Introduction. The effectiveness of investments in antiseismic reinforcement of a building is largely determined by seismic risk, while social risk accounting is an important part of seismic hazard assessment and is subject to serious analysis.

Aim. The article provides an assessment of the seismic risk and economic efficiency of anti-seismic strengthening of residential buildings taking into account human losses and situational seismicity at the construction site.

Materials and methods. The risk assessment methodology proposed by L.V. Kantorovich was used to conduct the research. The risk assessment was performed using known in the literature payoff matrices and data on the recurrence of earthquakes in regions with different situational seismicity. The study developed a method for assessing human losses based on the economic characteristics of residential development.

Results. The ratio of social and commercial seismic risk was estimated. In the conditions of the Russian Federation, social risk is about 5-10% of the economic risk. It is shown that the required degree of strengthening of buildings and structures for the conditions of the Russian Federation is largely determined by economic losses.

Concusions. With an increase in insurance payments for loss of life to 50 million rubles, social losses begin to determine the degree of anti-seismic strengthening.

The paper discusses the effectiveness of using pneumatic protection to reduce seismic loads on a water tower. The tower carries a reservoir with a capacity of 30 m3. Air tanks, used as pneumatic protection, are placed along the reservoir perimeter in the zone of maximum hydrodynamic pressure. The volume of air was accepted according to the recommendations of O.A. Savinov and M.M. Peychev and is equal to 4 m³. The analysis of the hydrodynamic equations makes it possible to divide the liquid in the reservoir into two parts. One part is rigidly connected to the reservoir (attached mass of liquid), and the second part is connected with the tank by a spring simulating an air shock absorber. In the performed calculations, the added mass was 14 tons. The effect of the seismic load decrease was less than expected. This is due to the fact that the structure of the tower itself is quite heavy, and the load from its own weight is approximately equal to the load caused by the weight of the liquid. Therefore, doubling the liquid load reduces the total load by only 25%.

Purpose: To increase the seismic resistance of water towers by applying pneumatic protection. Traditionally, the seismic resistance of water towers is provided by a constructive solution of the tower shaft; in this case, increasing the seismic resistance of already operated towers is problematic. In this regard, the task was set to change the dynamic characteristics of the structure through the use of pneumatic protection directly in the reservoir of the structure.

Methods: The article discusses the constructive solution of internal pneumatic protection and the method of calculating water towers with its application to seismic loads, and evaluates the effectiveness of this type of seismic protection. A numerical calculation of the volumes of pneumatic protection and numerical values of the parameters of the calculation-dynamic model of the design of a water tower with internal pneumatic protection in relation to the A.A. Rozhnovsky. Calculations for seismic impact have been performed and forces in the structural elements of a water tower without pneumatic protection and with its installation have been determined.

Results: A comparative analysis of the oscillations of a water tower without pneumatic protection and with it was carried out. The results show that in the presence of pneumatic protection, the dynamic characteristics of the system change, which leads to a decrease in seismic loads and a significant decrease in the forces in the design of the water tower, including in the shaft.

Practical significance: The device of internal pneumatic protection will ensure seismic resistance, including operated water towers in those areas where the seismicity of the construction site has been increased due to the revision of general seismic zoning maps. Internal pneumoprotection makes it possible not to provide for additional insulation of pneumoprotective installations, since they are located inside the tank. In addition, this solution facilitates the operation of a water tower equipped with pneumatic protection, since the structural elements of the device are protected from external influences.

The article discusses a method for analyzing the risk assessment of failures of the structure as a system by developing a "Fault Tree Analysis". Formulas were proposed for the numerical estimation of the probability of system failure, taking into account the stochastic dependence of the failures of its elements. On the example of a nuclear power facility, a "wet" stand-alone storage facility for spent nuclear fuel, an analysis of possible scenarios of a facility failure was carried out, a "Fault Tree Analysis" was developed and calculated under seismic impact. It has been determined that the risk of structure as a
system under seismic impact is determined by the risk of falling process
equipment and building structures on the overlap of storage compartments or
stored nuclear fuel. To increase the safety of building structures under
seismic impact, it is necessary to pay special attention to the design features
of the frame part and the interface between the monolithic storage compartment
and the frame part, as the most vulnerable link.