OTTOVONGUERICKE UNIVERSITT MAGDEBURG FACULTY OF VERFAHRENSTECHNIK UND SYSTEMTECHNIK

OTTO-VON-GUERICKE UNIVERSITÄT MAGDEBURG FACULTY OF VERFAHRENSTECHNIK UND SYSTEMTECHNIK STORAGE AND FLOW OF PARTICULATE SOLIDS PRESENTED BY: AHMAD GOHARI CALCULATION OF REINFORCEMENT AND WALL THICKNESS OF CONCRETE OR METAL SILOS Prof. J. Thomas 10. 12. 2013 1

TABLE OF CONTENTS 1. Introduction 1. 1. Why pressure in Silo Matter? 1. 2. Pressure in Silo, basic theory 2. Wall thickness calculation 3. The importance of flow patterns during discharge 3. 1. Eccentric discharge and its consequence 4. Structural damage and its cause, Reinforcment 4. 1. Steel and Aluminium Silo (metal) 4. 2. Concret Silos 4. 3. Reinforcement 5. Summary 10. 12. 2013 2

1. INTRODUCTION 1. 1 Why pressure in Silo Matter? Pressure in Silo is dominated by Frictional Phenomena There are many misleading on pressure calculating , not unerstanding the condition of stress nor the condiction which leads to failure Mteal and concrete Silos behave very different, different crictical consideration should be take on account (speak about it at 3. 1) 10. 12. 2013 3

1. 2. PRESSURE AND TENSTION IN SILO, BASIC THEORY Note: A smooth wall leads to higher pressure than a rough wall A slice of the wall 10. 12. 2013 4

JANSSEN PRESSURE PATERN 10. 12. 2013 5

PRESSURE IN HOPPERS 10. 12. 2013 6

SIMPLE STRUCTURE CONSEPT FOR SHAFT 10. 12. 2013 7

PRESSURE CHANGES DURING DISCHARGE OF SOLIDS (EMPTYING) Force increase in horizontal direction Force increase in vertical direction 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. 5 10. 12. 2013 8

PRESSURE 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 discharge Pieper & Wentzel 1964, in Braunschweig, much of the following comes from their work 10. 12. 2013 9

2. THICKNESS CALCULATION 10. 12. 2013 10

2. THICKNESS CALCULATION 10. 12. 2013 11

PARAMETES AND COEFICIENTS WE NEED FOR CALCULATION 10. 12. 2013 12

3. THE IMPORTANCE OF FLOW PATTERN 10. 12. 2013 A modern describtion (EN 1991 -4 2007) divides the possible flow pattern into three main categories under symetrical condition 13

3. THE IMPORTANCE OF FOLW PATTERN Note: Structural researche studies have shown that funnel flow is not critial to the strenght of metal and it is indeed beneficial (Rotter 1986 a; Teng & Rotter 1991) It is possible to determine with reasonable precision wether the silo will exhibit mass or funnel flow 10. 12. 2013 14

3. THE IMPORTANCE OF FOLW PATTERN Note: Here man can obviously see why mass flow is critical in design Typical pattern of average symetric wall pressure after filling and during emptying, for different flow channel geometries 10. 12. 2013 15

3. 1. ECCENTRIC DISCHARGE AND ITS CONSEQUENCE Flow channel geometry, typical pressure pattern and vertical wall stress during eccentric discharge 10. 12. 2013 16

3. 1. ECCENTRIC DISCHARGE AND ITS CONSEQUENCE The most damaging condition for most silos is unplanned occourence of unsymmetrical flow regimes, if the flow channel makes contact with Silo wall It 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. 10. 12. 2013 17

4. STRUCTURAL DAMAGE AND ITS CAUSE, REINFORCEMENT 4. 1. Steel and Aluminium Silos 1. 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. 10. 12. 2013 18

4. 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) 10. 12. 2013 19

4. 1. STEEL AND ALUMINIUM SILOS 4. Eccentric discharge buckling of the vertical wall This 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 wall Unsymmetrical top pile producing different height of solid-wall contact 7. Rupture, plastic deformation and buckling in hopper Hoppers made in bolted constructions are sensitive to fracture. 10. 12. 2013 20

4. 1. STEEL AND ALUMINIUM SILOS 8. Buckling and yielding in transitation rings The transition is subjecte to high compresions becuase hopper has a slop form. Both buckling and yielding failure can occur in these rings 10. 12. 2013 21

SILO FAILURE 10. 12. 2013 22

STRUCTURAL DAMAGE AND ITS CAUSE 4. 2 Concrete Silos Generaly 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 problem The thickness and good compressive strength all contribute to have an exellent strength 10. 12. 2013 23

4. 2 CONCRETE SILOS 1. Ductilty and delamination Concrete 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 pressure 3. Crack observation: care must be taken wether the cracks are caused by throu-thickness tension (very serious) or external surface tension. 10. 12. 2013 24

REINFORCEMENT 10. 12. 2013 25

REAL EXAMPLE OF A SILO REINFORCEMENT 10. 12. 2013 26

5. SUMMARY Why pressure in Silo Matter? Pressure in Silo, basic theory Wall thickness calculation The importance of flow patterns during discharge Eccentric discharge and its consequence Differences of Metal and Concrete Silos Differnt way of reinforcement of concrete 10. 12. 2013 27

QUESTIONS? 10. 12. 2013 28

REFERENCES Silo and hopper design for strength J. MICHAEL ROTTER Teaching Notes Dr. Ing. habil J. Thomas 10. 12. 2013 29