| dc.description.abstract | Reliability analysis in structural engineering is utilized in the initial design phase and its application
continues throughout the service life of a structural system in form of maintenance
planning and optimization. Engineering structures are usually designed with extremely high reliability
and with a long service life. However, deterioration with time and exposure to external
hazards like earthquakes, strong winds etc., increase the structure's vulnerability to failure.
In structural reliability analysis, stochastic processes have been utilized to model timedependent
uncertain variations in environmental loads and structural resistance. The Homogeneous
Poisson Process (HPP) is most commonly used as the driving process behind environmental
hazards and shocks causing structural deterioration. The HPP model is justi ed on
account of an asymptotic argument that exceedances of a process to a high threshold over a
long lifetime converge to HPP model. This approach serves the purpose at the initial design
stages. The combination of stochastic loads is an important part of design load estimation.
Currently, solutions of the load combination problem are also based on HPP shock and pulse
processes. The deterioration is typically modelled as a random variable problem, instead of a
stochastic process. Among stochastic models of deterioration, the gamma process is popularly
used. The reliability evaluation by combining a stochastic load process with a stochastic process
of deterioration, such as gamma process, is a very challenging problem, and so its discussion is
quite limited in the existing literature.
In case of reliability assessment of existing structures, such as nuclear power plants nearing
the end of life, an indiscriminate use of HPP load models becomes questionable as asymptotic
arguments may not be valid over a short remaining life. Thus, this thesis aims to generalize
stochastic models used in the structural reliability analysis by considering more general models
of environmental hazards based on the theory of the renewal process. These models include
shock, pulse and alternating processes. The stochastic load combination problem is also solved
in a more general setting by considering a renewal pulse process in combination with a Poisson
shock process. The thesis presents a clear exposition of the stochastic load and strength combination
problem. Several numerical algorithms have been developed to compute the stochastic
reliability solution, and results have been compared with existing approximations. Naturally,
existing approximations serve adequately in the routine design. However, in case of critical
structures with high consequences to safety and reliability, the use of proposed methods would
provide a more realistic assessment of structural reliability.
In summary, the results presented in this thesis contribute to the advancement in stochastic
modeling of structural reliability analysis problems. | en |
