Owing to developments in materials and in structural analysis, the control of deflection under service loads has recently began to play a large part in the design of reinforced-concrete structures. Creep and shrinkage of plain concrete has been the subject of a considerable amount of research during the last fifty years and there have been several studiers of the behaviour of statically-determinate beams under sustained load. However, most reinforced concrete structures are statically indeterminate and the behaviour of this type of structure under sustained load has received very little attention. It is important to establish the main differences in time dependent behaviour of statically determinate and indeterminate structure under sustained load so that the validity of extending existing methods of calculation of long term deflection (developed with limited success for determinate structures) to indeterminate structures may be assessed. This investigation is an experimental and theoretical study of the behaviour of statically-indeterminate structures under sustained service loads. All the experimental work was performed in a laboratory where the temperature and humidity were maintained constant. Concrete of the same mix proportions and strength was used throughout the programme and control shrinkage and creep tests were performed on the plain concrete. A theoretical study of the behaviour of plain concrete was made and compared with the experimental results. The sustained moment-curvature relationships of two reinforced concrete cross sections was investigated experimentally over eighteen months. The investigation was limited to the service moment range. A typical beam cross section, which was 200 x 380 mm and reinforced with approximately 1.5% of tensile steel, was studies using seven specimens and each subjected to a different value of sustained pure moment. The curvature of each specimen was measured at intervals over eighteen months so that sustained moment curvature diagrams could be plotted. A typical column cross section, which was 200 mm square and reinforced with approximately 1% of steel symmetrically distributed was studies under combined sustained axial load and moment. Each specimen was subjected to the same value of axial load but a different value of sustained moment. The curvature and axial strain of each specimen was measured at intervals over eighteen months and sustained moment curvature diagrams plotted. Computer programs were developed for the analysis of continuous beams and two storey single bay reinforced concrete portal frames under sustained service loads. The programs are based on the finite difference treatment of the basic equations of bending and include the effects of cracking in flexure and redistribution of moments under sustained load. The behaviour of the individual cross sections of the frame is defined by moment-curvature data input to the computer which calculates the force and deformation fields at various time and loading. Three full structures were tested under sustained service loads so that the results of the computer analysis could be compared with experimental results. Each member of each frame had one of the two cross sections tested under sustained load.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:463211 |
| Date | January 1971 |
| Creators | Lewsley, Christopher Stanto |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/72007/ |
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