The art of structures


chernetskiy090700066.jpgThe concept of structure has always been a fundamental aspect of building. Until the Renaissance the statics of constructions was based solely on experience, intuition, experimentation with models and empirical rules, but the scientific revolution transformed this discipline into a true science. Since the mid-1700s it has been possible to calculate structures, analyzing their mechanical behavior. Their most efficient form can be determined by mathematical means, and the measures required to ensure their strength and stability can be set by comparing the internal forces with the strength of the materials. Through the technological developments and new materials that have emerged during the industrial revolution, the science of construction has made a range of new structural solutions possible. This phase required greater specialization, and the builder was replaced by two professional roles: the architect and the engineer.

For the engineer the situation that sprang from necessity and permitted extraordinary creative evolution has, over time, also revealed its limits. Structural analysis and calculation have become increasingly precise and detailed, and these improvements have led to more daring and more efficient structures, but all this has unfortunately had its price in terms of the conceptual design of structures, bringing about a gradual but inexorable weakening of the creative side of the work. Also for the architect, the separation of these disciplines has had advantages and drawbacks. The increasing difficulty of understanding structures has undoubtedly led to compromises.

In recent decades an attempt has been made to rectify this situation. Certainly, the solution is not to return to the way things were done in the past. The separation of the professions, based on real necessity, cannot be reversed. To resolve increasingly complex problems, the only path is that of dialogue and collaboration between different professional figures.

In order to collaborate and to design together it is indispensable to have shared interests, to use the same language and, above all, to understand each other. This book on structures in architecture is an attempt to make a contribution to this mutual understanding.

In concrete terms, it will help readers to understand the functioning of load-bearing structures; in practice, this means how loads are carried and transmitted to the ground.

Therefore the book focuses on comprehension. The study of the acting loads, the determination of forces and analysis of internal forces are also geared toward comprehension of how structures function. To facilitate matters, the approach will above all be intuitive. The fundamentals of equilibrium and structural functioning are explained on the basis of everyday experience. In this perspective the equilibrium of the human body, which we have experienced since we took our first steps, represents a valid example. The method applied here is effectively very different from the conventional approach based on the logical deduction of the laws of mechanics, statics and strength of materials. We will use the tools of graphic statics, keeping the use of analytical calculations to a minimum. A similar approach has already been described in a book written by Joseph Schwartz and Bruno Thürlimann in the mid 1980s on the design and dimensioning of structures in reinforced concrete.

This text was developed from a course specially conceived when the Architecture Academy of Mendrisio was founded in 1996, in an attempt to develop a true course on statics for architects, rather than a simplification of the classic approach used for training engineers. For an architect, understanding structural functioning is useful in the design of structures. Concretely, the idea is to learn founded how to choose an efficient structural type and the most suitable materials, to determine its statically correct form, to understand which zones are subjected to the greatest stress and to develop details in the best possible way. The study covers only the most important aspects of the calculation of internal forces and dimensioning of structural members, in order to facilitate dialogue with engineers.

I think these themes should also be of interest to engineers. Their training is still highly influenced by the approach developed in the first engineering schools, toward the end of the 1700s. As the Encyclopedists proposed, the science of construction can be seen as an application of mechanics, and this is but one chapter of physics. The result is a logicaldeductive teaching whose aim is to provide the tools necessary for analyzing the stresses in structures and sizing their main parts. But unfortunately knowing how to calculate and dimension does not necessarily mean that one understands the functioning, or knows how to design a structure. So the approach taken by this book represents a necessary complement to classical teaching.

What is a loadbearing structure ?

The term structure has different meanings. From our point of view, what counts is the assembly of elements that constitutes the skeleton or framework of a construction. To be even more precise, we should talk about a loadbearing structure. This term, in building and other similar construction techniques, indicates the whole of the parts that have a load-carrying function.
On observing any building from the outside or the inside, it is usually quite easy to recognize at least part of the loadbearing structure. In the example shown here, the structure is clearly visible, and it is easy to distinguish a number of structural elements. For example, we can see vertical columns that have the task of transmitting loads to the ground, a series of horizontal trusses that support the floors of the building and transmit loads to the columns, bars arranged in X configurations and bars connecting the trusses to stabilize the construction and pick up the horizontal pressures caused by wind and earthquakes, also trusses attached to the columns and connected to other vertical bars, whose function we will learn later on, and other less obvious structural parts.

Upon closer observation, we can recognize vertical beams that make the facade more rigid and pick-up wind pressure, and a system of bars to which the escalator is attached, while the beams that constitute the structure of the escalator are part of the secondary structure.

At this point we may well wonder what is not part of the structure. An example is the air ducts we see on the roof, although they too have a structure capable of supporting their weight and standing up to wind pressure.

The purpose of a structure

The purpose of a structure is connected with its use and its architectural function. To simplify, we can indicate three possible main purposes of a structure:

– to enclose, cover or protect a space; – to create a surface useful for other purposes (for example, a floor, a structure that supports a parking area, the bridge over which a road passes);
– to resist loads or to support something (a support wall that resists the pressure of the ground; a pylon that supports a power line; a chair, a table).

So the function of support and the capacity to resist loads is not necessarily the main purpose of a structure. All structures inevitably have mass. As a result, the capacity of a structure to “carry” its own weight is a constant, qualifying characteristic.

Structure and architecture

In addition to the purposes we have presented here, loadbearing structures often serve other functions, and it is for this reason that they become an important element in architecture. Indeed, the load-bearing element can organize or “structure” space through the frame it imposes. In other cases, the presence of the structure can be exagerated and even become a fundamental element of the space…

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