FAILURES AND REPAIR

OF

SILOS AND BUNKERS

STRUCTURAL DISTRESS OF SILOS AND BUNKERS :DESIGN ERROR OR INADEQUACYCONSTRUCTION ERRORSMISUSEEXPLOSION OR OTHER UNEXPECTED LOADING

TYPES OF STRUCTURAL FAILURES :FOUNDATION FAILUREFAILURES IN WALLSROOFS FAILUREFAILURES IN HOPPER SYSTEMS

FOUNDATION FAILURES :TILTING OF CANADIAN PACIFIC RAILROAD (CPR) ELEVATOR,TRANSCONA, CANADA.

FAILURES OF CONCRETE SILO WALLS :DESIGN ERROR OR INADEQUACY

Failure to consider Overpressure Effect of horizontal variation of pressure Shock Loading Thermal Stresses Pressure due to Flow improving devices Use of incorrect material properties

FAILURES OF CONCRETE SILO WALLS :DESIGN ERROR OR INADEQUACYCONSTRUCTION ERRORS

Missing or misplaced hoop reinforcement Difficulties with slip forming

FAILURES OF CONCRETE SILO WALLS :DESIGN ERROR OR INADEQUACYCONSTRUCTION ERRORSUSAGE ERROR

Storing materials other than the material for which the structure was designed. Installing additional discharge openings.

FAILURES OF CONCRETE SILO WALLS :DESIGN ERROR OR INADEQUACYCONSTRUCTION ERRORSUSAGE ERRORFOUNDATION MOVEMENT

FAILURES OF CONCRETE SILO WALLS :DESIGN ERROR OR INADEQUACYCONSTRUCTION ERRORSUSAGE ERRORFOUNDATION MOVEMENTSHRINKAGE AND CREEP

FAILURES OF CONCRETE SILO WALLS :CORE REASON : Nothing will happen, we are designing from so many years its always like this only.! TAKE IT FOR GRANTED ATTITUDE..

FAILURES OF CONCRETE SILO WALLS :Horizontal bending, combined with horizontal tension is perhaps, most serious cause of wall cracking.

Horizontal bending will occur under all load conditions in any NON-CIRCULAR silos.

In CIRCULAR silos, that are subdivided .

FAILURES OF CONCRETE SILO WALLS :In SINGLE CIRCULAR SILO, horizontal bending will occur whenever lateral pressure vary around the circumference at any particular level.

This variation will be present under all condition except that of a single central discharge opening with a symmetrical centrally located flow channel.

FAILURES OF CONCRETE SILO WALLS :NO HORIZONTAL BENDINGHORIZONTAL BENDING MUST CONSIDERED

FAILURES OF CONCRETE SILO WALLS :Since many circular silos have been designed assuming the wall to be in tension only, (ignoring bending)It is not surprising that walls of circular silos often have bed vertical cracks.

When multiple openings are used, the horizontal bending may subject to reverse.

FAILURES OF CONCRETE SILO WALLS :ECONOMY : - A SAILENT KILLER Resistance to failure under combined bending and tension is highly dependent on reinforcement position in the wall. where the bending moment is reversible, two layers of reinforcing is preferred. then also, in the interest of economy, engineers frequently specify single layer reinforcement.

FAILURES OF CONCRETE SILO WALLS :ECONOMY : - A SAILENT KILLER The single layer is easier to handle than two layers during slip forming. Two layer reinforcing requires more labor to place than the single layer.

However, TWO LAYER DESIGN PROVIDES MUCH BETTER PROTECTION AGAINST WALL CRACKING.

FAILURES OF CONCRETE SILO WALLS : A CASE STUDY 1:-FAILURE OF POCKET BIN WALL : Group of Cement Storage Silos.CONSTRUCTION ERROR : The vertical spacing of the horizontal steel in the bin wall varied and most sections exceeded the specifiecd spacing. Location of horizontal bars were close to outside face of the wall, some were near the center and some near the inside face.

FAILURES OF CONCRETE SILO WALLS : A CASE STUDY 1:-FAILURE OF POCKET BIN WALL :DETAILING ERROR :The incorrect tie detail shown by the drawing Inadequate anchorage of the Main horizontal steel detail in the drawing.

FAILURES OF CONCRETE SILO WALLS :

FAILURES OF CONCRETE SILO WALLS :A CASE STUDY 2:-DAMAGED GRAIN ELEVATOR :

FAILURES OF CONCRETE SILO WALLS :A CASE STUDY 2:-DAMAGED GRAIN ELEVATOR : CONSTRUCTION PROBLEM : Missing Bars DESIGN DEFICIENCY : Ignoring Over pressure USAGE PROBLEM : Storing Peas rather than wheat as assumed in design.

FAILURES OF CONCRETE SILO WALLS :A CASE STUDY 3:-CEMENT SILO WITH SERIOUS WALL CRACKS :

FAILURES OF CONCRETE SILO WALLS :A CASE STUDY 3:-CEMENT SILO WITH SERIOUS WALL CRACKS : REASON : Stored Material Over pressure REPAIR METHOD : Post Tensioning using wire winding method

FAILURES OF CONCRETE SILO WALLS :A CASE STUDY 4:-COLLAPSED BIN AT AUSTRIA (WEAT STORAGE) : Continuous emptying and refilling kept the grain constantly in motion , creating high flow induced overpressure. Other silos subjected serious cracks. Repaired by External wire winding.

FAILURES OF CONCRETE SILO WALLS :A CASE STUDY 5 :-SERIOUS DEMAGE OF SILOS AT UNITED STATES : REASON : Reinforcement were inadequate and faulty construction

REPAIR TECHNOLOGIES :

REPAIR TECHNOLOGIES :REPAIR SCHEMES : Determination of full extent of damage & its effects on Safety. Cause of Damage Various possible Methods Economic Analysis.

REPAIR TECHNOLOGIES :ALWAYS REMEMBER.. An effective repair should not merely return the structure to its original unfailed condition, but should also Eliminate the cause of the Structure So strengthen the structure that those causes no longer pose a threat to it

REPAIR TECHNOLOGIES :GANERALIZED METHODS : EPOY GROUTING SHOTCRETING CAST IN SITU LINER CONSTRUCTION EXTERNAL PRESTRESSING ( WIRE WINDING)

REPAIR TECHNOLOGIES :EPOXY GROUTING : Filling the Cracks with epoxy where there is no other damage. Spalled area of walls were reinforcing steel will exposed, should be patched with grout.

REPAIR TECHNOLOGIES :SHOTCRITING : For patching lifts, fallouts and other holes and indentations in the silo walls. It is applied under high pressure. It sticks very well to a existing surface,. More dense than regular concrete.

REPAIR TECHNOLOGIES :STRENGTHN BY LINER : It is the construction of concrete wall over existing wall at internal or external face of the silos. It may be cast in place concrete slip formed shotcrete

REPAIR TECHNOLOGIES :STRENGTHN BY LINER :SHOTCRET LINER AROUND SILO WALLSHOTCRET LINER INSIDE SILO WALL

A CASE STUDY :

EXTERNAL REPAIR OF CRACKED GRAIN SILOS.

ABOUT CASE STUDY :The main grain storage : 60 concrete silos Arranged in 3 clusters One cluster consists of 20 silosConfigurations : Capacity : 3100 tons Diameter : 12 m Height : 37 mDraw-off openings are located concentrically at the base of the each silo.

ABOUT CASE STUDY :12 m37 mSteel Hopper180 mmOne Cluster of 20 silos

DISTRESS PROBLEM : Silos are located in a region of high rainfall.

Subjected to salt water spray from nearby ocean.

DISTRESS PROBLEM :CRACK PATTERN :

Cracks were typically 350 mm apart. Most cracks were wider than 0.2 mm Some cracks were wider than 1 mm A few cracks were so wide that water had penetrated into the silos.

REPAIR SCHEME :POST TENSIONE THE SILOS WITH EXTERNAL TENDONS CONSTRUCTING NEW RCC WALLS WITHIN THE EXISTING SILOS

REPAIR SCHEME : The repair scheme that was chosen involver adding reinforced concrete to the exterior walls of the silo clusters. No repair was made to any internal walls as they are surrounded by external silo walls.

POINT OF INTEREST :THE EXTERIOR REPAIR OF SINGLE SILO IS WELL KNOWNTHE EXTERNAL JACKETING OF AN ENTIRE SILO CLUSTER IS INNOVATIVE

POINT TO BE TAKEN CARE.. With the exterior walls repaired, the WEAK LINK in the structure would seem to be the buttress walls between exterior silos.

However, the buttress walls have two layers of reinforcement, and thus have batter crack control characteristics than the original exterior walls which had only one layer of reinforcement.

POINT TO BE TAKEN CARE.. Critical condition when two silos are unloaded simultaneously. During withdrawal, the horizontal pressure exerted by the grain is believed to increase by about 60% from the static case. To prevent overloading, an operational limitation was implemented

STRENGTHNING TECHNIQUE ..Original Reinforcement Detail of 180 mm thick silo wall

STRENGTHNING TECHNIQUE ..Roughened the surface of about 700 mm

STRENGTHNING TECHNIQUE ..

STRENGTHNING TECHNIQUE ..

STRENGTHNING TECHNIQUE ..External concrete wall of 125 mm extra was cased.

CONSTRUCTION METHODOLOGY..Method of Construction : SHOTCRITING

The silos were to be full of grain when the new concrete was applied to the outside in order to reduce the effect of restrained shrinkage.

The silos had to remain full until the shotcrete had cured sufficiently.

CONSTRUCTION METHODOLOGY..Method of Construction : SHOTCRITING

An appropriate shotcrete for this repair project is one that provides Required Strength Good bond to the original Concrete Corrosion protection for new reinforcement.

THANK YOU

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