Seismic Behavior And Retrofitting Study Of High Strength Steel Composite Eccentrically Braced Frames

In ordinary eccentrically braced frames design, the internal forces are magnifiedto resistant the effect of strain hardening in link. It will leads to higher steelconsumption and increases the difficulty of joints. To solve this problem, according theseismic philosophy of “relative strength”, the high strength steel is used for frame andbraces, and the low yield steel is used for link, and this new structure is called highstrength steel composite eccentrically braced frames. The purpose of the new structureis to ensure the elastoplastic deformation of link can be well developed without steeladded. In order to study the seismic behavior of new structure, the model experiment,numerical simulation and the theory analysis were conducted. The main content arepresented as follow.?1?4monotonic test and4cyclic test were performed, which included tests on1/2scaled one storey panel specimens in K and Y types specimens, to study theirinelastic seismic performance. The results show that the seismic behavior of K typespecimens by shear yielding is better than the others. In Y type specimens, as thedisplacement increasing, the yield mechanism is alternated from shearing toflexural-shearing, the length of link should be short in case that the failures appear inbeam firstly. In K type specimens, the failures are concentrated in the link while theframes keep in elastic, which make the seismic retrofitting easy to complete.?2?The seismic performance effect parameter were analyzed by ANSYSsoftware based the experiment data, the material and the geometry nonlinearities were considered simultaneously. The ultimate bearing capacity and the distribution aregreatly influenced by grades of steel, when the ratio of nominal yield stress betweensteel of frame and link equal to1.3, the seismic performance of the combinationstructure is the best.?3?In the K type specimens, the initial stiffness, ultimate bearing capacity andenergy dissipation are significant influenced by link length. In shear yieldingspecimens, at the identical link and the same stress ratio, the seismic performance ofthe high strength steel composite eccentrically braced frames are almost the same tothe Q345grade steel eccentrically braced frames, but14%steel consumption is savedin the former. In the Y type specimens, the initial stiffness and failure modes areinfluenced greatly by link length, but little impact on ultimate bear capacity. For shearyielding specimens, at the same condition, the seismic performance of the highstrength steel composite eccentrically braced frames are almost the same to the Q345grade steel eccentrically braced frames, but16%steel consumption is saved in theformer.?4?According the failures feature of the K type specimens with shear yieldinglink and the idea of replaceable member, the destructed specimen was repaired byreplacing the link with the same new one. To study the seismic behavior, the cyclic testwas performed on the repaired specimen. The result showed that the ultimate bearingcapacity is essentially equal. At the same drift, the difference of energy dissipationbetween the repaired model and the previous one is very small. The workload of thisrepaired method is less, and the cost is low. It would be helpful to return the life ofpost-earthquake to normal rapidly.?5?For convenience of dynamic elastoplatic analysis, the resilience model of Ktype and Y type specimens were built up based on experimental data. The resiliencemodel coincide well with the testing skeleton curves. The formula of ultimate bearingcapacity of K type and Y type specimens were deduced by assuming differentrigid-plastic collapse mechanisms. The theoretical calculating values match well withthe experimental values and simulated value. It can be used in resilience model.