70 research outputs found
Self-consistent solution of Kohn-Sham equations for infinitely extended systems with inhomogeneous electron gas
The density functional approach in the Kohn-Sham approximation is widely used
to study properties of many-electron systems. Due to the nonlinearity of the
Kohn-Sham equations, the general self-consistence searching method involves
iterations with alternate solving of the Poisson and Schr\"{o}dinger equations.
One of problems of such an approach is that the charge distribution renewed by
means of the Schr\"{o}dinger equation solution does not conform to boundary
conditions of Poisson equation for Coulomb potential. The resulting instability
or even divergence of iterations manifests itself most appreciably in the case
of infinitely extended systems. The published attempts to deal with this
problem are reduced in fact to abandoning the original iterative method and
replacing it with some approximate calculation scheme, which is usually
semi-empirical and does not permit to evaluate the extent of deviation from the
exact solution. In this work, we realize the iterative scheme of solving the
Kohn-Sham equations for extended systems with inhomogeneous electron gas, which
is based on eliminating the long-range character of Coulomb interaction as the
cause of tight coupling between charge distribution and boundary conditions.
The suggested algorithm is employed to calculate energy spectrum,
self-consistent potential, and electrostatic capacitance of the semi-infinite
degenerate electron gas bounded by infinitely high barrier, as well as the work
function and surface energy of simple metals in the jellium model. The
difference between self-consistent Hartree solutions and those taking into
account the exchange-correlation interaction is analyzed. The case study of the
metal-semiconductor tunnel contact shows this method being applied to an
infinitely extended system where the steady-state current can flow.Comment: 38 pages, 9 figures, to be published in ZhETF (J. Exp. Theor. Phys.
Shake-table testing of a stone masonry building aggregate: overview of blind prediction study
City centres of Europe are often composed of unreinforced masonry structural aggregates, whose seismic response is challenging to predict. To advance the state of the art on the seismic response of these aggregates, the Adjacent Interacting Masonry Structures (AIMS) subproject from Horizon 2020 project Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA) provides shake-table test data of a two-unit, double-leaf stone masonry aggregate subjected to two horizontal components of dynamic excitation. A blind prediction was organized with participants from academia and industry to test modelling approaches and assumptions and to learn about the extent of uncertainty in modelling for such masonry aggregates. The participants were provided with the full set of material and geometrical data, construction details and original seismic input and asked to predict prior to the test the expected seismic response in terms of damage mechanisms, base-shear forces, and roof displacements. The modelling approaches used differ significantly in the level of detail and the modelling assumptions. This paper provides an overview of the adopted modelling approaches and their subsequent predictions. It further discusses the range of assumptions made when modelling masonry walls, floors and connections, and aims at discovering how the common solutions regarding modelling masonry in general, and masonry aggregates in particular, affect the results. The results are evaluated both in terms of damage mechanisms, base shear forces, displacements and interface openings in both directions, and then compared with the experimental results. The modelling approaches featuring Discrete Element Method (DEM) led to the best predictions in terms of displacements, while a submission using rigid block limit analysis led to the best prediction in terms of damage mechanisms. Large coefficients of variation of predicted displacements and general underestimation of displacements in comparison with experimental results, except for DEM models, highlight the need for further consensus building on suitable modelling assumptions for such masonry aggregates
EXPERIMENTALLY VALIDATED RETROFIT SOLUTIONS Shake-table testing of securing solutions for face-loaded unreinforced masonry walls
One of the most critical deficiencies of historic clay brick
unreinforced masonry (URM) buildings [1] is the out-of-plane
failure mechanism induced by lateral earthquake loads [2-4]. This
failure mechanism is inhibited via the addition of adequate walldiaphragm
and wall-to-wall connections. However, in high and
moderate seismic zones the sudden and unstable out-of-plane failure
of walls mainly located at the upper building levels can result in
extensive damage and potentially catastrophic collapse, posing a
significant life-safety hazard to both building occupants and nearby
pedestrians.
A number of studies have been previously undertaken to investigate
the performance of as-built URM walls when subjected to out-ofplane
loads [5-7] and comparatively small number of studies were
undertaken on the dynamic behaviour of retrofitted URM walls and
validation of retrofit techniques. The study presented herein focuses
on developing and experimentally validating simple, practical, costeffective,
aesthetics, minimally-invasive and reversible seismic
securing techniques for URM walls when loaded out-of-plane, with
a main focus on practical applications in existing vintage buildings
Pullout strength of NSM CFRP strips bonded to vintage clay brick masonry
Abstract not availableD. Dizhur, M.C. Griffith, J.M. Ingha
Out-of-plane strengthening of unreinforced masonry walls using near surface mounted fibre reinforced polymer strips
Abstract not availableDmytro Dizhur, Michael Griffith, Jason Ingha
In-plane shear improvement of unreinforced masonry wall panels using NSM CFRP strips
The large number of earthquake-prone vintage unreinforced masonry (URM) buildings in many seismically active parts of the world results in a need for minimally invasive and cost-effective strengthening techniques to enhance the poor earthquake performance of such buildings. The objective of the research reported here was to investigate the applicability of using near-surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips as a retrofitting technique for improving the in-plane shear strength and displacement capacity of multi-leaf URM walls constructed using solid clay brick masonry. The use of this technique for repairing earthquake damaged URM walls was also investigated. Ten multileaf wall panels measuring approximately 1,200Ă1,200 mm were constructed using recycled vintage solid clay bricks and retrofitted using NSM CFRP strips with varying reinforcement ratios. These panels were loaded in diagonal compression, and the results were compared with those obtained from testing of nominally identical unretrofitted wall panels constructed using the same materials. In addition, four wall panels extracted from existing buildings were tested in an as-built condition and then later retested after being repaired using the NSM CFRP strip technique. Based on the experimental results it was established that the NSM CFRP strip technique provides a simple and cost effective method for substantially enhancing the shear strength and displacement capacity of understrength or damaged URM wall panels. © 2013 American Society of Civil Engineers.Dmytro Dizhur, Michael Griffith, and Jason Ingha
Earthquake performance of two vintage URM buildings retrofitted using surface bonded GFRP: case study
Abstract not availableDmytro Dizhur, Sara Bailey, Michael Griffith, Jason Ingha
Performance of unreinforced masonry structures in the 2010/2011 Canterbury earthquake sequence
Following the magnitude 6.3 aftershock in Christchurch, New Zealand, on 22 February 2011, a number of researchers were sent to Christchurch as part of the New Zealand Natural Hazard Research Platform funded âProject Masonryâ Recovery Project. Their goal was to document and interpret the damage to the masonry buildings and churches in the region. Approximately 650 unreinforced and retrofitted clay brick masonry buildings in the Christchurch area were surveyed for commonly occurring failure patterns and collapse mechanisms. The entire building stock of Christchurch, and in particular the unreinforced masonry building stock, is similar to that in the rest of New Zealand, Australia, and abroad, so the observations made here are relevant for the entire world.Moon, LM ; Griffith, MC ; Dizhur, D ; Ingham, J
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