Influence of Outrigger system in RC Structures for Different Seismic Zones
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This document analyzes the influence of outrigger systems in reinforced concrete structures in different seismic zones. It models and analyzes a 35-story building with and without outriggers using finite element software. The outrigger system is varied by changing the relative stiffness ratio (do/d) from 1 to 5 at different heights. Results show lateral displacement, inter-story drift, and base shear decrease as relative stiffness increases in all zones. Maximum reductions occur in Zone 5, while differences between zones are small. Inter-story drift is highest between 5-15m. Base shear is highest for the stiffest outrigger model and lowest for the bare frame. In conclusion, outrigger systems effectively reduce displacement and drift, while increasing base
![International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1752
A Similar variation in Inter-Storey drift for different
seismic zones has been observed and the maximum Inter-
Storey Drift for different seismic zones is tabulated in the
table 4.
Table4: Variation of maximum Inter-Storey Drift for
different models at different seismic zones
Seis
mic
Zone
s
Model
1
Mode
l
2
Mode
l
3
Mode
l
4
Mode
l
5
Mode
l
6
Zone
2
0.0004
22
0.000
243
0.000
233
0.000
223
0.000
217
0.000
213
Zone
3
0.0006
75
0.000
389
0.000
372
0.000
357
0.000
347
0.000
340
Zone
4
0.0001
013
0.000
555
0.000
532
0.000
51
0.000
496
0.000
487
Zone
5
0.0015
0.000
833
0.000
798
0.000
765
0.000
744
0.000
731
III) Base shear in Equivalent Static Method:
Fig.9 shows the variation of inter-storey drift for different
models at Zone 2.
Fig. 9: Variation of Base Shear for different models at
Zone 2.
A Similar variation in Base Shear for different
seismic zones has been observed and the maximum Base
Shear for different seismic zones is tabulated in the table 5.
Table4: Variation of maximum Base Shear in kN for
different models at different seismic zones
Seism
ic
Zones
Model
1
Model
2
Mod
el
3
Mod
el
4
Mod
el
5
Mod
el
6
Zone 2
3402.
40
4578.
21
4947.
6
5132.
1
5259.
3
8348.
1
Zone 3
5443.
84
7613.
14
7916.
2
8211.
4
8415.
0
8557.
0
Zone 4
8165.
77
11419
.7
1187
4
1231
7
1262
2
1283
5
Zone 5
12248
.6
17129
.5
1781
1
1847
5
1893
3
1925
3
5. CONCLUSIONS
1) The percentage reduction of lateral displacement and
inter-storey drift with respect to bare frame (Model1)
varies for different model configuration, however this
variation is not significant when compared between
different seismic zones.
2) Maximum inter-storey drift has been observed at
building height in the range of 5 to 15m.
3) Base shear is highest for Model 6 and Model 1
experiences least base shear in all seismic zones.
REFERENCES
[1]. Kiran Kamath, N. Divya, Asha U Rao, "A Study on Static
and Dynamic Behavior of Outrigger Structural System
for Tall Buildings" Bonfring International Journal of
Industrial Engineering and Management Science, Vol. 2,
No. 4, December 2012.
[2]. N. Herath, N. Haritos, T. Ngo & P. Mendis, "Behaviour of
Outrigger Beams in High rise Buildings under
Earthquake Loads" Australian Earthquake Engineering
Society 2009 Conference.
[3]. Navab Assadi Zeidabadi, Kamal Mirtalae and Barzin
Mobasher, "Optimized use of the Outrigger System to
Stiffen the Coupled Shear Walls in Tall Buildings" The
Structural Design of Tall and Special Buildings Struct.
Design Tall Spec. Build. 13, 9–27 (2004).
[4]. Taranath “Steel, Concrete, & Composite Design of Tall
Buildings” New York: McGraw-Hill.
[5]. Moudarres, “Outrigger Braced Coupled Shear Walls,
Journal of Structural Engineering”, ASCE, Vol. 110, No.
12, 1984.
BIOGRAPHIES
Sukesh H.S
Birth place: Madikeri, Karnataka,
Date of Birth 04/03/1993.
Completed Graduation in Civil
Engineering from VTU Belgaum
Karnataka in 2015.
Dr. H.S. Suresh Chandra,
Holds a B.E from University of
Mysuru, M.Tech from R.E.C
Warangal, A.P, and PhD from VTU
Karnataka. Research interests
include Masonry Structures and
Repair and RetrofittingofConcrete
Structure.
Lakshmi P.S
Holds a B.E from VTU Belgaum,
Karnataka and M.Tech from VTU
Belgaum, Karnataka. Research
interests include Concrete and
Repair and RetrofittingofConcrete
Structure.](https://image.slidesharecdn.com/irjet-v4i6566-180222093004/85/Influence-of-Outrigger-system-in-RC-Structures-for-Different-Seismic-Zones-4-320.jpg)
Influence of Outrigger system in RC Structures for Different Seismic Zones
- 1. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1749 Influence of Outrigger system in RC Structures for Different Seismic Zones H.S. Sukesh1, H.S. Suresh Chandra2, P.S. Lakshmi3 1 P.G. Student, Department of Civil Engineering, P.E.S.E Mandya, Karnataka, India 2 Professor, Department of Civil Engineering, P.E.S.E Mandya, Karnataka, India 3 Assistant Professor, Department of Civil Engineering, P.E.S.E Mandya, Karnataka, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - Construction of tall structures having residential and commercial purposeshasimprovedinconjunctionwiththe growth of construction technique. In general, earthquake(EQ) ground motion is unpredictable and the problem considered with tall buildings, especially under heavy earthquakes, it shouldbe extensivelystudied.Constructionoftallbuildingshas laid more challenges for engineers to meet the requirements with respect to the demand growth. In the recent trend of tall buildings, horizontal loads due to seismic or wind action are resisted by arrangement of coupled shear walls. When the structure increases in height, the structural stiffness becomes more significant and introduction of outrigger beamsbetween the exterior columns and shear wallsismorecommonlyusedto give lateral stiffness to the structure. The outrigger system is the most commonly used structural lateral load resisting system as to mitigate the excessive drift due to lateral load in an effective manner. The analysis has been carried out tostudy the effect and performance of outrigger system in a 35 story building. The outrigger system is provided at different levels along the height of the buildingbyvaryingtherelativestiffness. Loads are considered as per Indian Standards IS: 875(Part1)- 1987 and IS: 1893(Part-1): 2002. The analysis is done with Equivalent static method for different seismic zones. The modeling and analysis were performed using finite element software ETABS 9.7.4. It is found that, with the increase in relative stiffness of the outrigger system, there is a decrease in lateral displacement and inter-story drift. Further there is increase in base shear of the structure with higher relative stiffness in all seismic zones. Key Words: Influence of OutriggerSystem,RCStructuresfor Different Seismic Zones. 1. INTRODUCTION The main core in connection with the columns located at the exterior portion of the building by outriggers (stiffer horizontal members) formsthestructural arrangementof an outrigger system. The core is centrally located with outriggers spreading on both sides (Fig.1) or one side of the building with outriggers (Fig.2) and it may consist of reinforced concrete shear walls. When Horizontal load is applied to the structure,thecolumn with outriggers controls the core rotation. The main objective is to increase the structure’s effective depth when it acts like a vertically cantilever, which is done by inducing tension in the windward columns and Compression in the leeward columns. The peripheral columns are utilized to assist the columns located at the ends of the outriggers. A deep spandrel girder or a belt truss, around the structure is used to achieve it the outrigger levels. Fig -1: Outrigger system with a central core Fig -2: Outrigger system with a central core The use of Outriggers in High-rise buildings to control the Forces: The incorporation of an outrigger connecting the two elements together gives rise to stiffer component acting along with the core to resist the overturningforces. When an outrigger building undergoes deflection due to under wind or earthquake load, the outrigger which connects in between the core wall and the external columns, makes the whole system to act as a single unit in resisting the lateral load.
- 2. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1750 2. MODELING Table 1 below shows the details of the models considered in the study. Table -1: Details of the models considered in the study Details of the models considered in the study Plan of 35 storey building (60X48) m Building Type SMRF Center to Center distance of Column 6.0 m Storey Height 3.05 m Intensity of Live Load on each floor 3 kN/m2 Weight of floor finish 2 kN/m2 Intensity of roof live load 1.5 kN/m2 Soil type Medium Importance factor 1.0 Response reduction factor 5.0 Grade of steel Fe 500 for Beam Fe 550 for Column Grade of concrete M30 for Beam M50 for Column Beam details (300X600) mm Column details (900X900) mm Slab details 150 mm thick M30 throughout Wall details 200 mm thick M30 throughout Outrigger system are considered at different locationsalong the height of the building (H), such as 0.25H,0.5H,0.75Hand 1H. The dimensions of outrigger beam for different do/d ratio as shown in below Table 2 Table -2: Dimension of Outrigger beam for different do/d do/d ratio Size of Outrigger Beam 1 (300X600) mm 2 (300X1200) mm 3 (300X1800) mm 4 (300X2400) mm 5 (300X3000) mm In the present study there are 6 different models are considered for the analysis. Model 1: In this model only bare frame is considered with no shear wall and outrigger beams. The plan of the Model 1 has been shown in Fig.3. Model 2, Model 3, Model 4, Model 5 and Model 6 are considered with different do/d ratio as 1, 2, 3, 4 and 5 respectively. These models are considered with shear wall and outrigger beams. The plan, elevation and 3D view of these models are shown in Fig.4, Fig.5 andFig.6respectively. Fig -3: Plan of Model 1 Fig -4: Plan of Outrigger system model Fig -5: Elevation of Outrigger system model
- 3. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1751 Fig -6: 3D view of Outrigger system model 3. METHODOLOGY In the present study, an attempt has been made to evaluate the seismic performance of RC structures with central core wall with Outrigger and without Outrigger by varying the relative stiffness. For this purpose, Outrigger systems are placed at different locations along the height of the building by varying relative stiffness. The relative stiffness is varying by considering the ration of depthofOutriggerbeamtodepth of Convention beam (do/d) from 1 to 5 with interval of 1. Also the position of outriggers remainssamealongtheheight of the building for all models. Modelling and Analysis are carried out using ETABS finite element software, analysis is carried out using Equivalent Static method and Response Spectrum method. Loads are considered as per Indian Standards IS: 1875(Part 1) -1987, IS: 1875 (Part 2) -1987 and IS: 1893 (Part 1) -2002. The analysis is performed fordifferent seismic zones, results are tabulated and corresponding graphs are plotted. 4. RESULTS AND DISCUSSIONS Results obtained from the Equivalent static method are tabulated as follows and represented in the form of graphs. Lateral displacement, Inter-storey drift and base shear are parameters used to quantify the performance of RC structures with and without outriggers system for different seismic zones. I) Lateral displacement in Equivalent Static Method Fig.7 shows the variation of lateral displacement for different models at Zone 2. Fig. 7: Variation of lateral displacement for different models at Zone 2. A Similar variation in lateral displacement for different seismic zones has been observed and the maximum lateral displacement for different seismic zones is tabulated in the table 3. Table3: Variation of maximum lateral displacement in meters for different models at different seismic zones Seismi c Zones Mode l 1 Mode l 2 Mode l 3 Mode l 4 Mode l 5 Mode l 6 Zone 2 0.035 2 0.026 8 0.025 6 0.024 5 0.023 8 0.023 4 Zone 3 0.056 3 0.042 9 0.040 9 0.039 2 0.038 2 0.037 5 Zone 4 0.084 5 0.064 4 0.061 4 0.058 9 0.057 3 0.056 3 Zone 5 0.126 0.096 6 0.092 2 0.088 3 0.859 0.084 4 II) Inter-Storey Drift in Equivalent Static Method: Fig.8 shows the variation of inter-storey drift for different models at Zone 2. Fig. 8: Variation of Inter-storey for different models at Zone 2.
- 4. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1752 A Similar variation in Inter-Storey drift for different seismic zones has been observed and the maximum Inter- Storey Drift for different seismic zones is tabulated in the table 4. Table4: Variation of maximum Inter-Storey Drift for different models at different seismic zones Seis mic Zone s Model 1 Mode l 2 Mode l 3 Mode l 4 Mode l 5 Mode l 6 Zone 2 0.0004 22 0.000 243 0.000 233 0.000 223 0.000 217 0.000 213 Zone 3 0.0006 75 0.000 389 0.000 372 0.000 357 0.000 347 0.000 340 Zone 4 0.0001 013 0.000 555 0.000 532 0.000 51 0.000 496 0.000 487 Zone 5 0.0015 0.000 833 0.000 798 0.000 765 0.000 744 0.000 731 III) Base shear in Equivalent Static Method: Fig.9 shows the variation of inter-storey drift for different models at Zone 2. Fig. 9: Variation of Base Shear for different models at Zone 2. A Similar variation in Base Shear for different seismic zones has been observed and the maximum Base Shear for different seismic zones is tabulated in the table 5. Table4: Variation of maximum Base Shear in kN for different models at different seismic zones Seism ic Zones Model 1 Model 2 Mod el 3 Mod el 4 Mod el 5 Mod el 6 Zone 2 3402. 40 4578. 21 4947. 6 5132. 1 5259. 3 8348. 1 Zone 3 5443. 84 7613. 14 7916. 2 8211. 4 8415. 0 8557. 0 Zone 4 8165. 77 11419 .7 1187 4 1231 7 1262 2 1283 5 Zone 5 12248 .6 17129 .5 1781 1 1847 5 1893 3 1925 3 5. CONCLUSIONS 1) The percentage reduction of lateral displacement and inter-storey drift with respect to bare frame (Model1) varies for different model configuration, however this variation is not significant when compared between different seismic zones. 2) Maximum inter-storey drift has been observed at building height in the range of 5 to 15m. 3) Base shear is highest for Model 6 and Model 1 experiences least base shear in all seismic zones. REFERENCES [1]. Kiran Kamath, N. Divya, Asha U Rao, "A Study on Static and Dynamic Behavior of Outrigger Structural System for Tall Buildings" Bonfring International Journal of Industrial Engineering and Management Science, Vol. 2, No. 4, December 2012. [2]. N. Herath, N. Haritos, T. Ngo & P. Mendis, "Behaviour of Outrigger Beams in High rise Buildings under Earthquake Loads" Australian Earthquake Engineering Society 2009 Conference. [3]. Navab Assadi Zeidabadi, Kamal Mirtalae and Barzin Mobasher, "Optimized use of the Outrigger System to Stiffen the Coupled Shear Walls in Tall Buildings" The Structural Design of Tall and Special Buildings Struct. Design Tall Spec. Build. 13, 9–27 (2004). [4]. Taranath “Steel, Concrete, & Composite Design of Tall Buildings” New York: McGraw-Hill. [5]. Moudarres, “Outrigger Braced Coupled Shear Walls, Journal of Structural Engineering”, ASCE, Vol. 110, No. 12, 1984. BIOGRAPHIES Sukesh H.S Birth place: Madikeri, Karnataka, Date of Birth 04/03/1993. Completed Graduation in Civil Engineering from VTU Belgaum Karnataka in 2015. Dr. H.S. Suresh Chandra, Holds a B.E from University of Mysuru, M.Tech from R.E.C Warangal, A.P, and PhD from VTU Karnataka. Research interests include Masonry Structures and Repair and RetrofittingofConcrete Structure. Lakshmi P.S Holds a B.E from VTU Belgaum, Karnataka and M.Tech from VTU Belgaum, Karnataka. Research interests include Concrete and Repair and RetrofittingofConcrete Structure.