Analysis and Design of Conjoined Structural System for Tall Buildings

Abstract

Due to the rapid growth of urbanization, population, land cost, and race for sustainable buildings, the development of iconic skyscrapers (Tall buildings) has increased worldwide. A tall building is becoming an integral part of the developing economy. Advancements in technologies and materials promoted the development of tall buildings. Gravity loads and Lateral loads are governing factors in the design of tall buildings. As the height increases lateral load is increasing exponentially and as a result, the lateral load governs the design of the structural elements in addition to the gravity loading. Various structural systems are developed for efficient lateral load resistance in tall buildings. Shear wall, outrigger-belt truss, and tubular structures are widely used in tall buildings. A conjoined structural system is developed by joining individual tall buildings at different levels along the height of tall buildings. In the present major project, the behavior of conjoined frames structure is studied. Further, conjoined frame structure of different heights are analysed considering various loads and load combination. Various parameter related to seismic loading, wind loading are compared for individual buildings and conjoined buildings. To understand behavior of conjoined structure, first rigid jointed plane frame structure considered. The frame structures of different heights are connected at the top level and subjected to lateral loading. Modeling and analysis of structure are carried out in ETABS software. Analysis results in terms of storey displacement, stiffness, etc. are compared for single plane frame structure and conjoined plane frame structure. From the analysis results, it is found that a conjoined structural system possesses higher stiffness for lateral load resistance as compared to a single structure. So, a conjoined frame structure system can be more efficient in lateral load resistance in tall buildings. After understanding behavior of conjoined frame structure, regular buildings of plan dimensions 30m × 30m with number of storey 30, 40, 50, and 60 are considered. Both the individual and conjoined buildings are studied. In the conjoined building, four isolated buildings at a spacing of 20 m are connected using a link structure at the top. Four isolated buildings are arranged in two rows, with two buildings in each row. The report presents an assessment of gravitational and lateral loads resulting from earthquakes, as well as a methodology for designing steel-concrete composite structural elements. To evaluate the seismic loads, both equivalent static analysis and dynamic response spectrum analysis, as specified in IS 1893 (Part 1): 2016, are employed. The software ETABS is utilized for modeling, analysis, and designing tall buildings. The location of center of mass and center of rigidity of both the individual and conjoined buildings are included in this report. For the design of structural elements load combinations based on the recommendations outlined in relevant Indian standards are considered. Comparison is made between the structural response of individual buildings and conjoined buildings. Analysis results in terms of natural time periods, base shear, storey shear, lateral displacement, and inter-storey drift are compared for individual and conjoined buildings. A wind assessment study is carried out to determine the dynamic wind load on conjoined buildings. Three approaches are considered for this study: (1) IS 875 (Part 3):2015, (2) Tokyo Polytechnique University(TPU) database, and (3) Recently published Research Article. Comparison of wind load evaluation methods discussed in three approaches is presented in this report. Further an illustrative example is included to evaluate wind load on conjoined buildings using three approaches. Design of 30, 40, 50, and 60 storey individual buildings and conjoined buildings is carried out considering gravitational and lateral loads caused by earthquakes and wind. For the dynamic wind load, findings from a wind assessment study on a conjoined building are utilized, while earthquake and static wind loads are evaluated according to IS 1893(Part 1):2016 and IS 875(Part 3):2015, respectively. ETABS software is employed for the modeling, analysis, and design of tall buildings. The comparison includes designed sections, design forces, and governing load scenarios for structural members, as well as analysis results concerning time period, base shear, storey shear, storey displacements, and inter-storey drift ratio, for both individual buildings and conjoined buildings. To identify the optimum position for the link structure, five different locations are considered. Conjoined buildings are modeled and analyzed with link structures placed at H, 0.8 H, 0.6 H, 0.4 H, and 0.2 H while using the same dimensions for the structural elements. By comparing displacements, the optimal location for the link structure is determined. 'H' is the height of buildings. It observed that the optimum location of the link structure is 0.6 H level from the base. To assess the advantages of placing the link structure at the optimal location in a conjoined building, a comparative study is carried out, considering individual structures, conjoined buildings with link structures positioned at the top, and conjoined buildings with link structures located at the optimum positions. The comparison of analysis results and structural elements' design between individual and conjoined buildings demonstrates that the conjoined frame structure exhibits greater lateral stiffness. This increased stiffness is a critical factor in the design of tall buildings, as it enables them to better withstand static and dynamic wind loads as well as seismic loads. As the height of the structure increases, the utilization of a conjoined structural system proves to be highly effective in enhancing the flexural stiffness of the structure and reducing the lateral drift of the structures. Based on study carried out it is concluded that conjoined buildings becomes cost effective and efficient for buildings with more than 50 storeys.