Issue 39

J. Labudkova et alii, Frattura ed Integrità Strutturale, 39 (2017) 47-55; DOI: 10.3221/IGF-ESIS.39.06 48 There is currently no universally valid model to reflect the interaction of the foundation structure with the subsoil and to determine the appropriate distribution of the contact stresses and deformations in the footing bottom and the distribution of stresses and deformations in the deeper layers of subsoil under the footing bottom itself. Therefore the results also differ depending on the choice of the subsoil model. C URRENT STATE OF ART n order to refine the methods of calculation of subsidence, surveys and experimental measurements are still being conducted. The mentioned research project took eight years, conducted by Stavební geologie, n.p. The progress, results and conclusions from this research have been published by several authors – Feda, Havlíček and others in [6, 8]. Measurements of soil subsidence and contact stress on models during load tests in-situ takes place in the present as well. In 2013, Huang, Liang, X., Liang, M., Deng, Zhu, Xu, Wang, and Li from the Department of Civil Engineering of University of Architecture and Technology in China published an article [9] about study of interaction of two-way reinforced slab, gradually loaded with uniformly distributed load. Deformations and internal forces on the slab calculated based on the theory of elasticity were compared with the experimental results of an in-situ test. The development of cracks in the slabs was monitored and the diagram of work was drawn, showing the dependence of deformations on increasing loads. Interaction of foundations and subsoil has been the research subject at the University of Greenwich, UK for many years. In 2012, Alani and Aboutalebi published article [2] about observation of the effect of the rigidity of the foundation base on the mechanical behaviour of concrete slabs. This analysis was conducted on slab model with dimensions 3.0 x 3.0 x 0.2 m. Alani and Aboutalebi presented their results of another experimental measurement also in 2014, in article [1]. The research mentioned in this article contributes to a better understanding of the behaviour of foundation slabs from reinforced concrete and fibre-reinforced concrete for various types of loads. In 2012, Alani in cooperation with Beckett and Khosrowshahi published article [3], which focuses on design of concrete foundation slabs with special emphasis on use of steel and synthetic fibres and alternative to reinforcing. The Tongji University in China conducted tests and comparison of two foundation slabs. The test results are described in the 2004 article by Chen [10]. For reinforcement of the fibre-steel concrete slabs, two types of steel fibres were used, with fibre content 20 and 30 kg/m 3 . The effect of the steel fibre reinforced concrete (SFRC) foundation slab on the bending rigidity has been found and published. The common conclusion of all these scientific research works by many authors was determination and confirmation of significant difference between the test results and values obtained using calculation models, numerical models and available standards. E XPERIMENTAL LOADING TEST OF REINFORCED FIBRE - CONCRETE SLABS n late 2014, an experimental load test of reinforced fibre-concrete slab has been conducted. During the experimental load tests, the stress-strain relations of the foundation structure and subsoil during their interaction were monitored. The load test was carried out using the testing facilities at the Faculty of Civil Engineering, VŠB - TU Ostrava [4]. From a geological aspect these are simple foundation conditions. The top subsoil layer is formed by loess loam consistency with class F4 consistency, and its thickness is approx. 5 m. The soil was described by the following properties – weight density  = 18.5 kN.m -3 , Poisson coefficient  = 0.35, modulus of deformability E def = 23.7 MPa. The fibre-concrete slab had dimensions 2.00 x 2.00 x 0.17 m. The concrete class C25/30 was used for casting. The concrete was reinforced with fibre reinforcement. The reinforcement consisted of steel fibres of type 3D DRAMIX 65/60B6 – 25 kg.m -3 . During the test, the fibre-concrete slab was loaded in the centre by pressure exerted by hydraulic press (Fig. 1). The dimensions of the loaded area were 200 x 200 mm. During the load test of the fibre-concrete slab, the load cycle was set to 50 kN / 30 min. With this method of loading the slab breach occurred in the 6-th cycle, or at load of 280 kN. The slab failed by being pushed through. The slab was raised then in such a way so that development of the crack could be investigated – the crack had developed at the lower part of the slab which was in contact with the soil. Fig. 2 shows the cracks at the lower surface of the failed fibre-concrete slab. The testing facilities are used also for other experimental measurements of subsoil-structure interaction - the process, results and conclusions of other loading test are described in detail in [11]. I I

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