Concrete Structures: the Challenge of Creativity Reliability based assessment procedure for concrete structures Alfred STRAUSS Univ.Ass. University of Applied Sciences and Natural Resources Vienna, Austria Konrad BERGMEISTER Professor University of Applied Sciences and Natural Resources Vienna, Austria Ulrich SANTA Researcher. University of Applied Sciences and Natural Resources Vienna, Austria Summary The reliability assessment, which goes well beyond the boundaries of codes can bring a significant amount of money savings and provide new insight into bridge administration and decision-making processes. Therefore an engineering software programme has been developed which allows the reliability assessment of existing structures in an easy way. The software programme combines a non-linear FE-Method with probabilistic calculation tools and a database for stochastic models. The conception of this software programme also allows the inclusion of uncertainties due to inspection and the inclusion of degradation models. Keywords: Reliability Assessment, Existing Structures, Sensitivity Analysis, Safety Target, Monitoring. 1. Introduction The general approach for the safety evaluation of existing bridges is based on codes and different specific regulations. It has been found that reliability assessment, which goes well beyond the boundaries of codes can bring a significant amount of money savings and provide a new insight into bridge administration and decision-making processes, Casas et al. [1], Enevoldsen [2], Frangopol [3]. Latest developments show that the optimum balance between the cost and safety of concrete structures, e.g. bridges, is becoming a common problem worldwide. Methodologies for use in probabilistic based assessments are available and have been proven to work in practice. But suitable tools for use in design offices are generally missing. This paper shows the combination of efficient techniques, fracture mechanics, monitoring and reliability engineering to achieve this goal: to assess the realistic behaviour of concrete structures from the reliability point of view. The aim of this paper is to present a procedure that allows the probabilistic-based assessment of structures, which can be used in combination with degradation-models and monitoring data for an efficient life cycling planning. For degradation modelling a function will be presented which allows a continuous updating of the degradation line after each inspection. A further question that will be discussed is the demand of safety features for existing structures. Existing structures have already shown their load capacity. Regarding this thematic area, an approach for required safety indexes was worked out by Strauss [4]. However, it is also possible that the demanded safety index – safety standard is subjected to fluctuations due to social or other influences, such as the ruggedness of the structure and the loading situation, over a longer time period. 2. Probabilistic-Based assessment 2.1. Features and requisition of non-linear FE-analysis + stochastic software The procedure is based on a recently developed integrated system of non-linear fracture mechanics software ATENA and probabilistic module FREET called SARA (Structural Analysis and Reliability Assessment). The Latin Hypercube Sampling technique, which requires a rather small number of samples for accurate results in the opposite to the statistical Monte Carlo simulation shows an efficient technique to solve non-linear analysis which is computationally intensive. The presented approach has been applied recently for several reliability problems, Novák et al. [5], Pukl et al. [6], [7]. This approach was already used at several problem definitions of engineer nature and provides a deeper insight due to the included sensitivity analysis in the structural behaviour. In the necessary modifications of ATENA for implementation into the SARA system it was a crucial point to keep all of the existing features available, as well as for the repeated stochastic analysis. It was enabled due to versatile programming architecture and the construction of the ATENA system,