Behaviour of curved reinforcement bars

Bended or curved reinforcement bars are often met in assessment of existing reinforced concrete structures and are used in design of nodal regions such as frame corners. Although being present in many tested reinforced concrete structures, only little experimental work has been devoted specifically to the behaviour of curved bars and its interaction with the surrounding concrete. To contribute to a better understanding of this behaviour and functioning of curved reinforcement bars, a preliminary experimental programme has been conducted, the results of which are presented in this paper. The tested specimens were all 90-degree V-shaped beams subjected to constant bending, with the frame corner representing the region of interest. The varied parameter was the statical-height of the adjoining beam segments. The application of optical fibres, mounted on the curved reinforcement, allowed for assessment of the interaction between the curved bars and the concrete. This includes strain/stress variations from which the corresponding tension forces are estimated. The bar/concrete-interaction is qualitatively assessed based upon the gradient of the tension force. Photogrammetric measurements allowed for a detailed study of the accompanying crack development, which showed an area with few cracks at the corner region and a change in inclination of cracks near the corner region.

Dynamic Study of Feed-Effluent Heat Exchanger Addition on Double Bed Configuration Ammonia Reactor System within Varied Quenching Ratio

Ammonia is one of the most important industrial commodity due to its wide function. Ammonia synthesis reaction is an exotermic reaction. Therefore, Feed-Effluent Heat Exchanger (FEHE) is added to increase thermal efficiency. However, FEHE could lead the process to experience hysteresis phenomenon due to interaction between equipments as one steady state T feed could result several T outlet. Hysteresis phenomenon may result asset losses like explosion, leakage, and loosing material integrity. Double bed reactor configuration allows us to use several operating parameters as variation to overcome hysteresis. In this review, quenching ratio was chosen to be that varied parameter. This study aims to determine how quenching ratio affects hysteresis zone by utilizing Aspen Hysys® V8.8 as simulation tool. Simulation showed that quenching ratio would narrow hysteresis zone yet increased extinction temperature that lower the conversion. Conversion profile showed that 0.2 quenching ratio got the highest conversion for system with bed volume ratio 2:1 while total volume was 30 m3. However, the feed temperature was fallen at hysteresis zone. Dynamic simulation showed that highest conversion feed temperature (10%ΔTf above extinct temperature) was still able to preserve stability with descending temperature approach. Hysteresis itself started to occur at 1.7%ΔTf above extinct temperature

An Analysis of Bias in Groundwater Modelling Due to the Interpretation of Site Characterization Data

ABSTRACTBias is a difference between model and reality. Bias can be introduced at any stage of the modelling process during a site characterisation or performance assessment programme. It is desirable to understand such bias so as to be able to optimally design and interpret a site characterisation programme. The objective of this study was to examine the source and effect of bias due to the assumptions modellers have to make because reality cannot be fully characterised in the prediction of ground-water fluxes. A well-defined synthetic “reality” was therefore constructed for this study. A limited subset of these data were independently interpreted and used to compute groundwater fluxes across specified boundaries in a cross section. The modelling results were compared to the “true” solutions derived using the full dataset. This study clarified and identified the large number of assumptions and judgements which have to be made when modelling a limited site characterisation dataset. It is concluded that bias is introduced at each modelling stage, and that it is not necessarily detectable by the modellers even if multiple runs with varied parameter values are undertaken.