EXPERIMENTS ON SEISMIC PERFORMANCE OF METAL FLEXIBLE PIPES FOR SEISMICALLY ISOLATED BUILDINGS

The flexible pipes, which are designed according to the large deformation requirements of isolation layers, significantly affect the seismic resilience of seismically isolated building. However, the research on the seismic performance of flexible pipes is rarely reported. The vertical metal flexible pipes, which are widely used with important functions, are herein selected as the research object. With the consideration of real engineering application status and recommendations specified in regulation, experiments on 9 groups of 27 specimens which aims at a large deformation of 400 mm were conducted. The nominal inner diameter, pipe installation length and pipe design length are considered variables. The damage evolution mode, critical damage state, deformation and bearing capacity of metal flexible pipelines were investigated. The results indicate that:the design scheme of flexible pipes adopted in the current engineering cannot meet the large deformation requirements or exist security risk, while the scheme required by the regulation can fully meet the target; the damaged flexible pipes mainly experience two key states. The first state is that the coat metal net is stretched. The second state is that the coat net is unilaterally pulled out and destroyed, then the flexible pipes cannot bear the working pressure and a replacement is required; the horizontal deformation capacity mainly depends on the pipe installation length and pipe design length, it increases with the increase of these two lengths; the damage mostly depends on the vertical load component provided by the tension force of pipes, which is approximately proportional to the nominal inner diameter. The horizontal load at the failure moment increases with the increase of nominal inner diameter and the limit horizontal displacement. The research outcome can provide an important reference for the seismic design and fragility research of metal flexible pipes in seismically isolated building.