Antony Darby

Concrete structures using fabric formwork

Using fabric formwork, it is possible to cast architecturally interesting, optimised structures that use up to 40% less concrete than an equivalent strength prismatic section, thereby offering the potential for significant embodied energy savings in new concrete structures. This paper reports on the philosophy of and background to fabric formwork before techniques for the design, optimisation and shape prediction of fabric formed concrete beams are presented. The practicality of construction with non-orthogonal elements is discussed before the results of new structural test data, undertaken at the University of Bath on 4m span elements formed in reusable fabric moulds, are presented. Potential areas of future development for fabric formwork, including the use of woven advanced composite fabrics as permanent participating formwork and the feasibility of uniform strength prestressed beams, are then discussed.

Innovative Reinforcement for Fabric Formed Concrete Structures

Using fabric formwork, it is possible to cast architecturally interesting, optimised structures that use up to 40% less concrete than an equivalent strength prismatic section, thereby offering significant embodied energy savings. This paper reports on the latest techniques for the design, optimisation and shape prediction of fabric formed concrete beams before new test results of an innovative anchorage method for both steel and fibre reinforced polymer longitudinal reinforcing bars are presented. Two 2m span beams were tested and the ‘helically confined splayed bar’ was shown to provide full anchorage in both cases. The two beams both exceeded their design capacity and showed remarkably similar behaviour at the serviceability limit state, with the steel reinforced section going on to display considerable ductility. Potential areas of future development are then highlighted, with the use of woven advanced composite fabrics as participating formwork for both beam and shell elements being of particular interest.

Interpreting Conservativeness in Design Criteria for Flexural Strengthening of RC Structures Using Externally Bonded FRP

This paper presents the influence of various flexural strengthening design criteria specified by three important design guidelines (ACI440, TR55, FIB14) on the resulting strength, ductility and conservativeness of FRP strengthened RC elements. Various generalised mathematical relations in non-dimensional form are presented that can be employed to develop design aids for the FRP-strengthening process. A design methodology is prescribed based on these equations enabling the designer to optimally and intuitively incorporate sufficient ductility while designing for strength. In order to better interpret conservativeness within design codes, four distinct levels of embedded conservativeness are identified, which cover the entire range of sources of conservativeness. Finally, a detailed parametric study is presented, using the proposed design equations and methodology, to determine the influence of each of these four levels of conservativeness on final design solutions. Specific criteria that are useful while calibrating design guidelines are also presented.

Day one sustainability

Emissions reductions targets for the UK set out in the Climate Change Act for the period to 2050 will only be achieved with significant changes to the built environment, which is currently estimated to account for 50% of the UKs carbon emissions. The socio-technological nature of Civil Engineering means that this field is uniquely placed to lead the UK through such adaptations. This paper discusses the importance of interdisciplinary teaching to produce multi-faceted team approaches to sustainable design solutions. Methods for measuring success in education are often not fit for purpose, producing good students but poor engineers. Real-world failures to apply sustainable design present a serious, difficult to detect, and ultimately economically negative situation. Techniques to replace summative examinations are presented and discussed, with the aim of enhancing core technical skills alongside those required for sustainable design. Finally, the role of our future engineers in policy-making is discussed. In addition to carbon, the provision of water and food will heavily influence the work of civil engineers in the coming decades. Leadership from civil engineers with the technical knowledge and social awareness to tackle these issues will be required. This provides both opportunities and challenges for engineering education in the UK.

Plasticity Based Approach for Evaluating the Blast Response of RC Columns Retrofitted with FRP

Work is presented on an incremental plasticity based analytical model to predict the peak displacement of FRP retrofitted RC columns subjected to blast loads. Tests have shown that columns retrofitted with transverse FRP display much higher levels of ductility and deform flexurally rather than failing in shear. This assumption is employed in the current model. In the proposed model the peak deflection is reached when the strain energy in the plastic hinges equals the supplied kinetic energy from the blast. Through the incremental approach the strain rates can be accurately and easily determined. The model is intended to assess the response of columns subjected to high energy blasts where large deflections would be expected and shows encouraging results when compared with experimental data. It also shows improved results compared with the more commonly used SDOF method.

Innovative concrete structures using fabric formwork

© 2010 Taylor & Francis Group, London. This paper examines the state of the art in fabric formed beam design, providing a summary of previous work, experimental data and optimisation processes. The future of fabric formwork is considered and current work at the University of Bath is presented.

Prediction of Capacity for Moment Redistribution in FRP-Strengthened Continuous RC T-Beams

AbstractBecause of the premature debonding of fiber-reinforced polymer (FRP) materials that results in a reduction in ductility, the problem of how to exploit moment redistribution (MR) in FRP-strengthened continuous reinforced concrete (RC) structures is unresolved. To date, limited research has been conducted into MR in such structures; a reliable and rigorous solution for quantifying MR throughout the loading cycle remains elusive. This paper aims to quantify MR and predict the capacity at reasonable accuracy, to encourage the use of FRP for the strengthening of existing continuous RC structures. Experiments conducted on 12 continuous T-beams are reported, and the findings are discussed. Strengthening configuration and anchorage scheme are the main variables. A new analytical strategy is described for quantifying MR, and the analytical results are then validated against the experimental results. Both experimental and analytical results confirm that there is no reason to restrict MR into strengthened zo...

Shear strength theories for beams of variable depth

Flexibly formed reinforced concrete beams usually have varying cross sections along their longitudinal axis, capitalising on the fluidity of concrete to create optimised geometries. According to Orr et al. [1], these new shapes have led to challenges for shear design, especially when the depth of the beams is relatively small. It is crucial to be able to accurately determine the shear strength of such beams to maintain structural safety whilst achieving material optimisation. The effective shear force method is adopted for tapering beams in many design codes. Recent work by Paglietti et al. [2] has highlighted concerns over the use of such an approach. In this paper, the theoretical basis for stress distributions in tapered beams built by Timoshenko [3] and Oden [4] in their elastic range is reviewed and then extended to included cracked behaviour. It is found that the effective shear force method used in design codes does not accurately account for the stress distribution in a section both in elastic and cracked stage of concrete, underestimating the peak shear stress for beams with inclined soffits. This is important for flexibly formed beams, and has implications for designers As a result of this work, a new calculation and design method for shear reinforcement is proposed. Keywords: variable depth beam, shear strength, shear stress distribution, flexible formwork.

Extraordinary possibilities for future concrete structures

Concrete, most widely used construction material, is a fluid that offers the opportunity to economically create structures of almost any geometry. However, this unique fluidity is seldom capitalised on, with concrete instead being cast into rigid prismatic moulds to create high material use structures with large carbon footprints. This paper will demonstrate how replacing conventional orthogonal moulds with a flexible system comprised primarily low-cost fabric sheets can utilise the fluidity of concrete to create extraordinary possibilities for highly optimised, architecturally interesting, building forms.

Fabric formwork for ultra high performance fibre reinforced concrete structures

Using fabric formwork, it is possible to cast architecturally interesting, optimised structures that use up to 40% less concrete than an equivalent strength prismatic section, offering potentially significant embodied energy savings in new concrete structures. Fabric formwork allows elegant designs to be realised but its use also presents some unique challenges, including the practical provision of transverse reinforcement in slender, non-prismatic beam elements. This paper details how these challenges have been overcome with the use of ultra-high performance fibre reinforced concrete. Methods for the design, optimisation and construction of such elements cast using fabric formwork are illustrated and structural tests data are presented.