Research On Mechanical Behaviors Of Aluminum Foam/Polyurethane Composite Dampers And Their Application In Seismic Energy Dissipation

Spherical Cell Aluminum Foam/Polyurethane composite(SCAF/PU)is a new type of high damping material both with damping and stiffness.In order to explore the reliable form and effectiveness of SCAF/PU when applied in vibration control of civil engineering structures,two SCAF/PU dampers with different energy dissipation mechanisms and performance advantages are developed in this paper.There are two aspects deeply researched in this paper,including the mechanical behaviors of the SCAF/PU dampers and their application in seismic energy dissipation.More specifically,the first aspect contains performance test and mechanical model of the SCAF/PU dampers,while the vibration control of the SCAF/PU dampers is presented in the second aspect.Therefore,the main research works,and achievements are as follows:(1)Performance tests were carried out to investigate the influence of pre-compression,thickness of shear layer,porosity of SCAF,loading frequency,displacement amplitude and cyclic number on the SCAF/PU shear damper’s mechanical behaviors,including damping force,stiffness,dissipated energy and damping ratio.According to experimental results,the performance of this damper has a typical correlation with displacement amplitude and is relatively stable in the low-frequency range of civil engineering structures.Pre-compression or increasing the thickness of shear layer can significantly enhance this damper’s energy dissipation capacity,while its stiffness is weakened and its damping force decreases earlier as displacement amplitude increases.In addition,the damper made of SCAF/PU with higher porosity of SCAF,has a higher damping ratio during the cyclic loading process.(2)Experiments were taken to examine the influence of pre-compression,thickness of shear layer and displacement amplitude on the SCAF/PU friction-shear damper’s mechanical behaviors,including damping force,stiffness,dissipated energy and damping ratio.The results demonstrate that this damper has a typical mechanical characteristic of two-phase evolution.In the small displacement stage,the aluminum of SCAF/PU provides frictional energy dissipation and the damper’s hysteresis curves are full,revealing that the damper has a high-dissipated energy;in the medium and large displacement stage,significant energy is dissipated mainly by the shear deformation of SCAF/PU,meanwhile,the damper’s mechanical properties are basically similar to the SCAF/PU shear damper.The experimental results also show that reasonably increasing pre-compression can simultaneously enhance this damper’s mechanical properties and energy dissipation,while increasing the thickness of shear layer merely improves its energy dissipation.(3)According to experimental results of these two SCAF/PU dampers,a piecewise nonlinear exponential model for describing their hysteretic response and a three-parameter power function model for predicting their mechanical parameters are established respectively,and then used to simulate the mechanical characteristics of SCAF/PU dampers.The simulation results indicate that the piecewise nonlinear exponential model can reflect the effect of displacement amplitude on the hysteretic response of SCAF/PU dampers.For SCAF/PU shear damper,the model can accurately simulate its hysteresis loops when strain amplitude varies between 0.2 and 0.75.For SCAF/PU friction-shear damper,the model can accurately simulate its hysteresis loops when strain amplitude varies between 0.3 and 1.0.Meanwhile,the three-parameter power function model can effectively describe the change of the mechanical parameters of SCAF/PU shear damper within 50 loading cycles,and predict the final stable values of dissipated energy and damping ratio.(4)Based on the mechanical characteristics of SCAF/PU dampers,a five-story steel frame building is selected as the modelling example,and three different layout schemes of SCAF/PU dampers are adopted to analyze the seismic response of this building by finite element analysis software(ANSYS19.0),and thus illustrate the seismic response control of SCAF/PU dampers.The results show that under three earthquake waves which meet the requirements of Chinese seismic codes and have different spectral characteristics,SCAF/PU dampers can effectively reduce the seismic response indicators of this building,including top floor displacement and acceleration,story drift and non-top floor displacement.Specifically,in terms of these indicators,the seismic-reduction rate of SCAF/PU dampers can reach 10%～40% under different ground motions.It is obvious that increasing the number of SCAF/PU dampers,and setting them symmetrically on the second,fourth and fifth floors of the building can achieve the best seismic mitigation effect.