Categorization of Bridges by Failure Consequences

Categorization of bridge constructions by the failure consequences due to loss of ultimate capacity or serviceability is a difficult task that can be resolved using two different approaches: elementary method using currently valid standards advanced method based on risk assessment. The elementary method is grounded on subjective assessment of bridge malfunctioning or collapse. The bridge is classified into an appropriate category (consequence class) in accordance with the most severe consequence. It is a simple procedure that may be applied without the need of demanding mathematical procedures. However, the resulting categorization may be affected by uncertainties in the assessment of consequences. The advanced method is based on a comprehensive analysis of bridge malfunctioning using a procedure of risk assessment. This method takes account of the occurrence probability of unfavourable events and the significance of individual consequences. Classification of a bridge construction into an appropriate category depends on the resulting risk of the bridge failure. This more laborious approach provides credible results without excessive uncertainties. The most adverse difficulty of the method is a combination of some consequences like the loss of life and economic costs. Both the above-mentioned approaches to the categorization of bridges by failure consequences can be effectively used depending on the type of bridge, on the intensity of exploitation, on expected consequences, and on social impacts of bridge malfunctioning.

On the assignment of dependability level

The problem of assignment of optimum level of dependability is not new and has not yet been solved. The requirement of complete dependability is noted to be erroneous. However, insufficient dependability of buildings is fraught with significant social and economic losses. Hence is the problem of definition of the required, optimal level of dependability. In Russia, there are no quantitative guidelines for the dependability of buildings and structures. At the same time, the strengths of the materials of ferroconcrete structures are regulated by GOST 34028-2016 for rod reinforcement and GOST 18105-2010 for concrete, as well as by building regulations SP 63.13330-2012 Concrete and ferroconcrete structures. In this paper, the dependability of the “Loads – design” construction system is suggested to be defined using the total probability formula. We assume that the mechanical characteristics of a structure’s materials and the loads are independent and joint random values: the emergence of one random value does not depend on the emergence of another one; change of load changes the stresses in the structural section. Probabilistic calculations showed that over the period of 10 years facilities designed in accordance with SP 38.13330.2012 for operation in the Gulf of Finland, will be destroyed almost with the 100% probability. For normal consequence class facilities (KS-2) the required dependability must tend to 3σ (0.99865). In order to ensure the required dependability of construction system of about 3σ, the probability of loads of 0.99865 should be attempted to be ensured. The application of SP does not always guarantee the required dependability of construction facilities. The application of probabilistic approaches in solving engineering problems can prevent emergency situations.