Investigation of Flexural Strength of Reinforced Concrete Beams in Rwanda

Abstract

Present infiltration of substandard steel reinforcing bars on local market have had a serious concern and suspicion on strength and stability of buildings and other engineering structures that are being built with them. Some buildings have collapsed while others have developed signs of structural failures setting huge number of users into serious fears with subsequent vacation. Besides the failures in Rwanda, there has been disastrous incidences of collapsing buildings in neighboring countries where most of rebars are imported from and investigations have pinpointed substandard steel reinforcing bars. Primary objective of this study was to investigate the quality of steel reinforcing bars available in Rwanda and their performance on structural elements specifically reinforced concrete beams flexural behavior. So far only one research is known to have investigated quality of steel bars available in Rwanda with much focus on steel bars milled from scraps of which the results were equally disappointing. In this research 24 samples of steel reinforcing bars of 12mm and 10 mm ϴ from four different sources available in Rwanda were randomly picked from warehouses. Each source were represented by six specimens, three of which were 12mm ϴ and the other three of 10 mm ϴ. Samples were assessed for their physical features compliance, mechanical and chemical properties were examined and finally RC beam flexural performance behavior investigated through laboratory tests. Results obtained showed that rebars physical feature standard code requirements were not met by 75%, while 48.5% of tested samples failed to meet high yield strength BS and RS EAS code prescription of 460N/mm2 only meeting mild steel bars limits. Of the failed 48.5% only 12.5% were Y12mm while the remaining 87.5% were Y10mm. The ultimate load of RC beams made of Y12 mm were determined to be in range of 114.6 KN to 142.6 KN while their respective flexural strength ranged from 25.7 N/mm2 to 33.4 N/mm2 as compared to design load of 111.8 KN and design flexural strength of 25.1 N/mm2 respectively. The flexural load of RC beam made of Y10 mm was found to be in range of 93 KN to 131.5 KN while their respective flexural strength ranged from 20.89N/mm2 to 32 N/mm2 as compared to design load of 78.2 KN and design flexural strength of 17.6 N/mm2 respectively. It is revealed from research that substandard rebars are still at large but more so with rebars that were not labelled at all which failed at 100%, all sample from S3 were not labelled at all for both Y12mm and Y10mm and failed to meet code requirements.