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28 de março de 2014
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Steel in Construction Works: Method of analysis helps to define when to use it

For the expert, to select the most appropriate process of construction it is necessary to analyze most possible aspects involved, with priority to the mandatory and desirable features

 

 

 

 

 

 

 

 

 

 

 

The international economic crisis highlighted the competition problems of the Brazilian steel industry. According to the board of directors of the Instituto de Aço Brasil (Brazil Steel Institute), Brazilian manufacturers were among those more affected by the world economic crisis and are now developing strong efforts to overcome their difficulties through measures of continuous improvement of their productivity. Brazil is passing by a period of industry reduction, caused by the increase of direct and indirect importations of products, what is causing strong impacts on the country’s mechanical production chain. These problems were worsened by tax and exchange questions that prevented the national industry of steel to show its structural competitiveness.

According to the Instituto Aço Brasil, from 2011 to 2012 the industry increased its participation in the apparent total consumption from 35.4 to 37.7 percent. For 2014, the Institute foresees 23.9 million tons in internal sales, what corresponds to an increase of 4.1percent in relation to 2013. For the apparent consumption, 27.2 million tons were foreseen, corresponding to an increase of only 3 percent in relation to 2013. Apparent consumption is defined as the total of sales of steel companies plus the importations carried out by dealers and final consumers.

Since the World Cup will be carried out in Brazil, it was expected a leverage in Brazilian steel market. But this did not occur because infrastructure works were not been carried out as expected and the roofs of stadiums were made mostly with imported steel, although the internal production would be able to attend the internal market.

In spite of this bad scenario, civil construction industry is being an island of steel consumption growth, what is occurring in a constant way, breaking historic and cultural barriers. In spite of the proved advantages of this process, there are not too many buildings with steel structure in Brazil, in opposition to what occurs on the United States and in several European countries. In the United States, for example, the first buildings with steel structure started to be built from 1870 on in large cities such as Chicago, New York, Detroit and St. Louis. In Brazil, the use of metallic structures was not too known until the 1980s. In building construction, this solution was not even considered by engineers and architects. Historic and cultural factors that came from the lack of appropriate steel products at that time contributed to this reality. Therefore, by these reasons and due to the historic use of low-cost labor in the conventional concrete, this solution became more traditional in Brazilian civil construction.

The growing demand of steel for construction works represents therefore a recent phenomenon and even a welcome change in our culture. To follow this process of growth, the steel productive chain is investing in technology and productivity to promote this material as an efficient, technically feasible and sustainable option.

The use of metallic structures in civil construction is associated to the concepts of modernity, innovation, vanguard and sustainability, translated in works of huge architectural expression. Lightness, flexibility, beauty, economy and short terms to carry out the work are features that transformed steel in a preferential option for most projects. All these advantages, therefore, do not resist to the simple argument that steel structures are more expensive than concrete structures. Frequently this position ends the analyses of available construction processes with no more deepening.

But for the engineer Fernando Ottoboni Pinho, professor of steel structures and metallic bridges and chief of the Structure Department of the Civil Engineering Graduation Course of the University of Volta Redonda, these analyses are frequently based on studies of cost comparison with not too much deepening, that are no more than particular cases that cannot be used as a rule. “In other situations, the option for so-called conventional systems due to the lower knowledge of other alternatives—even leading to a cheaper solution—does not guarantee that this is the most appropriate decision”, says the engineer that is a member of Gerdau Açominas technical staff.

“The choice of a constructive system should not be a competition among the different types of structures, but a decision based on the features of each system. And the selection of the best solution has to consider most representative aspects of the work, with priority to mandatory and desirable features. Therefore, the question that has to be asked by the professionals, builders or investors with any trend or preference, concerned only about the best result for the work as a whole is: what type of structure fits better my work needs?¨, suggests the expert.

For Fernando Ottoboni Pinho, the main difficulty in identifying the type of structure that fits better to any work is the lack of a methodology of evaluation that would be more comprehensive than a cost comparison. And that would also consider all limiting and conditioning factors of each alternative in conditions that may be compared, taking into account important aspects that come from different quality and performance to the influence of the structures in other services, including gain transferences that may benefit the total cost of the works. A method of evaluation that identifies the most appropriate alternative of structure will involve the knowledge of all features of each structural system, the experiences and cultural aspects of the contractor and obviously the type of work that is being analyzed.

The method proposed by the engineer is based on an array that allows the crossing of the most important features for the job with the available structural systems. The idea is to classify these features defining a weight for each one in accordance with its importance for the work that is being considered and then establish a mark for each structure systems according to its influence on the analyzed feature in the work.

The table below, made by Fernando Ottoboni Pinho, shows a hypothetic example of practical application of the proposed method in selecting the most appropriate structural system of a multi-floor commercial building. Each feature received a weight from one to five, depending on its importance for the work and—for each structural system—a mark between 1 and 10 based on cost analyses and all other influences. The result is shown by the weighted average of each system. The highest value indicates the system that better fits to the works.show

In the site www.gerdau.com.br/arquivos-tecnicos/20.brasil.pt-BR.force.axd‎ this methodology of evaluation is detailed, in accordance with the criteria proposed by the engineer.

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