Seismic Performance Study And Fragility Analysis Of Pipeline System

Construction cost of nonstructural components represents a large portion of the total invest of a modern public building.The economic loss caused by nonstructural damage during an earthquake is commonly much higher than that caused by structural damages.Meanwhile,the intensity of an earthquake that causes damages to nonstructural components is ususlly much lower than those damage structural members.The damage of pipeline systems,in particular,once damaged,would cause significant leakage which further make the building out of function.Both experimental and analytical studies on pipeline systems are very rare in China.The fragility model and database still need to be developed and improved.This study conducted a series of quasi-static tests and shaking table tests on typical components of pipeline systems,such as the flexible pipeline in isolation layer,the grab-type joints of fire sprinkler systems,and aseismic braces of pipeline systems.The seismic performance,failure mode and seismic fragility of these components have been investigated.The main research works are summarized as follows:1.Three types of seals,namely rubber-based seal,metal-based seal and asbestine-based seal,and two types of connections,i.e.,the grab-type joint and ferrule fitting joint,in flexible pipelines are cyclically tested in this study.The water leakage and the mechanical degradation were taken as the failure indices of specimens.Damage states of the flexible pipelines are defined based on the test results,together with their fragility curves.A mechanical model for the flexible pipeline is then proposed and the associated parameters are identified from the experimental data.Calibrated by the forces at specific performance points,the model is demonstrated to be able to reproduce the seismic behavior of flexible pipelines accurately,which provides basis of mega models of hospital buildings for seismic performance evaluation.2.Twelve grooved fit joints were tested quasi-statically to investigate their mechanical behavior,the rotational capacity and the failure mode.These joints are categorized into two groups,namely DN150 elbow joints and DN150 to DN80 Tee joints.The test results show that the fracture of the grooved fit joints and the pull-out of pipes from the grooved fitting joints are the major damage patterns.Although slight abrasion and wear were observed on the contact surface between the galvanized steel pipe and the grooved fitting,they would not result in significant leakage.The elbow joints are the weak points of the fire sprinkler piping system and larger deformation shall be avoided during a strong earthquake.3.Test results of nine sets of quasi-static tests on three types of aseismic braces by use of the load protocol provided by FM1950 are presented.The three types of braces include the steel wire brace,the beam clamp brace,and the threaded rod brace.The maximum loading that the braces can bear corresponding to the limit displacement of FM1950 protocol was determined and further transformed to response acceleration of pipeline systems.Threaded rod brace is the one having the highest bearing force among the three types of braces and is also the most widely used in engineering.Therefore,another six sets of quasi-static tests on two types of threaded rod braces having hangers with the diameters of 12mm and 16mm respectively were further conducted following the FEMA461 protocol to investigate size effect of the threaded rod brace.It is found that the size of hangers has little influence on the seismic performance of the threaded rod braces,although those with smaller hangers have larger deformability.4.In order to investigate the seismic performance of pressurized fire sprinkler pipelines with and without aseismic braces,a series of shaking table tests were conducted using a tri-axial shaking table.No leakage of the pipelines was detected during the experiments and no obvious damages of the aseismic braces were observed.However,the pipelines without aseismic braces experienced significant damages at the largest input excitation(PGA=1.2g).It is observed that the aseismic braces did not reduce the acceleration responses,but they limited the displacements obviously.The pressurized fire sprinkler piping systems constructed with aseismic braces may survive a rarely-occurred earthquake to ensure the functionality of the building.5.Probabilistic seismic demand analysis and seismic fragility analysis of a 10-story RC frame were conducteds.The results indicate that damages under near-field ground motions are obviously larger than those introduced by far-field ground motions.Floor responses of the non-isolated structure are used to study seismic fragility of piping system.The exceedance probability of different limit damage states of vertical pipes and that of failure limit state of the threaded rod braces are all at relatively low levels.6.Finite element model of a base-isolated structure and flexible pipelines was built.Seismic fragility curves of different limit damage states were obtained.The probability of exceeding different limit states under the service level earthquake(SLE),design-basis earthquake(DBE)and maximum considered earthquake(MCE)are all at low levels.The deformation of isolator doesn't exceed the ultimate capacity.The results indicate that the flexible pipelines were robust enough to ensure their functionality before the damage of the structure.