Estimation of earthquake stability of reinforced arch viaduct of tunnel type strengthened by corrugated metal arch structure has been carried out. The structure calculation has been done using the finite element diagram including railway the embankment, the composite arch and soil base. Along the contour of the design area was placed the damping boundary. Obtained system mode parameters (frequencies and damping) were used for generating design accelerograms. It is shown that in the process of strong earthquakes (MDE) in the arch impost and crown may occur plastic hinges. When this becomes the arch turn from hingeless one into two or three — hinge arch, but does not lose bearing capacity. The recommendations for the reinforcement of structures under consideration are proposed.

It is shown that in many cases while calculating bridge spans it is necessary to take into account the soil-structure interaction. If the pier is higher than 5 m, energy dissipation for the main oscillation mode is determined substantially by energy losses, caused by wave propagation in the soil base, thereby the dynamic ratio drops significantly. Furthermore, if a bridge span is shorter than 55 m and the base modulus of deformation Eo < 30 MPa, the force in the piers can be determined by the second mode, for which the superstructure and piers oscillate in antiphase. For bridges with spans over 80 m long at Eo > 30 MPa, seismic forces for spans and piers are determined by the first oscillation mode. 

The results of the paper of Prof. Tan “An improved response spectrum method for non-classically damped systems”, previously published in Bulletin of Earthquake Engineering, are analyzed. It is noted that the paper contains important material which allows one to analyze systems with arbitrary damping. According to the authors, the method of constructing the velocity spectra of damped systems is important for calculating damped systems. The material presented in the paper is a kind of basis for explicitly taking damping into account in regulatory documents. To do this, it is necessary to link the existing regulatory documents with theoretical studies. Relevant proposals are set out in the presented response and are illustrated by an example. At present the most difficult thing is to carefully construct damping equations, in particular, to take account of internal friction in the material