Lifetime Oriented Design Concepts of Steel-Concrete Composite Structures Subjected to Fatigue Loading

Abstract

In current national and international standards for composite structures of steel and concrete the determination of the ultimate load capacity and the fatigue life of headed shear studs takes place with separate and independent verifications at the ultimate limit state, serviceability limit state and fatigue limit state. The fatigue resistance is verified in accordance with the design concepts for steel structures, based on nominal stress ranges and linear damage accumulation according to Palmgren and Miner. The effect of pre-damage due to fatigue loading on both the ultimate and the serviceability limit state is not considered. Because cyclic loading of headed shear studs leads to a decrease of static strength of stud connectors, the assumptions for independent limit states are not given and the reliability index of steel-concrete composite structures subjected to fatigue loading may fall below the target values in codes. This paper is dealing with the results of a comprehensive programme of experimental work with more than 90 standard EC4-push-out test specimens and two full scale-beam tests which consider the crack propagation through the stud foot and the local damage of concrete surrounding the studs resulting from high cycle loading. Based on the results of the push-out tests, new design concepts were developed to predict the fatigue life and the residual strength of headed shear studs after high cycle loading. Considering the interaction between the local damage and the behaviour of the global structure, these research results were taken as the basis to simulate the cyclic behaviour of composite beams by means of a new damage accumulation rule.