8.3.1
For simply supported beams and girders of span length, , where no lateral restraint to the compression flanges is provided, but where each end of the beam is restrained against torsion, the effective length of the lateral buckling to be used in 8.2.2.1 shall be taken as in Table 15.
Table 13(a) Design Bending Compressive Stress Corresponding to Lateral Buckling,
(Clause 8.2.2)
| fcr,b | fy | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 200 | 210 | 220 | 230 | 240 | 250 | 260 | 280 | 300 | 320 | 340 | 360 | 380 | 400 | 420 | 450 | 480 | 510 | 540 | |
| 10 000 | 181.8 | 190.9 | 200 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 8000 | 181.8 | 190.9 | 200 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 6000 | 181.8 | 190.9 | 200 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 4000 | 181.8 | 190.9 | 200 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 2000 | 181.8 | 190.9 | 200 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 1000 | 169.1 | 179.5 | 186 | 196.5 | 202.9 | 209.1 | 219.8 | 229.1 | 245.5 | 261.8 | 275.1 | 291.3 | 300.5 | 323.6 | 332.2 | 355.9 | 370.9 | 384.8 | 412.4 |
| 900 | 169.1 | 179.5 | 186 | 194.5 | 200.7 | 204.5 | 215.1 | 231.6 | 242.7 | 258.9 | 272 | 291.3 | 300.5 | 316.4 | 328.4 | 339.5 | 366.5 | 380.2 | 392.7 |
| 800 | 167.3 | 177.5 | 184 | 190.3 | 196.4 | 206.8 | 212.7 | 224 | 240 | 258.9 | 268.9 | 284.7 | 293.6 | 301.8 | 324.5 | 335.5 | 349.1 | 370.9 | 387.8 |
| 700 | 163.6 | 171.8 | 182 | 188.2 | 192 | 202.3 | 208 | 226.5 | 237.3 | 250.2 | 259.6 | 278.2 | 286.7 | 294.5 | 305.5 | 327.3 | 340.4 | 352.4 | 363.3 |
| 600 | 161.8 | 168 | 176 | 181.9 | 194.2 | 197.7 | 203.3 | 218.9 | 226.4 | 244.4 | 253.5 | 261.8 | 276.4 | 287.3 | 294 | 306.8 | 322.9 | 333.8 | 343.6 |
| 500 | 161.8 | 166.1 | 172 | 179.8 | 185.5 | 188.6 | 200.9 | 208.7 | 218.2 | 232.7 | 244.2 | 248.7 | 259.1 | 269.1 | 274.9 | 286.4 | 296.7 | 301.4 | 314.2 |
| 450 | 158.2 | 164.2 | 168 | 173.5 | 183.3 | 186.4 | 191.5 | 206.2 | 215.5 | 224 | 231.8 | 242.2 | 248.7 | 258.2 | 263.5 | 274.1 | 279.3 | 292.1 | 294.5 |
| 400 | 150.9 | 162.3 | 166 | 169.4 | 174.5 | 184.1 | 186.7 | 196 | 204.5 | 215.3 | 222.5 | 229.1 | 238.4 | 243.6 | 248.2 | 257.7 | 261.8 | 264.3 | 274.9 |
| 350 | 147.3 | 152.7 | 162 | 165.2 | 170.2 | 172.7 | 179.6 | 188.4 | 193.6 | 200.7 | 210.2 | 212.7 | 221.1 | 225.5 | 229.1 | 233.2 | 240 | 241.1 | 245.5 |
| 300 | 143.6 | 147 | 152 | 154.7 | 161.5 | 163.6 | 167.8 | 175.6 | 182.7 | 186.2 | 194.7 | 196.4 | 196.9 | 203.6 | 206.2 | 212.7 | 213.8 | 217.9 | 220.9 |
| 250 | 134.5 | 137.5 | 142 | 144.3 | 148.4 | 152.3 | 153.6 | 160.4 | 163.6 | 165.8 | 170 | 173.5 | 179.6 | 178.2 | 179.5 | 184.1 | 183.3 | 185.5 | 191.5 |
| 200 | 121.8 | 124.1 | 126 | 129.6 | 130.9 | 134.1 | 134.7 | 137.5 | 141.8 | 142.5 | 145.3 | 147.3 | 148.5 | 149.1 | 152.7 | 151.4 | 152.7 | 153 | 157.1 |
| 150 | 101.8 | 103.1 | 104 | 104.5 | 106.9 | 106.8 | 108.7 | 109.5 | 111.8 | 113.5 | 114.4 | 114.5 | 117.5 | 116.4 | 118.4 | 118.6 | 117.8 | 120.5 | 122.7 |
| 100 | 74.5 | 76.4 | 76 | 77.4 | 76.4 | 77.3 | 78 | 78.9 | 79.1 | 78.5 | 80.4 | 81.8 | 79.5 | 80 | 80.2 | 81.8 | 82.9 | 83.5 | 83.5 |
| 90 | 67.3 | 68.7 | 70 | 69 | 69.8 | 70.5 | 70.9 | 71.3 | 70.9 | 72.7 | 74.2 | 72 | 72.5 | 72.7 | 72.5 | 73.6 | 74.2 | 74.2 | 73.6 |
| 80 | 61.8 | 63 | 62 | 62.7 | 63.3 | 63.6 | 63.8 | 63.6 | 65.5 | 64 | 64.9 | 65.5 | 65.6 | 65.5 | 64.9 | 65.5 | 65.5 | 64.9 | 68.7 |
| 70 | 54.5 | 55.4 | 56 | 56.5 | 56.7 | 56.8 | 56.7 | 56 | 57.3 | 58.2 | 58.7 | 58.9 | 58.7 | 58.2 | 57.3 | 57.3 | 56.7 | 60.3 | 58.9 |
| 60 | 47.3 | 47.7 | 48 | 48.1 | 48 | 50 | 49.6 | 48.4 | 49.1 | 49.5 | 49.5 | 49.1 | 48.4 | 50.9 | 49.6 | 49.1 | 52.4 | 51 | 49.1 |
| 50 | 40 | 40.1 | 40 | 41.8 | 41.5 | 40.9 | 40.2 | 40.7 | 40.9 | 40.7 | 43.3 | 42.5 | 41.5 | 43.6 | 42 | 40.9 | 43.6 | 41.7 | 44.2 |
| 40 | 32.7 | 32.5 | 32 | 33.5 | 32.7 | 34.1 | 33.1 | 33.1 | 32.7 | 34.9 | 34 | 32.7 | 34.5 | 32.7 | 34.4 | 32.7 | 34.9 | 32.5 | 34.4 |
| 30 | 25.5 | 24.8 | 26 | 25.1 | 26.2 | 25 | 26 | 25.5 | 24.5 | 26.2 | 24.7 | 26.2 | 24.2 | 25.5 | 26.7 | 24.5 | 26.2 | 27.8 | 24.5 |
| 20 | 16.4 | 17.2 | 18 | 16.7 | 17.5 | 18.2 | 16.5 | 17.8 | 16.4 | 17.5 | 18.5 | 16.4 | 17.3 | 18.2 | 19.1 | 16.4 | 17.5 | 18.5 | 19.6 |
| 10 | 9.1 | 9.5 | 8 | 8.4 | 8.7 | 9.1 | 9.5 | 7.6 | 8.2 | 8.7 | 9.3 | 9.8 | 10.4 | 7.3 | 7.6 | 8.2 | 8.7 | 9.3 | 9.8 |
Table 13(b) Design Bending Compressive Stress Corresponding to Lateral Buckling,
(Clause 8.2.2)
| f_cr,b | f_y | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 200 | 210 | 220 | 230 | 240 | 250 | 260 | 280 | 300 | 320 | 340 | 360 | 380 | 400 | 420 | 450 | 480 | 510 | 540 | |
| 10 000 | 181.8 | 190.9 | 200.0 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 8 000 | 181.8 | 190.9 | 200.0 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 6 000 | 181.8 | 190.9 | 200.0 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 4 000 | 181.8 | 190.9 | 200.0 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 2 000 | 181.8 | 190.9 | 200.0 | 209.1 | 218.2 | 227.3 | 236.4 | 254.5 | 272.7 | 290.9 | 309.1 | 327.3 | 345.5 | 363.6 | 381.8 | 409.1 | 436.4 | 463.6 | 490.9 |
| 1 000 | 160.0 | 164.2 | 170.0 | 179.8 | 185.5 | 190.9 | 196.2 | 211.3 | 220.9 | 235.6 | 247.3 | 255.3 | 266.0 | 280 | 290.2 | 302.7 | 318.5 | 329.2 | 343.6 |
| 900 | 154.5 | 164.2 | 170.0 | 173.5 | 183.3 | 188.6 | 193.8 | 203.6 | 218.2 | 226.9 | 238.0 | 252.0 | 262.5 | 269.1 | 282.5 | 290.5 | 305.5 | 319.9 | 333.8 |
| 800 | 152.7 | 158.5 | 168.0 | 171.5 | 176.7 | 181.8 | 191.5 | 201.1 | 210.0 | 224.0 | 234.9 | 242.2 | 252.2 | 258.2 | 271.1 | 282.3 | 296.7 | 306 | 319.1 |
| 700 | 150.9 | 154.6 | 160.0 | 169.4 | 172.4 | 177.3 | 182.0 | 196 | 207.3 | 215.3 | 222.5 | 232.4 | 238.4 | 247.3 | 259.6 | 270 | 279.3 | 292.1 | 304.4 |
| 600 | 145.5 | 150.8 | 154.0 | 161.0 | 168.0 | 172.7 | 177.3 | 188.4 | 193.6 | 203.6 | 213.3 | 222.5 | 228 | 236.4 | 244.4 | 253.6 | 261.8 | 273.5 | 274.9 |
| 500 | 140.0 | 145.1 | 150.0 | 154.7 | 159.3 | 161.4 | 167.8 | 175.6 | 185.5 | 192 | 200.9 | 206.2 | 214.2 | 218.2 | 225.3 | 229.1 | 240 | 245.7 | 250.4 |
| 450 | 134.5 | 141.3 | 144.0 | 148.5 | 152.7 | 156.8 | 160.7 | 168 | 177.3 | 186.2 | 191.6 | 196.4 | 203.8 | 210.9 | 213.8 | 220.9 | 231.3 | 236.5 | 235.6 |
| 400 | 129.1 | 135.5 | 138.0 | 142.2 | 148.4 | 150 | 153.6 | 162.9 | 169.1 | 174.5 | 182.4 | 183.3 | 193.5 | 196.4 | 202.4 | 208.6 | 209.5 | 217.9 | 220.9 |
| 350 | 123.6 | 129.8 | 132.0 | 135.9 | 139.6 | 143.2 | 148.9 | 152.7 | 158.2 | 162.9 | 170 | 173.5 | 176.2 | 181.8 | 183.3 | 192.3 | 196.4 | 199.4 | 206.2 |
| 300 | 118.2 | 122.2 | 126.0 | 129.6 | 130.9 | 134.1 | 137.1 | 142.5 | 147.3 | 154.2 | 157.6 | 157.1 | 162.4 | 167.3 | 168 | 175.9 | 178.9 | 180.8 | 181.6 |
| 250 | 109.1 | 112.6 | 116.0 | 117.1 | 120.0 | 122.7 | 125.3 | 129.8 | 130.9 | 136.7 | 139.1 | 140.7 | 145.1 | 149.1 | 148.9 | 151.4 | 152.7 | 157.6 | 157.1 |
| 200 | 98.2 | 101.2 | 102.0 | 104.5 | 104.7 | 109.1 | 108.7 | 112 | 117.3 | 119.3 | 120.5 | 121.1 | 124.4 | 127.3 | 126 | 130.9 | 130.9 | 129.8 | 132.5 |
| 150 | 83.6 | 84.0 | 86.0 | 87.8 | 89.5 | 88.6 | 89.8 | 91.6 | 95.5 | 96.0 | 95.8 | 98.2 | 100.2 | 101.8 | 103.1 | 102.3 | 104.7 | 106.6 | 103.1 |
| 100 | 63.6 | 63.0 | 64.0 | 64.8 | 65.5 | 65.9 | 66.2 | 68.7 | 68.2 | 69.8 | 71.1 | 68.7 | 69.1 | 72.7 | 72.5 | 73.6 | 74.2 | 74.2 | 73.6 |
| 90 | 58.2 | 57.3 | 60.0 | 58.5 | 61.1 | 61.4 | 61.5 | 61.1 | 62.7 | 64.0 | 64.9 | 65.5 | 65.6 | 65.5 | 64.9 | 65.5 | 65.5 | 64.9 | 68.7 |
| 80 | 52.7 | 53.5 | 54.0 | 54.4 | 54.5 | 54.5 | 54.4 | 56 | 57.3 | 58.2 | 58.7 | 58.9 | 58.7 | 58.2 | 61.1 | 61.4 | 61.1 | 60.3 | 58.9 |
| 70 | 47.3 | 47.7 | 48.0 | 48.1 | 48.0 | 50.0 | 49.6 | 50.9 | 49.1 | 49.5 | 52.5 | 52.4 | 51.8 | 50.9 | 53.5 | 53.2 | 52.4 | 55.6 | 54.0 |
| 60 | 41.8 | 42.0 | 42.0 | 41.8 | 43.6 | 43.2 | 42.5 | 43.3 | 43.6 | 43.6 | 43.3 | 45.8 | 44.9 | 47.3 | 45.8 | 45.0 | 48.0 | 46.4 | 49.1 |
| 50 | 36.4 | 36.3 | 36.0 | 35.5 | 37.1 | 36.4 | 37.8 | 38.2 | 38.2 | 37.8 | 37.1 | 39.3 | 38.0 | 40.0 | 38.2 | 40.9 | 39.3 | 37.1 | 39.3 |
| 40 | 29.1 | 30.5 | 30.0 | 29.3 | 30.5 | 29.5 | 30.7 | 30.5 | 30.0 | 32.0 | 30.9 | 32.7 | 31.1 | 32.7 | 30.5 | 32.7 | 30.5 | 32.5 | 34.4 |
| 30 | 23.6 | 22.9 | 22.0 | 23.0 | 24.0 | 22.7 | 23.6 | 22.9 | 24.5 | 23.3 | 24.7 | 22.9 | 24.2 | 25.5 | 22.9 | 24.5 | 26.2 | 23.2 | 24.5 |
| 20 | 16.4 | 15.3 | 16.0 | 16.7 | 15.3 | 15.9 | 16.5 | 15.3 | 16.4 | 17.5 | 15.5 | 16.4 | 17.3 | 18.2 | 15.3 | 16.4 | 17.5 | 18.5 | 14.7 |
| 10 | 9.1 | 7.6 | 8.0 | 8.4 | 8.7 | 9.1 | 9.5 | 7.6 | 8.2 | 8.7 | 9.3 | 9.8 | 6.9 | 7.3 | 7.6 | 8.2 | 8.7 | 9.3 | 9.8 |
.
Table 14 Critical Stress,
(Clause 8.2.2.1)
| KL/r | h/t | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 8 | 10 | 12 | 14 | 16 | 18 | 20 | 25 | 30 | 35 | 40 | 50 | 60 | 80 | 100 | |||
| 10 | 22 551.2 | 22 255.1 | 22 092.6 | 21 994.1 | 21 929.8 | 21 885.7 | 21 854.0 | 21 805.4 | 21 779.0 | 21 763.1 | 21 752.7 | 21 740.5 | 21 733.8 | 21 727.2 | 21 724.2 | ||
| 20 | 6 220.5 | 5 947.9 | 5 794.5 | 5 700.0 | 5 637.8 | 5 594.7 | 5 563.8 | 5 515.8 | 5 489.7 | 5 473.8 | 5 463.5 | 5 451.4 | 5 444.8 | 5 438.2 | 5 435.1 | ||
| 30 | 3 149.3 | 2 905.9 | 2764.6 | 2 676.0 | 2 616.7 | 2 575.3 | 2 545.3 | 2 498.5 | 2472.8 | 2 457.1 | 2 447.0 | 2 434.9 | 2 428.3 | 2 421.7 | 2 418.6 | ||
| 40 | 2 036.1 | 1 821.2 | 1693.0 | 1 610.8 | 1 555.1 | 1515.8 | 1 487.0 | 1441.7 | 1416.5 | 1 401.1 | 1 391.0 | 1379.0 | 1 372.5 | 1365.9 | 1 362.8 | ||
| 50 | 1 492.9 | 1 303.2 | 1187.3 | 1111.8 | 1 059.9 | 1022.7 | 995.3 | 951.7 | 927.1 | 912.0 | 902.0 | 890.2 | 883.7 | 877.1 | 874.2 | ||
| 60 | 1 178.0 | 1009.5 | 905.0 | 835.6 | 787.4 | 752.4 | 726.4 | 684.6 | 660.9 | 646.1 | 636.4 | 624.7 | 618.2 | 611.7 | 608.7 | ||
| 70 | 973.9 | 823.2 | 728.5 | 664.8 | 620.1 | 587.4 | 562.9 | 522.9 | 500.0 | 485.5 | 476.0 | 464.4 | 458.0 | 451.7 | 448.7 | ||
| 80 | 831.3 | 695.4 | 609.2 | 550.7 | 509.1 | 478.4 | 455.3 | 417.2 | 395.1 | 381.2 | 371.8 | 360.5 | 354.1 | 347.7 | 344.7 | ||
| 90 | 725.9 | 602.6 | 523.6 | 469.5 | 430.9 | 402.2 | 380.4 | 344.2 | 322.9 | 309.3 | 300.2 | 289.1 | 282.8 | 276.5 | 273.5 | ||
| 100 | 644.7 | 532.0 | 459.3 | 409.3 | 373.2 | 346.4 | 325.8 | 291.4 | 270.9 | 257.7 | 248.8 | 237.9 | 231.8 | 225.5 | 222.5 | ||
| 110 | 580.4 | 476.6 | 409.3 | 362.9 | 329.2 | 303.9 | 284.5 | 251.8 | 232.1 | 219.3 | 210.8 | 200.1 | 194.0 | 187.8 | 184.8 | ||
| 120 | 527.9 | 431.9 | 369.5 | 326.0 | 294.5 | 270.7 | 252.3 | 221.2 | 202.4 | 190.1 | 181.6 | 171.2 | 165.2 | 159.1 | 156.2 | ||
| 130 | 484.3 | 395.0 | 336.8 | 296.1 | 266.5 | 244.1 | 226.7 | 197.1 | 179.0 | 167.1 | 158.8 | 148.6 | 142.8 | 136.7 | 133.9 | ||
| 140 | 447.6 | 364.2 | 309.5 | 271.5 | 243.4 | 222.3 | 205.8 | 177.5 | 160.2 | 148.7 | 140.7 | 130.8 | 125.0 | 119.0 | 116.2 | ||
| 150 | 416.0 | 337.8 | 286.6 | 250.6 | 224.2 | 204.2 | 188.4 | 161.5 | 144.8 | 133.7 | 126.0 | 116.3 | 110.6 | 104.7 | 101.9 | ||
| 160 | 388.7 | 315.2 | 266.8 | 232.8 | 207.8 | 188.8 | 173.9 | 148.2 | 132.0 | 121.3 | 113.9 | 104.3 | 98.8 | 93.0 | 90.1 | ||
| 170 | 364.9 | 295.4 | 249.6 | 217.5 | 193.7 | 175.6 | 161.4 | 136.7 | 121.3 | 111.0 | 103.6 | 94.4 | 89.0 | 83.2 | 80.4 | ||
| 180 | 343.9 | 278.0 | 234.6 | 204.1 | 181.5 | 164.2 | 150.6 | 127.1 | 112.2 | 102.2 | 95.2 | 86.0 | 80.7 | 75.0 | 72.3 | ||
| 190 | 325.2 | 262.6 | 221.3 | 192.3 | 170.7 | 154.2 | 141.2 | 118.6 | 104.3 | 94.6 | 87.8 | 79.0 | 73.7 | 68.1 | 65.3 | ||
| 200 | 308.3 | 248.8 | 209.6 | 181.7 | 161.2 | 145.4 | 133.0 | 111.3 | 97.5 | 88.1 | 81.4 | 72.8 | 67.8 | 62.2 | 59.5 | ||
| 210 | 293.3 | 236.5 | 198.9 | 172.4 | 152.7 | 137.6 | 125.7 | 104.8 | 91.5 | 82.4 | 75.9 | 67.5 | 62.6 | 57.1 | 54.5 | ||
| 220 | 279.5 | 225.3 | 189.3 | 163.9 | 145.1 | 130.6 | 119.1 | 99.0 | 86.2 | 77.4 | 71.2 | 62.9 | 58.1 | 52.7 | 50.1 | ||
| 230 | 267.1 | 215.2 | 180.7 | 156.3 | 138.2 | 124.3 | 113.3 | 93.9 | 81.5 | 72.9 | 66.9 | 58.9 | 54.1 | 48.8 | 46.2 | ||
| 240 | 255.8 | 205.8 | 172.8 | 149.4 | 132.0 | 118.6 | 108.0 | 89.3 | 77.2 | 69.0 | 63.1 | 55.3 | 50.6 | 45.4 | 42.8 | ||
| 250 | 245.3 | 197.3 | 165.6 | 143.0 | 126.3 | 113.4 | 103.2 | 85.1 | 73.5 | 65.5 | 59.7 | 52.1 | 47.5 | 42.4 | 39.8 | ||
| 260 | 235.7 | 189.5 | 159.0 | 137.3 | 121.1 | 108.7 | 98.8 | 81.3 | 70.1 | 62.3 | 56.7 | 49.3 | 44.8 | 39.7 | 37.2 | ||
| 270 | 226.8 | 182.3 | 152.8 | 131.9 | 116.3 | 104.3 | 94.7 | 77.9 | 67.0 | 59.4 | 53.9 | 46.8 | 42.2 | 37.3 | 34.8 | ||
| 280 | 218.6 | 175.7 | 147.2 | 126.9 | 111.9 | 100.2 | 91.1 | 74.7 | 64.1 | 56.8 | 51.5 | 44.4 | 40.0 | 35.2 | 32.7 | ||
| 290 | 210.9 | 169.4 | 141.9 | 122.3 | 107.8 | 96.6 | 87.7 | 71.8 | 61.5 | 54.3 | 49.2 | 42.2 | 38.1 | 33.2 | 30.8 | ||
| 300 | 203.8 | 163.7 | 137.1 | 118.1 | 104.1 | 93.2 | 84.5 | 69.1 | 59.1 | 52.1 | 47.1 | 40.4 | 36.2 | 31.5 | 29.0 | ||
In simply supported beams with intermediate lateral restraints against lateral torsional buckling, the effective length for lateral torsional buckling to be used in 8.2.2.1, shall be taken as the length of the relevant segment in between the lateral restraints. The effective length shall be equal to 1.2 times the length of the relevant segment in between the lateral restraints.
Restraint against torsional rotation at supports in these beams may be provided by:
- a) web or flange cleats, or
- b) bearing stiffeners acting in conjunction with the bearing of the beam, or
- c) lateral end frames or external support providing lateral restraint to the compression flanges at the ends, or
- d) their being built into walls.
8.3.2
For beams, which are provided with members giving effective lateral restraint to the compression flange at intervals along the span, in addition to the end torsional restraint required in 8.3.1, the effective length for lateral torsional buckling shall be taken as the distance, centre-to-centre of the restraint members in the relevant segment under normal loading condition and 1.2 times this distance, where the load is not acting on the beam at the shear and is acting towards the shear centre so as to have destabilizing effect during lateral torsional buckling deformation.
8.3.3
For cantilever beams of projecting length , the effective length to be used in 8.2.2.1 shall be taken as in Table 16 for different support conditions.
8.3.4
Where a member is provided intermediate lateral
supports to improve the lateral buckling strength, these restraints should have sufficient strength and stiffness to prevent lateral movement of the compression flange
at that point, relative to the end supports. The intermediate lateral restraints should be either connected to an appropriate bracing system capable of transferring the restraint force to the effective lateral support at the ends of the member, or should be connected to an independent robust part of the structure capable of transferring the restraint force. Two or more parallel member requiring such lateral restraint shall not be simply connected together assuming mutual dependence for the lateral restraint.
The intermediate lateral restraints should be connected to the member as close to the compression flange as practicable. Such restraints should be closer to the shear centre of the compression flange than to the shear centre of the section. However, if torsional restraint preventing relative rotation between the two flanges is provided, the intermediate lateral restraint may be connected at any appropriate level.
For beams which are provided with members giving effective lateral restraint at intervals along the span, the effective lateral restraint shall be capable of resisting a force of 2.5 percent of the maximum force in the compression flange taken as divided equally between the points at which the restraint members are provided. Further, each restraint point should be capable of resisting 1 percent of the maximum force in the compression flange.
8.3.4.1
In a series of such beams, with solid webs, which are connected together by the same system of restraint members, the sum of the restraining forces required shall be taken as 2.5 percent of the maximum flange force in one beam only.
8.3.4.2
In the case of a series of latticed beams, girders or roof trusses which are connected together by the same system of restraint members, the sum of the restraining
Table 15 Effective Length for Simply Supported Beams,
(Clause 8.3.1)
| SI No. | Conditions of Restraint at Supports | Loading Condition | ||
|---|---|---|---|---|
| Torsional Restraint | Warping Restraint | Normal | Destabilizing | |
| (1) | (2) | (3) | (4) | (5) |
| i) | Fully restrained | Both flanges fully restrained | 0.70 L | 0.85 L |
| ii) | Fully restrained | Compression flange fully restrained | 0.75 L | 0.90 L |
| iii) | Fully restrained | Both flanges fully restrained | 0.80 L | 0.95 L |
| iv) | Fully restrained | Compression flange partially restrained | 0.85 L | 1.00 L |
| v) | Fully restrained | Warping not restrained in both flanges | 1.00 L | 1.20 L |
| vi) | Partially restrained by bottom flange support connection | Warping not restrained in both flanges | 1.0 L + 2 D | 1.2 L + 2 D |
| vii) | Partially restrained by bottom flange bearing support | Warping not restrained in both flanges | 1.2 L + 2 D | 1.4 L + 2 D |
NOTES
- 1 Torsional restraint prevents rotation about the longitudinal axis.
- 2 Warping restraint prevents rotation of the flange in its plane.
- 3 D is the overall depth of the beam.
forces required shall be taken as 2.5 percent of the maximum force in the compression flange plus 1.25 percent of this force for every member of the series other than the first, up to a maximum total of 7.5 percent.
8.3.5
Purlins adequately restrained by sheeting need not be normally checked for the restraining forces required by rafters, roof trusses or portal frames that carry predominately roof loads provided there is bracing of adequate stiffness in the plane of rafters or roof sheeting which is capable of acting as a stressed skin diaphragm.
8.3.6
In case of beams with double curvature bending adequate direct lateral support to the compression flange in the hogging moment region may be provided as given above for simply supported beam. The effect of support to the tension (top) flange in the hogging moment region on lateral restraint to the compression flange may be considered as per specialist literature.