National Farm Building Code, Useful Calculations

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Bulk Densities of Agricultural Materials and Other Useful Equations

These tables and equations are all copied from the National Farm Building Code of Canada. The Code can be purchased online from the

Part 2 Structural Design

Table2.2.1.1. Minimum Specified Live Loads due to Use


Type of Load Minimum Specified Load
kPa Load between Adjacent Aisles kN/m length of aisle
Cattle Tie Stall Cow platforms, feed alleys 3.5
Cow traffic alleys (e.g. Litter alleys) 5.0
Cattle Loose housing 5.0
Holding Areas 5.0
Milking Parlours 3.5
Milking Rooms and Milk Houses 2.5 (* the floor under a bulk milk tank shall be designed to support the load from the tank plus its contents)
Sheep 1.5
Swine Solid Floors 2.5
Horses 5.0
Turkeys 2.0 (*Spaces under wire floors, slotted floors or cages shall have a minimum specified live load of not less than 1 kPa for each 100mm depth of manure)
Greenhouses 2.5
Chickens Housed without cages (including manure) 2.0
Housed in cages 2 levels of cage equipment with dropping boards Chicken cage manufacturers should be consulted for information on the type and spacing of supports (floor stand or suspended type)


Bird mass is based on eight 1.8 kg birds for each 300mm length of deck. On this basis a 3-deck cage row has 24 birds in 300mm of cage row length.


Dropping boards used to prevent soiling on the lower level cages are assumed to accumulate 50mm of wet manure between cleaning operations.

2 levels of cage equipment without dropping boards 1.4
3 levels of cage equipment with dropping boards 2.7
3 levels of cage equipment

without dropping boards

4 levels of cage equipment with dropping boards 3.0

Equipment Used for Manure Cleanout in a Poultry Barn

Where equipment up to 700kg including operator is used for manure cleanout in a poultry barn, the floor shall be designed for a two-wheel live load of 4.0 kN in addition to the distributed load of 1 kPa representing 100mm of wet litter.

Table Floor Loads for Groups of Animals on Slotted Floors

Livestock Live Loads for Design of a Floor Slat, kN/m of slat Distributed Live Loads for Design of Slotted floors and Their Supports,


Dairy and Beef Cattle 4.5 5.0
Dairy and beef calves up to 150kg 2.2 2.5
Sheep 2.0 2.5
Swine Weaners up to 25kg 0.7 1.7
Feeders up to 100kg 1.5 2.5
Sows up to 225kg 2.5 3.5


Farm Machinery

  1. Except as provided in sentence (2) the uniformly distributed live load on an area of floor used for farm machinery traffic shall not be less than 7.0 kPa
  2. Where it is anticipated that the area will be occupied by either loaded farm trailers and trucks or farm tractors having a mass in excess of 6 000kg, including the mass of mounted equipment, the live load shall be not less than 10 kPa.
  3. Concentrated love loads due to tractors and farm machinery shall not be less than 23kN per wheel, applied over an area of 750mm by 750mm, located to cause maximum effects.
  4. Where an area serves as a place for processing or for loading or unloading of vehicles, the minimum live loads for such areas shall be increased by 50% to allow for impact or vibration of the machinery or equipment.

Table A- Coefficients of friction for Grain and Silage

Type of grain Moisture Content % (wet basis)(1) Smooth Steel µ Corrugated Steel µ Plywood µ Concrete (2) µ Internal Friction within the Grain, tan (3)
Wheat and Barley 11.0 0.1 0.35 0.3 0.35 0.5
  13.0 0.25        
Shelled Corn 11.0 0.2 0.35 0.3 0.35 0.5
  16.0 0.35   0.45 0.6 0.6
Soybeans 11.0 0.2   0.35 0.5 0.5
Flaxseed 9.0 0.2   0.35 0.35 0.25
  11.5 0.25   0.4 0.45 0.23
Canola (rapeseed) 9.0 0.2   0.35 0.35 0.5
  12.5 0.25   0.35 0.35 0.6
Whole-plant silages   0.3-0.4(4)     0.4-0.5(4)  
High moisture ensiled grains, including ground shelled and ground ear corn   0.25-0.35(4)     0.35-0.45(4)  

(1) The moisture content of grain is the weight of water in the grain divided by the weight of the wet grain. For higher moisture contents, the friction coefficients will be appreciably higher, resulting in greater wall vertical loads, but maximum lateral pressures will occur with clean, dry grain.

(2) Values are for rough textured concrete. Where concrete is placed against smooth forms and polished by the repeated flow of grain, values will be approximately two-thirds of those shown.

(3) For horizontally corrugated or very rough surfaces, sliding my occur within the grain mass rather than on the surface, in which case the internal friction within the grain applies, if less than µ.

(4) For conservative design to resist lateral pressures, select the lower value of the range; for vertical friction force, select the higher value.

Table A- Ratio of horizontal to vertical pressure for grains and silages, k

Type of Grain Smooth Wall Rough Wall
Cereal grains 0.4 0.6
Canola (rapeseed) 0.4 0.6
Flaxseed and canary seed 0.55 0.8
Whole -plant silages 0.4 0.4
High-moisture ensiled grains, including ground shelled and ground ear corn 0.5 0.5

Storage for Dry Grains

  1. Pressures and loads for the design of storage for dry grains shall be determined by the analyses given in this article.
  2. In this article

F = maximum vertical load per unit of wall perimeter due to friction, kN/m

L = horizontal pressure against the bin wall, kPa,

Lb = horizontal pressure at the bottom of the vertical section of a bin wall

V = L/K = vertical pressure on the bin floor or within the grain mass, kPa

= coefficient of friction between the fill material and the bin wall (see table A-

k = ratio of horizontal to vertical pressure (see table A-

H = depth below surface of fill or where surface would be if fill was levelled, m

D = bin diameter, m

a = length of short side, m

b = length of long side, m

R = hydraulic radius

= D/4 for circular bins

= (2ab-a2)/4b for rectangular bins (long side)

= a/4 for rectangular bins (short side)

C = Reimbert coefficient

= bin wall slope measured from horizontal (see figure A-

= bulk density kg/m3 (see Table A-

g = acceleration due to gravity, 9.81m/s2

= 1.06g)/1000 = unit weight of material, kN/m3

= angle of internal friction

= angle of friction of fill material on bin wall = arc tan

e = natural log base = 2.71828

= hopper slope from horizontal

  1. In this Article a deep bin is defined as having a depth greater than 0.75 times the width and a shallow bin is defined as having a depth not greater than 0.75 times the width.
  2. Except as provided in sentences (7) and (8), the horizontal wall pressure in deep bins and in shallow bins with vertical walls shall be determined using the following Janssen formula:
  3. For shallow bins which have walls sloping at angles between 50o and 120o to the horizontal, the pressure normal to the wall surface shall be determined by multiplying the horizontal wall pressure calculated in Sentence (4) by the following Rembert coefficient


C =

  1. The vertical friction load of the bin contents on the bin wall shall be determined from the following formula:


F = R (H-)

  1. For bins which empty through a central discharge opening, the horizontal wall pressure during emptying shall be that determined in Sentence (4) multiplied by an over pressure factor as given in Table with values of C corresponding to H/4R between 2.5and 5 determined by linear interpolation. (See Appendix A.)


Overpressure Factors for Stored Grain

Forming Part of Sentence (7)


Grain Stored Overpressure Factor
Cereal grains, shelled corn, soybeans and canola 1.0 1.4
Flaxseed and canary seed 1.0 1.6


  1. For a bin which discharges through an opening which is eccentric by R/6 or more, the horizontal wall pressure during emptying shall be the pressure double on a strip of wall of width R extending from the discharge opening to the surface of the grain.
  2. The design vertical pressure for shallow bins with floors sloped 0o to 20o to the horizontal shall be V =
  3. The design vertical pressure for deep bins with floors sloped 0o to 20o to the horizontal shall be determined from the following Janssen equation:


  1. For bin bottoms sloped between 20o and 60o to the horizontal, the normal pressure which varies linearly from a maximum at the wall-hopper junction to a minimum at the projected apex of the hopper, shall be determined from the following equations.


2 = Lb [sin2 +

P3 =

Where P2 is the normal pressure at the top edge of the hopper, and P3 is the normal pressure at the apex of the projected hopper bottom.


  1. Bin bottoms sloped at 60o or greater shall be designed for mass flow. (See Appendix A.)

Table A- Bulk Densities of Agricultural Materials

Material Bulk Density
, kg/m3
Grains and Seeds(1) Alfalfa 750
Alsike 740
Barley 620
Castor Beans 590
Lima Beans 720
Navy Beans 770
Snap Beans 380
Bent grass 450
Birds foot Trefoil 740
Canada Bluegrass 270
Kentucky Bluegrass 280
Rough Bluegrass 270
Bromegrass 170
Buckwheat 640
Canola 640
Turnip o Polish Rape 640
Argentina Rape 770
Red Clover 750
Sweet Clover 780
White Clover 760
Husked Ear Corn 450
Shelled 720
Cottonseed 410
Cow Peas 770
Chewing Fescue 240
Meadow Fescue 290
Red Fescue 220
Tall Fescue 280
Flaxseed (linseed) 700
Grain Sorghum 720
Lentils 770
Milkvetch 820
Millet 640
Mustard 640
Oats 420
Orchard Grass 200
Peanuts Shelled 640
Peanuts Unshelled 240
Peas 770
Rapeseed (see Canola)  
Red Top 390
Reed Canary Grass 380
Rice Hulled 770
Russian Wild Rye 250
Rye 720
Ryegrass Annual 360
Perennial Ryegrass 300
Safflower Seed 720
Sainfoin 360
Soybeans 770
Sunflower Seed 310-410
Timothy 580
Wheat 770
Concentrated Feeds Alfalfa Meal 250-350
Alfalfa Pellets 650-700
Barley Ground Meal 380-450
Barley Malt 500
Beet Pulp Dried 180-250
Bone Meal 800-960
Bran, rice-rye-wheat 260-320
Brewers Grain Dry 220-290
Brewers Grain Wet 880-960
Corn Cobs Ground 270
Corn Cobs Whole 190-240
Corn Cracked 640-800
Corn Germ 340
Corn Grits 640-720
Corn Meal 510-640
Corn Oil Cake 400
Crumbled Ratio 550
Fish Meal 560-640
Flaxseed Oil Cake (Linseed Oil Cake) 770-800
Flaxseed Oil Meal (Linseed Oil Meal) 400-720
Malt Dry Ground 320-480
Malt Meal 580-640
Meat Meal 600
Oats Crimped 300-420
Oats Crushed 350
Oats Rolled 300-420
Pelleted Ration 600
Salt 1000-1100
Soya Bean Meal 550-650
Wheat Cracked 640-720
Wheat Germ 350-450
Roughage Feeds and Bedding Hay(air-dried) Baled 160
Hay(air-dried) Chopped 160
Hay(air-dried) Long 80
Hay(air-dried) Wafered 325
Silage 70% moisture wet basis(2) tractor-packed in horizontal silo 700
Silage 70% moisture wet basis(2) unpacked in horizontal silo 500
Silage in tower silos see table (A-  
Straw Chopped 100-130
Straw Field Baled 130
Straw Long 60
Wood Shavings, Baled 320
Fruits and Vegetables Apples, Bulk 600
Apricots 620
Beans shelled 800
Beans unshelled 400
Beets 700
Blackberries 610
Cabbage 500
Carrots 550
Cauliflower 320
Corn, Cob 450
Cranberries 480
Cucumbers 620
Onions Dry 650
Parsnips 500
Peaches 620
Pears 640
Peas 390
Peppers 320
Plums 720
Potatoes 670
Pumpkins 600
Squash 600
Sweet Potatoes 700
Tomatoes 680
Turnips 600
Miscellaneous Products Eggs in cases 200
Fertilizer 950-1000
Tobacco 550
Wool Compressed Bale 775
Wool Uncompressed Bale 200
Fresh Manure (feces and urine mixed) 1000


Notes to Table A-

  • Bulk Densities for Grain given in Table A- are test weights determined by filling a small container. When grain is dropped some distance into a bin, a 5% increase in bulk density may occur. If a grain spreader is used during filling, the bulk density will be increased further, but wall pressures will be more uniform and slightly less than if filling from a central spout. This increase has been dealt with by the 1.06 factor in the definition of
  • Bulk density at a moisture content other than 70% can be calculated as follows:

M= 30(­70) / (100 – M)


M = bulk density at moisture content M%, kg/m3

70 = bulk density at 70% (wet basis), kg/m3

M = moisture content, per cent (wet basis)


Table A- Average Silage Density in Tower Silos (av) at typical Moisture Percentage (M), kg/m3

Silo Diameter, m Alfalfa M (%) Corn Silage M (%) Ground Shelled Corn, M(%) Barley Silage, M(%)
  40 50 60 70 55 60 65 70 25 30 35 40 50 60
3.7 350 440 580 840 470 540 620 740 620 910 1030 320 350 400
4.3 370 460 620 890 500 570 660 780 6330 930 1050 630 390 420
4.9 390 490 660 950 530 600 690 810 640 950 1070 400 420 450
5.5 410 520 690 990 550 620 710 830 650 960 1080 420 440 460
6.1 440 550 730 1040 580 650 730 850 860 970 1090 460 470 480
7.3 470 590 780 1090 600 670 750 870 870 980 1110 490 500 510
9.1 530 650 850 1180 640 730 830 940 890 1000 1130 550 560 590