International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 02 | Feb -2017
p-ISSN: 2395-0072
www.irjet.net
Seismic study and performance of 30 storey high rise building with beam slab, flat slab and alternate flat-beam slab systems in Zone-V Navya Medasana1, Vinodh.Chintada2
1Post-graduate
student of Structural Engineering, GOKUL Institute of Technology and Sciences (GITAS), PIRIDI, BOBBILI, Vizianagaram District, AP, INDIA 2Assistant Professor, Department of Civil Engineering, GOKUL Institute of Technology and Sciences (GITAS), PIRIDI, BOBBILI, District, AP, INDIA ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - The use of flat slab building provides many
buildings’ periodic swaying. Stiffness and ductility considerations rather than strength would govern the design. The intent in seismic design then is to limit building movements, not so much to reduce perception of motion but to maintain the building’s stability and prevent danger to pedestrians due to breakage and falling down of nonstructural elements. Conventional RC Frame buildings are commonly used for the construction. The use of flat slab building provides many advantages over conventional RC Frame building in terms of architectural flexibility, use of space, easier formwork and shorter construction time. In this system, resistance to horizontal loading is provided by a combination of shear walls and rigid frames. The shear walls are often placed around elevator and service cores while the frames with relatively deep spandrels occur at the building perimeter. When a wall–frame structure is loaded laterally, the distinctly different deflected forms of the walls and the frames can be quite effective in reducing the lateral deflections to the extent that buildings of up to 50 stories or more are economical. The potential advantages of a wall– frame structure depend on the intensity of horizontal interaction, which is governed by the relative stiffness of the walls and frames, and the height of the structure. The taller the building and the stiffer the frames, the greater the interaction. Without a question, this system is one of the most—if not the most—popular system for resisting lateral loads in medium- to high-rise buildings. The system has a broad range of application and has been used for buildings as low as 10 stories to as high as 50 stories or even taller. The linear sway of the moment frame, combined with the parabolic sway of the shear wall, results in enhanced stiffness of the system because the wall is restrained by the frame at the upper levels while at the lower levels, the shear wall restrains the frame. Even for buildings in the 10- to 15story range, unreasonably thick shear walls may be required if the walls are placed only around the building’s service core. For such buildings, using a combination of rigid frames with shear walls might be a better option. Although relatively deep girders are required for a substantial frame action, rigid frames are often architecturally preferred because they are least objectionable from the interior space planning considerations. If the deflection modes of shear walls and moment frames were similar, the lateral loads would be distributed between the two systems more or less, according to their relative stiffness. However, in general, the two systems deform with their own characteristic shapes. The interaction between the two, particularly at the upper levels of the buildings, results in quite a different lateral load
advantages over conventional RC Frame building in Terms of architectural flexibility, use of space, easier formwork and shorter construction time. The structural efficiency of the flatslab construction is hindered by its poor performance under earthquake loading. Whereas the conventional beam slab buildings perform better in seismic regions. The main objective of this research is to study and compare the seismic performance of reinforced concrete buildings with conventional beam slabs, flat slabs and alternate flat – beam slab that are analysed as per India Standard IS 1893(2002). Response spectrum analysis (ETABS) was used as the tool to generate the necessary responses to allow for an in-depth comparison. When comparing the time period at 90 % mass participation in both x and y directions the time period of beam slab structure is more when compared with flat slab structure and alternate flat – beam slab structure. The response spectrum accelerations of the flat slab structure is found to be more when compared with beam slab building and alternate flat slab – beam slab building. Base shear of beam slab building is more when compared with both flat slab building and alternate flat slab – beam slab building. For all the cases considered drift values follow a parabolic path along storey height with maximum value lying somewhere near the middle storey. Story drift in buildings with flat slab construction is significantly more as compared to beam slab building. The drift values of alternate flat slab – beam slab buildings lies in between the two structures but somewhat nearer to the beam slab building. (due to rigidity of the beam slab structure). As a result of high drift ratios in flat slab building, additional moments are developed and columns of such buildings should be designed by considering additional moment caused by the drift. Key Words: Flat Slabs, Beam Slabs, Alternate Flat and Beam Slab, Shear, Story Shears, Story Displacements, Story Drifts, Model Participation Mass Ratios, Time Periods, Column Forces.
1. INTRODUCTION Need for High-rise buildings in Indian context need not be emphasised. Such buildings call for meticulous planning and design, if the large investments made in them are to give the maximum benefits in functional utility, comfort and safety. The art of designing high rise buildings in seismic area is to bestow them with enough strength to resist forces generated by earthquakes and enough stiffness or energy dissipation so that people working on upper floors are not disturbed by the
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