Lateral instability of slender reinforced concrete columns in a fire environment

The research concerns the development and application of an analytical computer program, SAFE-ROC, that models material behaviour and structural behaviour of a slender reinforced concrete column that is part of an overall structure and is subjected to elevated temperatures as a result of exposure to fire. The analysis approach used in SAFE-RCC is non-linear. Computer calculations are used that take account of restraint and continuity, and the interaction of the column with the surrounding structure during the fire. Within a given time step an iterative approach is used to find a deformed shape for the column which results in equilibrium between the forces associated with the external loads and internal stresses and degradation. Non-linear geometric effects are taken into account by updating the geometry of the structure during deformation. The structural response program SAFE-ROC includes a total strain model which takes account of the compatibility of strain due to temperature and loading. The total strain model represents a constitutive law that governs the material behaviour for concrete and steel. The material behaviour models employed for concrete and steel take account of the dimensional changes caused by the temperature differentials and changes in the material mechanical properties with changes in temperature. Non-linear stress-strain laws are used that take account of loading to a strain greater than that corresponding to the peak stress of the concrete stress-strain relation, and model the inelastic deformation associated with unloading of the steel stress-strain relation. The cross section temperatures caused by the fire environment are obtained by a preceding non-linear thermal analysis, a computer program FIRES-T.

Parametric study of the behaviour of reinforced concrete columns in fire

The research is concerned with the application of the computer simulation technique to study the performance of reinforced concrete columns in a fire environment. The effect of three different concrete constitutive models incorporated in the computer simulation on the structural response of reinforced concrete columns exposed to fire is investigated. The material models differed mainly in respect to the formulation of the mechanical properties of concrete. The results from the simulation have clearly illustrated that a more realistic response of a reinforced concrete column exposed to fire is given by a constitutive model with transient creep or appropriate strain effect The assessment of the relative effect of the three concrete material models is considered from the analysis by adopting the approach of a parametric study, carried out using the results from a series of analyses on columns heated on three sides which produce substantial thermal gradients. Three different loading conditions were used on the column; axial loading and eccentric loading both to induce moments in the same sense and opposite sense to those induced by the thermal gradient. An axially loaded column heated on four sides was also considered. The computer modelling technique adopted separated the thermal and structural responses into two distinct computer programs. A finite element heat transfer analysis was used to determine the thermal response of the reinforced concrete columns when exposed to the ISO 834 furnace environment. The temperature distribution histories obtained were then used in conjunction with a structural response program. The effect of the occurrence of spalling on the structural behaviour of reinforced concrete column is also investigated. There is general recognition of the potential problems of spalling but no real investigation into what effect spalling has on the fire resistance of reinforced concrete members. In an attempt to address the situation, a method has been developed to model concrete columns exposed to fire which incorporates the effect of spalling. A total of 224 computer simulations were undertaken by varying the amounts of concrete lost during a specified period of exposure to fire. An array of six percentages of spalling were chosen for one range of simulation while a two stage progressive spalling regime was used for a second range. The quantification of the reduction in fire resistance of the columns against the amount of spalling, heating and loading patterns, and the time at which the concrete spalls appears to indicate that it is the amount of spalling which is the most significant variable in the reduction of fire resistance.

De-industrialisation and the post-communist transition:Rowthorn and Wells' model revisited

In this paper we present a simple three-sector model explaining the structural change in employment, which is a modified version of Rowthorn-Wells (1987). We supplement the theoretical analysis with simple econometric tests, which illustrate how the modified Rowthorn-Wells model can be used to (i) motivate empirical estimates of the link between the level of development and structures of employment, (ii) illustrate structural distortions under the command economies, and the structural adjustment that happened during the post-Communist transition. We demonstrate that in the case of these economies, the transition process leads to an adjustment to the employment structures predicted by the model.

Researching with, not on:using photography in researching street children in Accra, Ghana

What is discussed in this chapter is work-in-progress, an opportunity for reflection upon elements of an on-going research project examining the lives of street children in Accra, Ghana. Street children have received much research in recent years but our project is, we believe, distinctive in two respects. The first of these is that access to reliable data on the growing presence of children on the streets of African cities is often problematic. Available research is often diffuse and hard to access, it is more often than not driven by the short-term requirements of specific programmes and interventions and as a consequence can be lacking in depth, rigour and innovation. Without the means to provide a sufficiently self-conscious and critical engagement with accepted understandings of the lives of street children, consideration of the experience of street children in Africa continues to rely heavily on the more capacious and better disseminated research from the Americas (e.g., Mickelson, 2000). At the very least, Africa's specific experience of large population displacements, diversity of family forms, rapid urbanisation, vigorous structural adjustment and internal conflict raise important questions about the appropriateness of such ready generalisations. Judith Ennew (2003, p. 4) is clear that caution is needed in an uncritical endorsement of the “globalisation of the street child based on Latin American work”. She is equally mindful, however, that as far as Africa is concerned the absence of reliable evidence continues to hinder debate.

Applications of Reissner's principle to structural dynamics

The analysis and prediction of the dynamic behaviour of s7ructural components plays an important role in modern engineering design. :n this work, the so-called "mixed" finite element models based on Reissnen's variational principle are applied to the solution of free and forced vibration problems, for beam and :late structures. The mixed beam models are obtained by using elements of various shape functions ranging from simple linear to complex cubic and quadratic functions. The elements were in general capable of predicting the natural frequencies and dynamic responses with good accuracy. An isoparametric quadrilateral element with 8-nodes was developed for application to thin plate problems. The element has 32 degrees of freedom (one deflection, two bending and one twisting moment per node) which is suitable for discretization of plates with arbitrary geometry. A linear isoparametric element and two non-conforming displacement elements (4-node and 8-node quadrilateral) were extended to the solution of dynamic problems. An auto-mesh generation program was used to facilitate the preparation of input data required by the 8-node quadrilateral elements of mixed and displacement type. Numerical examples were solved using both the mixed beam and plate elements for predicting a structure's natural frequencies and dynamic response to a variety of forcing functions. The solutions were compared with the available analytical and displacement model solutions. The mixed elements developed have been found to have significant advantages over the conventional displacement elements in the solution of plate type problems. A dramatic saving in computational time is possible without any loss in solution accuracy. With beam type problems, there appears to be no significant advantages in using mixed models.

Purchasing power parity and structural instability in the US/UK exchange rate

The aim of this study is to determine if nonlinearities have affected purchasing power parity (PPP) since 1885. Also using recent advances in the econometrics of structural change we segment the sample space according to the identified breaks and look at whether the PPP condition holds in each sub-sample and whether this involves linear or non-linear adjustment. Our results suggest that during some sub-periods, PPP holds, although whether it holds or not and whether the adjustment is linear or non-linear, depends primarily on the type of exchange rate regime in operation at any point in time.

Risk and structural instability in US house prices

This paper employs a Component GARCH in Mean model to show that house prices across a number of major US cities between 1987 and 2009 have displayed asset market properties in terms of both risk-return relationships and asymmetric adjustment to shocks. In addition, tests for structural breaks in the mean and variance indicate structural instability across the data range. Multiple breaks are identified across all cities, particularly for the early 1990s and during the post-2007 financial crisis as housing has become an increasingly risky asset. Estimating the models over the individual sub-samples suggests that over the last 20 years the financial sector has increasingly failed to account for the levels of risk associated with real estate markets. This result has possible implications for the way in which financial institutions should be regulated in the future.

KM governance:the mechanisms for guiding and controlling KM program

Purpose: To establish and sustain their KM programs organizations need to establish mechanisms to ensure their governance. KM programs require business integration, senior management involvement and decision making authority. The present research investigates the KM governance mechanisms organizations use to guide and control their KM programs. The research seeks to contribute to a better understanding of the governance of KM and to support organizations in the development of their KM programs. Methodology: The study employs multiple case research methodology to analyze the KM governance arrangements of twelve international organizations and identify patterns in their governance configurations. Findings: The analysis identifies a range of structural, process and relational mechanisms that are critical for governing an organizational KM program. Different patterns among the KM governance mechanisms are identified which lead to the development of generic KM governance typologies. Research implications: The development of the KM governance framework allows future research to systematically investigate the KM governance phenomenon. As the present study is based on a configurational analysis future research should particularly target the performance implications of different KM governance configurations. Practical implications: The research provides insights into the diversity of KM governance mechanisms and their impact on a KM program. The KM governance framework can assist managers in reviewing their present and prospective KM programs and thereby support benchmarking or re-organization efforts. Originality: Building on prior research that has focused on individual KM governance aspects, the present study adopts a comprehensive perspective integrating structural, process and relational governance mechanisms.