SEISMIC PERFORMANCE OF PIPING ANCHORED TO CONCRETE IN CASE OF NONLINEAR LOAD-BEARING BEHAVIOR OF POST-INSTALLED ANCHORS

In nuclear power plants, post-installed anchors are used for connections between concrete structure and non-structural components such as piping systems. Piping is usually connected to concrete fastenings by pipe hangers. Dynamic loading during an earthquake leads to dynamic interactions between concrete structure and non-structural component. These dynamic interactions result in dynamic loads which have to be transferred by fastenings such as anchor plates with post-installed anchors. Besides the vibrational behavior of the subsystems, the dynamic behavior of the coupled system concrete-fastening-piping is also influenced by the load-bearing behavior of the anchors. At anchor loads close to ultimate load, the load-bearing behavior of anchors is highly nonlinear due to plastic deformation of the anchor bolt and cracking of the concrete. Additionally, permanent displacement of anchors which already occurs at smaller loads can lead to change of pipe hanger stiffness characteristics and nonlinear vibrations of the component. For an ongoing research project, various numerical design calculations are carried out for a test set-up. The test set-up is designed to study the dynamic interactions and effects mentioned above. In order to investigate the necessity for a coupled analysis of the structural and non-structural part of the test set-up, one study in this paper deals with the effect of coupling/decoupling on calculated natural frequencies and pipe hanger loads. For simulating the nonlinear behavior of the fastening during seismic loading, anchor models with different levels of complexity were developed which were then implemented in a large-scale finite element model of the test set-up. Comparative seismic analyses in the time domain with different anchor models are presented which are carried out as preliminary simulations for the design of the test set-up.