IMPORTANCE OF ASPECT RATIO IN THE ANALYSIS AND DESIGN OF A 15 STORIED BUILDING USING ETABS CONSIDERING SEISMIC ZONES
Alavalapati Rupasree1, Dr. H. Sudarsana Rao2, Dr.Vaishali G Ghorpade3
1M. Tech (Structural Engineering), Department of Civil Engineering, JNTUA College of Engineering, Ananthapuramu, India.
2Professor, Department of Civil Engineering, JNTUA College of Engineering, Ananthapuramu, India.
3Professor, Department of Civil Engineering, JNTUA College of Engineering, Ananthapuramu, India.
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When it comes to population and economic growth, India is unrivalled. Large commercial/office space is needed in densely populated cities where the price of land is high and horizontal expansion is difficult due to a lack of available land. When land is at a premium, building upwards is the only option.
In the process the first step is architectural planning based on the requirement and later is the structural design based on the architectural intent. Generally, in India, during the architectural concept & planning the architects and structural engineers do not coordinate at the early stages. Architectural designs are generally finalised without giving much importance to the structural framing of the building. The structural engineers get involved only after finalizing the complete architectural layout plans and designs. Structural engineers do not have any option but just follow the final architectural plans and work on the same to develop structural drawings with lot of constraints, which will result in uneconomical designs. If the structural engineer is involved from the concept stage of the architectural design’s, it is possible to achieve most economical structure. Here an attempt has been made to show that most economical structure depends on the aspect ratio of a building plan due to lateral seismic forces.
A 15 storied Office space building is considered with floor-to-floor height as 3.6m, 8m x 8m grids and seismic zone II, III and IV. Three different building plan aspect ratios are considered for the building. Three final mathematical models are created with number of iterations to achieve ideal columns with optimum structural element sizes. Dead loads, live loads, imposed loads, wind loads, and seismic loads are all taken into account in Etabs modelling efforts, with reference to the requirements set forth by the IS coal provisions.
In high rise structures the vertical members generally requires high reinforcement bars when compared with other structural members, so if these vertical members are optimally designed then it is possible to achieve most economical design for the complete structure.
The primary goal of this project is to compare the consumption of steel in the vertical structural members for different building plan aspect ratios while keeping the floor area constant, and to finalise the best aspect ratio to achieve the most optimum design while also performing zone comparison for vertical structural members. This work helps to study different IS codes, learn mathematical modelling using Etabs software and AutoCAD software for drafting. By this project work the essential skillset that is needed for the industry will be acquired which is also one of the objectives of this project work.
Keywords: ETABS, Seismic Zones, Storied building