When designing a warehouse system, there is, in principle, always a mutual influence between the warehouse building and its architectural design. This means that a warehouse building has a significant influence on the design of the warehouse system and the logistics operations. Conversely, once the warehouse system has been finalised, this in turn determines the design and construction of the warehouse building.
There is therefore an interaction between these two components. We can characterise this as a functional relationship.
An important question here, of course, is which mutual aspects play a role in this and what their mutual influence is. In many situations, a warehouse building is involved or newly built based on immediately obvious assumptions, such as: how many pallet spaces do I need, how high can I build, what is the height of the existing warehouse, what is the site area, etc. There is something absolute about building or buying a warehouse. When renting a warehouse, this is the case to a significantly lesser extent, although the adjustment is also fairly strenuous.
The conclusion is, we should basically design from the inside out and include a range of aspects. Then we can put the architectural "box" around it or make a targeted choice for an existing warehouse hall. On top of that, not every situation is the same. But the fact is, the best situations are achieved by thinking about them and weighing up the options.
Forecasting and warehouse planning
Building a new warehouse with the associated equipment, or modifying/expanding existing warehouses, is an activity that does not take place with any regularity. If the right path is not chosen in warehouse planning, for a long time, there may be an inefficient situation. It is a well-known fact, that restoring an inefficient situation, this due to incorrect planning, costs a lot of effort and money and can lead to a significant disruption in business operations. When designing the warehouse layout, it is, partly for this reason, desirable to think in the medium term. Determining the storage requirement and forecasting this has a direct relationship with the size of the warehouse hall and the related size of the racking pattern/storage methodology.
The purpose of the prognosis calculation is to give the plan a more permanent character, so that it is not necessary to adapt the layout, the installation, or an expensive adaptation of the building after some time.
One of the techniques with which good results can be achieved in planning storage requirements is the so-called correlation and regression calculation.When calculating storage requirements, two aspects are important here, namely:
- Establishing a correlation between turnover and
stock levels; - Determining the regression between inventory and sales growth.
When establishing the correlation, it is necessary to determine whether the outcome and calculated value are reliable. Within the scope of this publication, we will not deal with this calculation method, but will assume that a reliable correlation has been established. However, it is then important to determine which regression coefficient applies in a particular situation. The regression coefficient refers to a ratio that indicates the extent to which stock growth lags behind the increase in turnover. In general, a five-year planning period can be regarded as realistic as it is manageable. For a specific project, the forecast indicates that a cumulative increase in turnover of more than 40 per cent is expected over a five-year planning period. Previous studies of commercial warehouses with similar dispatch and storage patterns have identified corresponding regression coefficients. The trend in the average regression coefficients is shown in the figure below.
Regression curve on turnover increase
From the graph shown on Figure 1, a regression coefficient of < 0.37 can be determined with respect to the projected sales increase of 40%.
For calculating the planning requirement, the following calculation factor can be compiled herewith:
100 + 40 x 0.37 (x %) = 1.148
For example, if, in a given situation, there is an inventoried storage requirement of 5200 pallet spaces, with the corresponding dimensions, the planning requirement can be determined as 5200 x 1.148 ≈ 5970 pallet plate equivalents.Also depending on the storage methods and operating equipment to be chosen, this can be the basis for the structural realisation or choice of a suitable warehouse building.
Note: If there is a view that a 40% increase in turnover will generate a 40% increase in storage, this is a fallacy, which will lead to excessive design situations.
Optimising structural layout
A warehouse building has, or can have, a technical/economic lifespan of 25-30 years. So after the planning period of 5 years, there is still a long period where optimal use should be made of the warehouse building. After choosing a particular warehouse system application, it is often difficult to change system applications. This is firstly due to the inflexibility of the warehouse due to the placement of the columns. In most cases, the placement of a number of column rows will have to be accepted in order to minimise the higher building costs that arise with a free or large span.
An important question here is how a form of optimisation can still be found between the architectural grid size in the partitioning of warehouse systems, over the following years. In the event of any rearrangement of a warehouse situation during the further course of the period of use, it often turns out that harmonisation cannot take place with regard to system components. Simply put how there can be a division within the displayed column rows into multiples of aisle sections.
Here we should always calculate in aisle sections, i.e. an aisle with a rack row on the left and right. If we assume two common alternatives, the following calculation elements are involved:
An aisle section for the reach truck/pallet rack alternative is 125 cm (storage depth) + 280 cm (aisle width) + 125 cm (storage depth) = 530 cm. The reach truck can be understood as the widely known sliding mast truck. An aisle section for the alternative high-stack truck/pallet rack is 125 cm + 175 cm + 125 cm = 425 cm. The high-stack truck or rota reach truck may be defined as a truck with side discharge capability.
Optimising warehouse layout
Harmonisation is then found with the following distribution form:
Reach truck/pallet racking : 4 aisle sections x 530 cm = 2120 cm. High-stack truck/pallet racking : 5 aisle sections x 425 cm = 2125 cm.
So the use of a grid dimension of 2125 cm between the column rows is desirable here, (see also Figure 2) for the distribution form referred to here. For the aforementioned form of harmonisation, a load depth of 125 cm was used. This calculation method also applies to a load depth of 105 cm, with a correspondingly narrower aisle width. However, it is important here to already anticipate the requirements of a changed system application. In particular, the floor tolerance and the point load will have to be based on the alternative high-bay truck/pallet racking. Figure 3 gives an impression of this.
Truck with side drop-off capability
The truck shown here with side discharge capability operates in a relatively narrow aisle. In a situation with large floor tolerances, this could lead to contacts with the stored pallet loads. Given the travel speed that the guided truck with side deposit can develop, while also performing the lifting and lowering movement, this would cause an undesirable situation.
The better flooring companies are very capable of realising a monolithic floor in floor tolerance class 3 and 4 (low floor tolerance), at very low additional cost. With regard to the likewise mentioned point pressure load, reference can also be made to Figure 3. The lateral drop-off situation creates a concentrated load on the left or right front wheel, which could create an additional point pressure load from the interface with the wheel. However, providing a double wheel set reduces the static point pressure load by 50%. By paying attention to aspects dealt with so far, there will be a longer lifetime of the warehouse/distribution centre, at a very low (additional) investment. This with a high return on investment.
Similarly, this achieves an important form of latent flexibility and further expansion potential, without the need for major structural changes.
Gerben W. Esmeijer - Constultant/dir. Logistics consultancy firm Esmeijer BV.
