Many Brazilian stadiums have been presenting structural problems in their stands, as a result of excessive vibrations on days of major events. These problems are caused, in most cases, due to infrequent structural maintenance. Furthermore, the stadiums were not designed to withstand the dynamic loads to which they have been submitted.

At the time they were built, the dynamic efforts induced by the public were of much lower intensity and of short duration, and not as it happens today during large musical shows, when the stands must withstand, for a long period of time, the rhythmic impact of an audience.

Even in cases where safety related to the collapse of the structure is guaranteed, it is necessary to verify that the vibrational levels are within the limits allowed by international standards, to ensure the comfort of the public, thus avoiding panic situations.

The Cícero Pompeu de Toledo Stadium (Morumbi), for example, was interdicted by CONTRU – Department of the Municipality of São Paulo that verifies and approves the safety conditions in buildings – in early 1995, and has undergone several renovations since that date. , with the aim of solving structural problems in its stands.

São Paulo Futebol Clube, owner of this stadium, carried out renovations that included the recovery of the concrete in the stands and the hiring of renowned Brazilian consultants who proposed some alternatives that are being analyzed. To verify the efficiency of the reforms carried out, São Paulo Futebol Clube contracted the Italian company Ismes Spa, associated in Brazil with Estudos Técnicos e Projetos ETEP Civil Ltda., of which we are directors, to carry out the first dynamic test of forced vibration carried out in the Brazil. The work was carried out in May 1995 and the results were presented by the club to Contru which, in June 1996, partially released the stadium.

Aimed at determining the dynamic properties of the structures (natural frequencies, proper modes of vibration, damping) and calculating the vibrational levels induced by the public, this test consists of exciting the bleachers through a mechanical vibration generator, called Vibrodina, which simulates the rhythmic effect of the crowd, without the presence of the crowd. Inside the Vibrodina, two disks rotate in the opposite direction, with two eccentric masses on each disk, which produce a centrifugal force, controlled and gradually varied, in order to reproduce all the frequencies that a crowd transmits to the stands. The test is carried out in three stages, which correspond to the application of the force produced by Vibrodina in the vertical, horizontal, radial and horizontal tangential directions, by repositioning the equipment at the same point.

A network of 21 sensors, installed at strategic points in the stands, captures the structure’s response to this excitation and transmits it to a system of filters and amplifiers that will debug these signals and archive them. This “response file” is processed in a software called ISA (Ismes Signal Analysis), which converts these signals into values analyzed by the associated companies – Ismes and Etep Civil – also responsible for issuing the final report. In the case of Estádio do Morumbi, the test on a single module of the stands was sufficient to carry out the analysis of the behavior of the structure, as the stadium is composed of 72 support pillars (“giants”) that are repeated. In this way, the results obtained in only one module could be considered representative of the others. In addition to providing all the dynamic characteristics of the structure, the test tested an alternative under study that aimed to reduce the vibrations of the stands. This alternative consisted of a metallic pillar located between the lower ring (numbered below) and the intermediate ring (numbered above). Thus, the test was performed twice: with and without the abutment. After 10 days of tests and dynamic calculations, the final results showed that:

1) the structures of the stands did not show any plastic deformations; 2) the alternative that considers the metallic pillar did not present significant reductions in vibrations; 3) with full capacity, the vibrational levels exceed the limits allowed by international standards. In order for these limits to be respected, the following condition must be obeyed: full occupancy in the lower and higher numbers, which corresponds to 40,000 spectators, and in the stands only one third of the capacity, which corresponds to over 14,000 spectators.

Currently, the stadium is cleared for a maximum capacity of 34,000 fans, as the lower ring is under construction. Another stadium that used the same Italian technology to test its stands was Palestra Itália, from Sociedade Palmeiras Sports. With the same problems of excessive vibrations presented in the previous case, the stadium was released with partial capacity.

At Palmeiras, it was necessary to carry out the test in five different modules, as the structures were built at different times, in addition to not being repetitive, as is the case with the Morumbi stadium. The results showed that parts of the curved section of the bleachers have vibrational levels higher than those allowed by international standards.

The same technology used in these Brazilian stadiums was used by Ismes during the adaptation of several Italian stadiums for the 1990 World Cup, among them the San Siro in Milan, Delle Alpi in Turin and Olímpico in Rome.

Currently, Ismes (Istituto Sperimentale Modelli e Strutture), considered the largest engineering technology center in the world, has been developing services and research in the areas of information technology, large structures and defense of the soil and the environment. Headquartered in Bergamo, Italy, since 1947 Ismes has accumulated extensive experience in the area of maintenance, automatic monitoring and structural recovery projects for tunnels, bridges, historic monuments, stadiums, dams, earthworks and buildings. Among his main works are the automated monitoring of the Tower of Pisa, Bruneleschi’s dome in Florence, the cathedral in Mexico City, the Humber Bridge in Great Britain, the cable-stayed bridge Zarate-Brazo Largo in Argentina, 300 dams Italian dams and 11 dams for the Electricity Generating Authority of Thailand (Egat). At the beginning of its activities, Ismes dedicated itself exclusively to controlling the safety of Italian dams to serve its majority shareholder, Enel (Ente Nazionale per l’Energia Elettrica).

In Brazil, the works carried out during the great impulse of civil construction, from the 50’s, began to show signs of deterioration due to the time of use, lack of maintenance, aggressiveness of the environment and, like the stadiums, for being submitted to efforts beyond those for which they were designed.

These facts, combined with the concerns, requirements and greater awareness of user safety, led Etep civil, a company of the Etep Group, which since 1966 operates in the field of consulting engineering in Brazil, to seek a partnership with Ismes, in order to bring for Brazil technologies that are widely used in Europe and that only recently found conditions to be applied in our country. The main objective of the association is to carry out preventive engineering and maintenance of existing works, providing conditions for use on solid and safe bases.

This partnership between Ismes and Etep Civil began in November 1994, with our visit to Italy to see the works carried out in stadiums, dams and Italian monuments. In October 1995, engineers Paolo Pezoli and Paolo Panzeri, directors of Ismes and professors at the Polytechnic Institute of Milan, spent a week in Brazil visiting the stadiums of São Paulo, as well as companies and public bodies in the areas of Energy and Transport . During the visit to Brazil, Ismes engineers participated in the “1st International Symposium on Dynamic Characterization and Safety of Structures”, organized by Etep Civil at the Engineering Institute of São Paulo, with the support of Ibracon. On that occasion, the problems and solutions adopted in Italian stadiums were presented, as well as the main experimental techniques in the area of structural dynamics. The consolidation of the partnership took place with the work carried out at the Morumbi and Palestra Itália stadiums.

Currently, Ismes and Etep Civil are setting up a joint venture that will have funding from the European Community for the implementation of a Technological Center that will be called Ismes do Brasil. The initial investment will be US$ 1 million and the start of operations is scheduled for the first half of 1997. This Technological Center will be equipped with special equipment, such as those used to carry out the aforementioned dynamic forced vibration tests. In addition to these dynamic tests in stadiums, the Center also intends to serve other types of structures, such as large dams, bridges, viaducts and tunnels. Monitoring for forecasting and risk situations, regarding landslides is another area in which the Center intends to act. Particularly in the area of dams, Ismes has developed the Midas software, which is the intelligent system for monitoring the safety of structures implemented in numerous dams, inside and outside Italy. This system consists of organizing, analyzing and interpreting the periodic readings, manual or automatic, taken by sensors installed in the structures and foundations of a dam and activating warning signals in case of anomalous situations.

The wide experience gained in almost 50 years of existence allows the Italian company to evaluate the efficiency of the network of sensors installed in the dams and to resize it, if necessary, increasing or reducing the number of existing instruments. Through the Midas system, it is also possible to develop static models, which use readings taken over the life of the dam, and calibrated deterministic models, which start from mathematical hypotheses related to its geometry and the characteristics of its materials. Thus, on the one hand, there are the parameters resulting from the theoretical models and, on the other hand, the readings, manual or automatic, obtained from the installed instruments. Through the comparison between the results, theoretical and observed, eventual anomalous behaviors are defined and alert signals are activated.

In addition, this system “self-diagnoses” itself by periodically checking the instruments, thus defining whether a discrepant reading is due to a failure in the sensor or whether it is an indication of some anomalous behavior of the structure.

All this technology will be available in Brazil, from the beginning of the year, in the new Technological Center Ismes do Brasil, which intends to operate throughout South America.

Eng. Liana Becocci and Eng. Marco Juliani

THE CONTRACTOR – April/1997 – No. 343