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

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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