An investigation into the behaviour of hollow ribbed (waffle) rectangular reinforced concrete slabs at ultimate limit state

  • Sai Lung Ho

    Student thesis: Doctoral Thesis


    The elastic to ultimate load behaviour of reinforced concrete waffle slabs subjected to uniformly distributed load and 4-point loads are reported in this thesis. A total of twenty 1/4- and one 1/2-scale reinforced concrete waffle model slabs, with different area of steel and rib depth to slab thickness ratio and various edge conditions were made and tested to destruction.

    The theoretical analysis of the slabs essentially consists of three phases:

    (i) elastic behaviour up to the appearance of first cracks;
    (ii) nonlinear behaviour due to progressive concrete cracking and yielding of reinforcements; and
    (iii) ultimate load behaviour.

    Two 2-dimensional elastic models viz., thin plate bending element and grillage element models, and one 3-dimensional elastic-fracture model using finite element package LUSAS/AN have been employed to investigate the applicability of these methods for the analysis of the slabs. In addition to these, three ultimate load methods viz., modified yield line method, equivalent open grillage analysis and modified strip method were developed and used to predict the ultimate load carrying capacity of the slabs.

    Based on the experimental and theoretical results, it is concluded that the behaviour of R.C. waffle slabs is very similar to that of R.C. solid slabs except that waffle slabs tend to attract more bending moments at the support. As a result, the span moments of the slab are reduced when compared to the span moments given by BS8110 for solid slabs. The combined bending and torsion interaction at the rib joints is also considered in this investiagtion. It is found that for slabs with restrained edges membrance action significantly increases the load carrying capacity. A method of predicting this enhancement has also been developed. The theoretical results obtained by the proposed methods of analysis for the three phases above show a good correlation with the experiemntal results.
    Date of AwardJul 1989
    Original languageEnglish
    Awarding Institution
    • Council for National Academic Awards

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