The influence of boundary conditions and axial deformability on buckling behavior of two-layer composite columns with interlayer slip

This paper presents a detailed analysis of the influence of boundary conditions and axial deformation on the critical buckling loads of the geometrically perfect elastic two-layer composite columns with interlayer slip between the layers. An investigation is based on the extension of our preliminary analytical study of slip-buckling behavior of two-layer composite columns. It is proved that the boundary conditions of composite columns with interlayer slip are interrelated in longitudinal and transverse directions. The parametric analysis reveals that the influence of different longitudinal boundary conditions on critical buckling load is significant and can be up to 20%, while, on the other hand, the influence of axial deformation is negligible. (C) 2010 Elsevier Ltd. All rights reserved

The effect of transverse shear deformation on the buckling of two-layer composite columns with interlayer slip

This paper presents an efficient mathematical model for studying the buckling behavior of geometrically perfect elastic two-layer composite columns with interlayer slip between the layers. The present analytical model is based on the linearized stability theory and is capable of predicting exact critical buckling loads. Based on the parametric analysis, the critical buckling loads are compared to those in the literature. It is shown that the discrepancy between the different methods can be up to approximately 22%. In addition, a combined and an individual effect of pre-buckling shortening and transverse shear deformation on the critical buckling loads is studied in detail. A comprehensive parametric analysis reveals that generally the effect of pre-buckling shortening can be neglected, while, on the other hand, the effect of transverse shear deformation can be significant. This effect can be up to 20% for timber composite columns, 40% for composite columns very flexible in shear (pyrolytic graphite), while for metal composite columns it is insignificant. (C) 2011 Elsevier Ltd. All rights reserved

Reliability analysis of a glulam beam

The present case study is an example of the use of reliability analysis to asses the failure probability of a tapered glulam beam. This beam is part of a true structure built for a super market in the town of Kokemaki in Finland. The reliability analysis is carried out using the snow load statistics available from the site and on material strength information available from previous experiments. The Eurocode 5 and the Finnish building code are used as the deterministic methods to which the probabilistic method is compared to. The calculations show that the effect of the strength variation is not significant, when the coefficient of variation of the strength is around 15% as usually assumed for glulam. The probability of failure resulting from a deterministic design based on Eurocode 5 is low compared to the target values and lower sections are possible if applying a probabilistic design method. In fire design, if a 60 min resistance is required, this is not the case according to Eurocode 5 design procedures, a higher section would be required. However, a probabilistic based fire analysis results in bounds for the yearly probability of failure which are comparable to the target value and to the values obtained from the normal probabilistic based design. (C) 2006 Elsevier Ltd. All rights reserved

An analytical model of layered continuous beams with partial interaction

Starting with the geometrically non-linear formulation and the subsequent linearization, this paper presents a consistent formulation of the exact mechanical analysis of geometrically and materially linear three-layer continuous planar beams. Each layer of the beam is described by the geometrically linear beam theory. Constitutive laws of layer materials and relationships between interlayer slips and shear stresses at the interface are assumed to be linear elastic. The formulation is first applied in the analysis of a three-layer simply supported beam. The results are compared to those of Goodman and Popov (1968) and to those obtained from the formulation of the European code for timber structures, Eurocode 5 (1993). Comparisons show that the present and the Goodman and Popov (1968) results agree completely, while the Eurocode 5 (1993) results differ to a certain degree. Next, the analytical solution is used in formulating a general procedure for the analysis of layered continuous beams. The applications show the qualitative and quantitative effects of the layer and the interlayer slip stiffnesses on internal forces, stresses and deflections of composite continuous beams

Analysis of composite beams exposed to fire

This thesis presents a numerical model and a computer program for stress-strain analysis of non-linear\ud multi-layered composite beams with interlayer slip, shear deformation and charring of timber when\ud simultaneously exposed to static loading and fire. The text is divided into two major parts. In the first part\ud we analyse the temperature and moisture content distribution in timber composite beams when exposed\ud to fire. The simultaneous heat and moisture transfer in porous media like wood is governed by the two\ud second order non-linear partial differential equations provided by Luikov. In this way, the anisotropy\ud and temperature and moisture content dependent permeability and material properties of timber and\ud char are assumed. A non-linear system of governing equations which describes the initial boundary\ud value problem of heat and moisture transfer in timber is discretized and solved by the use of numerical\ud procedure such as finite difference method. The calculated one-dimensional charring rate and depth are\ud compared to the results of empirical models and experimental results published in the technical literature.\ud In addition, the present numerical model is also used to analyse a two-dimensional behaviour of timber\ud solid and composite beams when exposed to fire from three sides. In the second part we introduce first\ud the governing equations which describe the mechanical behaviour of multi-layered composite beams\ud with interlayer slip and shear deformation. A special attention is devoted to the analytical treatment\ud of geometrically and materially linear multi-layered composite beams with a significant interlayer slip.\ud The solution algorithms for Bernoulli and Timoshenko composite beams are represent by the numerical\ud examples. A parametric study is performed also to investigate the influence of shear deformation on\ud the mechanical behaviour of the above mentioned structures. Further, a modified principle of virtual\ud work is used to derive the new strain-based family of finite elements for a non-linear analysis of multilayered\ud composite beams with interlayer slip and shear. The calculations with different number of finite\ud elements, degree of interpolation functions and different selection of collocation points confirm, that the\ud derived strain-based family of finite elements is completely locking-free. The same strain-based finite\ud elements are employed in the mechanical response analysis of the multi-layered composite beams when\ud simultaneously exposed to static loading and fire. The geometric strain increment is assumed to be the\ud sum of increments of elastic and temperature strains. The applicability of the present numerical model\ud for the stress-strain analysis of the non-linear multi-layered composite beams subjected to mechanical\ud and fire loads is clearly illustrated by the numerical examples

Analytical solution of two-layer beam taking into account interlayer slip and shear deformation

A mathematical model is proposed and its analytical solution derived for the analysis of the geometrically and materially linear two-layer beams with different material and geometric characteristics of an individual layer. The model takes into account the effect of the transverse shear deformation on displacements in each layer. The analytical study is carried out to evaluate the influence of the transverse shear deformation on the static and kinematic quantities. We study a simply supported two-layer planar beam subjected to the uniformly distributed load. Parametric studies have been performed to investigate the influence of shear by varying material and geometric parameters, such as interlayer slip modulus (K), flexural-to-shear moduli ratios (E/G) and span-to-depth ratios (L/h). The comparison of the results for vertical deflections shows that shear deformations are more important for high slip modulus, for ``short'' beams with small L/h ratios, and beams with high E/G ratios. In these cases, the effect of the shear deformations becomes significant and has to be addressed in design. It also becomes apparent that models, which consider the partial interaction between the layers, should be employed if beams have very flexible connections

Who Borrows from the Lender of Last Resort? * Itamar Drechsler

Abstract Understanding why banks borrow from the Lender of Last Resort (LOLR) during a financial crisis is crucial to understanding the macroeconomic impact of such largescale interventions. We document a strong divergence among banks' take-up of LOLR assistance during the financial crisis in the euro area, as banks which borrowed heavily also used increasingly risky collateral. We propose four explanations for this divergence: (1) illiquidity, (2) risk-shifting, (3) political economy, and (4) differences in banks' private valuations. We test these explanations using proprietary data on all central bank borrowing and collateral pledged in the euro area from 2008 to 2011, together with holdings data from the European bank stress tests. Our results strongly support the risk-shifting explanation. We find it both in the financially-distressed countries, where illiquidity and political economy are also at work, and in the non-distressed countries, where it appears to be the main driver of differences in bank's behavior

Cosmological perturbations in SFT inspired non-local scalar field models

We study cosmological perturbations in models with a single non-local scalar field originating from the string field theory description of the rolling tachyon dynamics. We construct the equation for the energy density perturbations of the non-local scalar field and explicitly prove that for the free field it is identical to a system of local cosmological perturbation equations in a particular model with multiple (maybe infinitely many) local free scalar fields.Comment: 21 pages, no figures, v3: presentation improved, results unchanged, references adde

Global inequities and emissions in Western European textiles and clothing consumption

YesRising demand for cheaper textiles and clothing in Western Europe is well documented, as are changes in the Textiles and Clothing industry's globalised production structure. We apply a sub-systems global multi-regional input–output accounting framework to examine the sustainability implications of meeting Western European demand for textiles and clothing goods between 1995 and 2009. Our framework estimates environmental and socio-economic impacts of consumption in a consistent manner and shows where these occur both geographically and in the value chain. The results demonstrate that Western European textiles and clothing consumption remains dependent on low-cost labour from Brazil, Russia, India and China (BRIC), principally in the Textiles and Clothing and Agricultural sectors. Conversely, we show that the wage rate for BRIC workers in the global value chains serving Western European textiles and clothing consumption has risen over time but remains low relative to the wage rate paid to Western European workers. Likewise, we find that profits are increasingly generated within BRIC and that they are now at comparable levels to those generated in Western Europe. We find a slight overall decrease in the amount of carbon emitted in the production of textiles and clothing goods for Western Europe between 1995 and 2009. However, the trend is not linear and the importance of different underlying drivers varies over the timeseries. We conclude by discussing the implications of these results for a more sustainable future for Western European textiles and clothing consumption

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead