Analysis And Design Of Diagrid Structural System For High Rise Steel Buildings

Abstract

Advances in construction technology, materials, structural systems and analytical methods for analysis and design facilitated the growth of high rise buildings. Structural design of high rise buildings is governed by lateral loads due to wind or earthquake. Lateral load resistance is provided by interior structural system or exterior structural system. Usually shear wall core, braced frame and their combination with frames are interior system where lateral load is resisted by centrally located elements. While framed tube, braced tube structural system resist lateral loads by elements provided on periphery of structure. It is very important that the selected structural system is such that the structural elements are utilized e ectively while satisfying design requirements. Recently diagrid structural system is adopted in tall buildings due to its structural ef- ciency and exibility in architectural planning. Compared to closely spaced vertical columns in framed tube, diagrid structure consists of inclined columns on the exterior surface of building. Due to inclined columns lateral loads are resisted by axial action of the diagonal compared to bending of vertical columns in framed tubular structure. Diagrid structures generally do not require core because lateral shear can be carried by the diagonals on the periphery of building. The aim of present study is to understand the behavior of diagrid structure under gravity and lateral loading. The methodology of preliminary design of diagrid system based on shear and bending sti ness is presented in this study. Design of 36 storey diagrid steel structural system having external columns at 74.5 slope is illustrated. Comparison of results of approximate analysis considering sti ness based approach and exact analysis using ETABS software is carried out for 36 storey diagrid building. Analysis results in terms of quantity of steel in diagrid members and top storey displacements are compared as obtained by approximate analysis and exact analysis. The in uence of factor 'S' (Ratio of bending deformation to shear deformation) on quantity of steel is also explored. It is found that approximate analysis is useful for preliminary design of diagonal column of diagrid structures. Further comparison of diagrid and tubular structural system is carried out to understand the advantages of diagrid structural system. Perimeter diagrid structural system saves approximately 14 percent structural steel compared to a conventional tubular structure for 36 storey building considered in this study. Optimal angle of inclined columns in diagrid structural system is evaluated using sti ness based methodology. For this purpose 40, 50, 60, 70 and 80 storey tall buildings are considered with di erent angle of inclination of diagonal column on periphery like 50.2, 67.4, 74.5, 78.2, and 80.5 degrees with 2, 4, 6, 8, and 10 storey modules respectively. It is observed that the optimal angle of 40, 50, 60, 70 and 80 storey diagrid structure ranges between 65 degrees to 75 degrees. Complete analysis and design of 36 storey diagrid steel building considering all load combinations is presented. A regular oor plan of 36 m x 36 m size is considered. ETABS software is used for modeling and analysis of structural members. All structural members are designed as per IS 800:2007 considering all load combinations. Dynamic along wind and across wind are considered for analysis and design of the structure. Load distribution in diagrid system is also studied for 36 storey building. Design and detailing of diagrid nodal connection is illustrated for 36 storey building. Similarly, analysis and design of 50, 60, 70 and 80 storey diagrid structures is carried out. Comparison of analysis results in terms of time period, top storey displacement and inter-storey drift is presented in this report. The design of diagonal column for all buildings is carried out and nal dimensions of perimeter column and interior column are presented. Finally e ects of sequential loading on analysis results are presented.