Table 2: The results of modal analysis and orthogonal experimental data with the upper beam.

Six factors and five levels The upper and lower plate thickness The left and right plate thickness The front and back plate thickness The front and back rib plate thickness The left and right rib plate thickness The ramp plate thickness The natural frequency 1 156 116 128 157 120 38 164.10 2 158 116 134 159 124 42 163.78 3 160 116 132 151 122 36 164.63 4 162 116 126 155 116 40 165.39 5 164 116 130 153 118 44 165.26 6 156 118 130 155 122 42 163.53 7 158 118 128 153 116 36 164.55 8 160 118 134 157 118 40 164.31 9 162 118 132 159 120 44 164.53 10 164 118 126 151 124 38 165.30 11 156 120 126 159 118 36 164.01 12 158 120 130 151 120 40 163.90 13 160 120 128 155 124 44 164.03 14 162 120 134 153 122 38 164.43 15 164 120 132 157 116 42 164.96 16 156 122 132 153 124 40 163.05 17 158 122 126 157 122 44 163.66 18 160 122 130 159 116 38 164.34 19 162 122 128 151 118 42 164.54 20 164 122 134 155 120 36 164.77 21 156 124 134 151 116 44 162.88 22 158 124 132 155 118 38 163.58 23 160 124 126 153 120 42 164.01 24 162 124 130 157 122 36 164.36 25 164 124 128 159 124 40 164.56