Tower Silo Capacities

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.