A Plasticity Theory Approach for the Stability Analysis of Vertical Layers of Concrete in the Fresh State

The industrial production of cement is currently responsible for around 5% of global CO2 emissions. Hence, the development of technologies aimed at minimizing the use of cement in concrete structures, while preserving their strength and durability properties, plays a vital role in the reduction of carbon emissions. The use of cement in concrete structures can be minimized through the manufacture of functionally layered structural elements where concrete with high cement content is used rationally only when it contributes significantly to the performance of the structure. In functionally layered concrete, horizontal variation in material composition can be achieved by casting adjacent vertical layers of different materials. Removable vertical panels can be used to demarcate the mixes during casting. A good bond between the layers can be achieved by removing the panels prior to concrete hardening. However, a major problem with this application is the control of the fresh-state deformations of the adjacent vertical layers. This study investigates the fundamental problem of fresh state stability of concrete prisms that consist of two vertical layers of different mixes. A novel limit-state approach based on plasticity theory is formulated to assess the stability of the system as a function of material properties and geometry. The relationship between material parameters, system stability and geometry is determined and the formulated limit-state approach is validated against experimental results.The authors would like to acknowledge the financial support of EPSRC - the Engineering and Physical Sciences Research Council (UK) [Project reference number: EP/N017668/1]

Fresh state stability of vertical layers of concrete

The production of cement is currently associated with around 5% of global carbon emissions. The manufacture of functionally graded structural elements, where the material composition is varied over the volume, allows the use of cement to be optimized and minimized. Horizontal gradation of material properties can be achieved by casting vertical layers having homogeneous composition. However, a key problem in this application is the control of the fresh state deformations of the layers. This study investigates for the first time the fundamental problem of the fresh state stability of concrete prisms that consist of two vertical layers of different mixes. Original experiments are designed to invoke stable and unstable behaviour. Two novel limit-state models are formulated to assess the stability of the system as a function of material properties and geometry. The results show that a relationship between system stability, geometry and material parameters exists, and that it is captured by the presented models

Functionally graded concrete elements composed of vertical layers of different mixes

The industrial production of cement is currently responsible for 5-7% of global CO2 emissions. The manufacture of functionally graded concrete structures, where the use of material is optimized by varying the material composition over the volume, opens up vast opportunities to reduce the use of cement. In functionally graded concrete, horizontal gradation can be achieved by casting vertical layers having homogeneous properties. However, a major problem with this kind of application is the control of the fresh state deformations. This study investigates the fresh state stability of concrete prisms that consist of two vertical layers of different mixes. Experiments are performed to invoke stable or unstable behaviour. The results show that, for a given geometry, a relationship between the material parameters and system stability exists.EPSRC - the Engineering and Physical Sciences Research Council (UK) [Project reference number: EP/N017668/1

Small area estimation: An application of a flexible fay-herriot method

The importance of small area estimation in survey sampling is increasing, due to the growing demand for reliable small area estimation from both public and private sectors. In this paper, we address the important issue of using statistical modeling techniques to compute more reliable small area estimates. The main aim is to assess the use of a flexible methodology for small area estimation. We formulate a new flexible small area model by incorporating a tuning (index) parameter into the standard area-level (Fay-Herriot) model. We achieve this using a combination of two methods namely, empirical Bayes (EB) approach and hierarchical Bayes (HB) approach. Our results suggest that the proposed model can be seen as advancement over the standard Fay-Herriot model. The novelty here isthat we have developed a flexible way to handle random effects in small area estimation. The Implementation of the proposed model is only mildly more difficult than the Fay-Herriot model. We have obtained results for both EB approach and the HB approach. Compared with the corresponding HB procedure, the EB approach saves a tremendous computing time and is very simple to implement.Key words: Area-level, empirical Bayes, Fay-Herriot model, hierarchical Bayes, small are

Functionally graded concrete: Design objectives, production techniques and analysis methods for layered and continuously graded elements

The pressing need to reduce global carbon emissions together with recent advances in automated manufacturing have driven a growing interest in functionally graded concrete. In functionally graded concrete, the material composition is spatially varied to meet performance demands that differ within regions of a structural element. This offers significant potential to reduce cement consumption. Step-wise layered and continuously graded concrete systems are introduced and investigations of concrete mix combinations to achieve durability, fracture resistance, strength, ductility, cost saving, weight reduction or lower embodied energy improvements are discussed. Production techniques for horizontally layered and vertically layered structural elements in the context of fresh-on-hardened and fresh-on-fresh casting as well as emerging continuously graded processes are presented. Challenges associated with fresh-state deformations, layer interfaces and the need for appropriate fresh and hardened-state modelling tools are critically assessed.EPSRC - EP/N017668/

Analytical and numerical seismic assessment of heritage masonry towers

Abstract The new Italian building code, published in 2018 [MIT in NTC 2018: D.M. del Ministero delle Infrastrutture e dei trasporti del 17/01/2018. Aggiornamento delle Norme Tecniche per le Costruzioni (in Italian), 2018], explicitly refers to the Italian “Guidelines for the assessment and mitigation of the seismic risk of the cultural heritage” [PCM in DPCM 2011: Direttiva del Presidente del Consiglio dei Ministri per valutazione e riduzione del rischio sismico del patrimonio culturale con riferimento alle norme tecniche per le costruzioni, G.U. n. 47 (in Italian), 2011] as a reliable source of guidance that can be employed for the vulnerability assessment of heritage buildings under seismic loads. According to these guidelines, three evaluation levels are introduced to analyse and assess the seismic capacity of historic masonry structures, namely: (1) simplified global static analyses; (2) kinematic analyses based on local collapse mechanisms, (3) detailed global analyses. Because of the complexity and the large variety of existing masonry typologies, which makes it particularly problematic to adopt a unique procedure for all existing structures, the guidelines provide different simplified analysis approaches for different structural configurations, e.g. churches, palaces, towers. Among the existing typologies of masonry structures there considered, this work aims to deepen validity, effectiveness and scope of application of the Italian guidelines with respect to heritage masonry towers. The three evaluation levels proposed by the guidelines are here compared by discussing the seismic risk assessment of a representative masonry tower: the Cugnanesi tower located in San Gimignano (Italy). The results show that global failure modes due to local stress concentrations cannot be identified if only simplified static and kinematic analyses are performed. Detailed global analyses are in fact generally needed for a reliable prediction of the seismic performance of such structures.</jats:p

A wireless bioimpedance device for abdominal fatness monitoring

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Application of artificial dynamics to represent non-isolated single-input multiple-output DC-DC converters with averaged models

This paper presents for the first time the application of a method based on the transformation of the differential algebraic equations of non-isolated Single-Input Multiple Output (SIMO) DC-DC converters into a set of ordinary differential equations, by using artificial dynamics whose asymptotic convergence to the solution is guaranteed by the satisfaction of the relevant Lyapunov conditions. The mathematical formulation is simpler than in other formulations applied in the literature to study non-isolated SIMO DC-DC converters, and encompasses the use of sensitivity functions. The results show that the proposed solution represents in a fully accurate way the dynamics of the averaged models of Zeta Buck-Boost and Cúk Boost Combination converters