Reliability of highly stressed UHPC Columns taking into account spatial variation of structural properties

• Applicant: Professor Dr.-Ing. Carl-Alexander Graubner
• Subject Area: Structural Engineering, Building Informatics and Construction Operation ; Construction Material Sciences, Chemistry, Building Physics
• Term: from 2010 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 167643844

Meanwhile, concrete-technological developments have allowed production of ultrahigh-performance concrete (UHPC) with a compressive strength of more than 150 N/mm². The dimensions of the cross-section can then be reduced significantly, especially in highly stressed compression members. On the other hand, the construction members become more slender and the danger of buckling failure increases. The reliability of such structures was not analyzed in detail up to now. A DFG-supported research project (Schm 2682/2-1) was therefore undertaken to determine the failure probability of slender columns made of UHPC and to identify the important material and system properties influencing the reliability. The result is that with increasing slenderness and small load eccentricity, the reliability decreases. Furthermore, fibre distribution and fibre orientation affect the material properties and, in consequence, the failure probability. First trial calculations show that using random field theory to take into account spatial distribution of material properties, the reliability of slender columns made of UHPC may be calculated much more accurately. However, the scientific investigation of spatial discontinuities (material and system) in UHPC-members is still missing. Due to this the research proposal deals with the influence of spatial scattering of material and system properties on the reliability of slender compression made of UHPC.The main goals of the research project are:A) Experimental validation of the scatter of material properties (compression strength, tension strength, Young´s-modulus) taking into account fibre distribution and fibre orientation.B) Investigation of the correlation values regarding spatial scattering of system parameters on the basis of load-bearing tests and experimental data.C) Derivation of auto-correlation functions of basic variables and implementation in the already developed software tool for the stochastic analysis of slender structures.D) Quantifying the consequences of spatial discontinuities on the reliability of compression members made of UHPC.Taking into account spatial scattering of structure properties, a holistic approach for a stochastic model can be developed, which incorporates spatial correlated parameters in material and geometry in order to determine the realistic probabilities of failure. This allows important scientific findings concerning the sensitivity of the system performance. The described knowledge gaps about the statistical basic variables of material properties and geometrical parameters are closed. Furthermore, the state of knowledge concerning the load bearing behavior of UHPC-members is significantly enlarged.

• DFG Programme: Research Grants