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Performance of an EBR CFRP-strengthened RC slab using 24-h and cyclic load tests : a real case study
No full textThis study investigates the performance of a case study reinforced concrete (RC) slab strengthened in flexure with Fibre Reinforced Polymer (FRP) sheets. The RC slab is at the top floor of a 17-storey building upon which three water tanks (of 1,000 l each) had to be built due to a change of use of the building's top floor. To assess the performance of the existing slab, site investigations and non-destructive testing (NDT) were carried out as per ACI 318 standards. To increase the load capacity of the slab, Externally Bonded Reinforcement (EBR) Carbon FRP sheets were bonded to the bottom of the RC slab. Following the strengthening intervention, the CFRP-strengthened slab was subjected to a 24-h load test (according to ACI 318) and to a Cyclic Load Test (following ACI 437) using an ad-hoc water pool built on top of the slab. The results from these tests (maximum and residual deflections of 0.92 mm and 0.34 mm, respectively) indicated that the CFRP-strengthened slab met satisfactorily the deflection criteria and performance indices of such tests. The CFRP-strengthened slab was then modelled and analysed in ANSYS® to calibrate and validate the experimental results. It is shown that the deflection and strains predicted by the finite element (FE) model match well the experimental measurements (errors < 15%), which confirms the suitability of the modelling approach adopted in ANSYS®. This article contributes towards the dissemination of real case studies of FRP-strengthened structures, which are scarce in the literature and thus can be useful to engineers and practitioners working in the field of structural strengthening
Rethinking energy geopolitics : towards a geopolitical economy of global energy transformation
Get PDFWe are in the midst of a global energy system transformation (GEST) which is rewiring the world economy, opening new axes of political contestation, and revolutionising the energetic basis of human civilisation. Energy geopolitics has not yet reconciled itself to this challenge. The field has traditionally been preoccupied with the dependence of Western states on cross-border flows of fossil fuels. More recently, efforts have been made to prospectively map out what the geopolitics of a fully renewable world might look like. What both literatures miss, however, is the very fact of the GEST: that we are living through a changing and contested process of global transformation, across interacting high- and low-emissions systems, whose contours are open and actively constructed over time. In this paper, we start to develop a provisional framework to make sense of the GEST, that is able to capture the full scale of the transformation, and its dynamic, contingent, constructed nature. We attend to three areas of geopolitical economy: the wide-ranging material dimensions of the transformation, its geographical space-making, and its conflict-ridden political economy. We then apply this framework to two case studies, one looking at the fraught role of fossil gas as a ‘transition fuel’, the other at lithium-ion batteries
Sensitisation instructions can reduce the misinformation effect and improve the eyewitness confidence-accuracy relationship
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A semi-analytic method for buoyancy-induced thermal stratification in hot water tanks during standby periods
No full textBuoyancy-induced thermal stratification is a spontaneous phenomenon arising from standby periods of hot water tanks. Accurate estimation of temperature levels is crucial for energy-efficient operations of hot water tanks and associated water heating systems. However, temperature estimation by numerical schemes requires sophisticated algorithms and considerable computation resources. This study proposes a novel semi-analytic method to address buoyancy-induced thermal stratification conveniently without iterative calculations. An explicit water temperature function to tank height and time is analytically derived from the modified energy balance equation where the heat convection term is disregarded. The convection effect is compensated for by artificial enhancement of heat conduction, which is indicated by a synthetic parameter, amplification factor. A comprehensive numerical study is carried out to investigate static and transient characteristics of buoyant flows and temperature distribution in a hot water tank during standby periods. The findings imply a strong analogy between buoyancy-induced thermal stratification and a bottom-initiated heat conduction process, which reinforces the physical rationale for the semi-analytic method. The experimental verification of the semi-analytic method is conducted against published experiment data, the proposed method shows excellent estimation accuracy with the rooted mean square error of less than 0.42 °C. Furthermore, suitable case-specific amplification factors are determined with numerical simulations, and a ready-for-use correlation equation of the amplification factor is formulated for a wide range of tank volumes and aspect ratios. This novel semi-analytic method substantially reduces computation time compared with numerical solvers, and the simple form of the water temperature function can help in formulating more detailed hot water tank models in energy system studies
Plural practical knowledge
Get PDFhe paper examines the thesis that participants in shared intentional activities have first-person plural ‘practical knowledge’ of what they are jointly doing, in the sense of ‘practical knowledge’ articulated by G.E.M Anscombe. Who is supposed to be the subject of such knowledge? The group, or members of the group, or both? It is argued that progress with this issue requires conceiving of collective activities (of the kind affording ‘plural practical knowledge’)as instances, not of supra-personal agency, but of interpersonal agency; specifically: as involving communication. There is a sense, it is suggested, in which the basic form of plural practical knowledge is relational: ‘I am doing x with you.
Sharp asymptotic estimates for expectations, probabilities, and mean first passage times in stochastic systems with small noise
No full textFreidlin-Wentzell theory of large deviations can be used to compute the likelihood of extreme or rare events in stochastic dynamical systems via the solution of an optimization problem. The approach gives exponential estimates that often need to be refined via calculation of a prefactor. Here it is shown how to perform these computations in practice. Specifically, sharp asymptotic estimates are derived for expectations, probabilities, and mean first passage times in a form that is geared towards numerical purposes: they require solving well-posed matrix Riccati equations involving the minimizer of the Freidlin-Wentzell action as input, either forward or backward in time with appropriate initial or final conditions tailored to the estimate at hand. The usefulness of our approach is illustrated on several examples. In particular, invariant measure probabilities and mean first passage times are calculated in models involving stochastic partial differential equations of reaction-advection-diffusion type
Effects of delayed testing on decisions to stop learning
Get PDFThis study explores whether people’s preference to restrict to-be-learned material is influenced by memory test timing. In Experiments 1a and 2a, participants studied word lists. For control groups, lists were displayed in their entirety, whereas participants in other groups could stop the lists early. We investigated whether participants decided to terminate learning when they expected their free-recall memory to be tested after a short (Experiment 1a) or long (Experiment 2a) delay. Experiments 1b and 2b tested participants’ theoretical assumptions about learning termination. Participants who terminated learning recalled fewer words than those who saw all to-be-remembered materials. When the memory test immediately followed the learning phase, more than half of the participants decided to stop learning. However, when there was any time delay between learning and testing, only around a quarter of them decided to stop. Delayed testing can effectively discourage a maladaptive learning strategy of learning termination
