Simplified Reliability Estimation for Optimum Strengthening Ratio of 30-Year-Old Double T-Beam Railway Bridge by NSM Techniques

Table 3

Statistics of random design variables (II).

	Mean/Nominal	COV	Average strength	Number of data	Standard deviation	Probability distribution
SD 30^a	1.20	0.064	360.0	822	23.04	Normal
SD 35^a	1.13	0.038	395.5	80	15.03	Normal
SD 40^a	1.09	0.048	436.0	773	20.93	Normal
Grade 40^b	1.13	0.116	317.0	—	36.72	Normal
Grade 60^b	1.12	0.098	472.5	—	46.31	Normal

aKS D 3504.
bASTM A 615: Standard Specification for Deformed and Plain Carbon Steel Bars for Concrete Reinforcement-AASHTO No.: M 31 [14].