Tower Silo Capacities


Factsheet - ISSN 1198-712X   -   Copyright Queen's Printer for Ontario
Agdex#: 100/732
Publication Date: 02/88
Order#: 88-033
Last Reviewed: 07/12
History: Replaces Factsheet #82-076, "Tower Silo"
Written by: J.C. Jofriet - School of Engineering/University of Guelph; T.B. Daynard - Crop Science/University of Guelph

Table of Contents

  1. Introduction
  2. Concrete Silo Capacities for Forages
  3. Steel Silo Capacities for Forages
  4. Concrete Silo Capacities for High Moisture Corn

Introduction

The capacity of a tower silo depends on: (a) the compressibility of the stored material; (b) the total volume of the silo; (c) the friction between the wall of the silo and the material; and (d) the ratio of the settled depth of silage to the diameter of the silo. This Factsheet contains estimates of tower silo capacities for alfalfa silage, whole-plant corn silage and various types of high moisture corn based on a series of analyses of silo capacity carried out at the University of Guelph and on research done at research establishments in the Netherlands and Sweden. Values shown are more accurate than those available in previous extension publications. Most previously published capacity tables overestimate capacities for corn silage and underestimate those for high moisture corn.

Tables 1 and 2 show the capacities, in tonnes, of most common silo sizes for alfalfa and whole-plant corn silage. The capacities in Table 1 were obtained using a friction coefficient of 0.6, a reasonable estimate for as-cast concrete walls. Table 2 capacities were calculated using a friction coefficient of 0.4; this coefficient has been found appropriate for glass-lined steel walls. Concrete silos coated inside with a hard glass-like coating will probably have capacities approximating those in Table 2. Badly corroded rough concrete walls, on the other hand, may well reduce the capacity below that shown in Table 1.

Table 1. Estimated concrete silo capacities for forages, in tonnes.(a)

Silo Diameter x Settled Depth Alfalfa Silage Corn Silage
(m) (ft) 40% 50%(b) 60% 70% 55% 60% 65% 70%
3.7 x 9.1 12 x 30 32 40 52 75 43 49 56 67 12 x 30
3.7 x 12.2 12 x 40 45 56 73 105 60 68 79 93 12 x 40
3.7 x 15.2 12 x 50 57 71 94 136 77 88 101 120 12 x 50
4.3 x 12.2 14 x 40 63 78 103 148 84 96 110 130 14 x 40
4.3 x 15.2 14 x 50 81 101 134 193 110 124 143 168 14 x 50
4.3 x 16.8 14 x 55 90 113 149 215 122 139 159 187 14 x 55
4.9 x 15.2 16 x 50 109 137 181 261 148 167 191 224 16 x 50
4.9 x 18.3 16 x 60 135 169 224 323 182 206 235 275 16 x 60
4.9 x 19.8 16 x 65 147 185 245 354 200 225 258 300 16 x 65
5.5 x 15.2 18 x 50 142 178 236 339 191 216 247 288 18 x 50
5.5 x 18.3 18 x 60 176 221 293 421 237 266 304 353 18 x 60
5.5 x 21.3 18 x 70 211 264 351 504 283 317 361 419 18 x 70
6.1 x 18.3 20 x 60 224 281 372 533 298 335 381 442 20 x 60
6.1 x 21.3 20 x 70 268 337 446 639 357 399 453 524 20 x 70
6.1 x 24.4 20 x 80 314 394 522 746 415 464 526 607 20 x 80
7.3 x 18.3 24 x 60 338 423 559 796 442 494 560 647 24 x 60
7.3 x 21.3 24 x 70 407 511 674 956 529 590 667 767 24 x 70
7.3 x 24.4 24 x 80 479 600 790 1118 616 685 773 888 24 x 80
7.3 x 27.4 24 x 90 551 690 908 1281 704 782 880 1009 24 x 90
9.1 x 24.4 30 x 80 796 993 1297 1813 989 1164 1343 1480 30 x 80
9.1 x 27.4 30 x 90 920 1146 1494 2079 1129 1341 1547 1706 30 x 90
9.1 x 30.5 30 x 100 1046 1301 1692 2346 1270 1520 1754 1934 30 x 100
9.1 x 33.5 30 x 110 1173 1457 1891 2614 1411 1701 1962 2165 30 x 110

(a) 1 tonne 1000kg: the capacity in tons (2000 lb) can be obtained by multiplying the capacities in the table by 1.1
(b) moisture content in percent (wet basis)  

Table 2. Estimated steel silo capacities for forages, in tonnes.(a)

Silo Diameter x Settled Depth Alfalfa Silage Corn Silage
(m) (ft) 40% 50%(b) 60% 70% 55% 60% 65% 70%
3.7 x 9.1 12 x 30 34 43 56 81 46 52 60 70 12 x 30
3.7 x 12.1 12 x 40 49 61 80 115 65 74 84 99 12 x 40
3.7 x 15.2 12 x 50 63 79 105 151 85 96 110 128 12 x 50
4.3 x 12.2 14 x 40 68 85 112 161 91 102 117 137 14 x 40
4.3 x 15.2 14 x 50 89 112 148 212 119 134 152 177 14 x 50
4.3 x 16.8 14 x 55 100 125 166 238 133 149 170 197 14 x 55
4.9 x 15.2 16 x 50 120 150 198 283 158 177 202 234 16 x 50
4.9 x 18.3 16 x 60 150 188 248 354 196 220 249 287 16 x 60
4.9 x 19.8 16 x 65 166 207 274 389 216 241 273 314 16 x 65
5.5 x 15.2 18 x 50 155 195 256 365 203 227 258 299 18 x 50
5.5 x 18.3 18 x 60 176 221 293 421 252 281 318 367 18 x 60
5.5 x 21.3 18 x 70 211 264 651 504 302 336 379 435 18 x 70
6.1 x 18.3 20 x 60 247 308 405 572 315 351 396 456 20 x 60
6.1 x 21.3 20 x 70 300 374 490 688 377 419 471 540 20 x 70
6.1 x 24.4 20 x 80 354 441 576 806 439 487 547 625 20 x 80
7.3 x 18.3 24 x 60 368 459 600 842 461 512 577 662 24 x 60
7.3 x 21.3 24 x 70 449 558 727 1013 551 611 686 784 24 x 70
7.3 x 24.4 24 x 80 432 660 857 1187 642 710 795 907 24 x 80
7.3 x 27.4 24 x 90 616 764 988 1361 734 809 905 1031 24 x 90
9.1 x 24.4 30 x 80 867 1070 1379 1892 1033 1269 1459 1606 30 x 80
9.1 x 27.4 30 x 90 1007 1240 1590 2169 1202 1472 1690 1860 30 x 90
9.1 x 30.5 30 x 100 1150 1411 1803 2447 1374 1678 1923 2116 30 x 100
9.1 x 33.5 30 x 110 1294 1584 2017 2726 1549 1886 2159 2374 30 x 110

(a) 1 tonne 1000kg: the capacity in tons (2000 lb) can be obtained by multiplying the capacities in the table by 1.1
(b) moisture content in percent (wet basis)

No tests have been carried out at Guelph for grass. Based on work done in the Netherlands grass consolidates somewhat more than alfalfa. Capacities for grass silage may be estimated from Tables 1 and 2 by increasing the alfalfa silage capacities by 10, 15 and 20% for moisture contents of 50, 60 and 70% respectively.

Table 3 presents silo capacities for high moisture corn. Capacities for whole shelled and ground shelled corn, as well as ground ear corn are shown. The capacity figures in Table 3 were calculated on the basis of a friction coefficient of 0.6 an appropriate estimate for concrete. High moisture corn is far less compressible than forage and, therefore, friction has a much less effect on capacity. It is recommended that for very smooth wall surfaces, such as glass-lined steel or epoxy coated concrete, that the capacities in Table 3 be increased by 3%.

Table 3. Estimated concrete silo capacities for high moisture corn, in tonnes.(a)

Silo Diameter Settled Depth Whole shelled corn Ground Shelled Corn Ground Ear Corn  
(m) (ft) 25% 30%(b) 35% 25% 30 35% 30% 35% 40%
3.7 x 9.1 12 x 30 74 81 89 77 86 96 66 75 67 12 x 30
3.7 x 12.2 12 x 40 99 109 120 104 116 131 89 102 118 12 x 40
3.7 x 15.2 12 x 50 125 137 152 131 146 165 113 129 150 12 x 50
4.3 x 12.2 14 x 40 137 150 165 143 160 180 123 141 161 14 x 40
4.3 x 15.2 14 x 50 172 189 209 180 202 228 155 179 208 14 x 50
4.3 x 16.8 14 x 55 190 209 231 199 223 252 172 198 230 14 x 55
4.9 x 15.2 16 x 50 227 249 275 267 301 205 237 276 224 16 x 50
4.9 x 18.3 16 x 60 274 301 333 288 323 365 249 287 335 16 x 60
4.9 x 19.8 16 x 65 298 327 362 313 351 397 271 313 365 16 x 65
5.5 x 15.2 18 x 50 289 318 351 303 340 384 263 303 353 18 x 50
5.5 x 18.3 18 x 60 350 384 425 367 412 466 318 368 429 18 x 60
5.5 x 21.3 18 x 70 410 451 499 431 484 547 374 434 506 18 x 70
6.1 x 18.3 20 x 60 434 477 528 456 512 579 396 459 535 20 x 60
6.1 x 21.3 20 x 70 510 561 620 536 602 680 466 541 631 20 x 70
6.1 x 24.4 20 x 80 585 644 713 616 692 782 536 622 727 20 x 80
7.3 x 18.3 24 x 60 632 694 768 663 745 841 578 670 781 24 x 60
7.3 x 21.3 24 x 70 742 816 902 780 876 989 681 790 922 24 x 70
7.3 x 24.4 24 x 80 852 938 1037 896 1007 1132 784 910 1063 24 x 80
7.3 x 27.4 24 x 90 963 1059 1172 1012 1138 1285 887 1030 1204 24 x 90
9.1 x 24.4 30 x 80 1346 1480 1637 1413 1587 1791 1242 1442 1681 30 x 80
9.1 x 27.4 30 x 90 1521 1673 1851 1597 1794 2025 1405 1633 1905 30 x 90
9.1 x 30.5 30 x 100 1697 1867 2064 1781 2001 2258 1569 1824 2128 30 x 100
9.1 x 33.5 30 x 110 1872 2060 2278 1965 2208 2492 1734 2016 2352 30 x 110
(a) 1 tonne 1000kg: the capacity in tons (2000 lb) can be obtained by multiplying the capacities in the table by 1.1
(b) moisture content in percent (wet basis)

The capacity tables are based on fully settled silage. The silo height may be used if the silo is topped up one to two weeks after initial filling. If this is not done the capacities in Tables 1, 2 and 3 should be determined on the actual settled depth of silage after about two to three weeks rather than the silo height. Silage may settle between 10 and 15% during the first two weeks after filling. Another adjustment should be made if space in the top of silo allows the piling up of material in a cone-shaped heap. To allow for this pile, one-third of the height of the cone can be added to the settled depth of the silage measured at the base of the cone.

There is no significant difference in capacity between topunloading silos and those with sweep-arm bottom-unloading equipment. However, the tables do not account for the large cavity formed with flail-type bottom-unloading equipment and should not be used directly for silos thus equipped.


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