Introduction. To ensure the functioning of earthquake-affected areas, it is very important to ensure the earthquake resistance of bridges and other transport infrastructure facilities. One of the characteristic damages of bridges during an earthquake is the dumping of superstructures from their supports. The discharge of superstructures is caused by different ground conditions under the supports along the length of the structure, which in turn leads to different perturbations of the supports during an earthquake.

Materials and methods. The assessment of the course of the supports of a girder split bridge in Uzbekistan is considered. The ground conditions under the supports of the bridge vary along the length of the structure. It is necessary to calculate the motion of the bearing of bridge in order to exclude the dumping of the superstructure. The authors propose to evaluate the course of the supporting part of the bridge in the development of the linear spectral theory of structures calculating for earthquake resistance, using the mathematical apparatus of the theory of random functions. Usually, the correlation coefficients e are determined under the assumption of stationary processes. In this case, each process is defined by its own spectral density. Various cases of correlation were considered: the correlation between fluctuations of the points of the daytime surface under the supports, the correlation between fluctuations of the top of neighboring supports and the correlation of fluctuations of the base and top of the supports. For all cases, the corresponding correlation coefficients were calculated, which were further taken into account when calculating the motion of the supports.

Results. For the considered three-span bridge crossing with different structural solutions of supports and different soil conditions at their base, the following displacements of the base, relative displacements of the top of the supports, and total displacements were calculated. An assessment of the mutual offsets from above has been performed. Displacements of the top of the channel supports, taking into account the heterogeneity of the acceleration field under the supports. The mutual displacements of the base points in the absence of correlation of vibrations, the mutual displacements of the top of the support in the absence of correlation of vibrations are determined, and the mutual displacements of the base points and the mutual displacements of the top of the support are calculated taking into account the correlation for the case of white noise.

Discussion. An analysis of the results showed that the displacements of the top of the supports are quite significant. Even estimating the displacements as the root of the sum of the squares gives the motion of the supporting part more than 50 cm. Based on the results obtained, recommendations were made for designers, firstly, on the need to develop the support head, and, secondly, on additional reinforcement of the support to compensate for the moment from the vertical reaction of the superstructure with a large motion of the support part, and, thirdly, on the expediency of installing stoppers to eliminate excessive displacements.

Conclusions. The calculation of the motion of the supporting part is a necessary element in assessing the seismic resistance of bridges. The motion of the support part depends on the relative displacements of the top of the supports and the heterogeneity of the acceleration field along the length of the bridge. When designing bridges with different supports and with different ground conditions under the supports, it is advisable to combine the spans into a chain, for example, by using rubber support parts.

The effect of the type of rubber-metal bearings on the vibrations of continuous reinforced concrete bridges was calculated based on real earthquake records. To solve problems, the finite element method and finite difference method were used. The results of the calculation of normal maximum stresses, and longitudinal and vertical displacements of a monolithic overpass under dynamic load, based on the records of two real seismograms, are presented. The calculations performed, show that the span structure and supports of the overpass have a sufficient margin of safety in the event of strong and very strong earthquakes according to MSK-64. To ensure the guaranteed seismic safety of bridge structures, it is required to conduct design calculations based on sets of records of past earthquakes that are close in dominant frequencies to the characteristics of the construction site.

Seismic isolation of a road bridge in the seismic region of Uzbekistan with a design seismicity of 9 degrees on the MSK-scale is considered. A special feature of the bridge is the large mass of the spans, which is almost 50 times greater than the reduced pier mass. At a first glance, this rules out tuning the isolation to mass dynamic regime. The rigidity of seismic isolation is determined basing on the condition of limiting the mutual displacement of spans. Even at this limitation, seismic loads were reduced by approximately two times, i.e. by one intensity number. A more effective isolation method has been proposed, that is, when one span is rigidly fixed to the pier and the other is seismically isolated, and then the isolation can be tuned, ensuring the operation of the isolated span as the mass damper. In this case, the load on one of the piers is reduced by more than two times and that on the adjacent pier by more than four times.