IntroductionWhen planning how a warehouse will operate, three factors need careful attention:Accessibility.Material handling and storage equipment.Packaging and unit loads.The previous lesson looked at the warehouse as a node in the distribution network (types of distribution centers, cross-docking, picking and location). This lesson moves to the warehouse floor: how to arrange materials and which equipment to use to move and store them.AccessibilityAccessibility means being able to reach the material you need as quickly and cheaply as possible, with the least effort. It depends on two things.The first is a well-structured location system that identifies where each material is stored. The most common approach treats the warehouse as a three-dimensional coordinate system: aisle, bay or column (the position along the aisle), and level (the height). Sometimes a fourth reference identifies the position within a level.Each pallet rack position has an address: aisle, bay and levelThe second is the physical layout: how materials are arranged. A good layout lets workers retrieve an item without moving others. One highly flexible example is a storage yard served by an overhead crane. Identical materials, such as steel coils, can be stacked and lifted out from above. Aisles are not even needed because access is vertical.The video above, from a report on coffee warehouses in southern Minas, shows how the arrangement of lots determines whether a product is easy or difficult to reach.What to consider when deciding where to store each materialStorage methods must follow the manufacturer's recommendations on temperature, weather protection and maximum stacking height. They should also account for:Size and weight. Bulky or very heavy items belong near the exit, preferably at floor level, to shorten travel distances and reduce risk.Frequency of movement. Fast-moving items belong near the shipping area. This applies the same logic as ABC analysis to the number of picks rather than item value (see the lesson on ABC and XYZ classification).Value. Expensive items belong in a controlled area to prevent loss, damage and theft.Packaging. The type of packaging determines the handling equipment and storage structure needed.How the material is supplied. Material delivered in standard units, such as boxes or pallets, is inexpensive to handle. Bulk material or material supplied in smaller quantities requires more labor and reduces productivity.A numerical measure: space per pickWhen two criteria conflict—an item takes up a lot of space but is picked frequently, for example—a simple index can help decide which item belongs closer to shipping. Divide the space an item occupies by the number of times it is picked during a given period. In the literature, this is called the cube-per-order index (COI). The lower the index, the closer the item should be to the exit: it generates more trips per unit of space occupied.ItemPositions occupiedPicks per dayIndex (positions ÷ picks)RankP1402000,203rdP2101500,071st (closest)P330301,004th (farthest)P45500,102ndNotice that P1, the most frequently picked item, does not rank first. Storing all of it beside the loading dock would take up so much space that it would push P2 and P4 farther away. Together, those two items account for 200 picks while occupying just 15 positions.Using the space ÷ picks index, which item should be stored closest to shipping? Item X: 20 positions and 40 picks/day. Item Y: 6 positions and 30 picks/day. Item Z: 50 positions and 100 picks/day. Item W: 12 positions and 12 picks/day.Answer: Item Y — the indexes are X = 0,5; Y = 0,2; Z = 0,5; W = 1,0. Y has the lowest index. Item Z is picked most often, but it occupies so much space that its index is the same as X's.Unit loadsA high-throughput warehouse needs unitized loads: materials are received, stored and shipped in standard units, such as pallets, rather than handled one package at a time. This brings:lower labor requirements;faster handling;better use of equipment;better use of cubic space, because standardized loads can be stacked and fit into storage structures.PalletsPallets are platforms made of wood, plastic, metal or cardboard on which loads are assembled. In Brazil, the most widely used standard is the PBR pallet, measuring 1,00 × 1,20 m. It was defined by the Brazilian Supermarket Association (Abras) to standardize the retail supply chain. Pallet types include:Disposable pallets, made of low-grade wood or cardboard, travel with the load and are not returned.Reusable pallets are more durable, circulate between supplier and customer, and require a system for tracking their return.Two-way or four-way entry describes how many sides a forklift's or pallet jack's forks can enter from.Single-face or double-face indicates whether only the top or both sides have a platform for the load.Advantages of palletization:Greater storage density and better use of height.Standardized and automated receiving and supply operations.Lower handling costs and shorter loading and unloading times.Disadvantages:Limited efficiency for slow-moving products or products picked in very small quantities.Dependence on equipment such as forklifts and pallet jacks.The cost of the pallets themselves, their repair, and tracking empty pallets that must be returned.Shipping containersA shipping container is a standardized metal box, generally 20 or 40 feet long (about 6 and 12 meters). It may be a dry container, refrigerated, or adapted for liquids and gases. Its advantage is that it can move between modes of transport—ship, train and truck—without the cargo being handled. This is the basis of intermodal transport, covered in the lesson on intermodal and multimodal transport. Port and ship capacity is measured in TEU (the equivalent of one 20-foot container); a 40-foot container counts as 2 TEU.Material handling equipmentHandling and storage equipment are closely linked: the width of a pallet-rack aisle depends on how much room a forklift needs to turn, and the height of the racks depends on how high it can reach. The two must therefore be chosen together, based on the materials, their packaging and the flow of goods through the warehouse. The goals of material handling are to:reduce costs;increase productivity;make better use of warehouse capacity;improve safety and ergonomics, reducing accidents and fatigue;improve the flow from receiving through storage to shipping.The main types of equipment are:EquipmentWhat it doesPallet jack (manual or electric)Moves pallets across the floor over short distances and along variable routes. It cannot lift loads onto racks.Forklift (electric, gas or diesel)Moves and lifts pallets. Electric forklifts are predominant indoors; reach trucks and three-way forklifts are available for narrow aisles.Tugger (industrial tractor)Pulls trains of carts along horizontal routes, for example to supply assembly lines.Belt or roller conveyorMoves packages along a fixed, continuous route; a core component of automated sorting systems.Overhead crane and craneMove heavy loads from above in storage yards and industrial buildings.Overhead monorailAn elevated rail carrying trolleys or hoists along a predetermined route.Automated guided vehicle (AGV) and autonomous mobile robot (AMR)Transport loads without an operator. An AGV follows a marked route; an AMR navigates using a map of the warehouse.Operators of forklifts and other motorized equipment need specific training and identification, as required by NR-11 (transport, movement, storage and handling of materials).Storage structuresThese structures, which the source calls frameworks, are generally made of steel. They are modular, can be dismantled and can expand as needed. The most common are:Selective pallet racking: each pallet can be reached directly without moving another. It offers maximum accessibility but requires substantial aisle space.Drive-in racking: the forklift enters the rack, and pallets are stored several positions deep. It offers high density but little selectivity: the last pallet in is the first out. It works well for large quantities of the same item.Gravity-flow racking: pallets or boxes slide down inclined rollers, entering from one side and leaving from the other in the order they arrived. It is ideal for items with expiration dates.Push-back racking: pallets sit on carts and are pushed back into the rack. It offers high density, with loading and unloading from the same side.Cantilever racking: projecting arms hold long loads such as pipes, bars and profiles.Light-duty shelving: holds boxes and loose items, typically in the picking area.Mezzanine: an intermediate floor that doubles usable area by taking advantage of the building's height.Automated storage and retrieval system (AS/RS): automated cranes travel through narrow, tall aisles, storing and retrieving pallets without an operator.The video above shows the Pallet Shuttle, a high-density system in which a motorized shuttle carries pallets to the back of the rack's storage lanes.How many positions will fit?Here is a simple capacity calculation: a pallet-rack aisle with 20 bays on each side, 3 pallet positions per level in each bay, and 5 levels (the floor plus four more) has 20 × 2 × 3 × 5 = 600 positions. Height makes a substantial difference: 6 levels instead of 5 would provide 720 positions in the same floor area, 20% more, provided the forklift can reach them, the floor can bear the load and the building has enough clearance. That is what it means to make use of cubic space.A pallet-rack aisle has 15 bays on each side, with 2 positions per level and 4 levels. How many pallet positions does it have?Answer: 240 — 15 bays × 2 sides × 2 positions × 4 levels = 240. The most common mistake is to forget that there are racks on both sides of the aisle, which gives an answer of 120.A company stores 400 pallets of a single soft drink. It is fast-moving, and the company does not need to track batches. It wants to store as many pallets per square meter as possible. Which storage structure is most suitable?Answer: Drive-in racking — with many pallets of the same item, individual access is unnecessary, and drive-in racking trades selectivity for density. Selective pallet racking provides access to every pallet but uses more space for aisles; cantilever racking is for long loads.Case studyThe video above, from Mecalux, shows a warehouse that handles many different product lines. As you watch, try to identify how locations are organized, which storage structures and equipment appear, where the fastest-moving items are kept, and what has been automated.RecapAccessibility depends on location codes (aisle, bay, level) and physical layout.Heavy, bulky and fast-moving items belong near the exit; the space ÷ picks index helps resolve conflicts between these criteria.Unit loads (the 1,00 × 1,20 m PBR pallet and the 20- or 40-foot container) reduce handling and make use of cubic space.Handling equipment and storage structures must be chosen together: selectivity (pallet racking) versus density (drive-in, push-back and gravity-flow racking).Capacity = bays × sides × positions per level × levels.ExercisesEasy1) A pallet-rack aisle has 25 bays on each side, with 3 pallet positions per level and 6 levels. How many positions does it have?2) Item K occupies 8 positions and is picked 40 times a day; item L occupies 12 positions and is picked 30 times a day. Based on the space ÷ picks index, which should be closer to shipping?3) A ship carries 300 40-foot containers and 200 20-foot containers. How many TEU does it carry?4) Name the most suitable storage structure for each case:a) 6-meter steel pipes;b) boxes of yogurt that must leave in the order they arrived;c) small spare parts picked one at a time.5) What is the difference between a pallet jack and a forklift? Which one can place a pallet on the third level of a pallet rack?Hard6) Rank the items below from closest to farthest from shipping using the space ÷ picks index, and comment on the position of the most frequently picked item.ItemPositions occupiedPicks per dayA60120B1296C2424D840E302007) A warehouse has 4 selective pallet-rack aisles, each with 20 bays on each side and 3 positions per level.a) How many positions are there with 5 levels?b) How many with 6 levels?c) The company needs to store 3.000 pallets. How many levels would it need if it keeps the 4 aisles? What must be checked before adding height to the racks?8) Boxes measuring 40 × 30 × 25 cm (length × width × height) are stacked on PBR pallets (1,00 × 1,20 m) without overhanging the edges. The maximum load height is 1,00 m above the pallet.a) How many boxes fit in each layer if all boxes face the same way? Compare both orientations.b) How many boxes fit on each pallet?c) How many pallets are needed for an order of 7.200 boxes? What fraction of a 600-position aisle would they occupy?9) A distribution center will receive four types of goods. Choose a storage system for each from selective pallet racking, drive-in racking, pallet flow racking, cantilever racking and light-duty shelving. Explain your choices:a) 400 pallets of a single soft drink, with no batch tracking;b) shelf-stable milk, with many pallets per product and stock dispatched in expiration-date order;c) 2.000 different pharmacy products, sold individually;d) 300 different products, with 2 to 4 pallets each, dispatched as full pallets.Answer Key1) 25 bays × 2 sides × 3 positions × 6 levels = 900 positions.2) K: 8 ÷ 40 = 0,20. L: 12 ÷ 30 = 0,40. K has the lower ratio, so it should be closer.3) 300 × 2 + 200 × 1 = 600 + 200 = 800 TEU.4) a) Cantilever racking, designed for long loads.b) Pallet flow racking (gravity-fed): goods enter on one side and leave on the other in the order they arrived.c) Light-duty shelving, commonly used in picking areas.5) A pallet jack moves pallets short distances across the floor but cannot lift loads onto racks; a forklift can move and lift them. Only a forklift can reach the third level.6) Ratios: A = 60 ÷ 120 = 0,50; B = 12 ÷ 96 = 0,125; C = 24 ÷ 24 = 1,00; D = 8 ÷ 40 = 0,20; E = 30 ÷ 200 = 0,15.Order: B (0,125), E (0,15), D (0,20), A (0,50), C (1,00).E has the most withdrawals (200), but ranks second: it occupies 30 positions, while B generates almost as many trips per occupied position (8 versus E's 6,7) using far less space.7) a) Per aisle: 20 × 2 × 3 × 5 = 600; four aisles: 4 × 600 = 2.400 positions.b) 4 × 20 × 2 × 3 × 6 = 2.880 positions.c) Each level adds 4 × 20 × 2 × 3 = 480 positions. 3.000 ÷ 480 = 6,25, so 7 levels are needed (with 7 levels: 3.360 positions). First, check that the forklift can reach the top level, the floor can support the load, the ceiling height is sufficient (with clearance for sprinklers and lighting), and the racking is rated for that height.8) a) Orientation 1: 40 cm along the 1,20 m side and 30 cm along the 1,00 m side: 120 ÷ 40 = 3 and 100 ÷ 30 = 3,33, so 3; 3 × 3 = 9 boxes. Orientation 2: 30 cm along the 1,20 m side and 40 cm along the 1,00 m side: 120 ÷ 30 = 4 and 100 ÷ 40 = 2,5, so 2; 4 × 2 = 8 boxes. The better arrangement fits 9 per layer.b) Layers: 100 ÷ 25 = 4. Boxes per pallet: 9 × 4 = 36.c) 7.200 ÷ 36 = 200 pallets; 200 ÷ 600 = 1/3 of the aisle.9) a) Drive-in racking: with many pallets of a single product, individual pallet access is unnecessary, and drive-in racking provides the highest storage density.b) Pallet flow racking: it offers high density while dispatching pallets in the order they arrived, making it suitable for products with expiration dates (drive-in racking would dispatch the last pallet in first).c) Light-duty shelving: for loose products stored as individual units.d) Selective pallet racking: many products with only a few pallets each require direct access to any pallet.
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