IStructE/Concrete Society Standard Method of Detailing Structural Concrete Appendix B 187 Large diameter bends Concrete strength class (fck/fcu) 32/40 Minimum mandrel size, bm,min (mm) bm,min = Fbt ((1/ab) + 1/(2b)/fcd where Fbt is the tensile force from ultimate loads (N) b is the size of bar (mm) ab is half the pitch of bars or nominal cover + b/2 (mm) fcd is the design concrete strength = acc fck/gc (MPa) Internal diameter of bend (mm) ab (mm) Actual Ult. stress in bar (MPa) Bar diameter b (mm) 10 12 16 20 25 32 40 25 100 150 200 250 300 350 400 450 35 55 75 95 115 135 155 175 50 75 100 125 150 175 200 225 75 115 155 195 235 275 315 355 110 165 225 280 335 390 450 505 160 240 320 405 485 565 645 730 50 100 150 200 250 300 350 400 450 30 45 60 75 90 105 120 135 35 55 75 95 115 130 150 170 55 85 110 140 170 195 225 255 75 115 155 190 230 270 310 350 105 160 215 270 320 375 430 485 155 235 315 395 470 550 630 710 225 335 450 560 675 785 900 1010 75 100 150 200 250 300 350 400 450 25 40 50 65 80 95 105 120 30 50 65 85 100 120 135 150 45 70 95 120 145 170 195 220 65 95 130 165 195 230 265 295 90 135 180 225 270 315 360 405 125 190 255 320 385 445 510 575 175 265 355 445 535 625 715 805 100 100 150 200 250 300 350 400 450 25 35 50 60 75 90 100 115 30 45 60 80 95 110 125 145 45 65 90 110 135 1660 180 205 60 90 120 150 180 210 240 270 80 120 160 200 240 280 320 365 110 170 225 280 340 395 450 510 155 230 310 385 465 545 620 700 150 and over 100 150 200 250 300 350 400 450 20 35 45 60 70 85 95 110 30 45 60 75 90 105 120 135 40 60 80 105 125 145 165 185 50 80 105 135 160 190 215 245 70 105 140 180 215 250 285 320 95 145 195 245 295 345 395 440 130 195 265 330 395 460 530 595 Notes 1 Maximum design stress = Characteristic yield stress / 1.15 = 435 MPa 2 Minimum mandrel size may govern: for bar size: < 20 4b mandrel size H 20 7b mandrel size
188 Appendix B IStructE/Concrete Society Standard Method of Detailing Structural Concrete Large diameter bends Concrete strength class (fck/fcu) 35/45 Minimum mandrel size, bm,min (mm) bm,min = Fbt ((1/ab) + 1/(2b)/fcd where Fbt is the tensile force from ultimate loads (N) b is the size of bar (mm) ab is half the pitch of bars or nominal cover + b/2 (mm) fcd is the design concrete strength = acc fck/gc (MPa) Internal diameter of bend (mm) ab (mm) Actual Ult. stress in bar (MPa) Bar diameter b (mm) 10 12 16 20 25 32 40 25 100 150 200 250 300 350 400 450 35 50 70 85 105 120 140 160 45 65 90 115 135 160 185 205 70 105 140 180 215 250 285 325 100 150 205 255 305 360 410 460 145 220 295 370 445 515 590 665 50 100 150 200 250 300 350 400 450 25 40 55 65 80 95 110 120 35 50 70 85 105 120 140 155 50 75 100 125 155 180 205 230 70 105 140 175 210 245 285 320 95 145 195 245 295 345 395 445 140 215 285 360 430 505 575 650 205 305 410 510 615 720 820 925 75 100 150 200 250 300 350 400 450 25 35 50 60 75 85 100 110 30 45 60 75 90 105 125 140 45 65 90 110 135 155 180 200 60 90 120 150 180 210 240 270 80 120 160 205 245 285 325 370 115 175 230 290 350 410 465 525 160 245 325 405 490 570 650 735 100 100 150 200 250 300 350 400 450 20 35 45 55 70 80 95 105 25 40 55 70 85 100 115 130 40 60 80 100 125 145 165 185 55 80 110 135 165 190 220 245 70 110 145 185 220 255 295 330 100 155 205 255 310 360 415 465 140 210 285 355 425 495 570 640 150 and over 100 150 200 250 300 350 400 450 20 30 40 55 65 75 85 100 25 40 55 65 80 95 110 120 35 55 75 95 115 130 150 170 50 75 100 125 150 175 200 225 65 95 130 160 195 230 260 295 90 135 180 225 270 315 360 405 120 180 240 300 360 425 485 545 Notes 1 Maximum design stress = Characteristic yield stress / 1.15 = 435 MPa 2 Minimum mandrel size may govern: for bar size: < 20 4b mandrel size H 20 7b mandrel size
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