RESEARCH ARTICLE Reliability and variance-based sensitivity analysis of arch dams during construction and reservoir impoundment M. Houshmand KHANEGHAHI a , M. ALEMBAGHERI b* , N. SOLTANI b a Department of Civil Engineering, Shahid Beheshti University, Tehran, Iran b Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran * Corresponding author. E-mail: alembagheri@modares.ac.ir © Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018 ABSTRACT The static performance of arch dams during construction and reservoir impoundment is assessed taking into account the effects of uncertainties presented in the model properties as well as the loading conditions. Dez arch dam is chosen as the case study; it is modeled along with its rock foundation using the finite element method considering the stage construction. Since previous studies concentrated on simplified models and approaches, comprehensive study of the arch dam model along with efficient and state-of-the-art uncertainty methods are incorporated in this investigation. The reliability method is performed to assess the safety level and the sensitivity analyses for identifying critical input factors and their interaction effects on the response of the dam. Global sensitivity analysis based on improved Latin hypercube sampling is employed in this study to indicate the influence of each random variable and their interaction on variance of the responses. Four levels of model advancement are considered for the dam-foundation system: 1) Monolithic dam without any joint founded on the homogeneous rock foundation, 2) monolithic dam founded on the inhomogeneous foundation including soft rock layers, 3) jointed dam including the peripheral and contraction joints founded on the homogeneous foundation, and 4) jointed dam founded on the inhomogeneous foundation. For each model, proper performance indices are defined through limit-state functions. In this manner, the effects of input parameters in each performance level of the dam are investigated. The outcome of this study is defining the importance of input factors in each stage and model based on the variance of the dam response. Moreover, the results of sampling are computed in order to assess the safety level of the dam in miscellaneous loading and modeling conditions. KEYWORDS concrete arch dams, reliability, randomness, improved Latin hypercube sampling, variance-based sensitivity analysis, exceedance probability, Sobol′ index 1 Introduction Structural reliability of concrete arch dams is one of the most important subjects because of disastrous conse- quences of their failure including not only economic losses but also human casualties. Their mass concrete body and rock foundation are continuously monitored even during the construction process and specifically during the reservoir impoundment. Those arch dams which are properly designed and constructed can survive common usual and infrequent unusual and extreme loading condi- tions [1]. The usual loading mainly consists of the dam self-weight, the normal reservoir hydrostatic pressure, and the thermal loads [2]. The arch dams are in a permanent interaction with their rock foundation. There is a “peripheral joint” between the dam and the abutment rock. The rock is commonly considered as a homogenous domain in numerical analysis; nonetheless, it can be a very complex medium with high levels of uncertainty contain- ing different layers, faults and fissures. The properties of the rock foundation may considerably alter the static and dynamic response of the dam-foundation system [3,4]. In particular, the presence of the soft rock layers may influence the response of the arch dams [5–9]. There is another type of joints within the arch dams’ body due to the stage-by-stage construction in individual cantilever monoliths. The monoliths are divided from each other by these joints called “contraction joints”. The Article history: Received Dec 9, 2017; Accepted Feb 7, 2018 Front. Struct. Civ. Eng. https://doi.org/10.1007/s11709-018-0495-1