Synopsis The effect of high temperutures upon the bond between the steel und concrete in reinforced concrete was examined over a temperature range of 20–750°C. The concrete mix was constant throughout und 16 mm deformed reinforcing bar (Tor bar) was used in most tests. Various parameters were examined including different test conditions and depths of cover. The four test conditions used were: (l) stressed during heating (a steady-state bond stress of 3·70 N/mm2 was applied) and loaded to failure when hot, (2) stressed during heating and loaded to failure when cooled, (3) no applied stress during heating and loaded to failure when hot, and (4) no stress during heating and loaded to failure when cooled. Four different depths of concrete cover (25, 32, 46 und 55 mm) were l for the stressed/residual test condition, but only tht 55 mm cover was used with the other three test conditions. The effect of heat upon the compressive und tensile strength of the concrete was also considered, together with its effect upon the bond performance. Some 16 mm plain bar specimens were used in the tensile strength studies. Introduction When a reinforced concrete structure has been involved in a fire. it is often possible for it to remain standing, because of the good fire-resisting properties of the concrete. This means that. in dealing with such a situation. a choice can be made between reconstruction and reinstatement. Often reinstatement can be the quicker and cheaper alternative. However, before a decision can be made, it is necessar/10 establish whether or not the damaged structure is suitable for such treatment. To do this, its residual capacity for structural performance must be assessed, which requires knowledge of the properties of steel and concrete, and of the bond between them at temperatures experienced in fires.
Institute of Higher EducationThe Author's conclusions concur with my own work on 1 m, 1.5 m, 3 m, 5 m, and 6 m span bridge test"-21 which have resulted in the idealization shown in Fig. 17. It is from this theoretical model that the assessing engineer may start and thus determine the relative significance of each component. This allows the different modes of failure to be studied. If the contribution by the spandrel walls to barrel stability is high (which in most cases it will be), transverse distribution becomes significant. This has been observed during the monitoring of a two-span stone bridge during the passage of an abnormal load.22 The bridge showed no signs of distress longitudinally, but transversely, local to the wheel loading, tensile strains were recorded which were commensurate with crack formation. As it was likely that transversely there was no precompression (unlike longitudinally where compression is guaranteed), it followed that the recorded tensile strains did cause cracking. Fig. 18 shows the transverse strain and deflexion profiles. This raises the question as to whether or not the adoption of a full width KEL as the standard loading case is restrictive, as it increases the likelihood of a classical fourhinge mechanism or a three-hinge snap-through failure depending on the spandrel wall stiffening and barrel backfill. It was reassuring, therefore, to see confirmation of this concern by the Authors' use of a half-width loading case. Other types of loading may cause local distress or even a mode of failure not hitherto considered. Certain types of arch bridge are more likely to be susceptible to non-standard modes of failure, e.g. skew, elliptical or multi-ring brickwork arch bridges. It has been shown21F22 that point loads can cause local distress to an arch.47. The real value of model testing lies in the prediction of the mode of behaviour and the load-carrying capacity of full-scale structures. The Authors' analysis considered only one of the variables, i.e. vertical loading. A more extensive analysis using the parameters identified in Fig. 17 results in a more complex situation. Assuming the densities of the prototype and model are the same for each of the constituents, it follows that, using the Authors' notation, Pp/Pm for the various parameters is related t0.L; (for the vertical dead load), L j (for the horizontal longitudinal soil pressure), L: (for dead load of the spandrel wall), L; (for cohesion of backfill with the spandrel wall), L: (for frictional resistance of the backfill with the spandrel wall due to self-weight) and Lf (for frictional resistance of the backfill with the spandrel wall due to the applied loading). Additionally, as the Authors correctly explored, there is the effect of relative strength.48. It follows that any extrapolation of the results for application at full scale should be treated with care as the scaling factors are not the same for each parameter.49. In spite of the doubts raised, it is interesting that the correlation between model and full-scale behavi...
Synopsis Tests were carried out to examine the effects of heat treatment upon the bond between concrete and steel by using direct displacement measurements and monitoring acoustic emission. A description of the experimental set-up has been given previously and, as before, it was used to test cylindrical pull-out specimens with an actual embedment length of 32 mm. The variables considered were type of bar (plain anddeformed bars of 16 mm diameter) and the effect of load cycling (for the deformed bar only) upon the bond after it has been subjected to heat treatment. The acoustic emission equipment was incorporated into the system to assess its validity in this type of testing and was used in all three of the different test situations investigated.
Experiments are described which support the application of the membrane theory of shell analysis in determining optimum shapes for underwater structures of constant strength. A relationship between marine life and such structures is considered and design procedures for shape selection are given. Proposals for the investigation of the behaviour of such structures under loadings otherthan the initial design forces are outlined both from an analyticaIJnumerica1 and an experimental approach.
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