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ABSTRACT Over 99% of multi storey structures in Uganda are of reinforced concrete framing. Steel and brick structures account for less than 1%. Of the reinforced concrete structures currently under construction, 75% use hollow clay blocks reinforced concrete slabs. This paper looks at the form of the hollow clay blocks that contribute to its ease of use, and enables it to be held in the slab both by mechanical interlock and friction. It explores its limitations and ways in which its form may be improved. Designs of single slab panel two storey reinforced concrete structures with one side having a constant dimension of 8 m while the dimension is varied from 2 m, 3 m, 4 m, 5 m, 6 m, 7 m up to 8 m were carried out for both solid and hollow clay blocks slabs construction. The design loads, moments, reinforcement, shear stresses and costs for each case of solid and hollow blocks slabs were compared. It was found that contrary to common beliefs; solid slabs are cheaper than hollow clay blocks slabs. This is because, hollow clay blocks need a minimum topping of 50 mm, and are manufactured in standard sizes of 125 mm, 150 mm, 175 mm, 200 mm and 225 mm. This implies that for spans of about 2 m, solid slabs can be 75 mm, 100 mm thick, while the minimum thickness of hollow blocks is 175 mm. Also unlike solid slabs, for hollow clay blocks slab over 6 m long, shear reinforcement may be needed. As the length increases to 8 m, the topping for hollow blocks increases to an uneconomic value. However for large structures with over two storeys, hollow blocks slab construction might be cheaper as the reduced weight leads to smaller columns and foundations. Furthermore hollow block slabs are easier to detail, construct and are less prone to errors on site. |
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