A design methodology to reduce the embodied carbon of concrete buildings using thin-shell floors

This paper explores the potential of thin concrete shells as a low-carbon alternative to floor slabs and beams, which typically make up the majority of structural material in multi-storey buildings. A simple and practical system is proposed, featuring pre-cast textile reinforced concrete shells with a network of prestressed steel tension ties. A non-structural ll is included to provide a level top surface. Building on previous experimental and theoretical work, a complete design methodology is presented. This is then used to explore the structural behaviour of the proposed system, refi ne its design, and evaluate potential carbon savings. Compared to at slabs of equivalent structural performance, signi cant embodied carbon reductions (53-58%) are demonstrated across spans of 6-18m. Self-weight reductions of 43-53% are also achieved, which would save additional material in columns and foundations. The simplicity of the proposed structure, and conservatism of the design methodology, indicate that further savings could be made with future refinements. These results show that considerable embodied carbon reductions are possible through innovative structural design, and that thin-shell floors are a practical means of achieving this

Fabric formed concrete: Physical modelling for assessment of digital form finding methods

Fabric formwork is a novel concrete construction method which replaces conventional prismatic moulds with lightweight, high strength sheets of fabric. The geometry of fabric formed structures is therefore dictated by the behaviour of fabric under hydrostatic loading. While there are numerous examples of digital and physical modelling of this problem, there have only been limited efforts to link the two through measurement. In this investigation, a number of small scale fabric formed beams were manufactured using both ‘free hanging’ and ‘keel mould’ methods, and the resulting forms were accurately measured with a digital 3D scanner. Computational form finding tools were also developed, enabling a comparison to be made between the predicted and build geometries. This allowed assessment of both the accuracy of the construction methods and the limitations of the form finding techniques used. The data collected provides a useful assessment of existing form finding techniques and will be used as a reference data set as these are developed further

Simulating reinforced concrete members. Part 2: displacement-based analyses

A companion paper described the partial-interaction localised properties that require the development of pseudo properties. If the quantification through experimental testing of these pseudo properties could be removed by the use of mechanics-based models, which is the subject of this paper, then this would: (a) substantially reduce the cost of developing new reinforced concrete products by reducing the amount of testing; (b) increase the accuracy of designing existing and novel reinforced concrete members and structures, bearing in mind that experimentally derived pseudo properties are only applicable within the range of the testing from which they were derived; and (c) reduce the cost and increase the accuracy of developing reinforced concrete design rules. This paper deals with the development of pseudo properties and behaviours directly through mechanics, as opposed to experimental testing, and their incorporation into member global simulations. It also addresses the need for a fundamental shift to displacement-based analyses as opposed to strain-based analyses.Deric J. Oehlers, Phillip Visintin, Jian-Fei Chen and Tim J. Ibel

Minimising embodied carbon in reinforced concrete beams

The construction industry has received attention due to its significant contribution to global carbon emissions. In this paper, conventional design and construction practices of reinforced concrete beams are scrutinised to explore the potential for reductions in embodied carbon. For a given set of design criteria, a family of discrete beam designs which have different geometries and corresponding reinforcements were developed to identify those with minimum embodied carbon. Two algorithms for shape optimisation were developed, one to identify the geometry of the theoretical optimum design, and another considering technical and construction feasibility. Prismatic beams were also optimised exploring alternative designs with different depths and widths along with the required reinforcements, for a reasonable comparison. Several cases were studied to understand the effect of different design parameters. Different design criteria suggested different geometries to minimise embodied carbon, even if the design span was the same. The importance of minimising web width was seen throughout the analysis. The expected deflection of each design was also estimated to understand the effect of optimisation on serviceability performance and found to be satisfactory in all the cases. Embodied carbon of beams can be reduced by up to 38% by optimising prismatic beams compared with conventional designs. Further savings up to 8% are possible with a feasible shape optimised design compared with optimised prismatic beams.</p

Thin-shell textile-reinforced concrete floors for sustainable buildings

Steel-reinforced concrete, cast in flat prismatic forms, dominates multi-storey building construction around the world. Despite the fluidity of the material, opportunities to create efficient geometries through manipulation of form are habitually overlooked, resulting in inefficient cracked sections, high steel requirements and large carbon footprints. This project brings together modern developments in computational design, materials and construction to propose a novel thin-shell concrete flooring system for multi-storey buildings, creating a low embodied energy and lightweight alternative to traditional reinforced concrete flat slabs. In this investigation, the performance of various shell geometries are compared using finite element analysis. A functional design is produced and found to offer reductions of 62% in embodied energy and 64% in weight compared to an equivalent flat slab

Anchorage and residual bond characteristics of 7-wire strand

© 2017 Elsevier Ltd The periodic assessment of our existing concrete infrastructure is a crucial part of maintaining appropriate levels of public safety over long periods of time. It is important that realistic predictions of the capacity of existing structures can be made in order to avoid unnecessary and expensive intervention work. Assessment is currently undertaken using codified models that are generally readily applied to infrastructure with simple geometric and reinforcement details that conform to design methods for new structures. This approach presents two significant challenges for prestressed structures: (1) design and construction practice has changed significantly in the past 50 years, and modern codified approaches can be incompatible with historic structures; and (2) deterioration of exposed soffits can lead to reduced cover to internal prestressing strand. Unless appropriate reductions are used in assessment of a structure with such problems, unnecessary load restrictions, or major strengthening or reconstruction work may be required, despite having carried a full service load since its construction. There are currently no widely accepted methods for the prediction of peak and residual capacities in prestressed concrete beams with inadequately detailed 7-wire strand. This paper presents a completely new prediction methodology, validated against new experimental results from 31 novel semi-beam tests. The proposed models for peak load, residual load, and bond stress-slip modelling provide reliable, accurate, and conservative results. Their results demonstrate feasible and appropriate capacity reduction factors for use in the assessment of existing concrete infrastructure

Preliminary investigation of water and nitrogen use efficiency in Mango

The aims of this preliminary investigation were to identify if natural abundance carbon (δ13C) and nitrogen (δ15N) stable isotopes reflect the dynamics of carbon and nitrogen between mango varieties, canopy function and management practices (fertilization and/or irrigation). This preliminary investigation has identified factors that increase water use efficiency, nitrogen efficiency and tree productivity. The natural abundance of stable isotopes of carbon and nitrogen show promise as new tools to study the drivers of mango productivity efficiency and will be useful in studying mango orchard systems and in selecting and evaluating breeding parents and progeny in mango breeding programs. Measurement of stable isotopes of carbon (δ13C) in three mango varieties grown under similar irrigation and environmental conditions (in Summer 2015) have shown significantly different WUE between the varieties. These findings were supported by traditional gas exchange analysis, taken during winter 2016 and foliar N concentrations in these varieties. There were significant relationships, between WUE and foliar N concentrations, in both the heredity and crop load experiments indicating an effect of both genotype and terminal function on terminal WUE and foliar N concentration. Results from the gas exchange assessments supported δ13C heredity results indicating greater WUE in the Keitt variety when compared to Calypso variety. The methods used in this project can help us better understand the integrated carbon and nitrogen dynamics of tree canopies and how nitrogen allocation is influenced by nitrogen nutrition. They also help us understand the photosynthetic components that influence light harvesting and electron transport efficiencies and hence contribute to growth and productivity. The report also discuss how gas exchange characteristics between varieties may be used to evaluate the productivity and canopy efficiency of different mango varieties growing in different planting configurations with varying light and shading characteristics. Finally, when measurements in trees with varying crop load from three sites data where pooled together, the δ15N was able to identify nitrogen dynamics in high and low nitrogen sites. This preliminary investigation of the use of stable isotopes of carbon (δ13C) and nitrogen (δ15N) to identify water use efficiency and productivity efficiency’s in mango has been successful and has potential application in studying orchard systems and in mango breeding. Application of these methods in future projects would enhance current studies of mango canopy architecture efficiency in the Small tree High productivity initiative and provide a new way of assessing mango breeding lines for production efficiency

Quantifying moment redistribution in FRP-strengthened RC beams

Consideration of moment redistribution (MR) in the design of continuous reinforced concrete (RC) beams results in an efficient and economical design. Adding fibre-reinforced polymer (FRP) materials to reinforced structures to enhance flexural capacity leads to a reduction in ductility, such that design standards severely limit use of the MR in their design. This has forced engineers to use elastic analyses for strengthening design, which can lead to FRP wastage. To overcome this, complicated or empirical solutions have been applied to solve the problem of MR in strengthened concrete members, with limited success. This paper presents a novel theoretical strategy for quantifying and tracking MR in such members by employing basic structural mechanics without any need for estimating rotation capacity or ductility. Fully non-linear flexural behaviour of continuous strengthened members can be predicted and any geometry, loading arrangement and strengthening technique or configuration can be considered. The numerical model is validated against existing experimental data from the literature. Good agreement is shown between the experimental and numerical data, with the significance of this work being that, potentially, for the first time MR could credibly and confidently be incorporated into design guides for FRP strengthening of RC structures.The authors gratefully acknowledge funding provided by the Engineering and Physical Sciences Research Council (EPSRC EP/K019015/1) and the project partners (Concrete Repairs Ltd, Fyfe, Highways England, WSP/Parsons Brinckerhoff and Tony Gee and partners) for this research project

Σύνθεση ιοντικών υγρών και βαθέων ευτηκτικών διαλυτών και εφαρμογή τους στο διαχωρισμό του αζεοτροπικού μίγματος αιθανόλης/νερού

Productivity in temperate tree crops such as apple has been lifted several-fold by research focusing on optimising a combination of canopy components including light relations, vigour control, tree architecture and crop load. This paper outlines the research behind the Small Tree-High Productivity Initiative (STHPI), which is focused on improving productivity of mango, avocado and macadamia. Preliminary results from work we are undertaking for each of the above canopy components in mango will be outlined. A rootstock screening trial to identify vigour-managing, high-productivity rootstocks is being undertaken, and we present a comparison of the best-performing low-medium vigour rootstock varieties compared with control 'Kensington Pride' (KP) rootstock at 6 months old. Comparisons between 'Keitt', 'NMBP 1243' and 'Calypso' scion cultivars with regard to tree diameter, height and canopy growth at different orchard densities and training systems will also be presented. Preliminary results from an orchard light-relations study indicate that mango yields continued to increase with light interception up to 50%, and reached a maximum of 20-30 t ha at 68% light interception in KP trees approximately 25 years old. In a crop load trial, inflorescence thinning in a 'Calypso' orchard did not significantly reduce yields when up to 90% of inflorescences were removed, but did when 95% of inflorescences were removed, as trees were unable to compensate by adjusting fruit set, size and yield. Inflorescence thinning beyond 80% increased the number of fruit set per panicle, and thinning up to and including 90% of inflorescences increased fruit weight from 340 g to >400 g per fruit. This project is still in its initial stages; however, early indications suggest there may be opportunities to improve early orchard yields through optimising light interception in an orchard's life, potentially through the use of higher densities, and that rootstocks and tree training methods, once identified, may help in the management of vigour. It is also hoped to obtain a better understanding of how crop load influences the balance between vegetative growth, flowering, fruiting, alternate bearing and fruit quality