steel silo failure case study

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ReviewReportClient Cement CompanyUnburned clinker steel silo

11/18/2011

11/18/2011 Eng.Amed Saeed Civil Eng.Khaled Eid,Msc,PE Civil

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Date Written by Reviewed by Approved by Version

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Contents1 Introduction .......................................................................................................................................... 3

2 Unburned clinker silo ............................................................................................................................ 3

2.1 Received documents and drawings .............................................................................................. 4

2.2 Review methodology .................................................................................................................... 5

3 Analysis input data ................................................................................................................................ 5

3.1 Finite Element Program ................................................................................................................ 5

3.2 Temperature effect ....................................................................................................................... 6

3.3 Wind load ...................................................................................................................................... 6

4 Design .................................................................................................................................................... 6

4.1.1 Silo wall ................................................................................................................................. 6

4.1.2 Silo bottom hopper ............................................................................................................... 7

4.1.3 Silo roof ................................................................................................................................. 7

4.1.4 Silo supporting concrete structure ....................................................................................... 7

5 Fabrication and erection ....................................................................................................................... 8

6 Summary and conclusion ...................................................................................................................... 9

7 Recommendation .................................................................................................................................. 9

References .................................................................................................................................................. 10

Appendix 1 ................................................................................................................................................. 11

Appendix 2 ................................................................................................................................................. 12

Appendix 3 ................................................................................................................................................. 13

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1 IntroductionClient Cement (CLIENT) plant is located in Client, El‐karak

Jordon 90 Km south Amman. The dry process plant has a

production of 5000 ton per day started commissioning in

September 2010.

Mechanically designed by XXX, Germany referred

in this report as “the mechanical designer”.

Managed by the consultant HOLTEC, India

referred in this report as “the consultant”.

Civil design engineer TEM, Turkey referred in this

report as the” designer or civil designer”.

The contractor is the MID CONTRACTING,

AMMAN referred in this report as” the

contractor”.

At the request of Client cement from RHI to review the

structural design and construction integrity for the

unburned clinker silo

RHI visited the site on 29th of November 2011and talked

to concerned parties then inspected the silo, it was

noticed the silo is empty and material is accumulated on

the concrete platform below as a sign of emergency

discharge. Stair access was covered with material in such

it is during initial filling operation the silo bottom deformed as shown and there are is sign of

deformation at the supporting ring beam also there is a crushing in the bearing area at the silo support

Refer to appendix 1 for photos.

2 UnburnedclinkersiloThe under burnet silo is designed to store the rejected clinker so it may be recycled by some ratio in the

process again. Usually stored in silos either steel or concrete. In our case it is a steel silo with a designed

capacity of 1500 ton based on clinker density of 1.3 ton/m3, the silo diameter is 10 meter and height of

16.0 meter with a flat bottom hopper bottom diameter of 7.5 meter and height of 3.75 meter. The silo

is supported at level 15.2 on four concrete beams supported in four concrete columns.

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2.1 ReceiveddocumentsanddrawingsThese drawing were submitted by Client Cement Company as the latest general arrangement drawings.

Fabrication details of under burner “XXX” 841‐89‐756‐B A sheet 1

Fabrication details of under burner “XXX” 841‐89‐756‐B A sheet 2

Clinker transport and storage gernal arrangement 841‐27‐249‐U A

KCP‐15‐C‐001_05.dwg ( 15‐UNBURNT CLINKER HOPPER) FOUNDATION PLAN

KCP‐15‐C‐002_01.dwg ( 15‐UNBURNT CLINKER HOPPER) +2.500 LEVEL FORMWORK PLAN




KCP‐15‐C‐006_01.dwg ( 15‐UNBURNT CLINKER HOPPER) COLUMN APPLICATION PLAN ‐ C1‐C2‐C3

KCP‐15‐C‐007_00.dwg ( 15‐UNBURNT CLINKER HOPPER) +2.500 LEVEL SLAB REINFORCEMENT

PLAN


PLAN


PLAN


PLAN

KCP‐15‐C‐011_00.dwg ( 15‐UNBURNT CLINKER HOPPER) REBAR DETAILS OF FOUNDATIONS

KCP‐15‐C‐011_01.dwg ( 15‐UNBURNT CLINKER HOPPER) REBAR DETAILS OF FOUNDATIONS

KCP‐15‐C‐012_00.dwg ( 15‐UNBURNT CLINKER HOPPER) BEAM DETAILS ‐ B001‐B002‐B003‐B004‐

B005‐B006 B101‐B102‐B103‐B104‐

B105‐B106‐B107B108‐B109‐B110‐B204

KCP‐15‐C‐013_03.dwg ( 15‐UNBURNT CLINKER HOPPER) BEAM DETAILS ‐B111‐B201‐B202‐B203‐

B205‐B206 B207‐B208‐B209‐B210‐

B211‐B212‐B213‐B214‐B215‐B216‐B301

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KCP‐15‐C‐014_02.dwg ( 15‐UNBURNT CLINKER HOPPER) STAIR PLAN AND DETAILS

2.2 ReviewmethodologyDespite of RHI requested several times from CLIENT to provide the original design calculation but we did not get anything till now which raise a question if this structure was already designed by XXX or not? And how it was approved if there is no supporting design document? Thus review methodology was applied by making an independent set of check analysis and calculations, according to material and plate thickness provided in the drawings. The following are the codes and standards used in review

BS EN 1991‐4:2006 Actions on structures Silos and

tanks.

Loads combinations to the ASCE 7‐05 “minimum design

loads of structure”

Wind, snow and thermal loads are according to the

Jordanian loading code.

Design of steel members as per the American code

AISC‐ASD.

Mechanical loads applied exactly as provided by XXX

only wind loads are calculated.

3 Analysisinputdata

3.1 FiniteElementProgramThere is no program yet to predict the material flow so in this study the silo buckling behavior was investigated with linear buckling analysis of SAP 2000 (Nonlinear v.14). SAP 2000 is a general purpose structural finite element analysis program. All circumferential and longitudinal stiffeners were modeled as frame elements.

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3.2 TemperatureeffectThe outer walls of the silo can expand during day and contract at night as the temperature drops , if there is no discharge taking place and material inside the silo is free flowing , it will settle as the silo expands because it cannot pushed back up when the silo wall contract . A temperature difference of 100 degree is considered due to the average effect of hot clinker when entering the silo.

3.3 Windload Circular bins, on the other hand, are very sensitive to wind loading because of the varying pressure/suction distribution of the wind loading around the circumference, and the lack of stiffness of the shell in resisting this loading. The required thickness of plate in the upper strakes of a circular bin is often determined by the wind loading. Wind buckling is characterized by the formation of one or more buckles on the windward face of the shell. Wind also produces an overturning moment on a tall bin, which induces a vertical compressive stress in the leeward face; this reached a maximum at the base of the bin, where the shell needs to be checked against buckling

4 DesignAs stated before no information

about how this silo is designed to

which code, did any changed in either

height or bottom during erection ? no

historical information available.

So this report will not be able to judge the design calculation but will only refer to the as built on site

and XXX drawing 841‐89‐756BA rev 2.

4.1.1 Silo wallSilo material does not act like a fluid; dry materials have frictional or cohesive resistance and tend to form domes with the silo wall that prevents it from falling freely downward. The lateral pressure on the silo shell from the dry materials is of different character than the lateral pressure on the retaining wall from soil at the back of the wall.

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The designer applies a constant 10mm thickness for the wall and the bottom hopper; practically it is too small when considering allowance for rust and aberration for such large size silos. The critical buckling stress in the wall is governing the thickness required to carry the vertical compression load. It was found by analysis that the silo wall is only safe at the top third of the silo but in all other location is unsafe stress and buckling.

4.1.2 Silo bottomhopperThe bottom hopper is designed as 10mm with a diameter of 7.5 meter stiffened by angle 75x10, it is found to be away unsafe as well. Refer to appendix 3 for details.

4.1.3 SiloroofThe top roof with plate 10mm is found to be sufficient to support the applied live loads but the supporting steel beams are unsafe (the beam spans for seven meters and supporting a width of one and half meter and assigned as UPN 200).

4.1.4 Silo supporting concretestructure

The silo is supported in four bearing points on a

200cmx90cm concrete beams by visual inspection

these beams suffering from diagonal cracks and

concrete crushing at one of the bearing points,

further more concrete beams at level 8.4 suffering

vertical cracks in both sides .

It is also visually noticed in some location some

concrete honeycombs creating a voids in the

concrete beams and left without curing that is also

raise a question about the concrete quality.

RHI requested the concrete structure drawings and run and in depended checking for the whole

structure.

IT was found that the supporting beams to be unsafe in shear with evidence of the shear crack, while

for level 8.4 all beams are safe according to the design so the cracks may be as a reason of the falling

material on the apron feeder when the silo bottom deforms.

Refer to appendix 2 for supporting structure checking.

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5 FabricationanderectionAlthough appropriate sizes as per the design drawing are used but many fabrication and erection errors

are spotted during inspection giving a bad impression about the quality control.

1. The bottom stiffeners are tack welded and not in full contact with the silo body.

2. The stiffeners are not continues with a gap at mid span where a beigest load.

3. The bottom stiffeners are not connected to the vertical ones thus they are not transferring the

load to the supports.

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6 Summaryandconclusion

Our study concludes that the

steel silo is under designed

suffering many design issues

These issues are summarized

as follows

The supporting

concrete beam is just

safe in bending but

unsafe in shear by 18% this explains the 45 degrees cracks .

Due to the bottom excessive deformation it damaged the apron feeder with a material falls

adding unexpected loaded on the concrete beams at level 8.4 creating cracks in these beams.

The party most responsible for the bottom collapse was the designer because all items are

unsafe the walls, the flat bottom, the stiffening, the ring beam and the roof, not a single item in

this silo is found to be safe.

The erector and fabricator work was away from standard leading to decrease more the capacity

however this will not alone lead to the collapse

There is no sign for any excessive usage, lack of maintenance or operational misuse.

7 RecommendationWe propose the following actions as part of the rectification

We tried many repair alternative but none of them solve all issues so we recommend

replacing the silo as the best option.

It is advisable to support the silo on eight points to distribute the concentrated load by

adding steel beams at 45degree.

The supporting beams will need to be strengthened against shear.

Cracked beams in level 8.4 should be strengthened.

Concrete building should be inspected for any construction deficiencies and repaired before

filling the silo.

Concrete core test may be required to evaluate the constructed concrete quality and if

possible to check the existing steel bars and stirrups at random location.

No access to the silo support to allow for inspection at bearings it is recommended to add ladder from level 8.4 to 15.2

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References

1. American Welding Society (AWS), 550 NW 42d Avenue, Miami, FL 22126.

2. Rubin M. Zallen, P.E., ”Collapse of steel silo”

3. American Iron and Steel Institute (AISI), 1101 17th St., NW, Suite 1300, Washington,

4. Bahaa Machaly., ”Structural systems for wind and earthquake loads”.

5. The Jordanian loading code “Arabic original copy” Amman 2006.

6. ACI standards 313‐91, “Standard practice fordesing and construction of concrete silos and

stacking for storing granular materials”

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Appendix1

Site Photos

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Appendix2

Concretebuildingreview

Notincludedinthiseducationalcopy

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Appendix3

Analysisanddesigncheckingforsilo

Not included in this education copy