ISE 312 Chapter 11 (Sule) Storage and Warehousing
Spring Semester
Warehouse/Storage
> Ownership
> Location
> Size of the site
> Building Placement
> Approach Roads & Railroads Sidings
> Layout, Dock Site, & Receiving and Dispatching areas
> Column Patterns & Clear Height Needed for Vertical Storage
> Aisle Layout & Width and Number, Sizes, and Arrangement of Stacks
> Lighting, Heating, Plumbing, & Air-Conditioning
Floor Space Determination for Storage in Warehouse:
Example: Plant production is 100 cartons / day to be stored in warehouse.
Safety Stock is a 3 day supply (for production if temporarily interrupted).
Maximum time between orders is 30 days.
1. Determine the maximum & average amount of stock to be stored.
> Maximum units in stock = (Inventory for Safety) + (Number of units for a single order)
> Average units in stock = (Inventory for Safety) + (Average Amount of Cartons in Stock)
2. Determine the floor space required for storage.
Carton Dimensions: 4 x 3 x 2 (feet) Height = 2 ft.
Maximum Stack Height: 6 cartons
> Maximum Storage Space is required for 3,300 cartons.
ISE 312 Chapter 11 (Sule) Storage and Warehousing
Spring Semester
Floor Space Determination for Storage in Warehouse:
Example: Plant production is 75 units / hour.
Unit Dimensions: .5 x .5 x 1 ft.
Store one week’s supply in containers measuring 7 x 7 x 4 feet. (See Drawing).
Minimum of 3 inches of space is required between adjacent units in each direction for packaging/handling.
7 feet
7 feet
1. Determine the number of containers needed.
2. Determine floor space required stacking containers (2) high.
The number of units that can be stored in each direction must satisfy the equation:
ni wi + (ni +1)si = di
where:
wi = the dimension of the unit
si = the packing space required
di = the dimension of the package in the i direction.
Length of the container is 7 feet:
Width of the container is 7 feet:
Height of the container is 4 feet:
Number of units that can be stored in a container is n1 x n2x n3 =
Now find the number of units for the week & container requirements.
The floor space required for each stack is:
ISE 312 Chapter 11 (Sule) Storage and Warehousing
Spring Semester
Storage/Warehousing Functions:
> Receiving
> Identifying and Sorting
> Dispatching to Storage
> Storing
> Picking the Order
> Assembling the Order
> Dispatching the Shipment
> Maintaining Records
Storage Policies:
> Physical Similarity (large or small > similar material-handling equipment)
> Functional Similarity (electrically, hydraulically, or mechanically operated)
> Popularity (closer to receiving/shipping; distance traveled)
> Reserve Stock Separation (easy picking areas)
> Randomized Storage (modern information processing systems allow)
> High Security Storage (valuable items)
Stock Location:
Coding system used to quickly identify location of items of stock.
Example nine-digit number: 152012102
Building Floor Row Stack Level
15 2 012 10 2
Automated Storage Retrieval System:
High-rise storage systems, controlled by a computer.
Commonly used where:
> Numerous items in large volume
> Company unable to expand
> Located in High Labor cost area
> Extended travel & search times in the warehouse
> Delivering all orders accurately is important
> Pilferage & breakage concerns.
Four major components:
1. Storage Retrieval machines
> Stacker cranes travel at speeds around 500’ per minute
> Floor-mounted rails
> 3,000 to 4,000 pound loads
> Narrow aisles
2. Storage Structure
> 80-90’ racks typical
3. Conveying Devices
> Methods to transport items to needed departments
4. Controls
> Hardware & software
> Inventory, Maintenance, Billing, Cost Calculations
ISE 312 Chapter 11 (Sule) Storage and Warehousing
Spring Semester
Find the required number of Loading Docks:
Example: Loading from warehouse loading dock to truck. Find the minimum number of docks needed.
Given:
Average Truck Load = 4,290 lbs.
Average Productivity Rate = 7,500 lbs per worker-hour.
Assume 1 operator per dock.
Ten minutes to change trucks; Leave & Enter.
If l trucks are to be served per hour: Number of docks needed = [ l / service rate] + 1
Truck arrival follows Poisson pdf with l = 3 trucks/hour
Number of docks needed =
With 3 docks available, what are the probability characteristics of your warehouse design?
Find the probability of a truck not having to wait.
P0 = [(2.22)0 /0! +(2.22)1 /1!+(2.22)2 /2! + (2.22)3 /3! (1-(2.22)/3))]-1 = 0.0788
P1 = (2.22)1 /1! x 0.0788 = 0.175
P2 = (2.22)2 /2! x 0.0788 = 0.194
P3 = (2.22)3 /3! x 0.0788 = 0.143
Find the average number of trucks in the queue.
LQ =
ISE 312 Chapter 11 (Sule) Storage and Warehousing
Spring Semester
Find the average waiting time for the truck:
The average time spent by a truck on the premises:
W =
Given: Cost of operating (1) dock = $12 per hour (includes: operator & forklift)
Cost of truck = $16 (truck operator & truck expenses)
Cost per truck =
Find total hourly cost for trucks & docks:
On the average (3) trucks arrive per hour:
Cost per hour = .
Cost per hour =
Total hourly cost of
Number of Docks Cost of Loading / Unloading per Hour
3
4
5
M/M/C: C-1
P0 = [{ å (l/m)n } + (l/m)C x 1 ]-1
n=0 n! C! 1 – ((l/m)/C)
Pn = (l/m)n x P0 For 0 £ n £ C
n!
LQ = P0(l / m)C x (l / (mC))
C! x (1- (l / (mC)))2
LS = LQ + (l / m)
l = Arrival rate in the system
m = Service rate of each server
n = Number of customers in queue system
Pn = Probability that exactly n customers are in queuing system
C = Number of service stations available
LQ = Expected number of customers in queue
LS = Expected number of customers in queuing systems
ISE 312 Chapter 11 (Sule) Storage and Warehousing
Spring Semester
AS/R System Design:
> Dimensions & Weight of loads > Number of Units
> Throughput Rate > Number of Cranes
> Number of Rows > Building Height & Load Heights
> Number of Bays > System Length & Width
Example: Storage Building Height = 60 ft.
Load Dimension = 42” x 48” Pallets > Load Total Height = 48”
Load Weight = 2,000 lbs.
Find number of Stacks:
(6” Clearance/between = 0.5)
( 1 for Floor/Ceiling Clearance)
Find the number of Cranes:
Throughput = 50 transactions / hour.
Typical Dual Cycle Cranes = 22 cycles/hour (Wait for pickup command).
Average System Efficiency = 0.85
Find the number of Bays:
Bay = one vertical stack of storage; floor to ceiling.
Total storage requirement = 10,000 unit loads.
One crane can service two rows.
Find Required System Length:
Crane clearance = 25 ft.
(6” Clearance/between)
Find Required System Width:
Clearance = 2 ft.
Aisle width = 4 ft.
Overall System Requirements:
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