International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 09 Issue: 07 | July 2022
p-ISSN: 2395-0072
www.irjet.net
Study on Torsional Response of Irregualr Buildings Under Seismic Loading Muhammed Mubashir p p1 1Muhammed
Mubashir p p, M.Tech Student, Department of Civil Engineering, Mar Athanasius College of Engineering, Kothamangalam ---------------------------------------------------------------------***--------------------------------------------------------------------Abstract - The demand for aesthetics and the scarcity of 2. METHODS OF SEISMIC ANALYSIS available land have led to an increase in the trends of building irregular structures in the modern world. Under seismic action, a structure's torsional reaction caused by abnormalities in the structural arrangement results in severe damage and early failure. One of the many irregularities that might occur in a structure and have a disastrous impact when an earthquake is triggered is torsional irregularity. The purpose of this study is to comprehend how irregular structures respond to torsional loads caused by earthquakes and how bracing can be used to control torsional irregularity. ETABS 19 programme is used to model and analyse a rectangle, L shape, T shape, and two models with vertical setback. Seismic analysis uses linear static and linear dynamic approaches.
Methods which are used in this study for the seismic analysis are Equivalent Lateral Force (ELF) method and Response Spectrum Analysis (RSA) method. There are various methods that are used for seismic analysis of structure. They can be classified based on its complexity. They are • Equivalent Static Analysis • Response Spectrum analysis • Push Over analysis • Time History Analysis
Key Words: Early Failure, Torsional Irregularity.
Static methods of analysis specified in the building codes are based on single mode response with simple corrections for including higher mode effects. While appropriate for simple regular structures, the simplified procedures do not take into account the full range of seismic behaviour of complex structures. Therefore, dynamic analysis is the preferred for the design of building with unusual or irregular geometry.
1. INTRODUCTION A system that is torsionally balanced will have its centre of mass and centre of rigidity coincide. Due to the uneven distribution of stiffness throughout the plan, when the centre of stiffness and centre of stiffness are not coincident, the system will tend to spin about the stiffness centre under seismic activity. This type of system is known as a torsionally coupled system. Buildings with irregular shapes will shift their centre of stiffness away from the centre of mass during an earthquake, creating a substantially bigger displacement to the flexible side compared to the stiffer side. The floor diaphragm will undergo a rigid body rotation as a result of this relative displacement, which will cause large stress concentrations at corner and edge columns. The building codes refer to the measurement of the torsional reaction as torsional irregularity. For diagnosing and controlling torsional irregularity, multiple codes describe distinct requirements. A schematic depiction of a torsionally coupled system is shown in Figure 1. The centre of mass of the building is where the quake's force strikes it, and the centre of stiffness is where the structure's reaction force strikes it. Due to the eccentricity, these two forces will combine to create rotation as well as translation in the earthquake's direction.
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3. TORSIONAL IRREGULARITY For quantifying the torsional irregularity of a structure, many codes around the world provide varying criteria. The 2016 revision of the Indian Code IS 1893 (Part 1) includes a provision for assessing torsional irregularity. According to the 2016 code, a building is deemed torsionally irregular when: a) Any floor's maximum horizontal displacement in the direction of the lateral force at one end of the floor is greater than 1.5 times its minimum horizontal displacement in that direction at the opposite end of the same floor. b) The fundamental torsional mode of oscillation has a longer natural period than the first two translational modes of oscillation along each major plan direction.
4. TORSIONAL STRUCTURES
RESPONSE
OF
IRREGULAR
The impact of plan configuration irregularity of buildings when subjected to the variable angle of the input response spectrum was assessed by Bharat Khanal and Hemchandra Chaulagain (2020). One conventional building frame and six variant L-shaped RC building frames were modelled and
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