| As a typical and important supporting structure in UHV(ultra-high voltage)substations,1000 k V outgoing line frame(OLF1000)bears the role of supporting electrical equipment and long-span transmission lines.Its seismic performance directly determines whether the trunk lines of UHV network can operate normally under strong earthquakes.There are two key problems in the seismic design of OLF1000.One is the significant OLF1000-tower-line dynamic interactions.The earthquake damage investigation showed that the tranmission lines connected with OLF1000 and remote towers aggravated the collapse of OLF1000 under earthquakes.It is an urgent need for designers and owners to reveal the OLF1000-tower-line dynamic coupling mechanism and quantify its impact on the OLF1000.The other problem is substantial effects of seismic incident directionality.In normal use,the OLF1000 in the OLF1000-tower-line coupling system exhibits asymmetric stress and deformation states.For the seismic performance of this kind of irregular coupling system,the direction of seismic incidence with high uncertainty may be a disadvantage.Therefore,the research on the siesmic incident directionality effect of the coupling system will promote the improvement of seismic design method of OLF1000,which can ensure its seismic safety in any incident direction.This study is based on the above two theoretical issues and the main research contents and achievements of this paper are as follows.(1)Equivalent simplified model of inclined transmission line.The frequency response function of horizontal tension in an inclined suspended cable structure(including damping and uniform)is theoretically derived.According to the frequency response function,the horizontal static stiffness and cable dynamic coefficient of suspended cables are proposed,and the horizontal dynamic stiffness is established.The dynamic stiffness fully condiders the geometric,material,dynamic and damping features of the cable.Then,the transmission line is simplified as a spring model based on the horizontal dynamic stiffness.The effectiveness of the equivalent spring model is verified by using shaking table test and numerical methods.It is found that the calculation efficiency of spring model is significantly improved while its accuracy is guaranteed.Finally,the parameter analysis indicates that the equivalent spring model can effectively simulate the dynamic interaction between the inclined transmission lines(showing different inclination angles,sag-to-span ratios and spans)and structure subjected to different earthquakes when the inclination angle is not more than 50 degrees.Note that,the spring model is based on the in-plane derivation,ignoring contributions of out-of-plane modes.(2)Frame-line dynamic coupling effect.The 1/15-scale experimental model of a single-span OLF1000-line coupling system is designed and constructed.Three sag-to-span ratios are selected as the analysis conditions,and 20 far-field ground motions are used to excite the experimental model in transverse and longitudinal directions with fortification intensity.The test results show that the OLF1000-line dynamic interaction,including the energy dissipation of suspended system and elastic restraint of transmission lines,greatly weakens the responses of OLF1000.The reduction of responses increases with the decrease in the sag-to-span ratio.Compared with longitudinal excitations,the dynamic interaction is more strong under transverse excitations.Additionally,the parameter analysis for the numerical prototype illustrates that the dynamic interaction is an attribute of the coupling system and thus is unaffected by external loads;compared with the three-span OLF1000-line coupling system,it is more significant in the single-span one.Finally,TAFT record is used to excite the coupling system in transverse direction.The results show that the dynamic interaction accelerates the damage development of OLF1000,reduces its bearing capacity,and affects its collapse direction under strong earthquakes.(3)Frame-tower-line dynamic coupling effect.Three finite element models based on ABAQUS are established,i.e.,non-coupling OLF1000,OLF1000-line and OLF1000-tower-line coupling systems,among which the first two are used as comparative models.The dynamic time-history analysis method is used to discuss the structural responses and plastic development law of OLF1000 under earthquakes with different intensities.Moreover,the whole process analysis is carried out by using the incremental dynamic analysis(IDA)method.Then,the failure modes,ultimate bearing capacities and collapse fragility of OLF1000 in different models are compared.It is found that the dynamic interaction changes the failure modes of OLF1000,reduces its bearing capacity,and significantly increases its collapse risk under strong earthquakes.In addition,the OLF1000-tower-line dynamic interaction consists of the excitation amplification effect of tower cross arms,the initial horizontal tension effect and elastic restraint effect of transmission lines,and the energy dissipation effect of suspended system.For the seismic performance of OLF1000,the former two are adverse effects,while the latter two are powerful effects.(4)Seismic incident directionality effect.Based on an unbiased sample,which includes 4 264 multi-dimensional ground motions,the variability of ground-motion characteristics(GMC)with angle of seismic incidence(ASI)is studied.The results illustrate that the GMC has substantial variability with the ASI,which is independent of the earthquake source,propagation distance,and site condition,and exhibits complex random characteristics.Additionally,a classification method for multi-dimensional ground motions is proposed by analyzing the GMC variability to establish a criterion for selecting ground motions based on directionality.Moreover,according to this selection criterion,the far-field record database is updated,and 40 ground motions are used to excite the numerical model of OLF1000-tower-line coupling system in multiple incident directions.The results show that the impact of the incident direction on the seismic response of OLF1000 can not be ignored;the change of the incident direction will change the participation of each vibration mode of OLF1000,and then affect its plastic distribution and collapse performance under strong earthquakes.Furthermore,the uncertainties of RTR and DTD are dicoupled theoretically,and the 95% guarantee models for seismic responses of OLF1000 —regarding elasticity and elastoplasticity and elastic and bearing capacity limits —are proposed.Finally,prediction models for the elastic structural responses and ultimate bearing capacity of the OLF1000,by considering the OLF1000-tower-line dynamic interaction and seismic incident directionality effect,are established.(5)Multi-ASI seismic fragility analysis.Based on the idea that the seismic demand and capacity are dependent and independent of the incident direction respectively,a new multi-ASI seismic fragility analysis method(N-MASI-SFAM),considering the orientation arrangement of structure and strike of fault zone,is proposed.This method fully reflects RTR,STS,and DTD uncertainties.Firstly,the Latin Hypercube Sampling method is used to obtain structure-record-ASI pairs and structure-record pairs to carry out probabilistic seismic capacity analysis and probabilistic seismic demand analysis for OLF1000-tower-line coupling system,respectively.Then,the fragility planes of OLF1000 for different limit states are established by using the N-MASI-SFAM,which provides suggestions for the orientation arrangements of OLF1000-tower-line coupling system outside UHV sustations.Moreover,the results obtained by the N-MASI-SFAM and seismic fragility analysis method based on the traditional excitation method(TEM-SFAM)are compared,which implys that the TEM-SFAM can not identify the maximum seismic risk of OLF1000,and its reliability in seismic fragility analysis of OLF1000 is low.Finally,a seismic risk assessment method based on the epicenter position is proposed,and the practical engineeing is quantitatively evaluated. |
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