Hybrid constructions - the best of both worlds

The adoption of composite solutions, enlisting the best qualities of concrete and of steel, begins to stand out as a wholesome transition between traditional methods and industrialized construction

There was a time when buildings made of steel and those in which concrete was the main building element seemed to compose scenarios of different worlds. Supporters of one or another technology strived to defend the advantages of one alternative to the detriment of the other (which did not contribute in the least toward the maturity of engineering and of the construction industry in Brazil). That time, however, is falling by the wayside. “Steel structures” and “concrete structures” no longer constitute different worlds in structural engineering and each of these two materials admittedly has its advantages and disadvantages and, very often, the best solution is a combination of both.

To many technicians and representatives of the academic community involved in this discussion, the adoption of composite construction would be the path to a change in culture, opening up opportunities for the use of steel structures and for industrialized concrete construction in Brazil. Composite steel-concrete buildings are found more and more all over the world and can help us leave behind the tradition of artisanal construction in our country.

Engineer Iria Lícia Oliva Doniak, president of the Brazilian Association of Industrialized Concrete Construction (ABCIC - Associação Brasileira da Construção Industrializada de Concreto) reveals that, in Brazil, the term that is likely to be adopted when referring to buildings with such characteristics is ‘hybrid constructions’. “Presently, ABCIC and the Brazilian Center of Steel Construction (CBCA - Centro Brasileiro da Construção em Aço)  are analyzing the theme and preparing a manual that will, possibly, be released during Construction Expo in 2013 in which composite structures should be referred to as “hybrid structures”.

She explains that in international literature we find the terms “composite, mixed and hybrid structures”, defining that composite structures are those structure in which there is the presence of both materials, with adhesion or solidarity between each other, to comprise a structural section. In flexing, the solidarity between the two materials affords compatibility between their deformations. Under this concept, strictly speaking, a section of steel-reinforced concrete (concrete plus a steel armature) is a composite section in the same way as a steel beam with shear connectors and a concrete slab form a composite section.

“The bibliography itself adopted in the Manual fib 19 refers to composite structures, as does the reference by the European Committee for Standardization, in 1991-1-1, Eurocode 4 – Design of Composite Steel and Concrete Structures. Brussels 2004,” she explains.

Further according to the engineer, the expression “hybrid or mixed structure” is related to the use of different materials to compose a building or structural system. However, contrary to what happens with composite structures, there is not necessarily the establishment of adherence/bonding between the materials, neither the ‘solidarizing’ of deformations. “As regards the term ‘hybrid’, European authors and the Concrete Centre define hybrid or composite as the same concept. However, the term ‘hybrid’ is directed more specifically toward the combination of prefabricated concrete elements with those cast in situ.”

In this article, generically speaking, we will use the term “composite constructions” for those in which more than one system of construction is applied. The utilization of composite elements and, consequently, of composite steel-concrete systems considerably enlarges the set of solutions in reinforced concrete and in steel.

In general, the growing utilization of composite structures is attributed to various factors, among which is the increasingly greater need for large free areas per floor, which means large spans for beams, an increase in vertical force on pillars and greater spacing between them.

Thus, free from pre-conceptions and sectarianisms, we can celebrate the marriage between these two methods of construction. That’s how Luiz Carlos Caggiano Santos, president of Brafer and of the Brazilian Association of Steel Construction (ABCEM - Associação Brasileira da Construção Metálica) sees it. To him, steel cannot live without concrete and the composite solution is the best alternative. “What one expects is that the multiplication of the use of the composite construction method can promote a wholesome transition between conventional construction and more modern processes, especially at this time in which the construction industry should play an important role in the new cycle of development in Brazil,” he assures.

Planning defines the success of the project

A scholar on the subject, Iria Doniak is convinced that one of the most important aspects for the success of projects that are developed based on hybrid construction is the planning and development of the project. “Usually, these are works that are strongly directed toward a concept of industrialization and, furthermore, to the treatment of interfaces (the transition between one system of construction and another). These are two important aspects, from a construction standpoint, to be addressed.”

She states that, from a contemporary architecture standpoint too, steel-prefabricated concrete systems have been used a lot lately, tapping the most of the potential that each element has to offer while also serving issues related to sustainability.

Among success stories acknowledged the world over, the president of ABCIC reminds us of the ‘Torre de Cristal’ (Tower of Glass), a skyscraper located in Madrid, Spain which utilized composite structures. She also recalls an award-winning architectural project in Brazil: the headquarters of Petrobrás, in the city of Macaé (RJ), designed by architect Sidônio Porto. Another good example of harmony in the use of the two construction methods is the head office of Teckma Engenharia - a building that capitalized on the advantages of steel and industrialized concrete construction to achieve excellent results in terms of a reduction in costs and in the time required for the execution of the project, as well as a reduction of the building’s environmental ‘footprint’.