Concrete Filled Steel Tube Diagrid Structural System for High Rise Buildings

Abstract

Advancement in construction technique, vertical transportation and development of analysis and design software has facilitated growth of tall building. Also, due to rapid urbanization and scarcity of land in urban area has increased the demand of the tall buildings. The design of tall building is governed by lateral load. There are various lateral load resisting structural systems like frame system, wall frame system, tubular system, outrigger system, diagrid system. Among which diagrid has emerged as most versatile structural system because of better aesthetics, high redundancy and high lateral stiffness. Generally steel tubular sections are used in construction of diagrid buildings. The use of concrete filled steel tube for diagrid building is explored to enhance the performance of the diagrid building and to reduce consumption of costly steel in diagrid structure to achieve economy. To compare behavior of steel tube and concrete filled steel tube diagrid structural system two sets of 50, 60, 70, 80 storey diagrid buildings with same plan dimension of 36m×36m are considered, One set of buildings is considered with steel tubular section and other set of buildings is consider concrete filled steel tube. The analysis and design are carried out in ETABS and various parameters like time period, top storey drift, lateral and gravity load resistance by diagrid and consumption of materials are compared. The results show that concrete filled steel tube (CFST) gives batter performance as compared to only steel tube, but with increase in overall weight of structure. Apart from this the design and detailing of joint at the intersection of inclined CFST column and at the base of the diagrid building is carried out for 50 storey CFST diagrid building. Also the design and detailing of piled raft foundation for the same is carried out. Seismic performance coefficients of CFST diagrid building are evaluated by FEMA P695 methodology. With assumed value of response reduction factor R as 5 for CFST diagrid of 4, 8, 16, 24 stories with 50 degree angle of inclined column are analyzed and designed. Over strength factor and ductility factors are determined from pushover analysis. Assumed value of response reduction factor is evaluated by non linear dynamic analysis and fragility curve, which shows that, assumed value of response reduction factor satisfies the criteria of FEMA P695. Subsequently seismic performance factor of 24 story diagrid building with 50, 67, 74 and 78 angle are compared using same procedure which shows that with increase in angle of diagrid over strength factor increases but for 78 diagrid it decreases. There is minor variation in ductility factor with variation of diagrid angle. With increase in angle of diagrid median collapse capacity decreases however, all diagrid angle satisfy assumed value of response reduction factor.