Edible Structures: The Application of Structural Engineering in Cake Design

Lisa Okamoto was a senior studying civil engineering. She hopes to work for an engineering/construction firm professionally. She loves baking cakes and everything delicious.

Rarely are cakes thought of as miniature buildings, but they are actually governed by the same physics that keep homes and offices upright. As such, multi-layered cakes are subject building like forces and need a support system that will hold the weight of the different layers. They share many structural elements with modern day skyscrapers like foundations and columns. When a cake falls, it resembles the disaster of a building failure, although without the extreme consequences.

Introduction

Many of us can easily claim to be cake demolition experts. We simply see, cut, and eat the sugary confection. Not many people put much thought into what goes into creating the delicious dessert, let alone the structural aspects of it. There may not be too much complexity to the basic homemade one layer cake, but professionally-made cakes can be over four feet high and take the form of anything from Hogwarts Castle to a box of crayons [1]. These complex cake designs require a strong support system to keep them from breaking apart or collapsing. It might sound odd to think of them this way, but cakes can be considered miniature buildings in their structural elements.

If you compare the structures of a multi-tier cake and a building, two important similarities can be seen: the importance of a foundation and the use of columns. Both of these elements are used to help carry the load of the structure and ensure its stability. Another common factor between cakes and buildings is the way they are both vulnerable to structural faults that can cause complete failure.

Foundations

Although virtually impossible to detect in both building and cake design, the foundation is the most important element of a structure. It is the under-layer of the entire project and will ultimately hold the majority of the load. Building a structure without a foundation is like building a house made of cards: the slightest disturbance could cause a complete collapse.

Irivine Geotechnical

Figure 1: Footing foundations are designed to take small loads typically seen in residential construction.

There are three basic types of structural foundations: footings, mats, and piles. Footing foundations (Fig. 1) are sections of concrete that are shallowly embedded into the ground and sit underneath the lowest layer of the building. They are designed for fairly small loads, on the order of a few hundred tons, and are mainly used in residential construction [2]. If the structure is much larger than a house, the foundation must be upgraded to a mat (Fig. 2). This is a shallow foundation that encompasses a large area and is usually made of a rebar skeleton that is filled with concrete. With a mat, the load is distributed over a greater area. Without it, a large, concentrated load will produce a significant amount of settling in the soil underneath, which could make the structure unsound and vulnerable to collapse [3].

The strongest of the three styles is the pile foundation, which can be designed to carry loads upwards of two million pounds [3]. Piles are columns that are either driven or drilled into the ground until they reach bedrock or a stronger soil. They are used for very large total loads, on the order of a few million pounds, or for structures built on soft and easily compressible soil, like clay. Most skyscrapers utilize pile foundations because these structures add extremely large loads over fairly small areas [4]. Piles take the load of the structure off of the top layer of soil and transfer it to the bedrock or stronger soil that can be found many meters beneath the surface. Some of the load is also counteracted by the frictional interaction between the pile and the soil. When the pile is pounded into the ground, an upward frictional force is created, helping to keep the pile in place [5].

Irvine Geotechnical

Figure 2: Mat foundations are used when loads will be much larger than that provided by a house. Unlike the footing foundation, the mat distributes loads over a much greater area.

Despite the benefits of footing and mat, most cake design uses the pile foundation. For a cake’s pile foundation, the principles are the same as in building design, but the materials and sizes differ. Think of the cake as the highly compressible soil and the board the cake sits on as the bedrock [6]. Instead of large steel or concrete columns, cakes use wood or plastic rods [7]. These dowels transfer the loads of the upper layers of cake straight to the board below instead of allowing the bottom cake layer to carry the load and risk failure (see Multimedia).

Columns

Columns have been used in structural design for thousands of years; there is still evidence of how they supported the buildings of the Roman Empire [8] (Fig. 3). In building design, columns are used as extra support so the walls do not have to carry the entire load of the upper floors. They are very similar to piles in that their purpose is to transfer a load from one location to another, but unlike piles, columns are designed to move the load of one level to the one below it, not to the bedrock. Each level of columns passes the load to the level below, until the load is finally put onto the piles and transferred to the bedrock. Like with piles, the diameter of a column depends on the load it needs to carry. The lower levels of a building are more likely to have larger columns than those at the top.

Orientalist/Wikimedia Commons

Figure 3: Columns have been used since the time of the Roman Empire. These structures provide extra support for walls by distributing the load of a building from one point to another.

In cake design, columns are, for the most part, the only structural support besides the cake itself. Columns are most obviously used when they separate tiers of a cake. But there are also interior cake columns that take the form of dowels [7]. These dowels differ from the pile-like dowels previously mentioned because they are not directly transferring the load to the base and do not need to carry the weight of the entire cake.

Failure

Structural failure is defined as “fracturing or giving way under stress” [9]. The two main forms of failure common to both buildings and cakes are settlement and collapse. Settlement occurs when the soil beneath the structure compacts, shifting previously level ground in such a way that leads the building or cake to sink [3]. Collapse happens when a component completely fails and a portion of or the entire structure suddenly falls.

Settlement

Alkarex Malin äger/Wikimedia Commons

Figure 4: The Leaning Tower of Pisa earns its namesake from uneven compaction of soil that causes a “leaning” of 3.8 degrees, as shown.

One of the best examples of settlement is the Leaning Tower of Pisa. Construction of the tower began in 1173 and it began leaning shortly thereafter. The lean has gotten significantly worse over the last eight centuries and currently leans at 3.8 degrees [10] (Fig. 4). The lean is caused by the uneven compaction of the soil beneath the tower. The cause for most building leans and ground settlement is an insufficient or weak foundation, which can occur either when the engineer overloads the foundation to the point that it cannot hold the weight of the structure, or the foundation is made unevenly and one side of the foundation is stronger than the other [3]. Had the builders of the Tower of Pisa used a pile instead of a mat foundation, there would be very little force on the weaker soil and the lean would be all but eliminated [11].

Settlement is extremely common in cake, creating problems for even well practiced professionals. If the dowels of the cake are cut too short, the weight of the upper layers of the cake will be transferred to the lower cake layer instead of the dowels, causing a settlement and giving the appearance of sinking cake tiers [7]. If the dowels are cut unevenly one side of the cake is likely to sink more than the other, thus giving it a lean like the Tower of Pisa.

See Fig. 5 for an interactive animation that compares the foundation of buildings and cakes, and simulates what happens next when settlement occurs.

Morton/Illumin

Figure 5: An interactive comparison of building and cake foundations. (Flash)

Collapse

The worst possible scenario for any structure is a collapse. For this to occur, at least one structural component has to fail completely. In building design, engineers use factors of safety to ensure that the capabilities of the support system are greater than the need. For example, a factor of safety of three will ensure that the component will be able to handle a load three times greater than the estimated load [3]. If a building does completely collapse, there has been a great miscalculation of the capabilities of the building or an unexpected event has occurred, like a high magnitude earthquake (Fig. 6).

Although the end result of cake and building collapses may look similar, their causes are very different. Unlike buildings, cakes almost always collapse because of direct human involvement; either someone bumps into the cake or takes off a necessary structural piece like a column. Despite having similar construction methods, cakes rarely collapse due to structural inconsistencies because they usually do not last long enough to fail. Unlike buildings, cakes are only meant to last a few hours. If they were expected to last much longer than that, it would be likely to see a great amount of deformation and possibly collapse.

H.G. Wilshire/Wikimedia Commons

Figure 6: Column failure caused devastating damage to a highway. These structural collapses are much scarier than a ruined cake.

Conclusion

Although you probably will not see a cake design course offered in the engineering department anytime soon, it is an interesting application of basic structural engineering concepts. Columns and foundations are just as important to the construction of cakes as they are to the construction of safe inhabitable buildings. Engineering principles can be found in the creation of almost any object. It is important to understand that engineering is more than just building bridges, circuits and engines, and that its concepts can be applied in new and interesting ways to bring to life the ideas of the imagination.

References

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