Chapter 13: Structural Failures

Portions of ancient structures such as the Roman Coliseum or The Greek Parthenon are still standing. Their demise may be attributed to age, inappropriate materials, lack of knowledge and forces of nature. Disastrous failures of more modern structures still occur though infrequently. Causes of such problems may originate in poor design and lack of understanding of loading conditions or violation of building codes. Computational errors have largely been eliminated by high-speed computers that have reduced the need for lengthy manual calculations but these machines are not infallible. Faults in construction and miscommunication between architect, engineer, and contractors may often be blamed. Poor quality control of materials or the use of the wrong materials is frequent culprits. Temperature changes cause expansion and contraction of structural members. If such movements are prevented components may break or buckle. Unexpected high and dynamic loads may not be adequately considered. Unbalanced rotating machinery, earthquakes, hurricane winds, and floods are not all-ways predictable but can be mitigated by proper design. Inadequate foundations may cause settlement, sliding, overturning or damaging structures. Heavy snow and rain loads on flat roofs without appropriate drainage are also dangerous. Lack of redundancy, the lack of load transfer capability from damaged components to others has caused many older structures to fail. A large number of repeated loadings of metal structures may result in fatigue failures. Regions of stress concentrations such as rivet holes and sharp corners are most vulnerable.You can use charts/figures/visuals to enhance your assignment.

Summary of Ideas Presented in Chapter 13

•Structures may fail as a result of bad design, computational errors, disregard of building codes, unexpected large loads, substandard materials, and weather-related problems.

•Wind, snow, and earthquake loads require special attention due to their high variability.

•Dynamic loads and undamped vibrations frequently are the cause of structural failures in extreme wind and seismic events.

•Restrained thermal movements can cause cracks and member failure. Inadequate foundations may cause wall cracking, as well as the building sliding or overturning.

•Progressive collapse may occur due to a lack of redundancy and lack of strength reserve.

•Fatigue and stress corrosion may result in failure after prolonged use.

•The consequences of structural failure may be fa financial loss, law suits, loss of reputation, and even injury and loss of life.

Chapter 14: Structural Aesthetics

With the exception of statues and monuments, ,the majority of structures are built for utilitarian purposes. While beauty may not be a prerequisite, an aesthetically pleasing appearance is desirable. A buildings may supply semiotic, non-verbal, messages that imply its uses.

Imitation of nature’s forms frequently make structures more acceptable than those that defy them. They should also fit their surroundings. Structural correctness usually conveys acceptability but correctness is often violated for the sake of aesthetics. It is also recognized that tastes are dependent on the culture of the observer as well as on changing times. Load carrying members of a structure are usually hidden inside walls and various coverings, but many modern structures show exposed components to good advantage.

Summary of ideas presented in chapter 14:

•Aesthetics of structures depend on the experience of the viewer.

•Structures that obey their natural surroundings may be more satisfying than the ones defying them. Purpose semiotically.

•Buildings constructed for aesthetic appeal do not always satisfy structural requirements

•Structurally correct buildings are usually pleasing to the observer.

•Structures with unusual geometric shapes indicate modernity.

15.1 Intuition and Knowledge

The preceding chapters have attempted a qualitative presentation of structural principles on the basis of general experience with forces, materials, and deformations. A casual reading of the foregoing pages may illuminate the structural actions most commonly encountered in architecture; a careful reading may clarify, in addition, more sophisticated types of structural behavior seldom considered by the layperson. In any case, the purely intuitive approach used to introduce these principles cannot be expected to lead to quantitative knowledge in a field as complex as structures. For this, an analytical, mathematical presentation is needed, of the kind required for an understanding of any branch of physics.

Intuition is an essentially synthetic process that brings about the sudden, direct understanding of ideas more or less consciously considered over a period of time. It becomes a satisfactory road to knowledge on two conditions: It should be based on a large amount of prior experience, and it should be carefully verified. Pure—that is,
unchecked—intuition is misleading most of the time.

Intuition may be greatly refined by experience. One of the best tools for refining structural intuition is the use of models demonstrating the diversified actions considered in this book. Since all structural actions involve displacements, and displacements are the visual result of these actions, models are ideally suited for the intuitive presentation of structural concepts. This is why, at times, the reader has been invited to build elementary models that demonstrate the structural behavior of simple elements more convincingly than any drawing ever will. The suggested exercises at the end of each chapter are a springboard for such ian nquiry.

On the other hand, it cannot be overemphasized that intuition without experience is a dangerous tool, since it leads to unchecked assumptions. The reader should be wary of what he or she “seems to feel should happen” in a given physical situation, and, in particular, of the suggestions from the purely geometrical aspects of a structure. For example, at first it is hard to believe that the straight sides of a stiffener-supported cylindrical barrel move inwards under load, because the curved section of the cylinder suggests arch action, and arches are “known” to push outwards, and yet such is the case.

15.2 Qualitative and Quantitative Knowledge

Qualitative knowledge should often be a prerequisite to quantitative analysis, since interest in a field is seldom aroused without some prior understanding. It is hoped that the reader interested in structures may obtain from the preceding chapters that minimum understanding of structural behavior required to arouse his or her interest, and be led by it to a serious study of the subject.

Structures are best presented in the language proper to the quantitative analysis of measurable phenomena: mathematics; not the complex mathematics required for an understanding of the more advanced aspects of science, but the simple mathematics of algebra, trigonometry, and, sometimes, elementary calculus. In this context, one cannot overemphasize the importance of numerical computations, and the fact that the calculator and the computer have made them fast, reliable, and painless for all. No thorough knowledge of structures may be acquired without the use of these mathematical tools. Mathematics does not explain physical behavior; it just describes it. But mathematical descriptions are so efficient that a short formula may clearly and simply express ideas that in verbal form would require pages of complex statements.

The availability of structural knowledge, made possible by the use of mathematics, has produced impressive results. Structures, which in the past could have been conceived and built only by architectural geniuses, are designed, at present, by modest engineers in the routine of their office work. This democratization of structural knowledge, while putting advanced structures within the reach of the average architect, introduces the danger of architectural misuse by the practitioner who lacks a solid structural foundation.

There is little doubt in the minds of both engineers and architects that modern structural concepts are used properly only when the architect has a thorough understanding of structures. This does not imply that all architects should become mathematicians; it simply suggests that those practitioners who wish to express themselves through structural forms should first learn to use the tools of quantitative analysis. They will be amazed to find, later on, that their cultivated intuition will often reach “correct” structural solutions without too many mathematical manipulations.

15.3 The Future of Architectural Structures

The twenty-first century has ushered in the digital age in all segments of society. We are similarly entering a new age of architectural structures. Complex structural analysis and design at one time only a dream is now enabling designers to generate and verify structures thought impossible as recently as the latter twentieth century—less than the span of time since the last publication of this text. New high-tech materials such as carbon fiber are joining the ranks of the traditional materials. These developments have arisen simultaneously with computer-controlled manufacturing that has allowed the fabrication of structures with remarkably small tolerances—a prerequisite for complex geometry since even the slightest deviation from a theoretical position in space creates structural elements that cannot be fit together (Figure 15.1). It is very conceivable that by the middle of the twenty-first century, robotic assembly and even self-assembling systems will begin to be the norm as well.

Figure 15.1 The Museo Soumaya

The Museo Soumaya in Mexico City is an example of daring architectural design and structural integration in the digital age. The irregular form and tight construction tolerances would have been impossible until recent developments in computer aided design, analysis, fabrication and construction management techniques. The building under construction (a)reveals the layers of structure: The primary structure consists of the widely spaced, white tubular members following the curvature of the form (each one is unique), surrounding a central structural core. Atop the frame is a double-layered space frame that defines the surface, onto which the final sheathing and façade are applied. The finished building (b) is covered with hexagonal mirrored aluminum tiles that form a rain screen. The hexagonal shape allows the tiles to follow the building contour, and the spaces between tiles allow rainwater to pass through and drain behind the actual façade surface.

Photo courtesy of Geometrica

New freedom brings new responsibility and new challenges, though. Forms that are highly irregular defy any intuitive understanding of their proportioning and require the closest collaboration between architect and engineer from the very start. In some regards ,it can be argued that nearly
any
structural form can be constructed today, but we must guard against mere arbitrary whim.

In the past, aside from structural and construction limits, ethe conomy was most often the main restraint on design. New challenges such as environmental sustainability and carbon neutral design, however, confront us with new limits. Recognizing the significance of climate change and the undesirable influence fossil fuels have on it, athe rchitecture will need to contribute its share in alleviating their effects. Energy efficient structures with improved insulation, heat reflecting/absorbing coverings, solar paneled walls and roofs, building locations/ orientations and new materials are just a few examples of the many environmentally friendly solutions. A future edition of this book may consider such problems in detail.

Architecture at its highest form can excite, enliven, and inspire, and pure structural pragmatism is antithetical to this aim. Nevertheless, just because one
can
design nearly any form does not mean we
should, especially if it comes at the cost of structural and material inefficiency (and thus excess).

Design practice is rapidly evolving to address these challenges while at the same time making complex forms possible in the first place. The building industry is beginning to model the assembly of structures in the manner led by the aerospace industry starting in the 1980s. It has taken this long for the architectural/engineering and construction industry (AEC) to catch up simply because of the complex nature of the building industry, with the many different entities involved (architects, engineers, fabricators, contractors—typically all from different companies). New approaches of Integrated Project Delivery (IPD), facilitated by the development of Building Information Modeling (BIM), are emerging as key components of this process. Though years away from the realization of its full potential, the goal of BIM is to digitally represent all aspects of a project in all disciplines, with all associated material and technical data tagged with each part, permitting designers to check and verify all components long before fabrication even begins, and to ensure that during construction errors and associated changes are minimized. The digital architectural model is becoming linked with the digital structural analysis model and environmental performance simulations in a symbiotic loop, enabling the exploration of a greater range of design alternatives. It portends to be the biggest revolution in building design and construction since the development of the modern materials of steel and concrete that literally built the contemporary world.

Nevertheless, however complex and challenging the future may be, and however sophisticated our computational tools become, at the core of
all
structural understanding are elemental principles that are fundamentally invariant. In a sense, they are akin to the nucleotides that comprise DNA, which in turn is the basis for all life as we know it. Whether simple or complex,
all
structures must be stable and strong.
All
structures obey the basic principles of linear and rotational static equilibrium. A true and deep understanding of these elemental structural principles comes only with time and continued practice, and combines intuitive knowledge plus at least elemental mathematical application. Such foundational understanding is the root of the development of any architecture in which the structure is integrally a part of the design as opposed to an afterthought.

So, to conclude this introductory overview of structures in this book, it is even more true today than when the closing paragraph in the first edition was written some 50years ago. The field of structures is evolving rapidly under the pressure of the growing needs of society. The structuralist and the architect must strive, by all means at their disposal, toward mutual understanding and fruitful collaboration. May the technician and the designer work together to the greater glory of architecture and in the greater service to humankind.