Reliability of highly stressed UHPC slender columns

摘要

Ultrahigh-performance concrete (UHPC) has been used successfully since the early 1990s. Meanwhile concrete-technological developments have allowed production of UHPC with a compressive strength of more than 150 N/mm~2. Thus, the field of application of reinforced concrete constructions currently in use can be extended. In particular, the cross-sectional dimensions required for highly stressed compression members can be reduced. However, in many cases this positive development increased the trend to even more slender and therefore likelier to buckle structural systems. Hence, it is to be expected that under certain conditions the safety level of such construction elements decreases. Because of this, the reliability of slender UHPC structural members is being investigated in a research project, supported by the Deutsche Forschungsgemeinschaft (DFG), at the Technische Universitat Darmstadt. The purpose of this project is the calibration of safety factors in order to achieve the target reliability for safe and efficient design. Realistic modelling of the load-bearing behaviour of slender UHPC columns requires material and geometric nonlinearities to be considered. Due to the load-dependent material behaviour, a sudden stability failure may occur long before the material's strength is exceeded. An adequate analysis of this phenomenon calls for realistic material laws. In this context a special FE-tool which takes into account this phenomenon was developed for stochastic simulations. As a first step, calculation results at cross-sectional level can be used to identify the sensitivity of the parameters. Therefore, specific moment-curvature-diagrams, which are based on stochastic simulation methods, are being developed to identify the influence of concrete compressive strength on the load-carrying behaviour of a structural member with rectangular cross-section. Moreover, the FE-Model is verified by experimental test results of slender columns. By applying the simulation method of adaptive importance sampling (AIS), preliminary results of the reliability analysis are presented in this paper. On the basis of the results of this research project, innovation potentials and limits of application of UHPC will be pointed out.