The testing of models of two parallel road bridges over the Don river near Aksai city

23 December 2013

Specialists of TsAGI’s structural strength center completed the testing of models of two parallel road bridges over the Don river near Aksai city (Rostov region) for aeroelastic stability in wind flow.

Studies of this kind are very relevant today. To increase the capacity of highways it is necessary to widen the narrowest place of highways — bridges. Construction of a second bridge parallel to the existing one is the most simple and inexpensive solution. This solution has been already used, for example, in Bronnitsy town during expansion of bridge over the Moskva river. Such reconstruction will follow for other highways.

Currently, in order to reduce traffic load on the highway M-4 “Don” a set of works on reconstruction of the bridge crossing over the river Don near Aksai city (Rostov region) is being performed. This year, a second bridge was built next to the existing bridge. To identify the stability boundaries of the two bridges in the wind flow the designer of bridges (JSC “Institute “Giprotransmost” ) turned to TsAGI experts.

“We faced a really pioneering, unique work,” the head of operations, Deputy Chief of strength, loads and aeroelasticity standards department of TsAGI Konstantin Strelkov explains. “The problem of aeroelastic stability of two parallel bridges has been little studied by domestic and foreign experts. TsAGI researchers have extensive experience in studies of aeroelastic stability of ‘single’ bridges. Double facilities located close to each other (the distance between the bridges is 7 meters) have not been examined experimentally before.”

Tests were conducted in TsAGI’s subsonic wind tunnel T-103 at full-scale wind speeds up to 35 m/s. For these works, TsAGI specialists designed and manufactured two dynamically similar models made ​​in 1:40 scale, and a special bench. In the future, this stand will be used for testing various bridges, both “single” and “double” ones.

The experiment showed that the mutual influence of two adjacent bridges is quite significant. At wind speed of 18–20 m/s, strong vibrations occurred on the bridge exposed to the wind with amplitudes of 300–400 mm, exceeding the level of the human comfort perception of vibrations.

To reduce vibration level, the Institute experts examined several options of various aerodynamic tools: screens, fairings and baffles. Screens provided the greatest effect in reducing the amplitude of vibrations. During the tests damping devices that increase decrements of bridge vibrations were also tested. As a result, the most optimal structure was developed, capable of ensuring safe operation of both the existing and the newly created bridge.

TsAGI recommended that the customer use the standard “soundproof” screens at both outer side ends of the longest spans of both bridges, as well as install in these spans special “mass dampers” that decrease bridge vibrations.

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