The Similarity Hypothesis in General Relativity

Self-similar models are important in general relativity and other fundamental theories. In this paper we shall discuss the ``similarity hypothesis'', which asserts that under a variety of physical circumstances solutions of these theories will naturally evolve to a self-similar form. We will find there is good evidence for this in the context of both spatially homogenous and inhomogeneous cosmological models, although in some cases the self-similar model is only an intermediate attractor. There are also a wide variety of situations, including critical pheneomena, in which spherically symmetric models tend towards self-similarity. However, this does not happen in all cases and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra

Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020

We show the distribution of SARS-CoV-2 genetic clades over time and between countries and outline potential genomic surveillance objectives. We applied three available genomic nomenclature systems for SARS-CoV-2 to all sequence data from the WHO European Region available during the COVID-19 pandemic until 10 July 2020. We highlight the importance of real-time sequencing and data dissemination in a pandemic situation. We provide a comparison of the nomenclatures and lay a foundation for future European genomic surveillance of SARS-CoV-2.Peer reviewe

Flexural, axial load and elongation response of plastic hinges in reinforced concrete member

Previous research in New Zealand has indicated that elongation of plastic hinges in reinforced concrete (RC) beams can have a significant effect on the seismic performance of RC structures. A number of empirical formulas have been proposed to predict elongation. However, no satisfactory analytical models are currently available which can be used to predict the influence of elongation on the seismic performance. This paper describes a plastic hinge model developed to predict the combined flexural, axial load and elongation response of plastic hinges in RC beam. The model is a filament type element which consists of layers of longitudinal and diagonal axial springs to represent the flexural, shear and elongation response of a plastic hinge. Analytical predictions for beams with different levels of axial load are compared with the experimental results. It is found that the plastic hinge model predicts the response satisfactorily. With this newly formed element, seismic analyses may be performed to assess the significance of beam elongation on seismic performance of RC structures

Analytical Model on Beam Elongation within the Reinforced Concrete Plastic Hinges

Research in New Zealand over the last two and a half decades has shown that elongation in plastic hinge regions can have a very significant effect on the seismic performance of reinforced concrete buildings. It was found that elongation arises due to (i) plastic strain in reinforcing bars caused by inelastic rotation, and (ii) unrecoverable tensile strains in compression reinforcement. A number of empirical formulas have been proposed to predict elongation. However, there are currently no analytical models that can accurately predict elongation in the plastic hinges. Consequently, the influence of elongation on the seismic performance of reinforced concrete structures cannot be predicted analytically. This paper describes a plastic hinge model for the computer analysis package, ‘RUAUMOKO’, which can predict both the flexural and elongation response of plastic hinges in reinforced concrete beams. Experimental and analytical results are compared in the study. With the completion of this newly formed element, seismic analyses may be made of structures containing potential plastic hinges to assess the significance of elongation on seismic performance

Modelling of RC Moment Resisting Frames with Precast-prestressed Flooring System

In this paper, the seismic performance of reinforced concrete moment resisting frames coupled with a floor containing precast-prestressed units is examined. Mechanisms associated with the beam strength enhancement arising from plastic hinges and floor interactions are described. A computational model is set up to predict the response of a 3D frame containing precast-prestressed floor units with cast-in-situ concrete topping. This model contains newly developed plastic hinge elements which account for flexural, shear and elongation response of plastic hinges in beams subjected to inelastic rotation and varying axial load levels. To allow for floor interaction with the beam plastic hinges, the model uses axial strut-and-tie elements to represent the linking slab between the longitudinal beams and the first precast unit. Analysis using this model shows good agreement with the experimental results indicating that the model can be used to analyse the seismic performance of RC frames containing precast-prestressed flooring systems

Experimental Investigation on the Interaction of Reinforced Concrete Frames with Precast-Prestressed Concrete Floor Systems

http://www.14wcee.org/Proceedings/isv7/main.htm Paper ID: 12-01-0042A three dimensional, approximately half scale experimental test has been carried out to investigate the effect of precast-prestressed floor units on the seismic performance of reinforced concrete moment resisting frames. This paper gives an overview of the experiment and summarizes the results obtained from the test. The paper focuses on the level of strength enhancement and elongation within the plastic hinges. The results show that the presence of prestressed floor units partially restrains elongation of plastic hinges such that elongation in the exterior and interior plastic hinges differs significantly. This increases the strength of the beams more than that specified in the major structural design codes. This is a cause of great concern as this underestimation of beam strength may result in brittle column failure modes in a major earthquake

Analytical model of ductile reinforced concrete frames allowing for elongation of plastic hinges

Elongation in reinforced concrete members can have detrimental effect on the seismic performance of reinforced concrete structures. For reliable assessment of seismic performance, analytical models should take into account this elongation phenomenon. In this paper, an analytical model of plastic hinges has been developed and implemented into an analysis package. This model consists of a layer of horizontal concrete and steel springs to simulate the flexural behavior, as well as diagonal springs to represent the diagonal compression struts and to resist the shear force. The model is verified against experimental results of beams and frame subassembly tests found in literature. Comparisons of the analytical predictions and the experimental results show that this model can make significant advancement in predicting elongation in beam plastic hinges. It can be used to assess the effect of beam elongation on the seismic performance of reinforced concrete frame structures