Failure Mode Optimization And Damage Control Of Tall Building Structures Under Seismic Excitations

In the recent two decades, the construction industry has been rapidly developedin China, and a large number of tall building structures have been built. However,China is located at the convergent boundaries of two worst seismic zones, so thecrustal movement is very active and the earthquake disaster is very serious. Since tallbuildings are characterized with large size, complex loading state and high density ofproperty and population, the earthquake disaster of such buildings is usually far moreserious than that of other buildings. Previous earthquakes have demonstrated that thecollapse of building structures is the primary cause for casualty and economic loss.Therefore, for the tall building structures under large earthquake, the study on damageprocess law and collapse mechanism, controlling the damage process and failuremode, and prevention from global structural collapse is of great theoreticalsignificance and engineering value in terms of increasing the structural seismic safety,reducing or preventing seismic disaster.In this dissertation, focusing on the steel frame structure, steel frame-steel plateshear wall structure and steel-concrete structure, the catastrophic process controlthrough failure mode optimization and the nonlinear seismic damage control usingMR dampers are intensively studied, and the failure mode optimization method anddamage control theory of tall buildings under seismic excitations are proposed. Inspecific, the innovations and achievements can be summarizes as follows:(1) An equivalent seismic performance optimization design method of tallbuilding structures is proposed based on the seismic performance indices of structuralmember and structure. By employing the damage index as the constraints, SPI as theobjective function and parameters of structural members as the optimization variables,the optimization is realized through multi-step iterations until the SPIs are convergentto the expected values so as to achieve the goal that each type of the structuralmembers has the same seismic performance. Taking a single-objective optimization ofa9-story steel frame and a multi-objective optimization of a15-story steel frame-steelplate shear wall (SPSW) structure as examples, the structural dynamic responses anddamage process before and after the optimization are numerically analyzed. It isindicated that the relative displacements and damage distribution of the optimized structure is uniform, the structural weaknesses and damage concentration are avoided,the material strength are extensively utilized, the steel usage is reduced and the globalseismic performance of buildings is significantly increased.(2) A nonlinear seismic damage control strategy of tall building structures usingMR dampers is proposed. The basic control equation based on central differencemethod is derived, the semi-active control platform is developed through thesecondary development of LS-DYNA program, and the structure and the nonlinearsemi-active control system integrated modeling, analysis and design are realized.Taking a9-story steel frame and a15-story steel frame-steel plate shear wall (SPSW)structure as examples, the dynamic responses and damage process of the structureswith and without MR dampers are analyzed, results indicate that the control platformis numerically stable with fast solution speed and high precise. The relativedisplacement, residual displacement and damage of each story are all significantlyreduced, the damage distribution is more extender, and the global seismicperformance is increased after MR damper is employed. However, because of thelimit output force capacity of the MR dampers, the control effectiveness decreaseswith the earthquake intensities.(3) The nonlinear seismic damage control strategy of steel-concrete hybridstructure using MR dampers is studied, and the damage criterion of reinforcedconcrete shear wall is proposed. Tanking a15-story steel-concrete hybrid structureunder large earthquake as a numerical example, the dynamic responses and damageprocess of the structure without MR dampers, with MR dampers located between steelframe and concrete tube, and with MR dampers installed between the columns of steelframe are analyzed. It is indicated that MR dampers can effectively control the storydrift, story shear force and damage process; the two styles of MR damper allocationhave similar control effectiveness, but both cannot restrain the weaknesses anddamage distribution. In all conditions, the steel frame is elastic while the concrete coretube is seriously damaged, which is not coincident with the control mechanism thatMR damper produce control force passively when certain inter-storey relativedisplacement occurs. The global seismic performance of steel-concrete hybridstructure is controlled by the concrete core tube.(4) The nonlinear seismic damage control of the scaled model structure is studiedthrough shaking table tests. Under different earthquake excitations, a series of shakingtable tests with semi-active control, Passive on control, Passive off control are conducted. It is indicated that the semi-active control and Passive on control are moreeffective than that of the uncontrolled and the Passive off control ones, the energydissipation capacity of the MR damper of semi-active and Passive on control is of2~3times’ excellence as that of the Passive off control ones, and the structural damagemainly increase during the Passive off and the uncontrolled cases, which proves thatthe MR dampers-based damage control is effective. Moreover, the uniaxialelastic-plastic damage material model of steel and concrete are developed through thesecondary development of LS-DYNA program, the equivalent fiber element modelwhich can quantitatively simulate the damage process of structure is developed, andthe simulation precision is verifies by the shaking table tests. An inversion strategy ofusing the measured strains to calculate the stress and damage process at thecorresponding position where strain gauges are attached is proposed, this methodmakes the most of the measured strain data to get the material stress and damageevolution process.