51989151-din-1055-6-2005silos

DIN 1055-6:2005-03

CONTENTS Page

Foreword 7

1 scope 8

2 references to other standards 10

3 terms and symbols 11

3.1 terms 11

3.2 symbols 15

3.2.1 General 15

3.2.3 Latin letters, capital 15

3.2.3 Latin letters, small 17

3.2.4 Greek letters, capital 20

3.2.5 Greek letters, small 20

4 illustration and classification of actions 21

4.1 illustration of action in silos 21

5.6 principles of calculations for explosions 30

6 bulk material parameters 31

6.1 general 31

6.2 bulk material parameters 32

6.2.1 General 32

6.2.2 Determination of bulk material parameters 34

6.2.3 Simplified procedure 35

6.3 measurement of bulk material parameters in tests 35

6.3.1 Experimental determination 35

6.3.2 Bulk material density, 36 6.3.3 Coefficients of wall friction 36 6.3.4 Angle of inner friction, i 36 6.3.5 Horizontal load ration,K 37

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6.3.6 Cohesiveness, 37 C

6.3.7 Bulk material correction value for the reference-surface load 37 opC

7 loads on vertical silo walls 38

7.1 general 38

7.2 slim silos 39

7.2.1 Fill loads on vertical silo walls 39

7.2.2 Discharge loads on vertical walls 44

7.2.3 Uniform increase of loads in place of reference-surface loads for fills and

discharges of the load-types for circular silos 49

7.2.4 Discharge loads for circular silos with large eccentricities during discharge 50

7.3 low silos and silos of medium slimness 55

7.3.1 Fill loads on the vertical walls

7.3.2 Discharge loads on the vertical walls 57

7.3.3 Large eccentricities for filling in of circular low silos and circular silos

of medium slimness 59

7.3.4 large discharge eccentricities for filling in of circular low silos and

Circular silos of medium slimness 60

7.4 silos with braced walls 61

7.4.1 Fill loads on vertical walls 61

7.4.2 Discharge loads on vertical walls 62

7.5 silos with fluidized bulk material 62

7.5.1 General 62

7.5.2 Loads in silos for storage of fluidized bulk material 62

7.6 temperature differences between bulk material and silo structure 63

7.6.1 general 63

7.6.2 loads due to a decrease in the surrounding atmospheric temperature 64

7.6.3 loads due to filling-in of hot bulk materials 64

7.7 loads in rectangular silos 65

7.7.1 Rectangular silos 65

7.7.2 Silos with internal braces 65

8 loads in silo hoppers and silo bottoms 65

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8.1 general 65

8.1.1 Physical parameters 65

8.1.2 General rules 67

8.2 horizontal silo bottoms 69

8.2.1 Vertical loads on horizontal silo bottoms in slim silos 69

8.2.2 Vertical loads on level silo bottoms in low silos and silos of

Medium slimness 69

8.3 steep hoppers 71

8.3.1 Mobilized friction 71

8.3.2 Fill loads 71

8.3.3 Discharge loads 71

8.4 flat hoppers 72

8.4.1 Mobilized friction 72

8.4.2 Fill loads 73

8.4.3 Discharge loads 73

8.5 hopper loads in silos with air-injection equipment 73

9 loads on tanks 74

9.1 general 74

9.2 loads due to stored fluids 74

9.3 parameters for fluids 74

9.4 suction loads due to insufficient aeration 74

Annex A (informative) Basis for the Planning of Structures

Rules that complement DIN 1055-100 for silos and tanks 75

A.1 general 75

A.2 border limit for load capacity 75

A.2.1 part-safety correction value 75

A.2.2 Actions on structures - Actions in silos and tanks correction value

75

A.4 conditions for calculation and action-combinations for the

Requirement categories 2 and 3 76

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A.5 action-combinations for the

Requirement category 1 77

Annex B (normative) Actions, Part-Safety Factors and Composite

Correction Values for the actions on tanks 78

B.1 general 78

B.2 actions 78

B.2.1 loads from stored fluids 78

B.2.2 loads from internal pressures 78

B.2.3 loads from temperature changes 78

B.2.4 intrinsic loads 78

B.2.5 loads from insulation 78

B.2.6 distributed working loads 79

B.2.7 concentric working loads 79

B.2.8 snow 79

B.2.9 wind 79

B.2.10 low pressure due to insufficient aeration 81

B.2.11 seismic loads 81

B.2.12 loads due to connecting structures 81

B.2.13 loads due to non-uniform settlement 81

B.2.14 catastrophic loads 81

B.3 part-safety correction values for actions 81

B.4 combination of actions 81

Annex C (normative) measurement of bulk material parameters for

Determination of silo loads 82

C.1 general 82

C.2 application 82

C.3 symbols 82

C.4 terms 83

C.5 taking of specimens and their preparation 83

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C.6 determination of bulk material density 84 C.6.1 short description 84

C.6.2 test apparatus 84

C.6.3 process / procedure 85

C.7 wall friction 85

C.7.1 general 85

C.7.2 co-efficient of wall friction m for the determination of loads 86 C.7.3 angle of wall friction wh for examining the flow behaviour 87 C.8 horizontal load ratio K 88

C.8.1 direct measurement 88

C.8.2 indirect measurement 89

C.9 stability parameters: cohesiveness c and angle of internal friction i 89 C.9.1 direct measurement 89


C.10 effective elasticity module Es 93

C.10.1 direct measurement 93


C.11 determination of the upper and lower characteristic values for the bulk

Material parameters and the determination of the conversion factor a 96

C.11.1 testing principle 96

C.11.2 assessment methods 97

Annex D (normative) assessment of bulk material parameters for determination

Of silo loads 99

D.1 goal 99

D.2 assessment of the wall friction co-efficient for a corrugated wall 99

D.3 internal friction and wall friction of a coarse-grained bulk material

Without fine particles 100

Annex E (normative) details of bulk material parameters 101

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Annex F (normative) determination of the flow profile, mass flow

And core flow 102

Annex G (normative) seismic actions 103

G.1 general 103

G.2 symbols 103

G.3 conditions for calculation 103

G.4 seismic actions 104

G.4.1 silo bottom and foundations 104

G.4.2 silo walls 104

Annex H (normative) alternative rules for determination of hopper loads 106

H.1 general 106

H.2 terms 106

H.3 symbols 106

H.4 conditions for calculation 106

H.5 loads on hopper walls 107

H.6 determination of connecting forces at the hopper junction 108

H.7 alternative equations for the hopper load correction values Fe for

The load discharge 108

Annex I (normative) action due to dust explosions 109

I.1 general 109

I.2 application 109

I.3 additional standards, guidelines and rules 109

I.4 dusts of explosive nature and their parameters 109

I.5 ignition sources 110

I.6 protective measures 110

I.7 calculation of components 111

I.8 calculation of explosive overpressure 111

I.9 calculation of negative pressure 111

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I.10 securing the closing element of the discharge opening 111

I.11 recoil forces due to pressure release 111

Diagrams

Diagram 1 illustration of silo bins with nomenclature of geometric

Parameters and loads 9

Diagram 2 basic flow profile 26

Diagram 3 flow profile with pipe flow 27

Diagram 4 flow profile with mixed bulk material flows 28

Diagram 5 effects of slimness (height to diameter ratio) on the mixed bulk

material flows and the pipe flows 28

Diagram 6 customized arrangements for fill and discharge 29

Diagram 7 conditions under which pressures due to mass flow arise 32

Diagram 8 symmetric discharge loads around the vertical silo walls 40

Diagram 9 longitudinal and cross-sectional illustrations of the load diagrams of

reference-surface loads 42

Diagram 11 longitudinal and cross-sectional illustrations of the load

diagrams of reference-surface loads during discharge 47

Diagram 12 flow channels and pressure distribution during discharge

with large eccentricities 52

Diagram 13 loads in low silos or silos with medium slimness after the

fill (fill loads) 56

Diagram 14 fill pressures during eccentric filled low silos or silos with 59

medium slimness

Diagram 15 fill pressures in a braced-wall silo 62

Diagram 16 boundaries between steep and flat hoppers 66

Diagram 17 distribution of the fill pressures in a steep and flat hopper 67

Diagram 18 bottom loads in low silos and in silos with medium slimness 70

Diagram 19 discharge pressures in a hopper with a steep and a flat inclination 72

Diagram B.1 coefficients of pressure for wind loads in circular cylindrical tanks 80

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Diagram C.1 equipment for determination of 85 Diagram C.2 test procedure for determination of the coefficients of wall friction 87

Diagram C.3 test procedure for determination of Ko 88

Diagram C.4 test procedure for determination of the angle of the internal

Friction i and c and the cohesiveness based upon the tension Created by pre-compression 90

Diagram C.5 test procedure for determination of the elasticity module during

loading and unloading 94

Diagram D.1 measurement of the profiling of the wall surface 100

Diagram F.1 demarcation of mass and core flow conditions in conical and

cuneiform hoppers 102

Diagram G.1 possible rearrangements oat the bulk material surface due to

Seismic actions 103

Diagram G.2 seismic actions on the substructure (e.g. braces) 104

Diagram G.3 cross-section through the vertical silo shaft with details of

the additional horizontal loads due to seismic actions 105

Diagram H.1 alternative rules for the hoppers 108 Tables

Table 1 classification of conditions for calculation 23

Table 2 relevant parameters for different load estimates 25

Table 3 categories of wall surfaces 34

Table A.1 composite correction values 77

Table C.1 test parameters 91

Table C.2 typical values for the coefficients of variation for the bulk

Material parameters 98

Table E.1 bulk material parameters 101

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Foreword

This standard was compiled in the NABau-AA 00.20.00 Actions on Buildings

(Spiegelausschuss zu CEN/TC/ 250/SC 1).

This standard is part of the new series DIN 1055 Actions on Structures, which consists of

the following parts:

Part 1:

Part 2:

Part 3:

Part 4:

Part 5;

Part 6;

Part 7:

Part 8:

Part 9:

Part 10:

Part 100:

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References to standards belonging to the series DIN 1055, contained in this standard,

refer exclusively to the above-mentioned new series DIN 1055.

This standard was developed by the Work Committee NABau 00.20.00 on the basis of

DIN V ENV 1991-4 and conforms largely to the draft manuscript prEN 1991-4.

Any deviations of this standard from the above-mentioned manuscript prEN 1991-4

conform by and large with possible commitments to the national safety standards so that,

in the case of an eventual ratification of EN 1991-4, this standard can be compatible in

the national context.

Revisions Vis--vis DIN 1055-6:1987-05 the following revisions have been made:

a) structural adaptation in line with the EN 1991-4

b) terminology adaptation in line with the EN 1991-4

c) adaptation of the calculation and safety concepts in line with the EN 1991-4

d) incorporation of regulations for actions due to dust-explosions

e) incorporation of regulations for actions due to earthquakes

f) incorporation of regulations for actions due to bulk material properties

Earlier Editions DIN 1055-6: 1964-11, 1987-05

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1. Scope

1) This standard contains general principles and information relating to the influences

for the design and calculations of silos for storage of bulk materials and for tanks.

It is to be applied in association with the other parts of the series DIN 1055.

2) This standard also contains stipulations for actions on silos and tanks which

extend beyond the direct action caused by the stored bulk material or fluids (e.g.

effects of temperature differences).

3) While applying the rules for calculations made for silo bins and silo structures the

following geometric limitations should be kept in mind:

--- The cross-sections of the silo bins are limited to the instances shown in diagram 1d.

Smaller deviations are allowed under the condition that the possible effects on the silo

structures due to the pressure changes resulting from these deviations will be taken into

account.

--- The foll. Limits will apply for the geometric measurements:

10 2.0, or one which fulfills the additional

conditions given in 5.3

3.1.37 Slimness Ratio of the height to diameter hc / dc of the vertical portion of the silo

3.1.38 Low silo A silo with a height-diameter ratio of 0.4 < hc / dc < 1.0 or one in which the additional

conditions as per 5.3 are fulfilled.

NOTE In case of a height-diameter ratio of hc / dc < 0.4, and if the silo contains a hopper, the silo will fall into the category of a low silo. Otherwise in case of a flat silo bottom it falls into the braced-wall

silo category.

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3.1.39 Steep hopper A hopper in which the full wall friction is mobilized after the filling

3.1.40 Stress in the bulk material Force per unit area within the stored bulk material

3.1.41 Tank A structure for storage of fluids

3.1.42 A thick-walled silo A silo with a diameter-to-wall thickness ratio which is less than dc /t = 200

3.1.43 A thin-walled silo A silo with a diameter-to-wall thickness ratio which is greater than dc /t = 200

3.1.44 Wall friction Force per unit area along the silo wall (vertical or inclined) on account of friction between

the bulk material and the silo wall.

3.1.45 Hopper junction The section between the hopper and the vertical silo wall, i.e. the transition from the

vertical part of the silo into the hopper

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3.1.46 Vertical Silo shaft The part of the silo which comprises of the vertical walls

3.1.47 Wedge-shaped hopper A hopper in which the surfaces converge at a slit for ensuring an even flow of the bulk

material; the walls of each of the other two hoppers run vertically

3.2 Symbols 3.2.1 General A list of basic symbols (letter symbols) is given in DIN 1055-100. The additional letter

symbols for this part of the standard are given below. The symbols used are based on

the conventions of ISO 3898:1997.

3.2.2 Latin letters, capital

A cross-section of the vertical shaft

Ac cross-section of the flow channel in case of eccentric discharge (large

eccentricities)

B depth parameter in case of eccentrically filled low silos

C load augmentation factor

Co discharge factor (load augmentation factor during discharge) for the bulk material

Cop bulk material parameter for the reference surface load (load augmentation factor)

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Cb load augmentation factor for the bottom loads

Ch load augmentation factor for the horizontal discharge loads

Cpe load augmentation factor for the reference surface loads during discharge

Cpf load augmentation factor for the reference surface loads in case of fill loads

CS correction value for slimness in a silo with medium slimness

CT load augmentation factor for making allowance for temperature differences or

changes

Cw correction value for discharge for the wall friction loads (load augmentation factor)

E ratio of eccentricity (during fill and discharge) to silo radius

Es effective elasticity modulus of the stored bulk material at the relevant stress level

Ew elasticity modulus of the silo wall

F relationship between the vertical loads on the silo wall and the mean vertical load

in the bulk material at this point

Fe load ratio in the hopper during the discharge (relationship between loads

perpendicular to the silo wall and mean vertical loads in the bulk material)

Ff load ratio in the hopper after the filling (relationship between loads perpendicular

to the silo wall and mean vertical loads in the bulk material)

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Fpe integral of the horizontal reference surface load for thin walled circular silos in the

case of discharge loads

Fpf integral of the horizontal reference surface load for thin walled circular silos in the

case of filling loads

G ratio of the radius of the flow channel to the radius of the internal cross-section of a

circular silo

K characteristic value of the horizontal load ratio

Km mean value of the horizontal load ratio

Ko value of K when horizontal elongation as well as principal stresses that run or are

aligned horizontally and vertically are ruled out

Pwe characteristic value of the sum total of the wall friction loads for each running

meter in the circumferential direction of the vertical silo wall in the case of

discharge loads

Pwf characteristic value of the sum total of the wall friction loads for each running

meter in the circumferential direction of the vertical silo wall in the case of fill loads

PzSk characteristic value of the wall loads for each running meter in the circumferential

direction of the vertical silo wall for low silos and large filling eccentricities

S geometry factors for the hopper loads (= 2 in the case of cone shaped hoppers, =1

in the case of wedge shaped hoppers)

U inner circumference of the cross-section of the vertical silo shaft

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Usc (inner) circumferential length of the flow channel in the contact zone up till the non

flow zone of the bulk material during discharge with large eccentricities

Uwc (inner) circumferential length of the flow channel in the contact area with the silo

wall during discharge with large eccentricities

Y depth variation function: function for the description of the increase in load with

increasing depth in the silo

YJ depth variation function of the theory acc. to Janssen

YR depth variation function for small silos

3.2.3 Latin letters, small a side length of a silo with a rectangular or a hexagonal cross-section (see figure 1d)

ax divergence-coefficient (-factor) or conversion factor for calculating the upper and

lower characteristic bulk material parameters from the mean values

aK divergence-coefficient or conversion factor for the horizontal load ratio

a divergence-coefficient or conversion factor for the bulk material specific gravity

a divergence-coefficient or conversion factor for the angle of the internal friction

a divergence-coefficient (-factor) or conversion factor for the coefficients of wall

friction

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b width of a rectangular silo (see figure 1d)

b empirical coefficient for the hopper loads

c cohesion of the bulk material

dc characteristic dimensions for the inner cross-section of the silo (see diagram 1d)

e the larger value of the eccentricities ef and eo

ec eccentricities of the central axis of the flow channel during discharge with large

eccentricities (see figure 11)

ef largest eccentricity of the bulk cone at the bulk material surface during filling (see

figure 1b)

ef,cr largest fill eccentricity for which the simplified rules for the allowance for marginal

eccentricities can be used (ef,cr = 0.25dc )

eo eccentricities of the centre point of the outlet opening (see figure 1b)

eo,cr largest eccentricity of the outlet opening for which the simplified rules for the

allowance for eccentricities can be used (eo,cr = 0.25dc )

et eccentricities of the peak of the fill-up cone at the bulk material surface when the

silo is filled up (see figure 1b)

et,,cr largest eccentricity of the fill-up cone at the bulk material surface for which the

simplified rules for the allowance for eccentricities can be used (et,,cr = 0.25dc )

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hb overall height of a silo with hopper, measured from the envisaged hopper peak, up

to the equivalent bulk material surface (see figure 1a)

hc height of the vertical silo shaft, measured from the hopper junction up to the

equivalent bulk material surface (see figure 1a)

hh height of the hopper measured from the envisaged hopper top up to the hopper

junction

ho distance between the equivalent bulk material surface and the lowest point at the

base of the bulk material cone (at the lowermost point of the silo wall which is not

in contact with the stored bulk material when the latter has been filled to the

specified extent)(see fig 1, 13 and 17)

htp total height of the back-filled cone at the bulk material surface (vertical distance

from the lowest point of the silo wall up to the tip of filled-up cone when the bulk

material, which is filled to the specified extent, is not in contact with the silo

wall)(see figures 1a and 17)

n parameters in the conditional equations of the hopper loads

p load as force per unit area

ph horizontal load from the stored bulk material (see figure 1c)

phae horizontal load in the area where the bulk material is at rest next to the flow

channel, during a discharge with large eccentricities

phce horizontal load in the flow channel during a discharge with large eccentricities

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phco asymptomatic horizontal load at a great depth in the flow channel during a

discharge with large eccentricities

phe horizontal load during discharge

phe,u horizontal load during discharge and use of the simplified calculating method

phf horizontal load after the filling

phfb horizontal loads after the filling at the lower end of the vertical shaft

phf,u horizontal loads after the filling using the simplified calculating material

pho asymptomatic horizontal loads at a great depth from the stored bulk material

phse horizontal loads in the bulk material (which is in a state of rest) at a great distance

from the flow channel during a discharge with large eccentricities

phT increase of horizontal loads as a result of temperature differences or changes

pn loads from the stored bulk material, that are perpendicular to the hopper walls (see

figure 1c)

pne loads during discharge that are perpendicular l to the hopper walls

pnf loads after the fill that are perpendicular to the hopper walls

pp reference surface loads

ppe basic value of the reference surface loads during discharge

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ppei complementary reference surface loads during discharge

ppe.nc strip shaped reference surface load for silos with non-circular cross-sections

during discharge

ppf basic value of the reference surface loads after the filling

ppfi complementary reference surface loads after the filling

ppe,nc strip shaped reference surface load for silos with non-circular cross-sections after

the filling

ppes reference surface load at the cylinder ordinate for thin walled circular silos during

discharge

ppfs reference surface load at the cylinder ordinate for thin walled circular silos after

the filling

pt friction load in the hopper (see figure 1c)

pte friction load in the hopper during discharge

ptf friction load in the hopper after the fill

pv vertical load in the bulk material (see figure 1c)

pvb vertical load at the bottom of a low silo

pvf vertical load in the bulk material after the filling

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pvft vertical load at the hopper junction after the filling (foot of the vertical silo shaft)

pvho vertical load at the foot of the filled cone at the bulk material surface according to

equation (86) and with the bulk material depth being z = ho

pvsq vertical load on the horizontal bottom of a low silo or a silo of medium slimness

pvtp geostatic vertical load at the foot of the filled cone at the bulk material surface

pw wall friction load along the vertical wall (shear force per unit area due to friction)

(see figure 1c)

pwae wall friction loads in the bulk material which is in a state of rest right next to the

flow channel during the discharge with large eccentricities (at the transition from

stationary to flowing bulk material)

pwce wall friction loads in the flow channel during discharge with large eccentricities

pwe wall friction loads during discharge

pwe,u wall friction loads during discharge using the simplified calculation method

pwf wall friction loads after the filling

pwf,u wall friction loads after the filling using the simplified calculation method

pwse wall friction loads in the bulk material which is at rest at a large distance from the

flow channel during discharge with large eccentricities

r equivalent silo radius (r = 0.5dc)

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rc radius of the eccentric flow channel during discharge with large eccentricities

s dimensions of the area subject to the reference surface load (s = dc /16 =

0.2dc)

t thickness of the silo wall

x vertical coordinate in the hopper with origin in the hopper peak (see figure 16)

z depth beneath the equivalent bulk material surface in the filled state (see figure

1a)

zo characteristic depth according to the theory of Janssen

zoc characteristic depth according to the theory of Janssen for the flow channel during

discharge with large eccentricities

zp depth of the mid-point of the reference surface load beneath the equivalent bulk

material surface in a thin-walled silo

zs depth beneath the highest point of contact between the bulk material and the silo

wall (see figures 13 and 14)

zV unit of measurement of the depth for determining the vertical loads in low silos

3.2.4 Greek letters, capital

Horizontal displacement of the upper part of a shear bin

Operator for incremental sizes (see symbols given below)

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T Temperature differences between the stored bulk material and the silo walls

v Incremental vertical displacements measured during the material examination

Incremental stress placed upon a specimen during material examination

3.2.5 Greek letters, small

Mean angle of inclination of the hopper walls with reference to the horizontal

w Coefficient of thermal elongation of the silo wall

Angle of inclination of the hopper wall with ref. to the vertical (see figures 1a and

1b) or the angle of the steepest hopper walls in a quadratic or rectangular hopper

Characteristic value for the specific gravity of the stored fluid or the stored bulk

material

l Specific gravity of the bulk material in fluidized state

u Upper characteristic values of the specific gravity of the stored fluid or the stored

bulk material

Standard deviation of a parameter

Cylindrical coordinate: angle in direction of the circumference

c Angle at circumference of the flow channel during discharge with large

eccentricities (see figure 11) with ref to the central axis of the silo shaft

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Wall contact angle of the eccentric flow channel with reference to the central axis

of the flow channel

Characteristic value of the wall friction angle at the vertical silo wall

heff Effective or mobilized wall friction coefficient in a flat hopper

h Wall friction coefficient in the hopper

m Mean value of the wall friction coefficients between bulk material and silo wall

Poissons number for the bulk material

c Characteristic value of the angle of internal friction of a precompressed bulk

material in case of relief (i.e. inclusive of the portion from cohesion)

i Characteristic value of the angle of internal friction of a bulk material in case of

equivalent load (i.e. without the portion from cohesion)

im Mean value of the angle of internal friction

r Angle of slope of a bulk material (conical bulk heap) (see figure 1a)

w Wall friction angle (arc tan ) between bulk material and hopper wall

wh Wall friction angle in the hopper (arc tan h) between bulk material and hopper wall

r Reference stress for the tests for determination of the bulk material parameters

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4 DESCRIPTION AND CLASSIFICATION OF SILOS 4.1 Description of Actions in Silos

(1) The actions on silos are to be estimated with regard to the silo structure, the

properties of the stored bulk material and the flow profiles that arise during

emptying of the silo.

(2) Ambiguities related to the flow profiles, the influence of the fill and discharge

eccentricities on the fill and discharge processes, the influence of the silo

shape and size on the type of the flow profile and those that are related to the

time-dependant discharge and fill pressures are all to be taken into

consideration

NOTE 1 The magnitude and the distribution of the rated loads depend upon the silo structure, the

material parameters of the bulk materials and the flow profiles which build up during emptying. The

inherent differences in the properties of the different bulk materials that are stored and the

simplifications in the load models lead to variations between the silo loads that actually appear and the

design loads (calculated loads) according to sections 6 and 7. Thus, to quote an example, the

distribution of discharge pressures along the silo wall changes with time. An exact prediction of the

prevailing mean pressure, its divergence and its temporal variability is not possible, given the present

level of knowledge.

(3) Allowance should be made for loads on the vertical walls of the silo when it is

filled and while it is emptying, with fill- and discharge- eccentricities being

marginal; this is to be done using a symmetric load component and an

unsymmetric reference surface load. In case of large eccentricities the loads

are to be described using a pressure distribution curve.

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(4) Should the chosen form of the silo structure show a sensitive reaction to

changes of the estimated load-guidelines, allowance has to be made for this

through appropriate investigations

(5) The symmetric loads on the silo walls are to be estimated as follows: a) by

means of horizontal load components ph upon the inner surface of the vertical

silo wall; b) by means of loads pn that act perpendicular to inclined walls; c) by

means of frictional loads pw and pt that act in the tangential direction of the

wall; and d) by means of vertical load components pv in the stored bulk material

(see figure 1c)

(6) The unsymmetric loads on the vertical silo walls in case of marginal

eccentricities during fill and discharge have to be taken into account by using a

reference surface load. These reference surface loads consist of horizontal

pressures ph that act upon the inner surface of the silo wall locally.

(7) The unsymmetric loads on the vertical silo walls in case of large eccentricities

during fill and discharge are to be additionally registered using a unsymmetric

distribution of horizontal pressures ph and friction loads pw

(8) Unplanned and unaccounted load influences are to be registered using the

load augmentation factor C.

(9) The load augmentation factors C for silo cells in categories 2 and 3 (see 4.5)

register unaccounted additional load influences alone, which arise due to the

bulk material flow during emptying of the silo.

(10) The load augmentation factors C for silo bins in category 1 (see 4.5) register

additional influences during emptying that are caused by the bulk material

movement as well as the influences due to the deviation of the bulk material

parameters.

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NOTE 2 The load augmentation factors C are intended to cover the ambiguities related to the flow

profile, the influences of eccentricities during filling and emptying, the influence of the shape of the silo

on the manner of the flow profile and proximity influences which arise when allowance is not made for

the presence of fill and discharge pressures that are time dependant. For category 1 silos (see 4.5) the

load augmentation factor also takes into account the deviation of the material properties of the bulk

material. In silos of categories 2 and 3, allowance for the deviation of the material parameters

influenced by the loads is not made by a load augmentation factor C but by the formulation of the

appropriate characteristic calculation values for the bulk material parameters , , K and i.

(11) In silos of category 1 (see 4.5) the allowance for unsymmetric loads is made by

means of an increase of the symmetric loads by applying a load augmentation

factor for the discharge loads C.

(12) In silos of categories 2 and 3 (see 4.5) allowance for the unsymmetric

reference surface loads can be made alternatively by a substitute

augmentation of the symmetric loads.

4.2 Description of Action on Tanks

(1) Allowance for loads on tanks as a consequence of filling them up is made

by hydrostatic load formulations

4.3 Classification of actions on silo bins

(1) Loads due to bulk materials stored in the silo bins are to be classified as

variable actions in accordance with DIN 1055-100.

(2) Symmetric loads on silos are to be classified as variable stationary actions in

accordance with DIN 1055-100.

40

DIN 1055-6:2005-03

(3) Reference surface loads for making allowances for the filling and discharge

processes in silo bins are to be classified as variable free actions in


(4) Eccentric loads for making allowances for the eccentric filling and discharge

processes in silo bins are to be classified as variable stationary actions.

(5) Loads arising from air or gas pressures in connection with pneumatic conveyor

systems are to be regarded as variable stationary actions.

(6) Loads due to dust explosions are to be classified as extraordinary actions as

defined by DIN 1055-100.

4.4 CLASSIFICATION OF THE INFLUENCES ON TANKS

Loads on tanks that arise due to the filling up of the tanks can be classified as variable

stationary influences acc. to DIN 1055-100.

4.5 STANDARDISED CATEGORIES

(1) Based upon the design of the silo structure and its susceptibility to different types of

malfunctions, various accuracy standards are used in the process of determining the

influences on silo structures.

(2) The silo influences should be determined in accordance with one of the following

standardized categories specified in this standard (see Table 1).

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DIN 1055-6:2005-03

TABLE 1 CLASSIFICATION OF THE DIMENSIONING CONDITIONS

STANDARDISED CATEGORIES

DESCRIPTION

standardized

category 3

Silos with a capacity of more than 10 000 tonnes

Silos with a capacity of more than 10 000 tonnes, in which one of the

foll. calculating conditions is present

a) eccentric discharge with 25.0>c

od

e (see fig 1b)

b) low silos with an eccentric filling of more than 25.0>t

od

e

standardized

category 2

all silos which are covered by this load standard and do not fall in the

other two categories

standardized

category 1 silos with a capacity of less than 100 tonnes

NOTE The differences amongst the categories listed in Table 1 have been determined

taking into account the shortfalls of an exact estimation of the influences. The rules for small silos

are simple and conservative on the safer side, as they have a robustness of their own and high

costs of an estimation of bulk material parameters for example, are not justified.

(3) A higher category for a silo than that which is required as per Table 1 can always be

chosen. For any part of the procedures (computation of loads) described in this standard,

a higher category than that in Table 1 can be taken as a basis, if required.

(4) In case several silos are connected to one another, the suitable category for each

bin should be individually determined, and not for the set of silos as a whole.

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DIN 1055-6:2005-03

5. CALCULATING CONDITIONS 5.1 GENERAL (1) The influences on silos and tanks, for each of the relevant calculating conditions,

are to be determined in compliance with the general specifications contained in DIN

1055-100.

(2) It is important that the relevant calculating conditions be observed and the critical

load types are determined.

(3) The combination rules depend on each of the verifications and are to be chosen in


NOTE The relevant combination rules are given in Annex A.

(4) Influences on account of the adjacent building structures are to be taken into

account.

(5) Influences of transporting equipment and pouring equipment are to be taken into

account. Special care is requested in case of permanently installed transporting

equipment. They can transmit loads to the silo structure across the stored bulk materials.

(6) Depending on the circumstances, the following extraordinary influences and

situations are to be taken into account:

- Influences caused by explosions

- Influences caused by vehicular impact

- Influences caused by earthquakes

- Influences caused by fire-load

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5.2 CALCULATING CONDITIONS CAUSED BY BULK MATERIAL STORED IN SILOS (1) Loads on silos caused by stored bulk materials are to be ascertained for the

maximum possible state of fullness.

(2) The loads estimates for filling and for discharge can be used as evidence for

supporting safety as well as performance capability.

(3) The dimensioning for filling and for discharge of bulk materials has to comply with

the principal load-types which can lead to differing boundary states for the structure:

- Max loads perpendicular to the vertical silo wall (horizontal loads)

- Max vertical wall friction loads on the vertical silo wall

- Max vertical loads on the silo bottom

- Max loads on the silo hoppers

(4) For determination of loads, the upper characteristic values of the bulk material

specific gravity are to be used always.

(5) The determination of the loads of a load type should always be made for a specific

combination of matching parameters , K and i , so that every boundary state is assigned a specific defined condition of the bulk material.

(6) For each of these load types its extreme value is attained when each of the bulk

material characteristic values , K and i acquires differing extreme values within the variance range of their characteristic bulk material parameters. In order to ensure

adequate safety for all boundary states during dimensioning, differing combinations of the

extreme values of these parameters have to be examined. Table 2 gives the extreme

values of the bulk material parameters which are to be used for each load types that are

to be examined.

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DIN 1055-6:2005-03

TABLE 2 - VITAL PARAMETERS FOR THE DIFFERENT LOAD CALCULATIONS

CHARACTERISITC VALUE TO BE CALCULATED

TYPE OF LOAD EXAMINED COEFFICIENT OF

WALL FRICTION

HORIZONTAL LOAD

RATIO

K

ANGLE OF INTERNAL

FRICTION

i SECTION OF VERTICAL WALL Max. horizontal load ratio

perpendicular to the vertical wall Lower limit value Upper limit value Lower limit value

Max. wall friction loads on the

vertical walls Upper limit value Upper limit value Lower limit value

Max. vertical loads on the hopper

or the silo bottom Lower limit value Lower limit value Upper limit value

Type of load examined Coefficient of wall friction

Load ratio in the hopper

F Angle of internal friction i

HOPPER WALLS Maximum hopper loads in the

filled state

Lower limit value for the

hopper Lower limit value Lower limit value

Maximum hopper loads during

discharge Lower limit value for the

hopper upper limit value upper limit value

NOTE 1 It is to be noted that the wall friction angle is always smaller or same as the angle of internal friction of the

stored bulk material ( )iwhei .. . Otherwise, when transverse stresses recorded at the wall contact surface are larger than those due to the internal friction of the bulk material itself, a slide surface develops within the bulk material. This means

that in all cases the coefficient of wall friction should not be taken as larger than tan i ( )iw tantan =

NOTE 2 The loads that are perpendicular to the hopper walls are as a rule largest when the wall friction in the

hopper is small, because thereby a smaller portion of the loads in the hopper are take away are removed through friction. It

is to be observed which maximum parameters become decisive for the individual dimensioning exercises (i.e. it is the

malfunctioning that is being examined, which determines whether the wall friction loads or loads that are perpendicular to

the hopper wall are to be calculated as maximum)

np

45

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(7) The above table notwithstanding, silos of category 1 can be dimensioned using the

mean values of the bulk material parameters, namely the mean value of the coefficient of

wall friction m , the mean value of the horizontal load ratio and the mean value of the angle of internal friction

mK

im .

(8) The fundamental equations for calculating the silo loads are given in sections 7

and 8. These are to be taken as the basis for the calculation of the following

characteristic loads:

- Filling loads on vertical wall sections (see section 7)

- Discharge loads on vertical wall sections (see section 7)

- fill and discharge loads on horizontal bottoms (see section 8)

- Fill loads on hoppers (see section 8)

- Discharge loads on hoppers (see section 8)

5.3 CALCULATING CONDITIONS CAUSED BY DIFFERING GEOMETRIC DESIGNS OF THE SILO GEOMETRY (1) Differences in slimness of silos (ratio of height to diameter), hopper geometries

and arrangements of vents lead to differences in calculating conditions and these

have to be observed.

(2) In a silo that has been filled-up, the trajectory of the filling stream of the filled up

bulk material may at times cause the build-up of an eccentric back-fill cone at the

bulk material surface (see fig 1b) and when this happens different storage

densities can arise in different parts of the silo which lead to un-symmetric loads.

While calculating the size of these loads, the largest possible eccentricity of the

filling stream is to be taken as a basis (see 7.2.1.2 and 7.3.1.2)

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(3) While dimensioning, the effects of the flow profiles are to be observed which can

be divided into the following Categories (see fig. 2):

-- Mass flow

-- funnel flow

-- mixed flow

1

2

3

4 4

3

5

4 4

2 a) MASS FLOW b) CORE FLOW C)CORE FLOW

(FUNNEL FLOW) (MIXED FLOW) Legend 1 Entire bulk material in motion 4 Bulk material at rest

2 flow 5 Effective passages

3 Limits of flow channel 6 Effective hopper

Figure 2 BASIC FLOW PROFILES

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(4) If it can be additionally ensured during funnel flow that the flow channel is always

located within the bulk material without coming into contact with the silo wall (see figures

3a and 3b), the emptying pressures can be ignored. Low silos with concentric discharge

aided by gravity and silos with a mechanical discharge system located at the bulk

material surface which ensures a build-up of funnel flow (see fig. 5a, 5b and 6a) fulfill

these conditions (see fig. 7.1 (9) and 7.3.2.1(2) and (4)).

NOTE A suitably designed central tube with lateral vents (anti dynamic tube) can

also ensure that this condition - i.e. building up an internal funnel flow - is fulfilled.

(5) In case of symmetric mass flow or a mixed flow (see fig. 2), the un-symmetric

loads that usually occur are to be taken into account during the dimensioning (see

7.2.2.2 and 7.3.2.2).

(6) In case of flow profiles with core flow (see fig 2) and partial contact of the moving

bulk material mass with the silo wall, other un-symmetric load components which

may arise specifically in this case are to be taken into account during

dimensioning (see fig 3c and 3d as well as fig 4b and 4c) (see 7.2.4).

(7) For silos with several vents and presuming a state of maximum fullness, one has

to take into account that during operation either all the vents may be opened

simultaneously or a single vent alone may be open.

(8) For silos with several vents, provisions of the combination of active vents for the

operation are to be regarded as normal calculating conditions. Other openings

which are not part of the planned operation are to be regarded as extraordinary

calculating conditions.

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(9) In case of an eccentrically filled very slim silo

> 4..c

cd

hei , the effects of mixed

flow in different areas could lead to either differing packing densities or cohesion of

the bulk material. In such cases the asymmetric alignment of the bulk material

particles can set off a unsymmetric core flow (see fig. 5d). This creates zones in

the silo where the bulk material flows along the silo wall and thereby gives rise to

un-symmetric loads. For such cases special load computations are to be used

(see 7.2.4.1 (2)).

1

2

3

1

2

3

2

3 4

1

4

1

2

3

INTERNAL CONVERGENTINTERNAL PARALLEL ECCENTRIC CONVERGENT ECCENTRIC PARALLEL Funnel flow funnel flow funnel flow funnel flow Legend 1 flow

2 flow channel limits

3 flowing funnel

4 bulk material at rest

Figure 3 FLOW PROFILES WITH FUNNEL FLOW

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DIN 1055-6:2005-03

1 3

6

31

6

2

1

3

4

5 5

(A) (B) (C) a) Concentric mixed flow b) Fully eccentric mixed flow c) Partially eccentric mixed flow Legend

1 At rest

2 Effective hopper

3 Limits of flow channel

4 Effective passage

5 Flow zone

6 Effective passage varies in the silos circumferential direction

Figure 4 FLOW PROFILE WITH MIXED FLOW OF BULK MATERIAL

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DIN 1055-6:2005-03

]

2

1

2

1

5

4

5

3

1

4 5

1

2

a) Braced wall silo b) Low silo c) Slim silo d) Very slim silo Legend 1 Bulk material at rest

2 Flow channel limits

3 Effective hopper

4 Effective passage

5 Flow

Figure 5 EFFECTS OF THE SLIMNESS (RATIO OF HEIGHT TO DIAMETER) ON THE MIXED FLOW OF THE BULK MATERIAL AND THE FUNNEL FLOW

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DIN 1055-6:2005-03

(10) For silos with pneumatically conveyed powdery bulk materials two calculating

conditions, both at maximum fullness, are to be considered:

- The bulk material filled in can develop a cone, as is the case with other bulk

materials.

- It is to be taken into account that the bulk material surface, independent of the

gradient of slope and the filling eccentricities, could possibly also be of even shape

(see fig 6c). In this case the eccentricities and can be fixed at zero. fe te

(11) In case of silos for storage of powdery bulk material where air-injection is used as

a discharge aid in the bottom area, (see fig 6b), the entire bulk material zone near

the bottom can become fluidized, which can generate an effective mass flow even

in low silos. Such silos are to be computed in accordance with the procedure for

slim silos, regardless of their actual slimnessc

cd

h .

(12) In case of silos for storage of powdery bulk material where air-injection is used as

a discharge aid in the bottom area, (see fig 6b), just a part of the bulk material

zone near the bottom can become fluidized. This can generate an eccentric mass

flow (see fig 4b), which is to be taken into account while dimensioning. The

eccentricity of the resultant flow channel and the resultant value of the eccentricity

that is to be computed are to be derived keeping in mind the fluidized zone, in

addition to the position of the vent.

0e

(13) The vertical silo walls with a discharge hopper which causes an expanded flow

(see fig 6d), can form the basis of the conditions for a mixed bulk material flow.

This can lead to un-symmetric discharge loads. In this type of silo the ratio

c

bd

h can be fixed for slimness instead of c

cd

h (see fig 1a).

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DIN 1055-6:2005-03

(14) A silo with a slimness of c

cd

h smaller than 0.4 and with a funnel hopper is to be

graded as a low silo. In case of a horizontal silo bottom this silo is to be graded as

a braced wall silo.

a) Mechanically aided discharge e.g. with a rotating space arm b) Air injection and air vents generate mass flow c) Pneumatic filling of powdery bulk material generally results in a level bulk

material surface d) Expanded flow hoppers lead to mass flow at least in the lower hopper Figure 6 - SPECIAL FILLING AND SICHARGE ARRANGEMENTS

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5.4 CALCULATING CONDITIONS CAUSED BY SPECIFIC STRUCTURAL SHAPES OF SILOS

(1) In case of dimensioning of silos fro usability, the size of fissures is to be limited to

suitable dimensions. The inspection of fissure size has to comply with the fissure

size limitation specified in DIN 1045-1 subject to the exposition categories based

on the ambient conditions of the silo.

(2) For metal silos which mainly consist of nuts and bolts, the specifications for un-

symmetric load values (reference surface loads) are to be complied with.

(3) For metal silos with rectangular cross-sections that contain beam ties within the

silo shaft for reducing the walls bending moment, the specifications in 7.7 are to

be followed.

(4) The effects of fatigue in silos and tanks are to be taken into account if they are

exposed to a load cycle more than once a day on an average. A load cycle is

equivalent to a complete filling and emptying cycle of a silo or, in the case of a air-

injection silo, a complete process conclusion (rotation) of the sectors subjected to

air-injection. Fatigue effects are also to be taken into consideration in silos which

are exposed to the influence of vibrating machines/equipment components.

(5) Prefabricated silos are to be dimensioned for the influences related to

manufacture, transport and assembly.

(6) In case of slip openings or observation holes in the silo or hopper walls, the loads

on the stopper covers are to be taken into account using double the value of the

maximum load-values upon the adjacent wall sections. These loads are to be

computed only for the dimensioning of the stopper cover and its support or

attachment structures.

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DIN 1055-6:2005-03

(7) If the silo roof has to bear loads imposed by dust filtering equipment, cyclones or

mechanical transporting equipment, then these loads are to be treated as live

loads.

(8) If pneumatic transport systems are used for filling and emptying of silos, then

loads resulting from differences in air-pressure are to be taken into account.

NOTE These loads normally amount to

DIN 1055-6:2005-03

5.6 PRINCIPLES OF DIMENSIONING FOR EXPLOSIONS

(1) As the liquids or bulk material stored in tanks or silos respectively may have a

tendency to explode, the potential damage could be limited or avoided by means

of the following measures:

-- Arrangement of adequate pressure relief areas

-- Arrangement of adequate explosion suppression systems

-- designing/dimensioning the structure for absorbing the explosive pressures

(2) A few bulk materials which are prone to explosions are listed in Annex I.

(3) The instructions given in Annex I for the explosion loads are to be followed.

Further instructions including rules for dimensioning for dust explosions can be

taken from DIN-Fachbericht 140.

(4) The effects of silo structure dust explosions upon the surrounding structures or

structural parts are to be taken into account.

6 BULK MATERIAL PARAMETERS 6.1 General

(1) For the estimation of silo loads the following influences have to be taken into

account:

the divergences from the bulk material parameters the fluctuations of the wall friction at the silo wall the silo geometry the filling and emptying processes

56

DIN 1055-6:2005-03

(2) Influences which have a favourable impact upon the bulk material stiffness may

not be taken into account while determining the loads and examining the

stability of the wall. A positive impact of a wall deformation upon the pressures

which develop in the bulk material may not be estimated, except if a

reasonable and verified method of calculation can be proved.

(3) If required, the manner of the flow profile (mass or core flow) is to be

determined from figure 7. Figure 7 may be used on the grounds of simplifying

hypotheses that have been taken as a basis - for example, the influence of

internal friction is ignored but may not be used for technical layout of silos.

NOTE The layout of the silo geometry for a mass flow is beyond the scope of this standard. The methods and procedures specific to bulk material technology have to be used for this purpose.

(a) conical hopper

0

0.2

0.4

0.6

0.8

1

1.2

0 20 24 40 60

Series1

1

2

Co-

effic

ient

of w

all f

rictio

n in

the

hopp

er

h

Angle of inclination of hopper

57

DIN 1055-6:2005-03

(b) cuneiform hopper

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 8

0

Series1

Co-

effic

ient

of w

all f

rictio

n in

the

hopp

er h

1

2

Angle of inclination of hopper

Legend 1 area with core flow

2 areas with the possibility of mass flow

Figure 7 CONDITIONS UNDER WHICH PRESSURES CAUSED BY MASS FLOW ARISE

6.2 Bulk Material Parameters 6.2.1 General

(1) The material properties of the bulk material stored in the silos, which are to be

quantified for calculating the loads, are to be derived or obtained either as test results or

as data in any other suitable form.

(2) While using values from test results and other sources of data, the same are to be

evaluated in a suitable manner keeping in mind the type of load in question in each case.

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DIN 1055-6:2005-03

(3) It should be kept in mind that there may be significant differences between the

material parameters measured in tests and the parameters that are determined by the

actual behaviour of the bulk material in the silo.

(4) While evaluating the differences in bulk material parameters mentioned in (3), the

following are some of the factors that must be kept in mind:

a lot of parameters are not constant, and may be dependant upon the stress level and the background of load application

Influences on account of particle shape, sizes and distribution of grain size can have a strong impact on the test and the silo in a variety of ways.

temporal influences

fluctuations of the moisture content

influences of dynamic actions

brittleness or ductility of the tested bulk material

the manner of putting-in the bulk material in the silo and in the testing apparatus

(5) While evaluating the differences in bulk material parameters mentioned in (3) with

ref. to the coefficients of wall friction, the following factors must be kept in mind:

corrosion and chemical reaction of the bulk material particles, dampness and the wall

abrasion and wear which can roughen or smoothen the wall of the silo

59

DIN 1055-6:2005-03

polishing of the wall surface

accumulation of fat deposits on the wall

particles which get impressed in the wall surface (usually an influence which leads to the roughening of the wall surface)

(6) While determining the values for the material parameters the following is to be

kept in mind:

the facts regarding the application of the relevant tests should be well-publicised and common knowledge

a comparison of the values of the individual parameters which have been measured in the tests with the corresponding published parameters, taking

into account the experimental values

the deviation of the parameters relevant to the calculations

the results obtained from the large scale measurements on silos of similar styles

correlation of results from different types of tests

perceptible changes in the material parameters during the period when the silo is in use

(7) The choice of the characteristic material parameters has to be made on the basis

of values the have been determined through laboratory tests, with due regard for

know-how acquired through experience.

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DIN 1055-6:2005-03

(8) The characteristic value of a material is to be chosen after a careful evaluation of

the value which has influenced the occurrence of the load.

CATEGORY DESCRIPTION OF WALL-

SURFACE TYPES OF MATERIAL

D1 Polished

Cold-rolled stainless steel

Scarred stainless steel

Polished stainless steel

Galvanized carbon steel

Aluminium

Extruded high-density polyethylene

D2 Smooth

Carbon steel with slight surface corrosion

Coated carbon steel

Cast high-density polyethylene

Smooth ceramic plates

Concrete surface manufactured with steel shell

D3 Rough

Rough shell concrete

Scarred carbon steel

Steel silos with bolts on the inside surface of the

wall

Roughly polished ceramic plates

D4 Corrugated

Horizontal corrugated wall

Contoured sheet metal with horizontal notches

Non-standardised walls with large deviations

The effect of wrinkling in these surfaces has to be very carefully examined by means of the

particles embedded in the wall surface.

NOTE The classification and description given in Table 3 refers to the friction

rather than the roughness. The main reason for this is that there is only a small

correlation between the degree of roughness and the measured amount of wall friction

caused by the bulk material that slides along the wall surface.

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DIN 1055-6:2005-03

6.2.2 Determination of the Bulk Material Parameter (1) The material parameters to be used for the design calculation may have deviations

due to the changes in the structure, the production procedure, the grain size

distribution, moisture content, age and electrical charging during handling; these

need to be taken into account.

(2) The bulk material parameters are to be determined either according to the

simplified procedure laid down in 6.2.3 or by means of test measurements in

accordance with 6.3.

(3) Bulk materials parameters which are not contained in Table E.1 are to be obtained

by means of test measurements in accordance with 6.3.

(4) The calculated correction values for the coefficient of wall friction of the bulk

materials should take into account the roughness of the wall surface along which

they glide. In Table 3 the different classes of wall surfaces are defined for use in

this standard.

(5) For silos with wall surfaces belonging to the class (category) D4 according to

Table 3, the effective wall friction coefficients should be determined according to

the procedure described in D.2.

(6) The bulk material correction value Cop for the reference surface loads is to be

taken from Table E.1 or calculated according to the equation (8).

6.2.3 Simplified Procedure

(1) The parameters of commonly known bulk materials are to be taken from the Table

E.1. The values given there for the specific gravity correspond to the upper

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DIN 1055-6:2005-03

characteristic value, while the parameters for the wall friction m, for the horizontal

load ratio Km and for the angle of the internal friction im represent mean values of

these characteristic quantities.

(2) If individual bulk materials cannot be clearly classified under the bulk material

categories listed in Table E.1, then their parameters are to be determined

experimentally in accordance with the procedure described under 6.3

(3) For determining the characteristic parameters of , K and i, the listed values of

m, Km and im are to be multiplied or divided by the so called conversion factor.

The conversion factors ax are given in the table E.1 for the bulk materials listed

therein. For calculating the maximum loads, the following combinations are to be

used:

Upper characteristic value of mk KaK = (1)

Lower characteristic value of k

ma

KK = (2)

Upper characteristic value of ma = (3) Lower characteristic value of

am= (4)

Upper characteristic value of imi a = (5) Lower characteristic value of

aimi = (6)

(4) For determining the effect of action on silos of the requirement category 1, the

mean values m, Km and im may be used instead of the upper and lower characteristic

values.

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6.3 Measurement of Bulk Material Parameters in Tests 6.3.1 Experimental Determination (Measuring System)

(1) The experimental determination of the parameters is to be executed with

representative bulk material specimens. For every bulk material property a mean value of

the relevant parameter is to be determined keeping in mind the deviation of its relevant

so-called secondary influence parameter such as bulk material structure, filtering curve,

moisture content, temperature, age and the possibility of electrical charging during

operation or manufacture.

(2) The characteristic values are derived from the experimentally determined mean

values with the aid of equations (1) to (6) and the corresponding conversion factors ax.

(3) Each conversion factor ax is to be carefully determined. While determining the

same one should take into account the fact that the bulk material parameters can

undergo a change during the service life of the silo. Likewise, the possible consequences

of the sedimentation phenomena in the silo and the inaccuracies during processing of the

material specimens are to be taken into account.

(4) If the test data is there, the conversion factors ax are to be ascertained acc. to

C.11 in order to determine the standard deviation of the parameters.

(5) The span between the mean value and the characteristic value of the bulk material

parameter is expressed by the conversion factor ax. If a secondary influence parameter is

by itself responsible for more than 75% of the conversion factor ax, it has to be raised by

a factor of 1.10.

NOTE The above-mentioned specifications serve to ensure that the values of xx adequately represent the probability of occurrence for the derived loads.

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6.3.2 Specific Gravity of the Bulk Material (1) The specific gravity of the bulk material is to be determined for such a packing

density of the bulk material particles and at such a pressure-level, which corresponds to

the packing density or the pressure level that is present in the zone of maximum vertical

fill-pressure bzw in the silo. The vertical pressure Pvft can be determined from the

equations (11) or (86) for the depth of the bulk material at the lower end of the silo shaft.

(2) For measuring the specific gravity the test procedures acc. to C.6 should be used.

(3) The conversion factor for deriving the characteristic value from the measured

value is to be determined in accordance with the procedure described in C.11. The

conversion factor a may not be less than a = 1.10, except when a smaller value can be

separately established through tests or a suitable estimation (see C.11).

6.3.3 Coefficient of Wall Friction

(1) The experimental determination of the coefficients of wall friction for the estimation of loads is to be determined for such a packing density of the bulk material

particles and at such a pressure-level, which corresponds to the packing density or the

pressure level that is present in the zone of maximum horizontal fill-pressure Phfb in the

silo. The pressure level Phfb can be determined from the equations (9) or (78) for the

depth of the bulk material at the lower end of the zone with vertical walls. (2) For measuring the coefficients of wall friction the test procedures acc. to C.7 should be used.

(3) The mean value m of the coefficients of wall friction and its standard deviation are to be determined and derived through tests. If only one mean value can be ascertained

from the data material, the standard deviation is to be estimated in accordance with the

method described in C.11.

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conversion factor may not be less than a = 1.10, except when a smaller value can be


6.3.4 Angle of Internal Friction i (1) The angle of internal friction i for the calculation of loads is to be determined as arc tangents from the ratio of the shear force to the normal force at the break under

equivalent load - for such a packing density of the bulk material particles and at such a

pressure-level, which corresponds to the packing density or the pressure level that is

present in the zone of maximum vertical fill-pressure Pvf. The pressure level Pvf can be

determined from the equations (11) or (86) for the depth of the bulk material at the lower

end of the zone with vertical walls.

(2) For measuring the angle of internal friction i the test procedures acc. to C.9 should be used.

(3) The mean value im of the angle of internal friction and its standard deviation are to be determined and derived through tests. If only one mean value can be ascertained

from the data material, the standard deviation is to be estimated in accordance with the




conversion factor a may not be less than a = 1.10, except when a smaller value can be


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6.3.5 Horizontal Load Ratio K

(1) The horizontal load ratio K for the estimation of loads (the ratio of mean horizontal

pressure to mean vertical pressure) is to be determined for such a packing density of the

bulk material particles and at such a pressure-level, which corresponds to the packing

density or the pressure level that is present in the zone of maximum vertical fill-pressure.

The pressure level pvft can be determined from the equations (11) or (86) for the depth of

the bulk material at the lower end of the zone with vertical walls.

(2) For measuring the horizontal load ratio K the test procedures acc. to C.8 should be

used.

(3) The mean value Km of the horizontal load ratio and its standard deviation are to be

determined and derived through tests. If only one mean value can be ascertained from

the data material, the standard deviation is to be estimated in accordance with the


(4) An approximate value for Km can be alternatively calculated according to the foll.

Equation (7) from the mean value of the angle of internal friction for first load application

im determined through tests (see 6.3.4)

Km = 1.1 (1- sin im) (7)

NOTE The factor 1.1 in equation (7) is used in order to ensure an appropriate derivative unit of measure for making allowance for the difference between a value of K (= Ko ) that was

measured under virtually absent wall-friction influences and a value of K that was measured in

the presence of wall friction influences (see also 6.2.2 (5)).

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conversion factor aK may not be less than aK = 1.10, except when a smaller value can be


6.3.6 Cohesion c

(1) The cohesion of bulk material varies with the consolidation stress to which the

specimen is subjected. It is to be determined for such a packing density of the bulk

material particles and at such a pressure-level, which corresponds to the packing density

or the pressure level that is present in the zone of maximum vertical fill-pressure Pvf. The

pressure level Pvf can be determined from the equations (11) or (86) for the bulk material

depth at the lower end of the zone with vertical walls.

(2) For measuring the cohesion c the test procedures acc. to C.9 should be used.

NOTE Alternatively the cohesion can be estimated by means of results of tests in the shear cells of Janike. A method for calculating the cohesion from test results is to be taken from C.9.

6.3.7 Bulk material Correction Value for the Reference Surface Load Cop (1) The bulk material correction value for the reference surface load Cop is to be

estimated on the basis of suitable test data.

NOTE 1 The discharge factors C make allowances for a host of phenomena which arise during the

emptying of silos. The symmetric increase of pressures is relatively independent of the stored bulk material,

yet the unsymmetric components are greatly dependant upon the material. The material-dependency of the

unsymmetric components is represented by the bulk material correction value Cop . This parameter is not

easy to determine with the help of experimental test procedures.

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NOTE 2 A suitable experimental test procedure for the parameter Cop has not so far been

developed. This factor is therefore based on evaluations of tests on silos and on experimental values of

silos with conventional filling and discharge systems, which were established within the usual structural

tolerances.

(2) Values for the bulk material correction values for the reference surface load Cop of

commonly known bulk materials are to be taken from Table E.1.

(3) For materials which are not listed in Table E.1, the bulk material correction value

for the reference surface load can be estimated from the divergence factors for the

horizontal load ratio aK and the wall friction correction value a acc. to equation (8):

Cop = 3.5 a = 2.5 aK 6.2

Where

a divergence factor for the coefficients of wall friction ;

aK divergence factor for the horizontal load ratio K of the bulk

Material.

(4) For special silos or special bulk materials (in the individual case) the suitable bulk

material correction value for the reference surface load Cop can be estimated by means of

large scale experimental investigations in silos with designs that are comparable.

7 LOADS ON VERTICAL SILO WALLS 7.1 General (1) For the filling and the emptying types of loads, the characteristic values of the

loads described in this section have to be fixed. For this purpose the loads are

differentiated as follows:

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slim silos silos of medium slimness low silos braced walls silos (silos consisting of braced walls) silos for the storage of bulk materials air pockets between the bulk material

particles (for example, due to pneumatic discharge aids and homogenizing

silos)

silo hoppers and silo bottoms

(2) The loads on the vertical silo walls are to be determined in accordance with the

following criteria pertaining to the slimness of the silos:

slim silos, with 2.0 < hc / dc (with exceptions acc. to 5.3) silos with medium slimness, with 1.0 < hc / dc < 2.0 (with exceptions acc. to

5.3)

low silos, with, 0.4 < hc / dc < 1.0 (with exceptions acc. to 5.3) braced wall silos (silos consisting of braced walls) with horizontal bottoms

and hc / dc < 0.4

silos for bulk materials with air pockets between the bulk material particles

(3) A silo with an aerated bottom is to be handled independent of its actual slimness

hc/ dc -- like a slim silo.

(4) The loads on the vertical walls are made up of a stationary load component, the

symmetrical loads and a free load component, the reference surface loads. Both the

components are to be assessed as acting simultaneously.

(5) Special types of loads are to be taken into account for large fill and discharge

eccentricities. These are not to be placed simultaneously with the symmetrical and

reference surface loads; each represents a separate and clearly defined load category.

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(6) Detailed guidelines for the calculation of fill and discharge loads are given within

the context of silo slimness in sections 7.2, 7.3 and 7.4.

(7) Rules for the additional types of loads for special types of silos and special design

conditions are given in 7.5 till 7.7:

see 7.5 for silos with air injection equipment for complete or partial fluidization of bulk material

see 7.6 for loads due to hot-filled bulk materials see 7.7 for loads in rectangular silos

(8) For circular silos with large fill and discharge eccentricities, load estimates are

given in 7.2.4. For non-circular silo bins corresponding load estimates should be derived

from these load estimates, if they are found to be suitable for design calculations.

(9) If funnel flow can be ensured within the bulk material without contact points

between the flow zone and the silo walls (see 5.3 (4)), the calculations can be limited to

the estimates of the filling loads, in which case the reference surface loads are to be

taken into account along with these, if required.

7.2 Slim Silos 7.2.1 Fill Loads on Vertical Walls 7.2.1.1 Symmetric Fill Loads

(1) The symmetric fill loads (see figure 8) are to be calculated acc. to the equations

(9) to (14).

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(2) After the filling is done and during the storage of the bulk material, the horizontal loads

Phf, the wall friction loads Pwf and the vertical loads Pvf are to be estimated as follows:

(9) ( ) ( )zYPzP jhohf =

( ) ( )zYPzP jhowf = (10)

( ) ( )zYKPzP jhovf = (11)

With

oho KzP = (12)

UA

Kzo

1= (13)

( ) ozzj ezY =1 (14) Where

The characteristic value of the bulk material specific gravity

The characteristic value for the coefficients of wall friction for the bulk material at the vertical silo walls

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K The characteristic value of the horizontal load ratio

z The depth of the silo material beneath the equivalent surface of the bulk

material

A The inner cross-sectional area of the silo

U The circumference of the inner cross-sectional area of the silo

(3) For the status after the filling is done, the resultant characteristic value of the wall

friction loads Pwf that have been added-up up till depth z with the force per unit of length

in the direction of the circumference e.g. [kN/M] is calculated using:

(15) ( ) ( )[ ]zYzzPdzzPP johoz wfwf == 0

(4) For determining the characteristic values for the required bulk material parameters

(specific gravity (), correction value for wall friction and horizontal load ratio K), the values given in 6.2 and 6.3 are to be used.

7.2.1.2 Reference Surface Load for Filling Loads: General Requirements

(1) For making an allowance for unplanned unsymmetrical loads due to eccentricities

and imperfections during the filling of the silos, reference surface loads or other suitable

load arrangements are to be placed.

(2) For silos of category 1 the reference surface load can be ignored for the filling

loads.

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Legend 1 equivalent bulk material surface

1

vfPwfP

wfP

z

hchfP

z1

hfP Figure 8 SYMMETRIC FILLING LOADS NEAR THE VERTICAL SILO WALLS

3) For silos in which powdery bulk material is stored and which are filled with the help

of air injection equipment, the placing of reference surface loads for the filling loads can,

as a rule, be done away with.

(4) The amount of reference surface load to be placed for the filling loads Ppf is to be

estimated on the basis of the maximum possible eccentricity ef the filled cone that

appears at the surface of the bulk material (see fig. 1b).

(5) The fundamental value of the reference surface load for the filling load Ppf is to be

fixed with:

hfpfpf PCP = (16)

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With:

( )

+=

15.1

2 12121.0 cc

dh

oppf eECC (17)

c

f

de

E2= (18)

But pfC > 0 (19)

Where

fe Is the maximum eccentricity of the filled cone which appears at the

Bulk material surface during filling;

hfP Is the local value of the horizontal fill pressure acc. to equation (9) at

the position at which the reference surface load is placed

opC Is the correction value of the bulk material for the reference surface

load (see table E.1).

(6) The height of the zone at which the reference surface load is to be placed (see

figures 9 and 10) amounts to:

cc dds 2.0

16= (20)

(7) The reference surface load consists of only a horizontally acting load component.

There are no frictional forces to be taken into account as a result of these

horizontal load components.

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(8) The form of the reference surface load for the filling loads depends upon the

structural design of the silo. The following structural designs of silos can be

distinguished with respect to the reference surface load to be placed:

-- Thick walled silos with circular cross-section see figure7.2.1.3 (e.g.

reinforced concrete silos);

-- thin walled silos with circular cross sections, see figure 7.2.14 (e.g. metal

silos without braces);

-- Silos with non-circular cross-sections, see 7.2.1.5

a) Thin walled circular silo b) other circular silo

S

Ppf1

Ppf

PpfPpf

S S

S

z php

a

hc

Ppfs

Ppf

h

Ppf

Figure 9 - Longitudinal Section and Transverse SectionDiagrams of the Reference Surface Loads b

s

Showing the Load

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Ppe,ncPpf,nc

P pe,

nc

P pf,n

c

P pe,

nc

] p

pf,n

c

S

a

h c

S a

h c

Legend

a smaller value of zo and hc/2

b as per choice

Figure 10 LONGITUDNAL SECTION AND TRANSVERSE SECTION SHOWING THE LOAD DIAGRAMS OF THE REFERENCE SURFACE LOADS FOR NON-CIRCULAR SILOS

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7.2.1.3 Reference Surface Load for Filling Loads: Thick-Walled Circular Silos

(1) For thick-walled circular silos of the categories 2 and 3, the fundamental value of

The reference surface load for the filling load is to be estimated as it acts outwards pfP

Along the opposite sides of a quadratic reference surface with the side length s (see

equation (20)). The unit of measurement for the side length s should be applied to

the curved surface in a suitable manner.

2) In addition to the reference surface load that acts outwards, a complementary pfP

Reference surface load that is directed inwards is to be placed in the remaining

portion of the silo circumference above the same wall-height (see fig. 9b):

pfiP

pfiP = 7pfP (21)

Where

pfP is the fundamental value of the reference surface load acting outwards

for the filling loads acc. to equation (16)

NOTE The amount and the impact area of the load which is directed inwards are chosen

such that the resultants of both the load components counterbalance each other in the

middle at the position at which these are to be placed.

pfiP

(3) The reference surface load for the filling loads is to be placed at any

position on the silo wall. However it may be placed in accordance with the manner

described in 7.2.1.3(4).

(4) In thick-walled circular silos of category 2, a simplified proof may be furnished.

Half the height of the vertical bin shaft may be regarded as the most unfavourable

Position for placing the reference surface load. The largest percentage increase of the

dimensioning sections which result from the placing of reference surface loads at this

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position can be carried over to the other areas of the wall by multiplying over there the

design sectional sizes with the value of the ratio between the horizontal fill pressure at

the observed position and the horizontal fill pressure at the position where the reference

surface load was placed.

7.2.1.4 Reference Surface Load for the Filling loads: Thin-Walled Circular Silos

(1) For thin-walled circular silos (dc/t > 200)

51989151-din-1055-6-2005silos

Documents

vertical loads

discharge loads

surface loads

rectangular silos

slim silos

circular low silos

uniform increase of

vertical walls