Building irregularities are an important concern when they are subjected to strong earthquakes. In structures, an abrupt change in the vertical or plan configuration tends to weaken the stability. It is necessary to study how irregular structures respond to lateral loads in order to prevent failure and reduce the risk of hazards. In this case study, a G+3 storey building is modeled using the existing beam and column cross sections. In addition, models with reduced cross sectional areas of 5%, 10%, and 15% were developed and static linear analysis was performed using Etabs software in accordance with IS1893 (Part-1):2016. The parameters considered in this study are storey displacement, storey drift, and base shear. The analytical results obtained are compared with those of the existing building model.
One of the most destructive natural occurrences on earth is an earthquake. Seismic waves are produced as a result of the abrupt release of energy in the earth's crust. The seismic wave moves both horizontally and vertically at the ground surface level as it approaches the foundation of the construction. Buildings, bridges, roads, dams, and other man-made infrastructure were all damaged as a result of the earthquake. In addition, it results in slope instability, liquefaction, landslides, and a general loss of life and property. It is not economically viable for structures to provide total protection against earthquakes of all magnitudes. It is important for the earthquake design to prevent fatalities and reduce property damage.
The concept of earthquake resistant design is that the building should be designed to resist the forces that arise due to a design basis earthquake, with only minor damage, and the forces that arise due to a maximum considered earthquake, with some structural damage but no collapse.
This study examines a commercial complex building as shown in fig 1. The building is designed to withstand seismic loads in accordance with IS 1893 (Part 1): 2016. The building is in a Moderate Seismic Zone (Zone III) and is a G+3 structure, although the section sizes of the structure appear to be large, increasing the project's cost.
1) To study the efficiency and e?ectiveness of existing structures
2) To analyse a new model with cost-effective sections using Etabs
3) To compare the results with the existing building details
III. MODELLING AND ANALYSIS
A. Analysis Consideration
In this proposed project, we have studied and analysed the existing building frame details. As an attempt to make the sections economical, the beam and column cross-sections were reduced by 5%, 10%, and 15% respectively, and then all the moment resisting frames were analysed by Etabs software using static linear analysis as per IS1893:2016.
B. Material Specifications
Grade of concrete, (fck): 25N/mm2
Grade of steel (fy): 500 N/mm2
Density of Concrete: 2.5 g/cm3
Density of Steel: 7850 kg/m3
C. Load Consideration
Load acting on the structure are dead load (DL). Live load (IL) and earthquake load (EQ).
Roof load: 1.5 KN/m2
Live load: 3 KN/m2
Floor finish load: 1.5 KN/m2
D. Model of RCC Frame
E. Building Models
The following models have been considered
Model-I: Basic model with 0% reduction
Model-II: Model with 5% reduction in columns and beam sizes
Model-III: Model with 10% reduction in columns and beam sizes
Model-IV: Model with 15% reduction in columns and beam sizes
IV. RESULTS AND DISCUSSIONS
The results are tabulated in order to focus on the parameters such as base shear, story drift, and lateral displacements in static linear analysis.
A. Storey Drift
A storey drift was considered the point at which the junction of beam and column met. These points, where the maximum drifts occurred, were compared in this study. Storey drifts among G+3 storey building models are subjected to X and Y directions. Figs 6 and 7 indicate the plot of storey number versus storey drifts for earthquake loads.
B. Storey Displacement
A storey displacement was considered the point at which the maximum storey displacement occurred. Figs 8 and 9 indicate the plot of storey number versus storey displacement for earthquake loads.
The major conclusions drawn from the studies after seismic analysis are as follows:
1) Results show that storey drift and storey displacement increase with a decrease in cross-section from 0% to 10%
2) The second and third floors will not meet the storey drift requirements in EQY direction for a 15% reduction in cross section due to plan irregularity and stiffness irregularity.
3) Despite a drop in cross-section of 0% to 15%, the base shear only decreased by 2 to 3% respectively
4) All of the above results suggest that the existing building satisfies all the earthquake requirements with only a 10% reduction in cross sectional area due to its plan irregularity and stiffness irregularity
5) As a result, in light of the safety considerations, it is not advised to modify the specified cross-section sizes. In other words, the existing building details are adequate to satisfy the earthquake criteria as described in IS1893 (Part-1):2016
 P A Krishna & N Thasleen, (2020) Seismic analysis of Plan irregular RC building frames.
 Battu Jaya, Uma Shankar, G Kiran Kumar, R Sai Kiran, (2020) Analysis and comparison of seismic behaviour of multi storied RCC building with symmetric and asymmetric in plan.
 V AnirudhRaajan, Balaji G C, Vasavi V, (2021) Response spectrum analysis of a G+4 building with mass irregularity on a sloped surface.
 Mohammed Akif Uddin & M A Azeem, Comparative Study on Seismic Behavior of Composite and RCC Plan Irregular Structure’s. Vol. 9 Issue 01, January-2020
 Sindhu Nachiar S, Anandh S, Ajith kumar, Abhinav Puskar and Fardeen mohammed (2003). Comparative seismic analysis of conical and pyramidal frustum shaped commercial building (G+6) at Janakpur, Delhi.
 Ahmed Yousef Alghuff, Samir Mohammed Shihada and Bassam A. Tayeh (2019) Comparative study of static and response spectrum methods for seismic analysis of regular RC building.
 N K Manjula, Praveen Nagarajan, T M Madhavan Pillai Performance evaluation of RC buildings designed as per Indian seismic codes: A study on frames with vertical geometric irregularity. Received: 22 September 2017 /Accepted: 30 August 2018
 Indian Standard Code Books and Hand books: IS 456:2000, IS 1893:2016, SP16, SP34.