ISSN: 2319-5967 ISO 9001:2008 Certified International Journal of Engineering Science and Innovative Technology (IJESIT) Volume 2, Issue 6, November 2013 115 Abstract— Ferro cement slabs having end restraints may achieve a load capacity different from those which are axially unrestrained. Consequently, analytical models proposed for flexural analysis of Ferro cement slabs may fail to predict the load capacity of slabs that are axially restrained against movement. In this paper a classical method for the analysis axially restrained slabs is modified and assessed as to its ability to predict the behavior of axially restrained Ferro cement slabs. The ultimate load based on this method grossly over predicted the slab strength mainly due to neglecting the role of important parameters such as elastic curvature and large deformation. A new approach based on the elastic and elastic-plastic behaviors of materials, large deflection and stability of the thin section slab strip was proposed for analysis. Both the ultimate load and the load-deflection response calculated using the proposed large deflection elastic- plastic method was found to be quite accurate and the obtained test / calculated ultimate load was found to be 1.05. Accordingly, the proposed analytical method can be used for calculating accurately the load capacity of axially restrained one way Ferro cement slabs having span / depth ratios up to 58. Index Terms— Curvature, Deflection, Ferro cement Slab, Stability. I. INTRODUCTION It is experimentally evident that in the case of fully axially restrained slabs, the ultimate load capacity is considerably higher than that obtained using yield line theory. This enhancement in load has been attributed to the effect of the induced compressive membrane action and the corresponding modification of the yield criterion [1]. Many analytical approaches have been proposed for calculating the ultimate load capacity of axially restrained RC slabs [2]-[6]. Such methods were found to give accurate ultimate load capacity for thick slabs. Eyre [7, 8], in two papers, presented the general concept of the maximum membrane force (MMF). The method was proposed in order to take into consideration the effect of geometric imperfections due to instability and large deformations. According to the MMF method, the maximum safe load occurs at the plastic deflection at which the maximum membrane force occurs. This load is usually smaller than the peak load associated with the load-deflection relationship. Welch [9] utilized Park and Gamble's modified rigid-plastic method [3] to develop a more general solution for axially restrained reinforced concrete slabs. The peak thrust according to compressive membrane theory occurs when the axial shortening of the slab and outward support movement (if the end supports are partially restrained) are at a maximum. It is demonstrated that estimating the peak thrust using a modification of Park and Gamble's theory gives an improved correlation with experimental data for a range of span to depth ratios ( L/h) between 2.7 and 28.3[9]. Since Ferro cement members are characterized as thin sections with large values of L/h, the methods proposed for analyzing axially restrained slabs may not be accurate for calculating the ultimate load capacity. This is due to the fact that thin sections usually suffer from large elastic deformation and instability due to flexural buckling. In this paper, simply supported ferrocement strips are analyzed as thin slabs. These strips are fully reinforced with wire mesh without skeletal reinforcement. The span / depth ratio of the slabs was larger than 22 which Welch [9] considers to be the limiting ratio for a thin slab. The proposed method for calculating the load-deflection relationship is essentially based on consideration of the elastic and plastic responses of the slab materials and its geometrical flexural instability. This paper presents a method for determining the capacity of thin, axially restrained, ferrocement slabs. Prior to presenting the final method of analysis, the possibility of using a modified form of rigid plastic analysis is considered. This approach is presented in section II. The more appropriate large deflection elastic-plastic method is presented in section III and is found to correlate well with the experimental results. Flexural Analysis of Axially Restrained Ferro cement Slab Strip Azad A. Mohammed, Yaman S. Shareef
Flexural Analysis of Axially Restrained Ferro cement Slab Strip
Jun 18, 2023
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