Seismic Retrofit Method Of RC Frame Structures With Viscous Dampers Based On Collapse Targets

In our daily life,we are faced with floods,tsunamis,earthquakes and other natural disasters,among which the earthquake is the most serious.Earthquake brought serious economic losses and casualties to people.It is particularly important to evaluate and predict the seismic performance and collapse-resistant performance of the structure,in an effort to assure Safety of people’s lives and property.Traditional seismic design of structures mainly relayed on their own strength,stiffness,and ductility to resist seismic effects.Later,due to structural aging and the damage of the components,the structure no longer meets the seismic performance requirements,so it needs to be strengthened.In this paper,the old reinforced concrete frame structures are strengthened with viscous dampers and their vulnerability to earthquake and seismic risk before and after reinforcement are evaluated.Based on a practical engineering case,the finite element modeling was generated by using Opensees software in this paper.On the base of the site conditions of the engineering example of case,this paper extracted 10 ground motion records from the PEER seismic wave database.and the incremental dynamic analysis method was used to analyze the earthquake vulnerability of the original structure.On the base of the analysis results,the probability of collapse of the structure was too large to satisfy the requirements of the collapse target,therefore the original structure demands to be reinforced and It is necessary to evaluate the vulnerability to earthquake and seismic collapse risk of the shock absorbing reinforced structure.This article’s main research content are followings:(1)Based on the anti collapse objective,the method for seismic reinforcement of RC frames using additional dampers was proposed.on the base of acceptable collapse probability under rare earthquake motion,the acceptable value of the adjusted collapse margin ratio was defined,and the uncertainty of the overall collapse of the structure was given.According to the anti-collapse target,this paper calculate the collapse resistance reserve paramet CMR based on the acceptable value of the adjusted collapse margin ratio.Secondly,through nonlinear static analysis of uncontrolled structures,parameters related to structural performance were calculated such as vertex displacement and maximum base shear force of the structure,and the structure calling for additional damping ratio can be carried out based on the collapse target set in this paper.Finally,the damping coefficient distribution method based on floor strain energy was used to allocate the damping to each floor(2)Ten ground motion records selected that match the site specification response spectrum was used to evaluate and analyze the seismic performance of structures before and after shock absorption reinforcement under frequent and rare earthquakes,and to evaluate the working performance of viscous dampers in seismic strengthening structures based on their hysteretic curves.(3)This paper evaluated the seismic collapse vulnerability of structure reinforced with viscous dampers,and checked whether the shock absorption reinforcement structure met the collapse resistance target set in this article under rare earthquake actions.In order to evaluate the anti-collapse capacity of the structure before and after shock absorption reinforcement,the collapse resistance reserve coefficient(CMR)of the two structures was analyzed and calculated,according to the analysis results,the structural collapse resistance reserve capacity has significantly improved.(4)This paper calculated the seismic collapse risk before and after structural seismic reinforcement based on the collapse vulnerability curve of the structure and combined with the seismic hazard curve.The research showed that this paper deduced a formula to calculate the additional damping ratio of the structure based on the requirements of the anti collapse target,and deduced the formula to calculate the damping coefficient of each floor based on the strain energy of the floor.A viscous damper reinforcement scheme was designed based on the above formula.The seismic performance before and after seismic reinforcement was evaluated under frequent and rare earthquakes,and the results showed that the reinforcement scheme met the seismic performance requirements under frequent and rare earthquakes,and And under rare earthquakes the hysteresis curve of a single viscous damper in the middle span of the second floor was relatively full,with good energy dissipation capacity.According to the seismic vulnerability curve,the collapse probability of the seismic reinforcement structure under rare earthquakes is 9.3%,which meets the set target collapse probability.Considering the uncertainty of seismic motion,based on the seismic hazard curve and combined with the seismic vulnerability curve,the collapse probabilities of the structure before and after seismic reinforcement within 50 years were calculated to be 1.60% and 0.83%,respectively.The collapse probability of the structure within 50 years was reduced by 48.1%.In summary,this article proposes a viscous damper reinforcement scheme based on the anti collapse target design,which satisfies the target collapse probability requirements of the structure under rare earthquake actions.