Performance-based Seismic Design And Optimization Of Diagrid Structures

Designing the diagrid structural system using conventional code provisions is not fair and not accurate regarding the real performance of the system.Studies has proven that diagrid can be more efficient and economical than conventional systems,using a method to design the diagrid structural system with more accuracy is needed,hence the Performance-Based Seismic Design(PBSD),due to is flexibility.This study aims to design a 60-story diagrid building using PBSD,propose an optimization of the system and show that the building is capable of resisting the seismic loads without assistance of the core(the optimization).To be more specific this thesis mainly focuses on diagrid buildings,their Performance-Based Seismic Design(PBSD)and optimization.This research was conducted in four phases,which are investigation on the diagrid structural system,modeling of this kind of system,the design of the system and its optimization.The investigation is conducted through literature,forums,lectures and internet.Thanks to the investigation,the history,the behavior,the load transfer and the preliminary design methodology of diagrid structural system is known,this knowledge is required before undertaking a research on diagrid structures due to their difference compared to conventional structural systems.The investigation also guides to the choice of the building’s configuration and geometry.It is again thanks to the investigation that the preliminary design method is depicted,the stiffness-based method.The building subjected to this study is a 60-story building with a circular shape and a diagrid system around its perimeter,the diagrid system is a uniformangle one composed by diagonals inclined at 73° and tie beams acting together to resist the lateral load.the building is configured so that all the lateral load is allocated to the diagrid system with the core only carrying gravity load.The modeling part is done on the SAP2000 software,modeling of diagrid is different from that of conventional system,the modeling is done with some check on some papers progressively until a satisfactory behavior of the building is gotten.For the preliminary design of the structural system a stiffness-based method is used.The PBSD is achieved by following the guidelines of the PEER and the proposed optimization consists of filling the diagonal tubes by concrete and increase the damping of the structure.The results show that for the response spectrum analysis(RSA)the building performs very well without even optimizing the system,but regarding the nonlinear time history analysis(NTHA)in order to get response within the acceptable limits prescribed by the guidelines the system needs to be optimized.Finally,the building is analyzed on SAP2000 through the PBSD approach,with the accelerograms selected.The results suggests that both filling the tubes by concrete and increasing the damping(combined)play a great role in reducing the drift and the residual drift.on one hand increasing the damping plays a greater role than filling the tubes,on the other hand filling the tube increase the mass of the building.On this basis the damping should keep our attention when optimizing this type of system,a special damper for the diagrid system may be design in the future.