International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 08 Issue: 06 | June 2021
p-ISSN: 2395-0072
www.irjet.net
COMPARATIVE STUDY ON SEISMIC ANALYSIS OF FLOOR DIAPHRAGM OPENINGS WITH RING BEAMS Sreelakshmi Ranjit¹ and Nincy Jose² 1PG
student, Dept of civil engineering, Federal Institute of Science and Technology, Angamaly, Ernakulam Professor, Dept of civil engineering, Federal Institute of Science and Technology, Angamaly, Ernakulam ---------------------------------------------------------------------***---------------------------------------------------------------------2Assistant
Abstract - Diaphragms, which transmit lateral forces to the vertical elements of the lateral force resisting system, must be designed as part of the seismic force resisting system of a building. Openings in the floor diaphragms are commonly used for a variety of purposes such as staircases, escalators, lifts, architectural lighting, and so on. These diaphragm openings put stress on the discontinuous joints with the building elements. Unaccounted for diaphragm openings may result in structural instability or diaphragm failure. The correct placement of openings will provide the structure with effective strength and serviceability. This study focuses on the general effects of floor diaphragm openings on seismic response of RC multistoried building having ring beam around openings of various shapes. The effect of ring beams around openings in the diaphragm is studied using structural parameters such as maximum storey displacement, storey drift, storey shear, slab stress and slab deflection of the building by time history analysis with the help of ETABS 2018 software. The results are compared with models having no ring beams around the openings.
Key Words: Diaphragm openings, Ring beams, Time history analysis, ETABS 2018.
1. INTRODUCTION Earthquakes typically begin in multi-story framed structures in the lateral load resisting frames at structurally weak points. During strong earthquakes, the action of multi-story framed buildings is dependent on the distribution of mass, stiffness, and intensity in each of the horizontal and vertical planes of the building. Changes in the stiffness, strength, or mass of the diaphragm can also cause these vulnerabilities in a few cases. Buildings with normal geometry and uniformly distributed mass and stiffness in plan and elevation sustain far less damage than irregular configurations.
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IS 1893-2002 part 1;clause 4.8 defines a diaphragm as a horizontal or nearly horizontal system that transmits lateral forces to vertical resisting elements such as reinforced concrete floors and horizontal bracing systems [8]. A diaphragm is a structural system used to transfer lateral loads to shear walls or frames in structural engineering. Wind and earthquake loads are the most common lateral loads, but diaphragm action can also resist other lateral loads such as lateral earth pressure or hydrostatic pressure. Horizontal diaphragms cause the walls or frames to resist lateral forces as a group.
1.1 DIAPHRAGM OPENINGS Openings are provided in reinforced concrete slabs in buildings to allow lifts, cables, or other instruments, such as escalators, to pass from one floor to the next. Escalators and lifts are increasingly being used in high-rise buildings to facilitate movement from one floor to another. The use of floor openings is also rising, introducing a new design aspect in architectural ways. The purpose of this research is to compare the seismic performance of RC structures with and without ring beams around diaphragm openings of various shapes using ETABS, as well as to investigate the effect of ring beams around openings in symmetric building plans. All analyses will be performed in RC structures with and without ring beams, with diaphragm openings of various shapes. Only the building's storey displacement, storey drift, storey shear, slab stress concentration, and slab deflection will be considered.
2. METHODOLOGY ADOPTED In ETABS 2018, 3D models of symmetric plan configurations with 10% openings of square, circular, and diamond shapes were created. Models with and without ring beams around the openings were created. Time history analysis is carried out. To reach conclusions, the results are evaluated using the parameters maximum storey displacement, storey drift, base shear, slab stress concentration, and slab deflection. Data from the El Centro California time history function was entered for the analysis process (magnitude 6.9). The Indian Standard Code IS 1893-2002 (Part I) [8] was used for modeling of the structures. Fixed joints are provided at the building's foundation. All structural sections are assumed to be rectangular.
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