EXPERIMENTAL INVESTIGATION INTO THE STRUCTURAL PROPERTIES OF PRECAST REINFORCED CONCRETE PLANKS

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Department of Environmental Design

ABSTRACT
The aim of this work was to carry out experimental investigation into the properties of precast reinforced concrete planks. Three different thicknesses of planks were used for the tests; 60, 50 and 40mm. Two values of concrete cover to reinforcement were used; 20mm and 15mm. Two grades of concrete were also used; grades 25 and 30. One type of reinforcement was used with average diameter and yield strength of 3.3mm and 318N/mm2 respectively. A total of 36 specimens were tested. The tests were carried out on the planks under static point loads to determine the mode of failure, maximum (failure) loads and the corresponding deflection as the loads were varied. The planks failed, in all cases, by the cracking of the concrete in the tension zone. The maximum load at which failure occurred varied depending on the plank thickness, the concrete cover to the reinforcement as well as the grade of concrete. The deflection of the planks also varied with the variation in each of these parameters. One thing was common in all cases; the load-deflection curve for each case was similar in shape to the stress-strain curve for steel at the initial stage of loading. The maximum practical load was 2.7kN for the 15mm cover using the grade 25 concrete and 2.9kN for the grade 30 concrete. The maximum design (theoretical) load was 1.9kN. To compare the maximum load with the design load, a ratio was defined (the differential load ratio). In all the tests, it was only in four cases that the value exceeded 0.20. All of them occurred in the 60mm thick planks. A minimum plank thickness of 60mm; minimum concrete cover of 15mm, a maximum aggregate size of 10mm, a minimum load differential ratio of 0.21 and a minimum yield strength of 318N/mm2 were recommended for the design and production of reinforced concrete planks.