Seismic Performance Research On Abnormal Joint With Unequal Height Section Of Beam In Rigid Steel Frame Aftre Strengthening

In recent years, many achievements has been received for the research on the strengthening of beam-column joints in steel frame, but most are based on the conventional nodes, enhanced or reduced new-type nodes, and the literature about the performance research on abnormal joint with unequal height section of beam in rigid steel frame after strengthening rarely has been reported.In this paper, on the basis of related experimental study has been completed by the research group, using the finite element software, through two different strengthening methods including separately welded web plate of the core zone and welded haunch, respectively, put the thickness of the strengthening steel plate and the form of welded haunch plate as control variables. Considering the actual working condition, which need to unload part of the load but cannot completely uninstall in the reinforcement. The study focuses on the failure mode, ultimate bearing capacity and the seismic performance including hysteretic curve, skeleton curve, ductility performance, energy-dissipating capacity.The results show that hysteretic curve shape of specimens with abnormal joint after separately welded web plate of the core zone (equivalent to thicken web plate) is full, with strong plastic deformation and energy-dissipating capacity. The seismic performance is good. In the range of 4mm to 12mm, the ultimate bearing capacity is improved about 17.6%～34.9%, with the increase of the strengthening steel plate thickness, the bearing capacity is higher. The ductility coefficient is in the range of 3.672 to 6.509.When the thickness of strengthening steel plate is not more than 2/3 thickness of the web plate, the energy-dissipating capacity and ductility performance are better than the original specimens. When the thickness of strengthening steel plate exceed 2/3 thickness of the web plate, the energy-dissipating capacity and ductility performance become relatively worse, with the increase of the thickness of strengthening steel plate, the ductility performance become worse more obviously. The hysteretic curve shape of specimens with abnormal joint after welded haunch is less full than the original specimens. After welded haunch, the energy-dissipating capacity is generally poor, the ultimate bearing capacity is improved about 31.1%～41.4%, and the improvement of the trapezoid haunch is more obvious than rectangular haunch. The ductility performance of specimens with rectangular haunch is better than which with trapezoid haunch, but the ductility coefficient decreases obviously after welded haunch, the ductility performance becomes worse. Therefore, in the case of welding haunch designed for such box-column with abnormal joint, the internal diaphragm cannot be added in the box-column because of the objective condition, but the external stiffening rib should be welded outside the box-column, to make the mechanical property of abnormal joint with unequal height section of beam more reasonable.