Seismic performance evaluation of high-rise steel frame with eccentric K- and V-bracings

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    International Research Journal of Engineering and Technology  (IRJET)  e-ISSN: 2395 -0056 Volume: 03 Issue: 07 | July-2016  www.irjet.net p-ISSN: 2395-0072   © 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 1387 Seismic performance evaluation of high-rise steel frame with eccentric K- and V-bracings Mrutyunjay.S.Hasarani 1 , M.B.Iswhwaragol 2 1 Post Graduate Student, Structural Engineering ,  Department of Civil Engineering , B.L.D.E.A’ S V.P. Dr. P.G.H. C.E.T, Vijayapur, Karnataka  2  Assistant Professor, Department of Civil Engineering , B.L.D.E.A’ S V.P. Dr. P.G.H. C.E.T, Vijayapur, Karnataka  , India ---------------------------------------------------------------------***---------------------------------------------------------------------  Abstract -   In past decades, the steel structures have played an important role in growing construction industry. It is essential to design a structure to perform well under earthquake loads, especially in seismic prone areas. The seismic design of a multi-story steel frame building is carried as per IS 800: 2007. By introducing steel bracings in a structure, its shear capacity can be increased. They can be also used as strengthening an existing building. In various patterns steel bracings can be arranged. A 15-story steel frame building is designed for eccentric K- and V- bracings as per the IS 800:  2007. Eccentric K and V type bracings in a steel frame having different configurations are selected for this study. Performance of the each frame is studied under Response Spectrum and Time History analysis. The results of analysis have shown that, performance of the eccentric V-bracing system is better than eccentric K-bracing system.   Key Words :  High-rise steel frame, Eccentric bracings, Displacement, Story drift ratio, Story shear 1. INTRODUCTION Steel is a vital progress material and plays a very significant role in growing social orders. Most of structures for e.g., home, parking lots, educational institutes and skyscrapers rely on steel because of its high strength and good ductility. Steel likewise affords high-quality engineering perspective and it offers a greater possibility of outline for auxiliary experts.   Steel structures must be designed and guarded against corrosion and fireplace. They ought to be designed for easy fabrication & erection. To restrict the progress of crack under fatigue and earthquake loads, the connections particularly the welds must be properly designed. Special steels and protecting measures for corrosion and fireplace are available and the designer should be aware of these options.   Steel is playing the major role in structures. Steel has higher strength, good ductility and toughness compared to alternative construction materials. Its properties makes it most suited material for earthquake and blast loading. Steel usage in infrastructure allows quicker and safer installation with least impact on surrounding. [1] Simply stated, earthquakes are vibrations emanating from a source of disturbance within the earth crust which release energy in form of seismic waves. These travel through earth’s surface leading to a greater destruction of property and also increase the death toll. Poor construction practices are more prone to such damages. So structural components must be designed carefully. [2] Steel braced frames are the widely used for their structural adequacy in providing sufficient lateral strength and stiffness to a structure. The steel braces contribute to seismic energy dissipation by deforming elastically under ground motion. Various steel braces are used in practice, such as x-braces, diagonal braces, V-braces, and eccentric braces. Steel brace can be designed to resist only tensile forces, or to resist both tensile and axial compressive force. Recent earthquakes and experiments have shown that the tension-compression braces provide better performance under cyclic loading (during an earthquake) as compared with tension only braces having almost no compressive strength. [3] 1.1 Objectives Following are the main objectives of present study, a)   To compare the natural time period and frequency of the eccentric K- and V-bracing models with various configurations. b)   To compare the story displacement of eccentric K- and V-bracings with different configurations. c)   To evaluate the inter-story drift and base shear various frames by performing Response Spectrum and Time History analysis in Etabs 2013. d)   To identify the efficient lateral load resisting system. 2. METHODOLOGY    2.1 Response spectrum analysis The seismic design of a structure at any location requires    International Research Journal of Engineering and Technology  (IRJET)  e-ISSN: 2395 -0056 Volume: 03 Issue: 07 | July-2016  www.irjet.net p-ISSN: 2395-0072   © 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 1388 actual time records. It is not possible to have time records at all required locations. It is a system to evaluate peak response of structure during an earthquake without the need of time history is referred to as Response Spectrum evaluation. A typical design response spectrum (IS: 1893) is shown below. Chart -1 : Response spectra for rock and soil sites (5% damping) 2.2 Time history analysis In this the response of a structure is computed at a number of next time instants. Time history analysis provides for linear or nonlinear evaluation under seismic loading. In time history analysis, the structural response is computed at a number of subsequent time instants. In other words, Time history of structural response to a given input are obtained as a result. In this, the structural response is evaluated as a time function considering inertial effects.   2.3 Validation A bare steel building with ten stories having plan dimension 20m x 12m is considered. Typical story height is 3m. The horizontal and vertical beam spacing is taken as 3m and 4m respectively. [4]   3. STRUCTURAL MODELLING For present study, steel building with 15 stories is adopted. The dimension in plan of the building is 40 m X 20 m. The structural models have the same story height of 3m and have a uniform mass distribution over the height. Bay width is of 5m in both X- and Y- directions. Building plan is shown in fig2. 3.1 Types of models The types of models considered are, 1. Bare model 2. Eccentric K-bracing model 3. Eccentric V-bracing model Table -1: Description of building   No of Stories G+15 Story Height 3m Base Story 1.5m Type of Soil Medium Seismic Zone 3 Importance factor 1 Response reduction factor 5 Material Property Column Steel Beam Steel slab Concrete Grade of Concrete M25 Grade of Steel Fe415 Thickness of Slab 150 Live Load 4 kN/m 2 Live Load on Roof 1.5 kN/m 2 Floor Finish 2 kN/m 2   Table -2: Sample Table format    Story Column Beam Brace S-6 to S-15 400X750 400X600 ISB172X92X4.8 Story5 400X750 400X600 ISB172X92X4.8 Story4 400X750 400X600 ISB172X92X4.8 Story3 400X750 400X600 ISB172X92X4.8 Story2 400X750 400X600 ISB172X92X4.8 Story1 400X750 400X600 ISB172X92X4.8 GF 400X750 400X600 ISB172X92X4.8 Fig -1 : Eccentricity of the K-and V-frames (m)    International Research Journal of Engineering and Technology  (IRJET)  e-ISSN: 2395 -0056 Volume: 03 Issue: 07 | July-2016  www.irjet.net p-ISSN: 2395-0072   © 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 1389 Fig -2 : Plan of steel building  Fig -3 : 3-D view of bare model  Fig -4 : Typical side elevation of K1 model  Fig -5 : Front elevation of K-frames with different configurations  Fig -6 : Front elevation of varying percentage of K-bracing at corners in a frame (Type 1)      International Research Journal of Engineering and Technology  (IRJET)  e-ISSN: 2395 -0056 Volume: 03 Issue: 07 | July-2016  www.irjet.net p-ISSN: 2395-0072   © 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 1390 Fig -7 : Front elevation of varying percentage of K-bracing from left bottom to right top diagonally in a frame (Type 2)  Fig -8 : Front elevation of varying percentage of K-bracing from left top to right bottom diagonally in a frame (Type 3)  Fig -9 : Front elevation of varying percentage of V-bracing at corner diagonally in a frame (Type 4 )   Similarly, the V-braced frame with all above configurations have been considered for this study. 3.2 Analysis input Table 3: Input for response spectra analysis for various types of models For Time History analysis, ground motion record of 1940 El-Centro is used.   Types of models All models R value 5 Function input 0.1 Spectrum case name SpecX Structural and function damping 0.05 Model combination CQC Directional combination SRSS Input response spectra 981 Eccentricity ratio 0.05
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