Shape Optimization Design of Arch Type Dams under Uncertainties Due to an increased need for hydro electricity water storage and flood protection it is assumed that a series of new dams will be built throughout the world. Comparing existing design methodologies for arch type dams model based shape optimization can effectively reduce construction costs and leverage the properties of construction materials. To apply the means of shape optimization suitable variables need to be chosen to formulate the objective function which is the volume of the arch dam here. In order to increase the consistency with practical conditions a great number of geometrical and behavioral constraints are included in the mathematical model. An optimization method namely Genetic Algorithm is adopted which allows a global search. Traditional optimization techniques are realized based on a deterministic approach which means that the material properties and loading conditions are assumed to be fixed values. As a result the real world structures that are optimized by these approaches suffer from uncertainties that one needs to be aware of. Hence in any optimization process for arch dams it is nec essary to find a methodology that is capable of considering the influences of uncertainties and generating a solution which is robust enough against the uncertainties. The focus of this thesis is the formulation and the numerical method for the optimization of the arch dam under the uncertainties. The two main models the probabilistic model and non probabilistic models are intro duced and discussed. Classic procedures of probabilistic approaches un der uncertainties such as RDO (robust design optimization) and RBDO (reliability based design optimization) are in general computationally ex pensive and rely on estimates of the system’s response variance and fail ure probabilities. Instead the robust optimization (RO) method which is based on the non probabilistic model will not follow a full probabilistic approach but works with pre defined confidence levels. This leads to a bi level optimization program where the volume of the dam is optimized under the worst combination of the uncertain parameters. By this robust and reliable designs are obtained and the result is independent of any as sumptions on stochastic properties of the random variables in the model. The optimization of an arch type dam is realized here by a robust optimiza tion method under load uncertainty where hydraulic and thermal loads are considered. The load uncertainty is modeled as an ellipsoidal expression. Comparing with any traditional deterministic optimization (DO) method which only concerns the minimum objective value and offers a solution candidate close to limit states the RO method provides a robust solution against uncertainties. All the above mentioned methods are applied to the optimization of the arch dam to compare with the optimal design with DO methods. The re sults are compared and analyzed to discuss the advantages and drawbacks of each method. In order to reduce the computational cost a ranking strategy and an ap proximation model are further involved to do a preliminary screening. By means of these the robust design can generate an improved arch dam structure which ensures both safety and serviceability during its lifetime.