PhD thesis
Rissbildung und Zugtragverhalten von mit Stabstahl und Fasern bewehrtem Ultrahochfesten Beton (UHPC)

Publication Details
Leutbecher, T.
kassel university press GmbH
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Schriftenreihe Baustoffe und Massivbau
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Ultra high performance concrete (UHPC) is a very densely structured cementitious material, which is not only characterised by a high compressive strength but also by a high resistance against every kind of physical and chemical attack. A ductile post-failure behaviour under compression is mostly achieved by adding thin short fibres. In combination with conventional bar reinforcement or prestressing steel, UHPC enables to build slender, long-span structures and offers the opportunity for new application fields, i.e. coating of bridge decks by reinforced UHPC layers. Due to the interaction of continuous reinforcement elements and discontinuously distributed short fibres under tensile loading differences compared to common reinforced concrete and prestressed concrete can by observed. Concerning this, within the scope of this thesis a model is developed and confirmed by an extensive test series. The work is based on experimental and theoretical investigations on the bond behaviour of reinforcing bars embedded in an UHPC-matrix and on the influence of fibre addition on the cracking and tensile behaviour of UHPC. The modelling of UHPC tensile members with a combination of reinforcing bars and fibres is based on the consideration of discrete cracks. Therefore, the essential mechanical relationships are treated in detail. For the elastic range of the reinforcing steel (serviceability range) the load-deformation-behaviour of structural elements with combined reinforcement can be described consistently considering the shrinkage strain that is significant for UHPC. For practical use, an approximation procedure is derived by introducing some simplifications. Both the theoretical and the experimental investigations confirm, that in combination with bar reinforcement the fibre reinforced UHPC itself does not need to show a hardening behaviour to achieve an overall hardening behaviour and to enable a distributed crack formation with small crack widths and crack spacings. Model ideas available so far, which primarily suggest a superposition of the stress-strain-relationship of fibre concrete and of plain steel, both determined separately, are not able to reproduce this observation. According to the own investigations, with sufficient bar reinforcement, a reliable tensile behaviour of UHPC can be achieved purposefully without uneconomically high fibre contents. At the same time, the secure limitation of crack width significantly below 0.1 mm guarantees durability even under unfavourable environmental conditions. Because of the minimised demand of material and energy and on account of the expected high service life within the meaning of sustainability optimised structures can be realised.


Last updated on 2019-25-07 at 17:40