Infrastructure plays a crucial role in our society, supporting our communities; and as such, there are expectations for an acceptable level of safety. But structures do degrade over time due to various factors, including environmental conditions and loads (e.g. wind and traffic). ASCE’s 2021 Infrastructure Report Card reported that of the 617,000 bridges across the U.S., 42% have served for at least 50 years currently, and 7.5% (46,154) are structurally deficient with poor condition. Structures need to be evaluated regularly to ensure they can fulfill their service requirements.

Researchers Cao Wang, Ph.D., M.ASCE; Michael Beer, Dr.Eng., M.ASCE; and Bilal M. Ayyub, Ph.D., P.E., Dist.M.ASCE, present an overview on the assessment approaches for structural time-dependent reliability. Their study “Time-Dependent Reliability of Aging Structures: Overview of Assessment Methods” in the ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering discusses four aspect of assessment management that are widely applied today, including structural service life, maintenance reliability assessment, single structure reliability methods, and structural reliability.

This state-of-the-art review discusses the necessity of performing ongoing reliability assessments on aging structures due to the time-variation of both the structural resistance and the external load process. The full paper is available in the ASCE Library at


Reliability assessment of engineered structures is a powerful and useful concept to estimate the structural capacity of withstanding hazardous events during their service lives. Taking into account the time variation of both structural resistance and the external load processes, the structural safety level is dependent on the duration of service period of interest, due to the accumulation of hazards by exposure in time. This paper presents an overview on the nonempirical assessment methods for time-dependent reliability of deteriorating structures. Generally, these methods can be classified into two types, namely simulation-based and analytical methods. The former is usually brute, and is especially suitable for solving high-dimensional reliability problems. Conversely, analytical solutions may improve the calculation efficiency significantly, and offer insights into the reliability problem that otherwise could be difficult to achieve through Monte Carlo simulation. Both the simulation-based and analytical methods will be reviewed in this paper. Furthermore, the application of time-dependent reliability methods in practical engineering is discussed. Recommendations for future research efforts are also presented.

Read the full paper in the ASCE Library: