Study on Mechanical Properties of Reinforcement Bars Manufactured in Nepal with respect to NS-191

Abstract

The deformed bars are graded according to their specified yield strength. These are Fe415, Fe500, Fe500D and Fe550. CTD bars of grade more than Fe415 are scarcely available in market. However, TMT bars of Fe500 grade are easily available in market. Deformed bars are one of the mandatory product must have NS-191 certificate grant before commercial production. NS standard establishes minimum criteria for the mechanical properties of deformed bars. However, they do not set maximum limits nor do they address instances where properties may significantly exceed the standard. This project was carried out to investigate the status of mechanical properties of deformed bars manufactured in Nepal. The tested data and obtained statistics of different mechanical properties for the separate and combined data takes on an important practical significance and may be used in calibrating local specifications and design. This thesis outlines the output of mechanical test results of grade Fe500 and Fe500D TMT bars. Total 745 numbers of TMT bar samples were collected and tested at NBSM mechanical testing laboratory. The tested samples were representing reference samples of FY 2073-74 and FY 2074-75 stored at NBSM. These samples were from nineteen different rolling mills and twenty-two different brands. The COV values for yield strength, tensile strength and UTS/YS ratio were found below 5 percent. The value of COV for percentage elongation were found between 5 to 10 percent for different bar size. The mean yield strength and tensile strength was found 554.4 MPa, and 663.4 MPa respectively for Fe500 grade TMT bars. The mean yield strength and tensile strength for Fe500D grade was found 565.2 MPa and 678.1 MPa respectively. The mean value of percentage elongation and UTS/YS ratio for both grade were found 22% and 1.2 respectively. Higher range of variation were observed for Fe500 TMT bars than Fe500D grade. These variations were believed to be caused by varying rolling practices and quality control measures used by different manufacturers. Comparing tested data with NS standard indicates the mechanical properties of deformed bars manufactured in Nepal are well above set standard value and comply with product standard requirements.