Optimization And Control Of Failure Modes Of Steel Frames With Rocking Truss And BRBs

The ideal failure mode of building structures is the beam-hinge mode. However, in the actual earthquakes, the beam-hinge failure mode is unpredictable due to the existence of various uncertainties. In the past, it could be found that the structures were prone to collapse induced by weak floor failure mode during the earthquake. Actually, only parts of structural components yield, while other components remain elastic, structural damage is not uniform, and material properties have not been fully used, which reveals that the energy dissipation capacity and the ductility and the ultimate load capatity of the structures are still very low. In this thesis, the optimization and control of failure modes of steel frames will be achieved with rocking truss and BRBs. The beam hinge failure mode, the maximum seismic energy dissipation, and the disaster resilience of the new structural system can be obtained.The main research contents of this thesis are as follows:(1) Identification of seismic failure modes of structures. Two methods, i.e, pushover analysis(POA) and incremental dynamic analysis(IDA), are used to identify the main seismic failure modes of steel frames and the steel frame with rocking truss. Then the failure probability, failure sequence and structure damage are analyzed.(2) Optimization of structural seismic failure modes. A new structure system, i.e., the steel frame with rocking truss frame, is proposed in this thesis. The design method of steel frame with rocking truss was explored and researched, a design suggestion was put forward based on stiffness ratio. By comparing the seismic failure mode of steel frame and steel frame with rocking truss, the role of the rocking truss on optimizing seismic failure mode of steel frame was evaluated.(3) Seismic collapse resistance and damage evolution of structures. The seismic collapse performance of steel frames and the steel frame with rocking truss are analyzed through the collapse margin ratio. The seismic damage of the two structures are compared based on four kinds of damage states in HAZUS. On the basis of the above analysis, the damage evolution process of the two structures, which are composed of elastic state, yielding, elastoplastic state, and collapse, is obtained.(4) Control of structural seismic failure modes. Considering that large deformation might occur at the regions between steel frame and rocking truss in earthquakes, a new structure system, i.e., the steel frame with rocking truss and BRBs, is proposed in order to enhance the energy dissipation capacity and allevitate the damage of the structure. Based on time history analysis, the energy consumption, the time history curves of energy consumption and the cumulative displacement ductility of the BRB components are studied. The seismic failure paths and the damage of the steel frame with rocking truss and the steel frame with rocking truss and BRBs are obtained. The mechanism and the process of seismic failure mode control of steel frames wiith rocking truss and BRBs are investigated.(5) Evaluation of structural seismic performance. Three suites of 22 records of far-field ground motions from FEMA P695 are used to evaluate the seismic performance of steel frame, steel frame with rocking truss and steel frame with rocking truss and BRBs. These three ensembles represent exceedance probaiblities of 63.2% in 50 year, 10% in 50 year, and 2% in 50 year for the building site, respectively. The structural response parameters, including the peak story displacement, the peak story drift angle, the damage concentration factor, the residual story displacement, the residual story drift angle, and the roof displacement, are adopted to evaluate seismic performance of structures.Through the researh of this thesis, it has been found that the seismic failure modes of steel frames could be optimized and controled with rocking truss and BRBs. The rocking truss and BRBs could aslo improve the seismic performance and collapse resistance of steel frames. As two new types of rocking structures, the resilience of the steel frames with rocking truss and BRBs canl be significantly improved than that of the traditionally designed structures.