PowerPoint Presentation
Otto-von-Guericke Universitt MagdeburgFaculty of
verfahrenstechniK und SystemtechnikStorage and Flow of Particulate
Solids
Presented by: AHmad Gohari
Calculation of reinforcement and wall thickness of concrete or
metal silos110.12.2013
Prof. J. Thomas112/10/2013Otto-von-Guericke Universitt
MagdeburgTable of contents10.12.201321. Introduction1.1. Why
pressure in Silo Matter?1.2. Pressure in Silo, basic theory2. Wall
thickness calculation3. The importance of flow patterns during
discharge3.1. Eccentric discharge and its consequence4. Structural
damage and its cause, Reinforcment4.1. Steel and Aluminium Silo
(metal)4.2. Concret Silos4.3. Reinforcement5. Summary1.
Introduction1.1 Why pressure in Silo Matter?
Pressure in Silo is dominated by Frictional PhenomenaThere are
many misleading on pressure calculating , not unerstanding the
condition of stress nor the condiction which leads to failureMteal
and concrete Silos behave very different, different crictical
consideration should be take on account (speak about it at 3.1)
310.12.2013312/10/2013Otto-von-Guericke Universitt Magdeburg1.2.
Pressure and Tenstion in Silo, Basic theory
Note: A smooth wall leads to higher pressure than a rough wallA
slice of the wall410.12.2013Otto-von-Guericke Universitt
Magdeburg12/10/20134Janssen Pressure Patern
510.12.2013Pressure in hoppers
610.12.2013Simple structure consept for Shaft
710.12.2013Pressure changes during discharge of solids
(emptying)
Note: Kp/Kf at first considered to be order of 9 and then 6,
this much pressure increase had been never reported before, several
theories (Arnold 1980, Jenke 1973) showed that Kp/Kf should be
around 2.5Force increase in horizontal directionForce increase in
vertical direction810.12.2013Pressure changes during discharge of
solids (emptying)
Note: The most critical finding for silo design was the pattern
of unsymmetrical pressures, both after filling and during
discharge. The ratio of the largest sustained pressure to the
smallest at a single level could be high as 2.8 under static
condiction after filling and 5.6 during dischargePieper &
Wentzel 1964, in Braunschweig, much of the following comes from
their work 910.12.20132. Thickness calculation10
10.12.20132. Thickness calculation11
10.12.2013Parametes and coeficients we need for calculation
12
10.12.20133. The importance of flow patternA modern describtion
(EN 1991-4 2007) divides the possible flow pattern into three main
categories under symetrical condition
1310.12.20133. The importance of folw patternIt is possible to
determine with reasonable precision wether the silo will exhibit
mass or funnel flow
Note: Structural researche studies have shown that funnel flow
is not critial to the strenght of metal and it is indeed beneficial
(Rotter 1986a; Teng & Rotter 1991)1410.12.20133. The importance
of folw pattern
Typical pattern of average symetric wall pressure after filling
and during emptying, for different flow channel geometriesNote:
Here man can obviously see why mass flow is critical in
design1510.12.20133.1. Eccentric discharge and its consequence
Flow channel geometry, typical pressure pattern and vertical
wall stress during eccentric discharge
1610.12.20133.1. Eccentric discharge and its consequenceThe most
damaging condition for most silos is unplanned occourence of
unsymmetrical flow regimes, if the flow channel makes contact with
Silo wallIt is mabye necessary to have off-center discharge outlet
for functional reasons and conditions in silo such as blockage of
the feeders, therml or moisture or segregation of
content.1710.12.20134. Structural damage and its cause,
reinforcement4.1. Steel and Aluminium Silos1. Bolted and welded
construction:The first big differnce in metal silos are the Joints
that is used in metal Silos construction. The joints are the lines
of weakness, so the should be made stronger than is strictly
necessary.2. Brusting of vertical wall: Brusting failurs are very
uncommon and are almost all found in bolted silos where a joint
details has failed.3. Axial compression bulcking of vertical wall:
This failur is not also so common but should be seriously
considered because this mode of failure is often dramatically
catastrophic. It can be also result of unsymmetric pressure against
the silo wall.
1810.12.20134. Structural damage and its cause
Note: Bulking under axial compression occur at very low stresses
compared with the material strength (perhaps at 20 Mpa in a metal
with yield stress 250 Mpa)1910.12.20134.1. Steel and Aluminium
Silos4. Eccentric discharge buckling of the vertical wallThis is
the commonest cause of axial compression buckels, where the low
pressure against the wall in the flow channel cause high vertical
compressive stresses over part of the perimeter near the mid-height
of the silo, in which the whole silo falls over in the direction of
discharge outlet.5. External pressure buckling of the vertical wall
When a Silo is empty the thin wall is very sensitive to buckling
under extreme wind.6. Shear buckling of the vertical
wallUnsymmetrical top pile producing different height of solid-wall
contact7. Rupture, plastic deformation and buckling in
hopperHoppers made in bolted constructions are sensitive to
fracture.
2010.12.20134.1. Steel and Aluminium Silos8. Buckling and
yielding in transitation ringsThe transition is subjecte to high
compresions becuase hopper has a slop form. Both buckling and
yielding failure can occur in these rings
2110.12.2013Silo Failure10.12.201322
Structural damage and its cause4.2 Concrete SilosGeneraly
Concrete is good in compression but can not resist tensile stress
at all .When concrete is subjected to tension, it cracks at right
angles to the tension.Concrete should be reinforced for sure.The
simpleset way is to prestresse the concrete with steel. It can
avoid the tension.Vertical compressions does not usually cause
problemThe thickness and good compressive strength all contribute
to have an exellent strength
2310.12.20134.2 Concrete Silos1. Ductilty and
delaminationConcrete is a brittle material, but most structural
design relies on ductile manner. In particular shear failures in
concrete wall can cause serious cracking. With appropriate
reinforcement concrete structure behave also like ductile. An other
brittle problem delamination, layer of concrete separate.2.
Cracking under bending moment:The main problem of conrete is
cracking under bending moment induced by unsymmetric pressure3.
Crack observation: care must be taken wether the cracks are caused
by throu-thickness tension (very serious) or external surface
tension.
2410.12.2013Reinforcement25
10.12.2013Real Example of a Silo Reinforcement10.12.201326
5. SummaryWhy pressure in Silo Matter?Pressure in Silo, basic
theoryWall thickness calculationThe importance of flow patterns
during dischargeEccentric discharge and its consequenceDifferences
of Metal and Concrete SilosDiffernt way of reinforcement of
concrete2710.12.2013Questions?2810.12.2013ReferencesSilo and hopper
design for strengthJ. MICHAEL ROTTER
Teaching NotesDr.Ing.habil J. Thomas2910.12.2013