Probabilistic limiting tolerable displacements for serviceability limit state design of foundations

The design of a geotechnical work should satisfy both the ultimate limit state and serviceability limit state requirements. The limit state design approach addresses various performance requirements and aims to accommodate uncertainties. At present, most limit-state design codes use reliability principles to design for ultimate limit states. However, serviceability limit states are still considered in some design codes using the conventional deterministic approach. To develop reliability-based serviceability criteria for more consistent design, the probability distributions of the limiting tolerable displacements should be studied. The objectives of this paper are to study the variability of tolerable displacements of structures and to propose a procedure to establish probability distributions of the limiting tolerable displacements. To formulate appropriate probability distributions of the limiting tolerable displacements of structures, performance information was studied and evaluated for 171 bridges and 95 buildings that experienced certain settlement, and for 204 bridges and 205 buildings that experienced certain angular distortions. A method employing a fragility curve to represent the cumulative probability distribution of the limiting tolerable displacement has been proposed. Using this method and the collected performance data, the probability distributions of the limiting tolerable settlements and angular distortions have been established for steel bridges, concrete bridges, buildings on shallow foundations and buildings on deep foundations.