An High-efficiency Assessment Method For Seismic Resilience Of Seismically Isolated Medical Buildings Considering The Vulnerability Of Flexible Pipes

The seismic resilience of medical buildings is of great significance to the seismic resilience of urban.Isolation technology is an effective mean to improve the seismic resilience of medical buildings.In this paper,the existing RC frame medical building is selected as the research object.The seismic performance of the metal flexible pipes,which are the key elements in the isolated layer of the isolated building,were tested firstly.The mechanism of seismic damage and failure characteristics were investigated,and the vulnerability model and loss consequence function were constructed to improve the isolation model system for building resilience evaluation.Considering the computational efficiency and accuracy,a simplified model with emphasis on the critical requirements of seismic resilience improvement of regional RC frame using seismic isolation,including the computational efficiency,capacities on the prediction of critical design indices,seismic responses and resilient performance,was investigated.Based on the vulnerability model of metal flexible pipes and this simplified model,the seismic resilience of typical RC frame medical buildings was evaluated,and the impact of flexible pipes on the seismic resilience of such structures was clarified.The main research work and conclusions are as follows:(1)Considering the effect of nominal inner diameter,installation height and design length,the seismic performance test study of 27 metal flexible pipeline specimens in 9 groups of tests was carried out.The test results show that: the damaged flexible pipes mainly experience two key states,that is the coat metal net is stretched and the coat net is unilaterally pulled out and destroyed,then the flexible pipes cannot bear the working pressure and a replacement is required;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 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.(2)The vulnerability model construction method recommended by FEMA is used to construct the vulnerability model and loss consequence function of the metal flexible pipes based on the test data: the damage state is divided into DS1(the coat metal net is stretched),and DS2(the coat metal net is unilaterally pulled out and destroyed);DS2 repair plan is to replace the pipeline,the repair cost varies according to the nominal inner diameter,and the repair time is 0.306h;the median value of damage engineering requirement parameters of the metal flexible pipes increase with the increase of the nominal inner diameter,while the probability of failure decreases with the increase of the nominal inner diameter.(3)The prediction accuracy of the existing hybrid simplified model based on shear beams(referred to as “HSS model” hereafter)was evaluated.The results indicate that such model can accurately predict the displacement of the isolation layer,but cannot predict base shear ratio well.Furthermore,it is not capable of predicting the maximum absolute floor acceleration,which is the critical seismic response affecting seismic resilience;in view of these,a hybrid simplified model based on Timoshenko beam(referred to as “HST model” hereafter)was recommended and validated to be capable of predicting the abovementioned critical design index and seismic response;based on HST model,the seismic resilience improvement using seismic isolation was successfully conducted for an existing RC frame structure.The results indicated that the HST model can efficiently and accurately grasp its resilience level,and can guide the fine design to determine the isolation scheme.(4)Considered the vulnerability model of metal flexible pipes and based on the simplified model,the seismic resilience of the RC frame structure after isolation was evaluated and analyzed.The results indicated that: the damage of the flexible pipes affects the repair cost of the building,but it has no effect on the repair time,which is mainly because of pipes can be repaired in parallel with other non-structural components,and its repair time is much shorter than other components.The number of damaged pipes decreases with the increase of the nominal inner diameter;when the displacement of seismic isolation layer of the RC frame isolation structure is small,a metal flexible pipe with a nominal inner diameter of 40 mm can meet the resilience requirements;when the displacement of seismic isolation layer of the RC frame isolation structure is large,a metal flexible pipe with a nominal inner diameter of 50 mm can well meet the resilience requirements.