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, γ 36
6.3.3 Coefficients of wall frictionµ 36 6.3.4 Angle of inner friction, ϕi 36
6.3.7 Bulk material correction value for the reference-surface load Cop 37
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
8.1 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
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.6 determination of bulk material density γ 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 µm for the determination of loads 86 C.7.3 angle of wall friction ϕwh 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 ϕi 89
C.9.1 direct measurement 89
C.9.2 indirect measurement 91
C.10 effective elasticity module Es 93
C.10.1 direct measurement 93
C.10.2 indirect measurement 95
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
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.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
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 ϕi and ϕc 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
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:
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-à-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
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 < c b d h m hb <100 m dc <60
--- The transition from the vertical silo shaft into the hopper takes place in a simple horizontal plane (also possible in several steps) (see diagram 1a).
and inbuilt things such as discharge cones, discharge girders, consoles and spots, etc., are not covered (apart fro discharge hoppers).
4) While applying the rules for calculations made for silo bins and silo structures the following limits should be kept in mind with regard to the stored bulk material:
--- The calculation for a particular property of the bulk material has to be made for every single silo.
--- The bulk material is free flowing or it can be ensured that in special cases it behaves as free flowing material (see 3.1.12 and Annex C).
--- The maximum grain size of the bulk material is not more than (see diagram 1d). c d 03 . 0
NOTE If the bulk material particles are large in comparison with the thickness of the silo wall, the effects of the contact of individual large particles with the wall are to be regarded as a form of a deposit of individual loads.
5) While applying the rules for calculations made for silo bins and silo structures the following limits should be kept in mind with regard to the operational conditions during filling and discharging:
--- During filling the action of the forces of inertia and impact are very slight and may be ignored
--- in case of use of discharge aids (e.g. transporting equipment (feeders) or central well with absorption opening), the bulk material flow is uniform, undisturbed and central.
(a) Geometry
φ
rh
c 1h
h 2 Z *φd
ca
h
b βh
wh
of
3 4 ef β e* α eo (b) Eccentricity Legend: 1 Junction2 Equivalent bulk material surface 3 Surface contours in filled silo 4 central axis of silo
Figure 1: DIAGRAM OF SILO BINS WITH DESCRIPTION OF THE GEOMETRIC AND CHARACTERISTIC SIZES AND LOADS
2 r U A = 4 a U A = ph Pw Pv Pf Pn φdc 2r
( )
(
ba)
h U A + = 1 2 φdc a φdc b a (c) Loads φdc a r φdc( )
4 4 3 a dO U A = = 4 O d U A =( )
4 4 3 a dO U A = =6) The given load deposits on silo hoppers are applicable only for conical (generally axial symmetric shape or pyramid shape with quadratic or rectangular cross-sections) and cuneiform (generally with vertical walls at the front and the reverse sides) hoppers. Hoppers that deviate from this or hoppers with inbuilt things require specialized and greater attention.
7) Silos with symmetric axes of the geometrical horizontal projection type which change along the vertical axis are not covered by this standard. For example, silos with a hopper which blends from a cylindrical shape into a cuneiform shape fall in this category.
8) The rules for calculation for tanks apply only for fluids under normal atmospheric pressure.
9) Loads on the roofs of silos and tanks are subject to the relevant standards DIN 1055-3, DIN 1055-4, E DIN 1055-5, DIN 1055-9 and DIN 1055-10.
10) The calculations for silos with rotary operation are not within the scope of this standard.
11) The calculations for silos against dynamic stresses, which can appear during discharge, such as silo tremors, jolts, hooting and silo knocking, are not within the scope of this standard.
NOTE These phenomena remain unexplained to date. Thus, in terms of the applicability of this standard, one can neither rule out their occurrence nor ensure that the silo structure is sufficiently dimensioned for the stresses they cause.
2 REFERENCES TO OTHER STANDARDS
The documents mentioned below are required for using this standard. In case of dated references, only the edition mentioned is applicable. In case of undated references the latest edition of the document mentioned is applicable (inclusive of all revisions).
DIN 1045-1 Plain concrete, reinforced and prestressed concrete structures - Part 1: design and construction
DIN 1055-1 Actions on structures – part 1: specific gravity and surface loads of building materials, building components and storage materials
DIN 1055-3 Actions on structures – part 3: self loads and superimposed loads for high buildings
DIN 1055-4 Actions on structures – part 4: wind loads
DIN 1055-5 Actions on structures – part 5: snow and ice loads
DIN 1055-7 Actions on structures – part 7: temperature actions
DIN 1055-9 Actions on structures – part 9: unusual actions
DIN 1055-10 Actions on structures – part 10: actions due to cranes and machines
DIN 1055-100 Actions on structures – part 100: bases of structural planning: security concepts and rules for design calculations
DIN EN 26184-1 Explosion protection systems – part 1: determination of explosion indices of combustible dust in air
DIN EN 1127-1 Explosive atmospheres – explosion protection – part 1: basic concepts and methodology
DIN EN 50014 Electrical equipment for areas with explosion hazard – general specifications
ISO 3898:1997 Bases for design of structures – notations, general symbols
VDI 2263 Dust fires and dust explosions; dangers, evaluation and protective measures
VDI 3673 Sheet 1 Pressure relief of dust explosions
3 DEFINITIONS AND SYMBOLS
3.1 Definitions
The definitions given below as well as those given in DIN 1055-100 are applicable to this standard.
3.1.1
Aerated silo bottom
A silo bottom in which grooves (aeration channels) have been provided, through which air is injected in order to activate the bulk material flow in the area above the silo bottom (see figure 6b).
3.1.2
Internal diameter of a silo cross-section dc
The diameter of the largest inscribed circle of the inner cross-section of a silo bin (see figure 1d).
3.1.3
Circular silo
A silo whose ground plan or shaft cross-section shows a circular form (see figure 1 d)
3.1.4 Cohesion
Shear strength of the bulk material when direct stress does not act in the plane of breach
3.1.5
Conical hopper
A hopper in which the inclined side-surfaces converge at a point, which can – as a rule – ensure an axially symmetric flow of bulk material
3.1.6
Eccentric discharge
A flow profile in the bulk material in which the distribution of the moving bulk material is unsymmetrical with relation to the vertical central axis. This is usually due to an eccentrically placed outlet opening (see figures 3c and 3d, 4b and 4c). It can, however, also happen due to other phenomena which lead to non-symmetry (see figure 5d).
3.1.7
Eccentric filling
A situation during or after the filling of the silo, in which the peak of the banked-up bulk material surface (peak of the banked-up cone) is no longer centered in the vertical central axis of the silo (see figure 1b).
3.1.8
Equivalent bulk material surface
Height of the envisaged leveled (horizontal) bulk material surface, which is the result of the volume balance between the envisaged and the actual pattern of the surface shape (see figure 1a)
3.1.9
Hopper for “expanded flow”
A hopper in which the side surfaces in the lower part of the hopper are steep enough to create a mass flow, while the side surfaces in the upper part of the hopper have a more gradual inclination so that a core flow can be expected there (see figure 6d). This arrangement reduces the height of the hopper and at the same time ensures a reliable discharge.
3.1.10
Horizontal (silo) bottom
The inner bottom surface of the silo with an inclination that is less than 5o
3.1.11
Flow profile
The geometric form of the bulk material that is flowing out, when the flow is fully developed (see figures 2 to 5). The silo is in this case is almost completely filled-up (state of maximum fill).
Fluidized bulk material
That state of a stored powdery bulk material in which it contains a large proportion of air pockets with a pressure gradient which acts against the weight of the particles and counterbalances the same. The air can either be drawn in by means of specific ventilation or be introduced through the filling process. A bulk material is designated as fluidized even if only a part of the weight of the bulk material is counterbalanced by the air pockets.
3.1.13
Free-flowing granular material
Granular bulk material in which the flow pattern is not noticeably influenced by cohesion
3.1.14
Fully filled state
A silo is in the fully filled state when the surface of the bulk material has achieved the highest position that it can possibly acquire within the service life of the structure while the silo is in operation.
NOTE: This is taken as the ruling condition for design calculations of silos.
3.1.15 Core flow
Flow profile, in which a flow channel develops in the bulk material above the outlet opening, while the bulk material remains undisturbed in the area between the flow channel and the silo wall (see figure 2)
NOTE: The flow channel can, in such case, come into contact with the vertical silo wall – one would then term it “mixed flow” – or it can stretch right up to the surface without any point of contact whatsoever with the silo wall, in which case the term “ funnel flow” or “shaft flow” is used to describe it.
3.1.16
Granular material
Material which is composed of separate and individual grains of specific particles, with the particles having more or less equal dimensions and where the air between the individual grains plays only a marginal role in the determination of the loads and has only a marginal influence on the bulk material flow.
3.1.17
High fill speed
That condition in a silo, in which the speed of the filling leads to an intake of air of such an order that it would affect the pressure ratios at the wall.
3.1.18
Homogenizing silos
Silos in which the bulk material is homogenized with the help of fluidization, i.e. homogenized by means of mixing.
3.1.19 Hopper
Silo bottom with inclined walls
3.1.20
Hopper load ratio value F
A value which specifies the relationship between the normal load pn on the inclined hopper walls and the mean vertical load pv at this position in the bulk material.
3.1.21
Silo of medium slimness
A silo whose ratio of height to diameter lies between 1.0 < hc / dc < 2.0 NOTE: exceptions are defined in 5.3.
Flow profile with funnel flow in which the flow channel limit stretches up to the surface of the bulk material without the flow area coming into contact with the silo wall in the process (see figures 2 and 3).
3.1.23
Horizontal load ratio K
A value which specifies the relationship between the mean horizontal load pn acting on the vertical silo walls, and the mean vertical load pv at this position in the bulk material.
3.1.24
Marginal cohesion
A bulk material sample shows a marginal cohesion when the cohesion c is smaller than 4% of the pre-consolidation stress σr
NOTE a process for the determination of cohesion is given in C.9
3.1.25 Mass flow
Flow profile in which all the bulk material particles in the silo are simultaneously in motion during discharge (see figure 2a)
3.1.26 Mixed flow
Core flow profile in which the flow channel, which is still beneath the bulk material surface, comes into contact with the vertical silo walls (see figures 2c and 4)
3.1.27
Non-circular silo
3.1.28
Bulk material
A term used to describe a granular material ranging from a dust-like to a large-grained variety with and without cohesion, which contains pores in addition to and in-between the individual solid material particles that may be filled with air or moisture.
3.1.29
Reference surface load
Local load perpendicular to the vertical silo wall to be placed at any chosen height in a specific portion of its surface.
3.1.30 Funnel flow
Flow profile in which the bulk material is in motion above the outlet opening in a vertical or almost vertical flow channel, but is in a state of rest next to the flow channel (see figures 2 and 3).
NOTE If the outlet opening is placed eccentrically (see figures 3c and d) or if due to certain factors the flow channel deviates from the vertical axis above the discharge (see figure 5), the flow of the bulk material can appear against the wall.
3.1.31 Level flow
Flow profile in a silo with a rectangular or a quadratic cross-section and a slit-shaped outlet opening. The discharge slit runs parallel to two silo walls. Its length corresponds to the length of both these silo walls.
3.1.32
Powdery bulk material
Silo with braced wall
Silo with a horizontal bottom and and a height to diameter ratio of hc / dc < 0.4
3.1.34 Flat hopper
A hopper in which the full amount of wall friction is not mobilized
3.1.35 Silo
A structure for storage of bulk material
3.1.36 Slim silo
A silo with a height-diameter ratio of hc / dc > 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.
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
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
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
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)
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
aγ divergence-coefficient or conversion factor for the bulk material specific gravity
aφ divergence-coefficient or conversion factor for the angle of the internal friction
aµ divergence-coefficient (-factor) or conversion factor for the coefficients of wall
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 andeo
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
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
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 horizontalloads 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
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 thereference 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 θ for thin walled circular silos during
discharge
ppfs reference surface load at the cylinder ordinate θ 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
pvho vertical loadat 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
rc radius of the eccentric flow channel during discharge with large eccentricities
s dimensions of the area subject to the reference surface load (s = π 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 thehighest 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
∆v Incremental vertical displacements measured during the material examination
∆σ Incremental stress placed upon a specimen during material examination
3.2.5 Greek letters, small
α Mean angle of inclination of the hopper walls with reference to the horizontal
αw Coefficient of thermal elongation of the silo wall
β 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
γ Characteristic value for the specific gravity of the stored fluid or the stored bulk
material
γl Specific gravity of the bulk material in fluidized state
γu Upper characteristic values of the specific gravity of the stored fluid or the stored
bulk material
δ Standard deviation of a parameter
θ Cylindrical coordinate: angle in direction of the circumference
θc Angle at circumference of the flow channel during discharge with large
ψ Wall contact angle of the eccentric flow channel with reference to the central axis of the flow channel
µ Characteristic value of the wall friction angle at the vertical silo wall
µheff Effective or mobilized wall friction coefficient in a flat hopper
µh Wall friction coefficient in the hopper
µm Mean value of the wall friction coefficients between bulk material and silo wall
ν Poissons number for the bulk material
φc 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)
φi Characteristic value of the angle of internal friction of a bulk material in case of
equivalent load (i.e. without the portion from cohesion)
φim Mean value of the angle of internal friction
φr Angle of slope of a bulk material (conical bulk heap) (see figure 1a)
φw Wall friction angle (arc tan µ) between bulk material and hopper wall
φwh Wall friction angle in the hopper (arc tan µh) between bulk material and hopper wall
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.
(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.
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 γ, µ, K and φi.
(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.
(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 accordance with DIN 1055-100.
(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).
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 >0.25 c
o
d
e (see fig 1b)
b) low silos with an eccentric filling of more than >0.25 t o d 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.
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 accordance with DIN 1055-100.
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
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 γ 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 parametersµ, K andϕi, 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 valuesµ, K and ϕi 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.
TABLE 2 - VITAL PARAMETERS FOR THE DIFFERENT LOAD CALCULATIONS
CHARACTERISITC VALUE TO BE CALCULATED TYPE OF LOAD EXAMINED
COEFFICIENT OF WALL FRICTION µ HORIZONTAL LOAD RATIO K ANGLE OF INTERNAL FRICTION i ϕ 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
µ
Load ratio in the hopper
F Angle of internal friction ϕi
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
(
i.e.ϕwh ≤ϕi)
. 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 ϕi(
µ =tanϕw ≤tanϕi)
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)
n
mean values of the bulk material parameters, namely the mean value of the coefficient of wall frictionµm, the mean value of the horizontal load ratio and the mean value of the angle of internal friction
m
K
im ϕ .
(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)
(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
(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.
(9) In case of an eccentrically filled very slim silo ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ . . > 4 c c d h e
i , 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 un- symmetric 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 CONVERGENT
INTERNAL PARALLEL ECCENTRIC PARALLEL ECCENTRIC CONVERGENT
Funnel flow funnel flow funnel flow funnel flow
Legend
1 flow
2 flow channel limits 3 flowing funnel 4 bulk material at rest
1 3 6 3 1 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 silo’s circumferential direction
] 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
(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 ef and can be fixed at zero. et
(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 slimness
c c
d
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.
0
e
(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 b
d
h can be fixed for slimness instead of
c c
d
(14) A silo with a slimness of c c
d
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
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 wall’s 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.
(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 <10kPa as a rule, but higher sub pressures (generally 40kpa ≈ 0.4 bar) may also arise as a result of defective dimensioning of specific transporting equipment or in case of an operational fault. Silos must therefore be equipped with suitable pressure-relief devices for unforeseen occurrences, if the designing engineer cannot otherwise rule out the same.
(9) If vibrating equipment, air guns or rotary extraction arms on the silo bottom have been used, the load changes caused by these have to be examined with respect to the boundary state of fatigue, vibrations due to pneumatic transporting equipment are likewise to be taken into consideration.
(10) In case of reconditioning of existing silos by putting a lining on the silo walls, the effects of modified wall friction on silo dimensioning are to be considered, including the possible effects of a flow profile that may have undergone a change.
5.5 DIMENSIONING CONDITIONS CAUSED BUY FLUIDS STORED IN TANKS Loads on tanks caused by the fluids stored therein are to be calculated for the state of
(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
