In the backyard of a single-story house in Butantã, which has been transformed into an engineering office, a machine doesn’t call much attention, except for its yellow color. The small size, with dimensions not much larger than a dining table, disguises its weight of 2.5 tons and hides its incredible power, which can reach up to 10 tons-force. This is Vibrodina, used to test the vibrations of large constructions, such as bridges and stadium stands.

Finding it parked on the IEME Brasil lot was a happy coincidence: it had just returned from Arena Corinthians, the popular Itaquerão, and would be traveling in a few days to Natal, where it will be used at Arena das Dunas — both stadiums must be used in the World Cup 2014. In both, Vibrodina fulfills the same function: applying dynamic loads to the stands to simulate the vibration of the fans and, thus, help to check if everything is right in the construction.
But how can this compact and sturdy equipment simulate the jumps of a soccer crowd? Make no mistake: despite its reduced dimensions — 1.2m wide by 1m long and 1.2m high — the Vibrodina is powerful enough to be in our Monster Machines section.

The secret is in the use of centrifugal force. It has two discs of 60 cm in diameter, on which lead masses are placed. With the machine fixed to the floor of the structure to be tested, an electric motor drives the discs, which rotate and transmit the force to the construction, causing it to vibrate.
Power is provided by a 380V and 40 KVA generator powered by diesel oil. Almost all of the generated power goes to the machine. The intensity of the vibrations varies according to the position of the mass on the disk, while the frequency, which reaches up to 20Hz, depends on the speed of the engine — all of which is electronically controlled. To get to the test site, it is taken by a Munck truck and needs to be loaded by a crane to the high places.

But it’s not enough just to make the bleachers shake: the vibration has to be measured. According to Marco Juliani, technical director of IEME Brasil, there are three magnitudes involved in the process: displacement, speed and acceleration — the latter is the measurement that matters to ensure the safety and comfort of the public. Therefore, twenty accelerometers are used to measure the vibration — if the structure is too large, they are changed places and the test is repeated, to cover the entire area.
Once the results are obtained, comes the analysis phase, in which the experimental values are compared with those predicted in the project. If they are close, the work is approved; otherwise, it is a sign that the structure presents some anomaly in the execution, which must be corrected. According to Juliani, there is no consensus on an acceptable limit in stadiums, but the value is between 500 and 600 mm/s².

In addition, situations of maximum vibration are sporadic and rarely occur during an event — think of the home team’s goal or the great hit of the band that is playing: it is for moments of excitement like these that the structure is tested.

Adapting to the New Crowd

Vibrodina was commissioned — it is not produced in series — by the company in 1996, to carry out vibration tests at the Morumbi Stadium, which had been banned a year earlier by Contru (Department of Control of the Use of Real Estate of the City of São Paulo ). Even after renovations, the stadium was still shaking a lot, since, in addition to the lack of maintenance, it had been designed at a time when the behavior of the fans was different: the stadium was a place to go with a suit and headband, applaud and watch the game sitting down. A lot has changed.

The test with the machine — the first of its kind to be carried out in a Brazilian stadium, something totally unusual at the time — identified the problem and allowed a solution to be identified: the stands received shock absorbers, to provide stability and reduce vibrations.

Since then, Vibrodina has shaken old stadiums such as Pacaembu, Canindé and Maracanã. With the confirmation of Brazil as host in 2014 and the construction and adaptation of several stadiums across the country, the machine is being used more and more, and has traveled a lot — it has already been in the future stadiums of Corinthians and Palmeiras. In addition, over the years, the machine received updates in the electronics, gaining new sensors and control software.

The equipment, according to Juliani, is also used in other types of projects, such as bridges and dams.

Testing with dynamic loads has some nice advantages: First, it’s non-destructive—you don’t need to drop or crush anything to prove that the place can withstand such an impact. Secondly, Vibrodina simulates a realistic situation of use, in addition to requiring less effort than a static load test — imagine filling a stadium with sandbags to reproduce the weight of the crowd. In addition to safety, all this contributes to you feeling the right emotion in the stands when your team scores a goal: not fear, but joy.

Originally posted by GizModo

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