Seismic Evaluation of Reinforced Concrete Building with Friction Dampers

Abstract

Dynamic action is caused on building by both wind and earthquake. But design of structure for these forces are different. With increase in infrastructure growth the need of structural response control is increased around the world. The paper mainly emphasized use of one such device friction damper for response control of structures. In this paper the comparison of reinforced concrete building connected with and without damper for G+5,G+10,G+15 storied building for seismic zone IV is considered. Analysis is done using equivalent static method, response spectrum method and time history method in finite element software package, ETABS version 16.2.For seismic load combination IS 1893:2016 is used. The model analysis is carried out by all four methods of analysis and results are discussed in terms of storey displacement, storey drift, base shear, bending moment and axial forces. From result obtained it is concluded that storey drift and displacement in friction damper building is reduced where as base shear is less in building without damper. 1.Introduction Earthquakes are most unpredictable and devastating of all-natural disasters. Earthquakes have the potential for causing the greatest damages among all the natural hazards. They not only cause great destruction in human casualties, but also have a tremendous economic impact on the affected area. With increase in infrastructure growth the need of structural response control is increased around the world. When a structure is subjected to ground motions in an earthquake, it responds by vibrating. Those ground motion causes the structure to vibrate or shake in all three directions; the predominant direction of shaking is horizontal. By looking after the destruction, it has become necessary to design building considering seismic codes. With the advancement of technology, it is observed that as mechanical engineers are busy with are providing shock absolver to vehicle similarly it can be done for building. Thus, the use of one such shock absolver friction damper is discussed in this paper. During an earthquake, seismic energy is input into the structure which results in increased vibration response. Mechanical devices e.g. dampers are provided throughout the height of structure to increase the damping hence reduce the response either by absorbing or dissipating energy. Friction dampers dissipate specifically kinetic energy through sliding of plate /surfaces. 2. METHODOLOGIES FOR SEISMIC EVALUATION The various method used in seismic analysis of reinforced concrete building connected with and without damper are a) Equivalent static analysis b) Response spectrum analysis c) Time history analysis Table: 1 Load combinations as per IS: 1893-2016 Load Combination Load Factors Equivalent static analysis 1.2[DL+IL±(EQX±0.3EQY±0.3EQZ)] 1.2[DL+IL±(EQY±0.3EQX±0.3EQZ)] 1.5[DL±(EQX±0.3EQY±0.3EQZ)] 1.5[DL±(EQY±0.3EQX±0.3EQZ)] 0.9DL±1.5(EQX±0.3EQY±0.3EQZ) 0.9DL±1.5(EQY±0.3EQX±0.3EQZ)] Response spectrum analysis 1.2[DL+IL±(RSX±0.3RSY±0.3RSZ)] 1.2[DL+IL±(RSY±0.3RSX±0.3RSZ)] 1.5[DL±(RSX±0.3RSY±0.3RSZ)] 1.5[DL±(RSY±0.3RSX±0.3RSZ)] 0.9DL±1.5(RSX±0.3RSY±0.3RSZ) 0.9DL±1.5(RSY±0.3RSX±0.3RSZ)] International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 4758 3.Plan details Modelling means the formation of structural body in the structure software and assigning the loads to the members as per loading consideration. Here we considered a 3-D RC frame with the dimensions of 4 bays @ 4m in x-axis and 4 bays @ 5m in y-axis. The z axis consisted of G+5, G+10, G+15 floors. The plinth height is 2.5m and rest of the floors had a height of 3.5m. DESIGN DATA FOR ALL THE BUILDINGS 1 Details of building i) Structure OMRF ii) Number of storey G+5,G+10,G+15 iii) Type of Building Regular in plane iv) Storey height Ground storey 2.50 m Upper storey 3.50 m v) Type of building Residential Building vi) Seismic zone IV 2. Material properties i) Grade of concrete M25 & M30 ii) Grade of steel Fe415 iii) Density of reinforced concrete 25 kN/m3 iv) Density of steel 78.50 kN/m3 3. Member properties a Slab i) Grade M25 ii) thickness 0.125m b Beam i) Grade M25 ii) Size ( for all storey) 0.23x0.4m c Column i) Grade M30 ii) Size ( for all storey) 0.3x0.5m 4 Type of loads & their intensities i) Floor finish 1 kN/m2 ii) Dead load 4.125 kN/m2 iii) Live load on floors 2.5 kN/m2 iv) Live load on roof 1.5 kN/m2 5 Seismic properties i) Zone factor (Z) 0.24 ii) Importance factor (I) 1 iii) response reduction factor (R) 3 iv) Soil Type Medium (II) 6 Link ( Friction damper ) properties i) Effective stiffness, K 2.925x1010 kN/m ii) For storey G+5 Weight of one damper 5585.14kg Effective damping 25.65x106kN-s/m iii) For storey G+10 Weight of one damper 10409.088kg Effective damping 34.89x106kN-s/m iv) For storey G+15 Weight of one damper 14923.39kg Effective damping 41.78x106kN-s/m International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 4759 4.Loading Details The structures are acted upon by different loads such as dead load (DL), Live load and Earthquake load (EL). A. Self-weight of the structure comprises of the weight of the beams, columns and slab of the structure. B. Dead load of the structure consists of self weight of slab and floor finish according to IS 875 (Part1). Dead load on slab: density of concrete x depth of slab x one square meter area+ floor finish = 25x0.125x1 +1= 4.125 kN/m2 C. Live load: It consists of Floor load which is taken as 2.5KN/m2 and Roof load as 1.5 KN/m2 , according to IS 875 (Part 2). D. Seismic Load: Earthquake loads have been defined and assigned on the building as per IS 1893:2002 (Part-I). ▪ Seismic zone (Zone Factor): IV (z = 0.24), ▪ Soil type: Medium soil ▪ Importance factor: 1 ▪ Response reduction factor: 3 (OMRF) 5.Result and Discussions The result obtained after the analysis of G+5,G+10,G+15 reinforced concrete building by Equivalent Static Method(ESM), Response Spectrum Method(RSM) and Time History Method(THM) are in terms of base shear, bending moment, axial force and displacement. An efforts are being made to study the reinforced building by pushover analysis method and compare the results of all four method. Fig.1-G+5 storey building without damper Fig.2-G+5 storey building with damper International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 4760 A. Base Shear The base shear of each building frame using equivalent static method(EQM), response spectrum method (RSM) and Time History method (THM) are given in tabular form. Story shear is a force that acts on any story in a direction perpendicular to its extension and is measured in ‘KN’. Table-2 and table -3 shows the Base Shear in X-direction and Y-direction respectively for different storey building bye different method. It has been concluded that the story shear tends to decrease with the increase in height of the story. For all the structures it is highest at bottom and it decreases linearly towards top. G+5 storey building has less story shear compare to G+10 and G+15 storey building. Fig.3 and Fig 4 shows the graphical representation of base shear in X and Y direction with different storey and different method. Fig.3.showing Base shear (kN) in X-direction Fig.4.Showing Base shear (kN) in Y-direction International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 4761 B. DISPLACEMENT Story displacement is the displacement of one level of a multi-story building relative to the base of the building. Table that story displacement is linearly increasing from bottom to top for all the structures. According to Codal provision, maximum or permissible story displacement should be equal to or less than 0.4% of total building height. Hence here the maximum permissible story displacement = ((0.4 / 100) x 56000) = 224 mm. Table 4 & 5 shows the tabular format of maximum story displacement for different stories using EQM, RSM and THM and Fig.5 shows the graphical format of maximum story displacement for different storey building. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 4762 C.AXIAL FORCE The base reactions in terms of axial force for each building frame using 3 methods are given in tabular form. As can be seen the base shear for building with damper against the building without damper has higher values for large fraction of time indicating that on the time scale of the event the building experiences high amount of force over the run of the event. This increased force is evidently resisted by the friction damper system. The increased force in case of the building with damper can be attributed to increased mass due to addition of damper brace system to the building.