been carried out to back analyse the observed data using the London Clay soil parameters. The model was then extended to include a depth and a structural stiffness variable and demonstrate sensitivity to those factors

Shear capacity of reinforced concrete pile caps

Reinforced concrete pile caps may be considered to act either as deep beams, or analogous to a truss. When designed as a deep beam, there is currently a contradiction in the shear design between two UK structural engineering codes of practice – the design code BS 8110 for reinforced concrete buildings, and BS 5400: Part 4 for bridges. The majority of this difference in shear design is concerned with the width of the cap for which a shear enhancement factor for short shear spans may be applied. BS 8110 permits the factor to be applied across the full width of the cap if the pile spacing is no more than three pile diameters, whereas BS 5400 allows the factor to be applied only for the width of the pile diameters. Given that the shear enhancement factor is a very significant component of the design strength of the cap, this difference can give a factor of two or three between the shear strengths according to the two codes of practice.This paper describes research that has been carried out with the aim of resolving the issue of the width of shear enhancement. A series of sixteen four-pile caps of close to full size, with spans in the range 500mm – 1200mm and depths from 230mm – 400mm have been tested to failure in the laboratory. The test results have been used to verify three-dimensional nonlinear finite element analyses conducted using the commercial package DIANA. The results have shown good agreement of behaviour between the tests and the numerical analyses, and have also indicated that the BS 8110 shear enhancement approach is safe. It is anticipated that the results of this research will inform the next revision of the Structural Eurocode, EN 199

Three-dimensional modelling of the interaction between buildings and tunnelling operations

An extensive programme of research has been carried out at Oxford University on finite elementanalysis of the interaction between masonry buildings and ground movements induced by tunnelling. The focushas been on the development of a predictive tool for assessing the probable damage to buildings. This paperpresents a brief summary of the work, with reference to other more detailed papers. The method is illustratedwith reference to the case of the Ramsgate harbour approach tunnel, in which a large diameter tunnel in chalkwas excavated at very low cover directly beneath a row of cottages. Both field measurements and analyses revealthat in this case the building responds flexibly, following rather closely the greenfield settlements, which weresmall. The slight damage to the buildings was also correctly modelled

Remote assessment of tsunami damage in Japan by means of Google Street View images

The devastating Great East Japan tsunami of 2011 highlighted the vulnerability of urban habitations to such major disasters and the need to improve survivability. As has become the norm after such events, field teams were sent to investigate and learn lessons to aid future design guidelines. In addition, Google Street View cars were sent around inundated areas once roads were cleared and the resulting images were displayed online allowing ready comparison with images taken before the event. This report is the output from a project which examined this remote assessment tool to determine its usefulness for engineers. It was found that much of what is observable in the field is also visible in the online archive. Performance of structures of different types can be assessed both quantitatively, as a function of distance from the shoreline, and also qualitatively for beneficial features such as open ground floors. Advantageous features of urban design such as sheltering by trees and other buildings, and siting of structures to serve as vertical evacuation centres could, also be assessed.Overall, although the online images cannot completely replace a field survey, they have the potential to exploit untapped resource in researchers around the world collaborating with local engineers to learn lessons and improve tsunami resistance of vulnerable coastal communities

Modelling granular soil to predict pressures on integral bridge abutments

Presented here is a granular soil model created to investigate the soil pressureswhich develop behind integral bridge abutments. The problem is introduced along with a briefsummary of the fundamental behaviour, the model produced, and the initial validation. The paperlooks at the initial outcome of the final validation procedure where experimental behaviourof an abutment is compared to the modelled behaviour, and the influence of the Young’smodulus profile applied is investigated. The results show that the model behaves as expectedproducing lateral stresses close to those measured experimentally. Comparisons show that theYoung’s modulus profile adopted influences the resultant lateral stresses sufficiently to warrantfurther investigation

Advanced polymer composite and concrete beam and slab systems

This paper reports on an investigation into the feasibility of a structural slab system consisting of a sheet of carbon fibre reinforced polymer in tension and concrete in compression. The system is a development of a design for an APC/concrete composite Tee beam, in which the APC serves as both permanent formwork and tension reinforcement. The design, fabrication and testing of the system are described. Particular issues to be addressed were obtaining an optimal profile for the CFRP formwork, and providing adequate bond between CFRP and concrete. The bond was made using an adhesive, the performance of which is described. A non-linear finite element analysis was performed in support of the laboratory experiments, and parametric studies carried out to explore the important influence of fibre direction upon transverse bending stiffness. The CFRP layer was tested before the concrete was cast, to model the temporary construction case, under concentrated and distributed loads. The behaviour of the finished slab under cyclic loading was also examined

Strengthening a steel bridge with CFRP composites

The present paper reports the successful strengthening of Acton Bridge on the London Underground system using carbon fibre reinforced polymer (CFRP) plates. The adhesive used to bond the plates to the steel had to cure while trains continued to run over the bridge. Concerns arising from this were the effect of cyclic load during curing on the final bond strength and whether adhesive flexibility affected the reinforced sectionproperties. Tests to investigate these concerns are also reported.These tests involved reinforced beams subjected to cyclic loading of different intensities in bending during adhesive cure and tested statically at intervals to determine the build up of stiffness. The tests showed that, generally, adequate bond develops but at higher load intensities the strength of the bond is reduced and above limiting values of slip or developed shear stress at the steel/CFRP interface no bond will develop. A furtherconclusion was that adhesive flexibility does reduce section properties but by less than about 7%.Lap-shear tests conducted on specimens cut from the reinforced beams confirmed the bending test results. These showed that the biggest reductions in bond strength were at the ends of the beams where slip and shear stress were greates

An advanced polymer composite and concrete slab system

This paper reports on an investigation into the feasibility of a structural slab system comprising of a sheet of carbon fibre reinforced polymer (CFRP) in tension and concrete in compression. The CFRP serves as permanent formwork as well as tension reinforcement. It was found that the slab system performed satisfactorily at ultimate and serviceability limit states. A design for a slab for use in a typical building is presented