In the design of reinforced concrete structures, a designer must satisfy not only the strength requirements but also the serviceability requirements, and therefore the control of the deformation becomes more significant. To ensure serviceability criterion, it is necessary to accurately predict the cracking and deflection of reinforced concrete structures under load. For accurate determination of the member deflections, cracked members in the reinforced concrete structures need to be identified and their effective flexural rigidities determined. The effect of concrete cracking on the stiffness of a flexural member is largely dependent on both the magnitude and shape of the moment diagram, which is related to the type of applied loading. The aim of the present investigation is to study the cracking behaviour (crack spacing and crack width) of reinforced concrete beam elements constructed from high performance concrete and subjected to bending. An initial optimization was performed to identify a suitable mix design, which has the different required performance attributes of high performance concrete, such as strength, workability, dimensional stability and durability. It is likely that this stage will confirm two mixes, which can be used to compare and contrast the cracking behaviour and to isolate the effect of creep on the long-term performance of such elements constructed from high-strength concrete. Typically, a concrete compressive strength of approximately 100MPa will be sought. High performance concrete is made by partially replacement of cement by silica fume. Once the mixes identified, a series of beams (typically 4.2 m span with a constant moment zone of one and half metres) were tested under 2 point loading (also called 4-point loading including the reactions). These elements were subjected to a constantly applied load for at least three months. The intention was to isolate the effect of creep on the long-term performance of such elements constructed from high-strength concrete. This has not been achieved before. Complimentary tests were also performed on the concrete itself (strength, stiffness, shrinkage, creep (compressive and tensile) etc.). Finally, the deflection, crack width and spacing calculation procedures in several major international concrete codes, including EC2-92 and MC 90, were assessed and some deficiencies in the existing approaches exposed. A comparison between the experimental results, and international codes was presented for all beam specimens time-dependent behaviour. Overall, the programme provided much needed data, which verify the influence of creep and shrinkage on the long-term performance (deflection) of high strength reinforced concrete beam elements.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:713470 |
| Date | January 2013 |
| Creators | Ahmed, Kawa Taha Abualwafa |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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