Seismic isolation analysis of exposed steel penstock based on a simplified model of a friction pendulum bearing
[Objective]The Central Yunnan Water Diversion Project is situated in a high-seismic-intensity area,and the seismic safety of the water conveyance structure is prominent.Specifically,the significant mass of water within the exposed steel penstock and the inadequate restraint provided by bearings often result in obvious seismic displacement responses of the steel penstock.As a result,damage predominantly occurs at the bearings.Therefore,the mechanical properties of bearings are essential for the seismic resistance of steel penstocks.With the exposed steel penstock from the Central Yunnan Water Diversion Project as the research object,the seismic isolation effect of friction pendulum bearings is examined.[Methods]Suppose that the friction pendulum bearing adopts an elliptical sliding surface.A simplified mechanical model of the bearing is derived.Based on this model,a simplified finite element model of the friction pendulum bearing is developed by spring elements and applied to the finite element simulation of the exposed steel penstock.Dynamic time history analysis of the steel penstock using friction pendulum bearings and flat sliding bearings is conducted.In the simplified spring finite element model of the friction pendulum bearing,the COMBIN39 and COMBIN40 elements in the ANSYS software are used to simulate the horizontal nonlinear force-displacement curve of the friction pendulum bearing,and the COMBIN14 element is used to simulate the vertical stiffness of the bearing.[Results]The results revealed that the structural acceleration and displacement distribution and values computed by using the simplified model were close to those of the fine model.Thus,it was obvious that the simplified finite element model of a friction pendulum bearing constructed by spring elements could simulate the mechanical properties of a friction pendulum bearing well and enhance the efficiency of the finite element simulation analysis of the exposed steel penstock structure.The seismic dynamic response law of the steel penstock with friction pendulum bearings was close to that with flat sliding bearings.In the horizontal direction,the ratio of the acceleration of the upper bearing plate to that of the lower bearing plate of the friction pendulum bearing was between 0.25 and 0.55,while that of the flat sliding bearing was between 0.45 and 0.80,demonstrating that the damping effect of the friction pendulum bearing was slightly higher.In the vertical direction,the acceleration of the friction pendulum bearing was slightly greater than that of the flat sliding bearing.Although the friction pendulum bearing could lower the acceleration response of the structure,it augmented the displacement response of the structure.The transverse residual displacement of the friction pendulum bearing was less than 1 mm,and the axial residual displacement was less than 2 mm,which were much smaller than those of the flat sliding bearing.The stress of the steel penstock of the friction pendulum bearing scheme was approximately 10％lower than that of the flat sliding bearing scheme,and the maximum lateral and axial shear forces of the friction pendulum bearing scheme could be decreased by 38.3％and 59.7％,respectively,compared with those of the flat sliding bearing scheme.[Conclusions]Generally,compared with the flat sliding bearings,the friction pendulum bearings can lower the acceleration response of the pipe and the horizontal forces of the bearings more effectively,and the residual displacements of the bearings are small.The friction pendulum bearing has a more obvious effect on the seismic isolation of the exposed steel penstock.
exposed steel penstockfriction pendulum bearingseismic isolationfinite element simulation
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