Experimental Investigation of yield values of locally manufactured steel reinforcing bars in Uganda in relation to capacity design.
Mwesigwa, Mbabazi Julius
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Capacity design procedure for reinforced concrete (RC) structures is effective when actual member capacities do not greatly exceed the assumed design capacities. Since flexural capacity and postyield behavior of an RC member is largely controlled by steel reinforcing bars, it places certain special requirements on their properties, such as, yield strength (YS), ultimate tensile strength to yield strength ratio (UTS/YS ratio) and elongation, which are usually sensitive to the method of rebar manufacturing. Steel reinforcement manufacturers usually comply with the minimum code specifications. However, actual values of the steel rebar properties may greatly exceed the specified minimum yield strength. If these values are far greater than the specified value, it may cause brittle shear failure instead of more ductile and desirable flexure mode of failure. Tensile tests were carried out on 200 samples of diameters 8mm, 10mm, 12mm, 16mm and 20mm, from local sources coded W, X, Y, Z, and the values obtained were recorded and analysed. Results revealed that for sources X and Y, more than 50% of the values of yield strength fell below the expected range of 500-650MPa, by more than 150MPa. For the percentage elongation and ultimate tensile strength to yield strength ratio, all samples satisfied the code requirements. It is recommended to emphasize the engineering material properties while purchasing rebars for sound and durable RC structures, and also further research should be carried out to investigate how the steel bars fracture in comparison to their manufacturing processes and the economic significance of steel recycling in Uganda.