Experimental And Design Method Study Of Energy Dissipating Outriggers

In recent years,the outriggers have been widely adopted in super-tall buildings.The issue of improving the seismic performance of outriggers has become an important research frontier in civil engineering.In this thesis,a framecore tube-outrigger super-tall building located in the eight-degree seismic design region was adopted as the engineering prototype.Both the seismic performance and design method of three different outriggers(the conventional outrigger,the outrigger with a damper at the end and the damped outrigger with bucklingrestrained braces(BRBs))were studied through experimental study,numerical simulation and theoretical analysis.The main research work is summarized as following.(1)During the experimental process of the conventional outrigger,global buckling of the braces,local buckling of the chords,and rupture of steel plate in the chord were found.Consequently,the energy dissipation capacity and ductility of the conventional outrigger is limited,which result in a poor resilience of the outrigger after earthquake.(2)Experimental studies of the outrigger with a mild steel damper and the outrigger with a friction damper were conducted.It is found that the auxiliary devices should be set up to ensure the full performance of the damper.Through adopting the auxiliary devices,the outrigger with a friction damper is capable of maintain the outrigger's main body in elastic state throughout the loading process,ensuring the energy dissipating capacity and resilience of the outriggers.(3)Experimental test on the damped outriggers with BRBs was also conducted in this research.It is found that the sufficient deformation capacities of the chords are critical for meeting the energy dissipation demand of BRBs.The reduced beam section(RBS)can effectively improve the chord's deformation capacity,making the energy dissipating capacity of the outrigger with BRBs much better than that of the conventional one.Furthermore,through applying high-strength steel in the chords,the RBSs of damped outrigger could remain unyielding within the story drift ratio corresponding to maximal considered earthquakes regulated in the Chinese code,which means the resilience of the damped outrigger with BRBs after earthquake can be further improved.(4)The finite element(FE)models of the three different outriggers(the conventional outrigger,the outrigger with a friction damper at the end and the improved damped outrigger with BRBs)were built in this thesis.By comparing the results of the FE models with and without initial imperfection,it is found that considering the effect of initial imperfection is very important in such FE analysis.(5)Through the experimental study,FE simulation and theoretical analysis,the calculation method for the rotational capacity of RBS under compresionbending-shear coupling force state is proposed.The design method of the damped outrigger with BRBs is also proposed.Besides,this thesis proposes a design method for the auxiliary device in the damped outrigger.The effects of the strength-stiffness coupling on the engineering design of outriggers with mild steel dampers are also analyzed.The results indicate that futher studies are required for the outrigger with a mild steel damper.