Loading Tests of Thin-Walled Ferro-Cement Panels for Horizontal Slab Structures

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1 Loading Tests of Thin-Walled Ferro-Cement Panels for Horizontal Slab Structures MARCELA KARMAZÍNOVÁ, JINDRICH MELCHER and MICHAL ŠTRBA Faculty of Civil Engineering Brno University of Technology Veveří St. 331/95, Brno CZECH REPUBLIC Abstract: - The paper deals with the basic results of experimental verification of thin-walled panels based on ferro-cement, which are developed for the usage in the slab horizontal load-carrying structures, especially roof or floor ones. The aim of loading tests was to verify the typical strain and failure mechanisms and to obtain and evaluate the load-carrying capacities of ferro-cement panels mentioned. The full-scale loading tests of these panels have been performed to investigate their actual behaviour in the loading process with regards to the following possible influences: real dimensions, i.e. mainly the panel thickness with respect to the possible size effect, and real marginal conditions, too. During the loading process, the following parameters, among others, have been monitored and measured: load deflection relationship and cracks initiation and progress. Key-Words: - Loading test, ferro-cement, thin-walled panel, horizontal, slab, floor structure, roof structure, load-carrying capacity, failure mechanism. 1 Introduction Ferro-cement elements are composed of materials based on cement mortar and extremely slender steel reinforcement. The resulting products made of this material are characterized by the total slab thickness in the range from 20 to 50 mm. The base is usually small-grained cement mortar; physical-mechanical properties are provided by steel mesh, as a rule. This material solution is relatively technically simple and can decrease material and overall costs, in general, compared to classic reinforced concrete. The economically positive characteristics have been recently taken as a reason for the wide expansion of ferro-cement elements to the underdeveloped world. These components can be used both in the housing buildings and in the agriculture and industry. The common attribute of this solution is material saving contrary to the comparable solution based on classic reinforce concrete, where it is necessary to take into account the structural durability, which is provided just by enough reinforcement protection increasing the overall dimension of the panel. The characteristic tensile-bending strengths of ferro-cement matrix are higher than strengths of normal concrete. Also the high toughness under mechanical impact load is the important mechanical characteristics. However, the actual behaviour of the panel significantly depends on its particular shape, production technology and properties of matrix. 2 Description of Test Specimens For the floor component, the simple shape of the prefabricated component has been chosen and subsequently verified by loading tests. The arrangement of test specimens is based on the structural detailing of newly developed ferrocement panels for the slab horizontal floor structure. The nominal plan dimensions of this panel are x 690 mm. The actual (measured) dimensions of the test specimens are seen in the scheme in Fig. 1. The rectangular floor component is stiffened by ribs of the total height of 205 mm, which are located on the edges of the 45 mm thick slab. It was assumed to test 3 specimens in total test specimens A ( 1), B ( 2) and C ( 3) aimed to verify the influence of different types of reinforcement on the actual behaviour of panels. Because during the production and transport process the failure of B specimen occurred, another new specimen D with the same configuration as the origin specimen B has been produced. The main longitudinal reinforcement of the test specimens is represented by 5 reinforcing bars, that means 1 bar on the bottom edge of each longitudinal ribs and another 3 bars reinforcing the slab, which are placed on the top longitudinal edges and in the middle of the slab panel. The overview of test specimens including their weight and basic description of their reinforcing is shown in Table 1. ISBN:

2 The aim of loading tests was to verify the actual load-carrying capacity, deformation and deflection and real failure mechanism of test specimens, with regard both to the informative comparison of the different reinforcement types of developed panels, and to the verification of the accurate calculating model, but primarily, the loading tests should verify the possibility of the usage of these components in floor structures, in comparison with usual traditional reinforced-concrete panels. 3 Loading Test Performing Test specimens have been simply supported on both opposite shorter sides with the bearing width of 50 mm in the support. Then, if the total length is mm, the real span of the panel is L = mm. The typical shots of loading tests of all three specimen types are illustrated in Fig. 2. A - A Fig. 1 Scheme of ferro-cement floor panel The detailed sources, especially with respect to the reinforcement type, can be given in the technical documentation of the producer, i.e. in this case the subject ordering loading tests. Table 1 Overview of test specimens Specimen Weight [kg] A B 2 C D B Informative description of the reinforcement Ø R14 bottom edge of longitudinal rib; Ø R8 longitudinal edge and middle of slab; stiffening mesh in slab Failed during production not tested Ø R14 bottom edge of longitudinal rib; Ø R14 longitudinal edge and middle of slab; no stiffening mesh Ø R8 bottom edge of longitudinal rib; Ø R8 longitudinal edge and middle of slab; no stiffening mesh Fig. 2 Illustration of loading tests ISBN:

3 The photos of experiments illustrate the unique and effective method of the vacuum loading of plate components by Prof. J. Melcher (see [1] and Fig. 3), which has been developed, elaborated in detail and in the long term used in the test room of the authors' workplace. The effect of full uniform loading is caused using vacuum method and the supported slab specimen is mounted to the testing box represented by rigid frame. The tested panel is together with the frame covered by transparent plastic matter foil glued to the floor. Air is sucked out of this closed space, that tested specimen is uniformly loaded overall on its area due to atmospheric overpressure. 4 Loading Test Results The results of the measuring load deflection relationship during the loading process have been graphically elaborated by drawing the increase in deflections in the points Nos. 1 to 15 in the meaning of the scheme in Fig. 1. The reaching load-carrying capacities are listed in Table 2. Table 2 Load-carrying capacities Specimen Load-carrying capacity (above self weight) [knm -2 ] A B 2 Not tested C D B Appropriate photographs illustrate failures of the particular test specimens in the moment of reaching their objective ultimate load-carrying capacity. p [knm -2 ] Fig. 3 Vacuum loading test method The mode of the uniform loading or unloading can be simply regulated and loading intensity can be determined by measuring the overpressure between outside and inside of the box. During loading tests the slab components have been subjected by the uniform loading in the steps. The size of the interval of load increasing is chosen that the whole range of the load is divided to 10 steps minimally. For the deflection measurement the digital and mechanical sensors with the accuracy of 10-2 have been used. The overpressure caused by the vacuum loading has been measured using the electric sensors with the digital indicator of the pressure and, for the control, in parallel it has been verified by the liquid manometer. During the loading process the loaddeflection relationship has been monitored. The loading has been applied up to the failure of test specimens. The primary outcomes of loading tests are the knowledge on the strain and failure mechanisms during the loading process and also in the moment of reaching the objective load-carrying capacity. To obtain the basic information about the influence of loading and unloading on the support bearing and permanent deformations, the loading effect was applied in the periodical repeated cycles. w [mm] Fig. 4 Test specimen A : p w relationship Fig. 5 Test specimen A : failure mechanism The progress of the deflection w due to the effect of the full uniform loading p (excluding and above the self weight of the panel) for measured points of the specimen A is drawn in Fig. 4. It is evident that the slab of the floor panel supported on the longitudinal ribs has enough transverse stiffness and ISBN:

4 practically does not deflect on the line rectangular to the specimen span. Deflections in measured points on all transverse lines are practically the same. The failure mechanism of the test specimen A is evident from Fig. 5. In the middle-span zone the cracks in edge longitudinal ribs and in the slab are very good shown. has (among all components) the most effective main longitudinal reinforcement of the edge ribs and slab, which gives assumptions for comparably the best load-carrying capacity and stiffness of the specimen as a whole. However, reaching this load-carrying capacity is eliminated by the low, not-enough loadcarrying capacity of the slab, which is not stiffened by the mesh. p [knm -2 ] p [knm -2 ] w [mm] Fig. 6 Test specimen C : p w relationship w [mm] Fig. 8 Test specimen D : p w relationship Fig. 9 Test specimen D : failure mechanism Fig. 5 Test specimen C : failure mechanism The progress of the deflection due to the loading effect (excluding and above the self weight of the panel) for measured points of the specimen C is drawn in Fig. 6. The failure mechanism of the test specimen C is evident from Fig. 7. In this case the slab of the tested specimen does not have enough load-carrying capacity because the slab has been failed by braking through practically on the whole length excluding support zones, where the positive influence of the end transverse rib was shown. The specimen C The progress of the deflection due to the loading effect (excluding and above the self weight of the panel) for measured points of the specimen D is drawn in Fig. 8. It is evident, that the specimen D with comparably the smallest dimensions of the longitudinal reinforcement has significantly lower load-carrying capacity than has been verified in the case of specimens A and C. The ultimate load is minimal, that overload nor primer failure of the slab does not occur, although no stiffening mesh is in the slab. The stiffness of the slab is also evident from the relationship w p on all transverse lines of the test specimen, which are practically the same. The failure mechanism of the specimen D is shown from the shots in Fig. 9. It is evident, that the load-carrying capacity of this panel is determined by the failure of longitudinal edge ribs. ISBN:

5 5 Test Evaluation and Conclusions Based on test results and their analysis the following conclusions and recommendations can be deducted for the investigated type of test specimens: The experimental results document the loadcarrying capacity of particular test specimens (see Table 2) and corresponding relationships load deflection (see Figs. 4, 6, 8) allowing to define the conventional load-carrying capacity according to the limit deflection. The load-carrying capacity following from the dimensions of the main longitudinal reinforcement of the ribs and slab requires the optimal transverse reinforcing of the slab, which cannot cause primary initiation of the failure of whole component. Experimentally verified objective load-carrying capacity of test specimens and corresponding load deflection relationships allow to verify calculating models. Acknowledgement: The paper has been elaborated within the solution of the projects of the Czech Ministry of Education, Youth and Sports FAST S-11-32/1252 (university specific research) and CZ.1.05/2.1.00/ ( AdMaS ) and the Czech Science Foundation grant project No. 103/09/H085. References: [1] J. Melcher, M. Karmazínová, M. Pilgr, M. Frank, Defined load-carrying capacity of fibrecements slabs technology, tests, tables, graphs (original in Czech language), VUSTAH, a.s Brno, 2011, 102 pp. [2] M. Karmazínová, Design assisted by testing a powerful tool for the evaluation of material properties and design resistances from test results, International Journal of Mathematical Models and Methods in Applied Sciences, Vol. 6, No. 2, 2012, pp ISSN [3] M. Karmazínová, M. Pilgr, J. J. Melcher, Methods based on the approach of the design assisted by testing applied to the determination of material properties, In Proceedings of the 2 nd Intl. Conference on Mathematical Models for Engineering Science, Institute of Environment, Engineering, Economics and Applied Mathematics, WSEAS Press, Puerto de la Cruz, 2011, pp ISBN [4] M. Karmazínová, J. J. Melcher, Methods of the design assisted by testing applicable tools for the design resistance evaluation using test results, In Proceedings of the 2 nd International Conference on Mathematical Models for Engineering Science, Institute of Environment, Engineering, Economics and Applied Mathematics, WSEAS Press: Puerto de la Cruz, 2011, pp ISBN [5] M. Karmazínová, J. J. Melcher, Design assisted by testing applied to the determination of the design resistance of steel-concrete composite columns, In Proceedings of the 13 th WSEAS International Conference on Mathematical and Computational Methods in Science and Engineering, WSEAS Press: Catania, 2011, pp ISBN [6] J. Melcher, M. Karmazínová, J. Pozdíšek, Experimental verification of behaviour of composite steel and glass-fibre-concrete beam, In Proceedings of the 9 th International Conference on Steel-Concrete Composite and Hybrid Structures held in Leeds, Singapore: Research Publishing Services, 2009, pp ISBN [7] M. Karmazínová, Analysis of the actual behaviour, stress and moment capacity of composite beams composed of steel and glassfibre-concrete, International Journal of Mechanics, Vol. 6, Issue 2, 2012, pp ISSN [8] J. J. Melcher, M. Karmazínová, Influence of Atmospheric Physical Effects on Static Behavior of Building Plate Components Made of Fiber-Cement-Based Materials, In Proc. of the International Conference on Architectural and Civil Engineering ICACE 2012, WASET: Bali 2012, Issue 0070, pp pissn X, eissn [9] J. Melcher, M. Karmazínová, M. Pilgr, Evaluation of strength characteristics of fibrecement slab material, International Conference AMSE 2012, TTP: Seoul 2012, in print. [10] J. Melcher, M. Karmazínová, Experimental verification and design of glass-frp composite grids, International Conference EME 2012, TTP: Seoul 2012, in print. [11] J. Melcher, M. Karmazínová, Load-carrying capacity of cantilevers of anti-flood barriers made of FRP composite structural profiles, International Conference on Applied Mechanics, Materials and Manufacturing ICAMMM 2012, TTP: Changsha 2012, in print. [12] J. Melcher, M. Karmazínová and M. Filip, To design and experimental verification of actual behaviour of selected all-frp structural ISBN:

6 components for civil engineering, The 1 st Conference on Advances in Polymer-Fibre- Reinforced Structures, Hong Kong (2007). [13] J. Melcher, M. Karmazínová, Strength characteristics of material of fiber-cement building components and verification of warming and sprinkling influence on their behavior (original in Czech language), In Proceedings of the XIV th International Conference on Ecology and new building materials and products held in Telč, pp , VUSTAH, a.s. Brno, ISBN [14] J. Melcher, M. Karmazínová, J. Knězek, L. Lederer, The influence of physical effects on behavior of structural components made of fiber-glass-concrete (original in Czech language), In Proceedings of the XI th Conf. on Ecology and new Building materials and products held in Telč, VUSTAH, a.s. Brno 2007, pp ISBN [15] J. Melcher, M. Karmazínová, M. Knězek, L. Lederer, Experimental verification of glassfiber-concrete components of façade claddings (original in Czech language), In Proceedings of the X th Conference on Ecology and new building materials and products held in Telč, VUSTAH, a.s. Brno, 2006, pp ISBN [16] J. Melcher, M. Karmazínová, Loading tests of glass-fiber-concrete façade panels stiffened by rib (original in Czech language), In Proceedings of the IX th Conference on Ecology and new building materials and products held in Telč, VUSTAH, a.s. Brno, 2005, pp ISBN [17] M. Karmazínová, J. Melcher, R. Pokorný, P. Pospíšil, Material characteristics of glass-fiberconcrete facade components (original in Czech language) In Proceedings of the VII th Conference on Ecology and new building materials and products held in Telč, VUSTAH, a.s. Brno, 2003, pp ISBN [18] J. Melcher, M. Karmazínová, J. Knězek, Experimental verification of glass-fiberconcrete façade panels under wind loading actions (original in Czech language), In Proceedings of the VI th Conference on New building materials and products held in Telč, VUSTAH, a.s. Brno, 2002, pp [19] ČSN EN ( ) Fibre-cement flat sheets Product specification and test methods (original in Czech language) the Czech Standard Institute, Prague 2005, 48 pp. [20] EN 1990 Basis of Structural Design: Annex D Design assisted by testing, CEN Brussels, ISBN: