Department of Science, Technology and Engineering

Permanent URI for this collectionhttp://erepository.kibu.ac.ke/handle/123456789/113

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Browsing Department of Science, Technology and Engineering by Author "Khakina, Peter Nyongesa"

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    A Reduction Factor for Buckling Load of Spherical Cap Shells
    (Research Journal of Applied Sciences, Engineering and Technology, 2011-12-26) Khakina, Peter Nyongesa; Zhou, H.
    The classical buckling theory usually overestimates the buckling load of shells. In this study, a reduction factor is determined using geometrical parameters so as to reduce the classical buckling load to a more realistic value based on the post-buckling load. It is observed that the buckling load is directly proportional to the thickness and rise and inversely proportional to the span of the spherical cap. Finite element modeling and simulation using ABAQUS was conducted to determine the buckling behavior of a spherical cap shell subjected to different initial geometrical imperfections. The load-deflection curves drawn from the simulation formed a plateau at the post-buckling load. It is observed that as the initial geometrical imperfection is increased, the value of the initial buckling load is almost the same as the value of the post-buckling load on the plateau. The results obtained from different shells were used to derive a formula for the reduction factor.
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    Approximate Critical Load of Cambered Double-Layered Grids by Shell Analogies
    (Research Journal of Applied Sciences, Engineering and Technology, 2012-08-01) Ali, M. I.; Khakina, Peter Nyongesa; Fan, F.
    Studies have shown that design of double-layered grids based on classical theories may lead to unsafe design. For square-on-diagonal grids, the load carrying capacity is almost the same as the buckling load. Therefore the buckling load can be used as the critical load in the design. In this study, the non-linear behavior of the grids is considered using shell analogies to determine the critical load. By applying the theorem of study and energy to a dimple, an empirical formula to predict the buckling load of thin spherical shells was derived. Then using finite element modeling, post-buckling load was identified and used to calculate the value of constant C. It is observed that the buckling load is proportional to t2.5, which gives a critical load close to what is observed in experiments and a more realistic load as compared to the Classical theory prediction. Load deflection curves drawn for the grids and their equivalent continuum shells correlate closely showing that the findings are valid.