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.

The manufacture and utilisation of architectural terracotta and faience.

The revival of terracotta and faience in British architecture was widespread, dramatic in its results and, for two decades, the subject of intense debate. However the materials have been frequently denigrated and more generally disregarded by both architects and historians. This study sets out to record and explain the rise and fall of interest in terracotta and faience, the extent and nature of the industry and the range of architectural usage in the Victorian, Edwardian and inter-war periods. The first two chapters record the faltering use of terracotta as an 'artificial stone', until the material gained its own identity, largely through the appreciation of Italian architecture. In the mid-Victorian period, terracotta will be seen to have become symbolic of the philosophy of the Victoria and Albert Museum and its Art School in attempting to reform both architecture and the decorative arts. The adoption of terracotta was furthered as much by industrial as aesthetic factors; three chapters examine how the exploitation of coal-measure clays, developments in the processes of manufacture, the changing motivation of industrialists and differing economics of production served to promote and then to hinder expansion and adaptation. The practical values of economy, durability and fire-resistance and the aesthetic potential, seen in terms of colour and decorative and sculptural modelling, became inter-related in the work of the architects who made extensive use of architectural ceramics. A correlation emerges between the free Gothic style, exemplified by the designs of Alfred Waterhouse and the use of red terracotta supplied from Ruabon, and between the eclectic Renaissance style and a buff material produced by different manufacturers.These patterns were modified as a result of the adoption of faience for facing external walls as well as interiors, and because of the new architectural requirements and tastes of the twentieth century. The general timidity in exploiting the scope for polychromatic decoration and the increasing opposition to architectural ceramics is contrasted with the most successful schemes produced for cinemas, chain-stores and factories. In the last chapter, those undertaken by the Hathern Station Brick and Terracotta Company between 1896 and 1939 are used as a case study; they confirm that manufacturers, architects and clients were all committed to creating a modern and yet decorative architecture, appropriate for new building types and that would appeal to and be comprehensible to the public.

The spalling of concrete in fires

The occurrence of spalling is a major factor in determining the fire resistance of concrete constructions. The apparently random occurrence of spalling has limited the development and application of fire resistance modelling for concrete structures. This Thesis describes an experimental investigation into the spalling of concrete on exposure to elevated temperatures. It has been shown that spalling may be categorised into four distinct types, aggregate spalling, corner spalling, surface spalling and explosive spalling. Aggregate spalling has been found to be a form of shear failure of aggregates local to the heated surface. The susceptibility of any particular concrete to aggregate spalling can be quantified from parameters which include the coefficients of thermal expansion of both the aggregate and the surrounding mortar, the size and thermal diffusivity of the aggregate and the rate of heating. Corner spalling, which is particularly significant for the fire resistance of concrete columns, is a result of concrete losing its tensile strength at elevated temperatures. Surface spalling is the result of excessive pore pressures within heated concrete. An empirical model has been developed to allow quantification of the pore pressures and a material failure model proposed. The dominant parameters are rate of heating, pore saturation and concrete permeability. Surface spalling may be alleviated by limiting pore pressure development and a number of methods to this end have been evaluated. Explosive spalling involves the catastrophic failure of a concrete element and may be caused by either of two distinct mechanisms. In the first instance, excessive pore pressures can cause explosive spalling, although the effect is limited principally to unloaded or relatively small specimens. A second cause of explosive spalling is where the superimposition of thermally induced stresses on applied load stresses exceed the concrete's strength.