Load deflection relationship of a solid slab under the action of construction loads

Abstract

In Uganda, concrete placement methods have kept on improving over the years. There has been a shift from manual methods to the current use of concrete pumps which place very high volumes of concrete per minute. Small volume slabs are thus able to be cast in a short time but even before they set, their self-weight and that of its supports is taken up by the lower supporting slab. While execution of building operations is taking place, construction materials such as bricks, blocks, sand and aggregates are usually loaded onto the slabs. These construction loads, usually higher than design live loads are not considered at design stage of the slab. 87% of 118 construction sites which were picked at random and surveyed in Kampala had their slab supports removed and placed on top of them to provide support for an upper floor slab. Also 80.6 % of 124 construction sites surveyed had various construction material loads on them such as concrete blocks, fine aggregates, formwork etc. A three level building was constructed having 4000 mm length, 2000 mm width, 2000 mm elevation height from 1st to 2nd level, 2000 mm to 3rd level and resulting slab deflections monitored with the help of dial gauges exerted by loads contributed by freshly cast upper level slab and concrete blocks. Block construction loads were 26.57% more than the ultimate design slab loads. Deflections due to fresh concrete and its supports and that from loads due to concrete blocks which were loaded instantly were 1.15 mm and 11.815 mm respectively while the immediate deflection was 0.103 mm calculated using 2 KN/m2 design live load. Keywords: Reinforced Concrete, Construction loads, Load deflection relationship.