Probabilistic concept for deformation-based design of hybrid elements like composite beams

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The design method for composite members is based on the semiprobabilistic safety concept. The safety factors for resistance are based on the characteristic behavior and the statistical spread of materials. But, depending on material combinations and ductility of joints, for a specific composite member it can be necessary to use different safety factors with other weighting of the influences. From a scientific point of view, a simple transformation of safety factors based only on the behavior of the material or of the composite joint is not correct. In order to realize the required safety level a generalizable safety concept has to be developed for composite members.The basic principles of this safety concept will be developed using the example of the well known composite beams. Out of existing and new composite beam tests the statistic spread of load-deformation-behaviour will be determined at different states. Additional FEM analysis will enlarge the number of available data by parametric studies. The behavior of composite beams will be evaluated at serviceability limit state and at ultimate limit state using the reliability theory. Evaluation will be done at the level of cross section performance taking into account the slip in the composite joint and its statistical spread.Systematic calculation using reliability method will lead to a weighting of the relevant input parameters in ultimate limit state. So the necessary partial safety factors for resistance can be justified. The behavior of composite beams at serviceability limit state will be evaluated on basis of deformations. In this process slip in the composite joint will be taken into account. The exceeding of deformation limits will be a new failure criterion in the probabilistic evaluation of the beam behavior. This leeds to a new approach in the design method for composite beams that is necessary to guarantee the required safety level.Finally the new concept for the justification of safety factors will be generalized so that it can be applied for different types of composite members.