choosing storage options - geapsangola.com · part i: concrete vs. steel bins michael blough...

4/17/2017

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Choosing Storage OptionsPART I: CONCRETE VS. STEEL BINS

Michael Blough

Project Engineer, Clear Creek & Associates

Presentation OverviewStorage History

• Brief Summary

Design and Planning

• Site Layout

• Design & Applied Loading

• Cost

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Presentation Overview

Construction

• Concrete Construction Process

• Steel Construction Process

• Time Lapse Videos


Grain Management

• Filling and Unloading

• Flow of Materials

• Aeration

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Structural Maintenance

• Corrosion

• Damage

• Repair Methods

• Life Expectancy

Storage History

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History of Grain Storage• Facilities that handled over 2 million bushels

used to be concrete clusters

• Grain bin storage was maxing out at 750k

bushels per bin

• Conveying at 40k bph was high speed

• Filling large dia. bins took days to weeks

• Soil loads at 4000psf allowable bearing

pressure were great to build on.

Grain Facilities Today• Facilities can have over 2 million bushels in 2

corrugated bins

• A single grain bin is capable of storing 1.3

million bushels

• Conveying has moved toward 100k bph

• Now able to fill large diameter bins in hours,

not days.

• Geopiers, pilings, soil additives, & soil with

5000psf allowable bearing pressure is being

required.

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Grain Facilities Today• Grain facilities have evolved to a highly

complex operation compared to the past.

• More automation for high volume incoming &

outbound grain.

• Higher level of consideration to operations,

safety, cleanliness, & maintenance.

Design and Planning

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Design and Planning:Site Layout

Site Layout – Concrete

• Located in areas with limited space

• Built taller than steel bin structures

• Towers often not required for conveying equipment

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Site Layout – Concrete• Circular bin layout

• Capacity increased by using the interstice

bins (star bins)

Site Layout – Concrete• Hexagonal bin layout

Reference: www.rmdkwikform.com

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Site Layout – Steel• Located throughout the site to allow space

for vehicular traffic, flow of materials, and

rail lines

• Don’t require soil to be as firm (lower bearing

capacity) as concrete in order to support the

weight of the structure

Design and Planning:Design & Applied

Loading

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Typical Grain Bin Loads• Filling

• Unloading

• Temperature Cables

• Wind

• Seismic (Earthquake)

• Snow

• Aeration

Design & Applied Loading

Concrete

• Able to withstand more intense filling and

unloading cycles

• Better for resisting high impact loading

• Typically able to better resist wind and snow

loading

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Design & Applied Loading

Steel

• Flexible structural behavior

• Empty steel bin generally provides better

behavior in seismic event than concrete silo

• Provides poor resistance for lateral bracing for

towers or equipment

Design and Planning:Costs

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Costs

• The current difference in cost per

bushel for construction is low as

compared to historical differentials.

• Steel silos generally provide a

greater storage capacity per dollar

and tend to be more cost-effective

as compared to concrete.

Factors to Consider

• Increasing diameter – larger

foundation, larger and/or greater

capacity roof, increased catwalk

length

• Increasing height – longer bucket

elevator, larger tower foundations

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Cost per Bushel vs. Bin Capacity

Reference: Kenkel, P. Oklahoma State University

Construction

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Construction:Concrete Construction

Process

Construction Process• Concrete silos are typically

constructed by jump-forming or

slip-forming.

• Slip-forming

• Complicated process requiring extensive

supervision because it is continuous.

• Rebar placement and concrete affect the

quality of the final product.

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Production of Materials• Concrete is batched in a controlled

environment, but variability of strength is

introduced with variations in ingredients size

and quantity.

• Individual strength tests of concrete can fall

below up to 10% of f’c (compressive

strength) as long as the average of tests

equal or exceed f’c.

Reference: ACI 318-11, Sec. 5.6.3.3

Site Storage Before Installation

• Concrete is greatly affected by delivery time

and weather.

• Concrete produced must be placed very

soon after arriving on site. In general,

concrete starts to lose its optimal

characteristics after 2 hours (From time of

production at batch plant).

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Concrete Silos Time Lapse

Concrete Silos Time Lapse

Reference: YouTube.com, “Trupointe Cooperative, Inc.” YouTube

channel

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Construction:Steel Construction

Process

Construction Process• Erection of bin can be done with minimal

supervision.

• Installation of openings in bins (e.g. doors)

and accessories (e.g. ladders) are easy to

complete.

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Production of Materials• Steel bin components are manufactured in

a controlled environment . Slight variance of

quality.

• ASTM specifications require minimum yield

and ultimate steel strength used in design

• To meet the ASTM specification (e.g. A36,

A992) the steel is produced to be greater

than or equal to minimum yield and ultimate

steel strength.

Site Storage Before Installation• Steel bin

components that are not installed immediately maintain structural strength over a long period of time on site.

• Moisture between galvanized sheets

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Steel Bin Time Lapse

Steel Bin Time Lapse

Reference: YouTube.com, “Grass Roots Media” YouTube channel

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Grain Management

Grain Management:Filling and Unloading

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Filling and Unloading – Concrete• Concrete has the rigidity to withstand the

effects of eccentric loading

• Concrete wall thickness

• Bracing against other bins

Filling and Unloading – Steel• The sheets and

stiffeners of steel bins are susceptible to damage and/or collapse if they experience off-center unloading or loading

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Filling of Grain Bins• Center Fill

• Vertical Drop

Off-Center Loading

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Maintaining Unloading Conditions

Free Flowing

• Clean

• Dry

• In Condition

Issues with Poor Conditions

• Grain develops clumps

• Foreign items end up in the

conveyors

• Grain goes out of condition and

becomes non-free flowing

• Gates plug

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1. Core bin from

center gate

2. Unload from

center gate

until grain

stops flowing

3. Unload from

intermediate

gates, moving

out from bin

center

Correct Unloading - Floor Gates

Off-Center Unloading

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Concrete Hopper Bottoms• The construction process lends itself to

hopper bottoms underneath making complete

cleanout possible without sweep augers

Filling and Unloading – Steel• Large bins require quality, commercial-

grade sweep auger for complete cleanout

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Steel Hopper Bottom• Hopper bottoms typically 36 ft. diameter or less

• Require structural columns to elevate tank

• Generally 10 rings tall or less

Grain Management:Flow of Materials

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Flow of Materials

Reference: ASABE EP 433

Dec. 1988 (R2006)

Funnel Flow

Reference: Jenike & Johanson (www.jenike.com)

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Mass Flow

Reference: Jenike & Johanson (www.jenike.com)

Flow of Materials

Function of:

• Finish of the interior surface (smoothness)

• Angle of the hopper

• Height/Diameter ratio

• Grain material properties

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Flow of Materials – Concrete

• Higher coefficient of friction

of grain

• Mass flow difficult to achieve,

likely funnel flow

• Funnel Flow = First-In,

Last-Out (FILO)

Flow of Materials – Steel

• Lower coefficient of friction of grain

• Mass flow or funnel flow

• Mass Flow = First-In, First-Out

(FIFO)

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Grain Management:Aeration

Aeration

• The horsepower required to

operate an aeration system is a

non-linear function of grain depth

• Often impossible or impractical

to provide the same airflow in

concrete silos that could be

achieved in shorter, wider

steel bins.

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Structural Maintenance

Structural Maintenance :

Corrosion

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Corrosion

• Corrosion is a concern for both

concrete and steel

• Concrete protects steel in

concrete silos

• Sheets on steel bin are exposed

Corrosion –Concrete Silos

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Exposed Reinforcing Steel


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Concrete Cracking

Concrete Cracking

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Moisture Infiltration


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Corrosion – Steel Bins

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Steel Corrosion

Steel Corrosion

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Steel Corrosion

Steel Corrosion

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Stiffener Buckling Caused by Corrosion

Steel Material Loss• Bins are not designed with a

corrosion allowance.

• Many older bins were not designed using

current, typical grain loads (ASABE 433).

• Recommendations for material losses:

• 0% to 5% - Acceptable for regular use

• 5% to 10% - Close monitoring and

regular inspections

• > 10% - Replace component/sheet

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Damage and Repair Methods

Concrete Damage

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Excessive Wearing

Spalling

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Spalling


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Delamination

Delamination

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Concrete Cracking

Concrete Inspection

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Delamination Test

Solid sound • Good bond between

rebar and concrete

Slapping/Popping sound • Delamination of the

rebar and concrete

Delamination Test

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Delamination Test

Reference: YouTube.com, “Tyler Smith” YouTube channel

Crack Monitoring

Recommended to better understand

damage and to determine if there is

cracking growth

• Marked with marker or paint for growth

progress

• Crack monitors installed across cracks

• Easy to install

• Very inexpensive

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Crack Monitors

•

Concrete Repair

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Crack and Patch Repair

Remove Concrete Damage

• Remove loose, delaminated concrete or

debris in the affected region.

• Undercutting of corroded reinforcing steel

may be required if concrete is delaminated

behind the reinforcement.

• Cut the spalled area perpendicular to

the surface.

• Reference: ICRI 310.1R-2008

Delamination Repair

Reference: International Concrete Repair Institute

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Crack and Patch RepairPrepare Steel Reinforcement

• Review and check steel reinforcement to determine if

the reinforcement will still meet the original diameter

specification after the cleaning the bar of rust.

• If it is suspected that the reinforcement will not meet

the original diameter specifications, contact a

structural engineer to replace or reinforce the steel.

• Remove rust from steel reinforcement using a wire

wheel or sandblasting.

Reference: ICRI 310.1R-2008


Prepare Concrete Surface

• Prepare the surface with a wire wheel

grinder to remove dust, debris, damaged

concrete that prevent proper bonding.

• For cracking, grind out and open cracks.


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Repair Concrete and Steel

• Treat the steel reinforcement with a

rust inhibitor.

• Apply bonding agent to concrete surface.

• Patch small concrete areas with high-yield

non-shrink cement grout

• Patch large areas with Shotcrete/Gunite

• Inject high-yield, non-shrink caulk into cracks.


Sealing Cracks

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Surface Repair vs. Structural Repair

• Surface Repair

• Patch repair

• Crack injection

• Structural Repair

• Shotcrete/Gunite liner in silos

• Carbon fiber

Shotcrete Installation

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Shotcrete Installation

Reference: YouTube.com, “mhvone” YouTube channel

Steel Damage

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Damage from Unloading

Buckled Stiffeners

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Wind Damage

Damaged Sheets and Stiffeners

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Damaged Sheets and Stiffeners

Roof Damage

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Steel Repair

Steel Bin Repair

• Refer to manufacturer’s

recommendations

• Remove damaged bin components

and replace with new components

• If bolts are removed always

replace with new bolts

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Life Expectancy

Life Expectancy - Concrete

• Concrete silos have a longer

useful life expectancy than steel

bins. With proper maintenance

concrete silos can last 70+ years

• Repair methods (e.g. silo liners)

can extend this life

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Life Expectancy - Steel

• A steel bin’s useful life is around 40

to 50 years even with proper

maintenance

• Repair methods like replacing

components usually cost as much

or more than replacing the

structure at this age

Thank youQuestions can be emailed to [email protected]

choosing storage options - geapsangola.com · part i: concrete vs. steel bins michael blough...

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