Characteristic of strength of materials

Two (2) type specimen (RA & RB) was subjected to tension in accordance with the MS 146:2006 provisions by using universal testing machine. The results of the tensile tests indicating the yield stress and ultimate stress is shown in Table 1 below.

Table 1: Table 2: Average Value for  Yield Stress and Ultimate Stress

Sample Designation	Yield Stress (N/mm2)	Ultimate Stress (N/mm2)
RA	518.18 ± 7.12	585.64 ± 4.32
RB	432.16 ± 5.32	570.08 ± 3.12

i)         Given f_k = f_m -1.86s. Calculated the characteristic of strength for those concrete rebar steel.

ii)   Given the minimum provisions of MS 146:2006 - Specification for Carbon steel bars for the reinforcement of concrete is as Table 2 below. Determine the safety of those samples as reinforcement steel bar. 

Table 2: The minimum provision of MS 146: 2006

Standard	Characteristic Strength (N/mm2)	Ultimate/Yield Strength Ratio
MS 146:2006	460	1.05

Answer

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i)   Given f_k = f_m -1.86s

      Characteristic of strength for RA sample è f_{k =} 518.18 – 1.86(7.12) = 504.94

      Characteristic of strength for RB sample è f_{k =} 432.16 – 1.86(5.32) = 422.26

ii)   Characteristic of strength for RA sample è = 504.94 (above the code) = Safe #

       Characteristic of strength for RB sample è = 422.26 (below the code) = Unsafe #