Effective Location of Different Outrigger System in Seismic Respond RCC High Rising Building Using ETABS

Abstract

The rapidly growing number of high-rise structures around the world poses new obstacles, and lateral stiffness becomes one of the most critical issues as building height rises. The lateral stiffness and resistance capacity of high-rise buildings have a significant impact on structural efficiency, and structural engineers have introduced numerous capable constructions. The outrigger system is one of the most frequent and effective lateral loads resisting structural systems for improving structural stiffness and stabilizing the structure. The core shear wall provides structural strength in the main structural system, while the outrigger like X bracing adds lateral stiffness. In this study building with the outrigger and shear wall system has been analysed by Response Spectrum Analysis, The concept of illumination of outrigger structural systems is evaluated by comparing multiple X braced outrigger system and shear wall system models types utilizing a 25-story reinforced concrete building using ETABS software under seismic load to better understand the performance and load transferring mechanism of outrigger system.

Introduction

I. INTRODUCTION

The seismic action of the earth on multi-storey building located around the area of epicentre, the wave creates severe harmful effect on structure. As height of the building increase, building becomes more crucial to provide sufficient stiffness against the lateral loads. In modern tall building lateral load is caused by wind load and seismic/earthquake load. The parameter that to check are strength of structure, resistance against the lateral deflection of structure. These wind load & seismic load action are often resisted by different types of system, that is braced frame structure system, rigid frames structure system, shear wall structure system, couple wall system, core and outrigger structure system etc. Sometime moment resisting frames and braced frame system become inadequate to resist all lateral forces and inefficient to provide stiffness against the wind load and seismic load. The deflections cause by lateral forces should be prevented both structure and non-structural damage to maintain the building strength and also the building stiffness against the lateral forces in the analysis of RCC tall building and also for design In this paper seismic load is resisted by shear core with outrigger-braced system. Stiff shear core is provided in mid of the structure by stiff truss arm that will help in resisting the complete structure and transfer its all the lateral load to the beam and column connection with stiff shear core.

Outrigger systems are lateral load-resisting systems that successfully reduce lateral loads while also strengthening tall structures. The external and interior structures in this system work together to with stand lateral stress. Outrigger trusses serve as stiff arms that connect the building's core to the exterior columns (Fig.1). When all the lateral loads are act on the face of the building, the core tries to rotate generating force to the outrigger trusses, which cause tension in force acting on columns side and cause compression in another columns. As a result of this response, a restoring moment operates on core at the position of outriggers, increasing the effective depth of the structure to resist the bending moment. To further strengthen outrigger truss rotation constraint, all outside columns can be mobilized with a one or two storey deep wall around the structure known as a "belt wall."

Due to the rotation of the core and the overturning moment, floor diaphragms above and below the belt truss will try to shift right and left. The belt truss or braced system connected to the floors will move in return & rotate itself by one face-up and one face-down. The exterior columns of structure will constrain this movement by developing opposing forces.

II. TYPE OF OUTRIGGER SYSTEM

They are classified into two groups depend on how the outrigger systems connect to the core. The conventional or direct outrigger system is the first. These outriggers are directly attached to the braced shear core or shear walls to the outer columns, as the name implies. On the other hand, virtual or indirect outrigger and the belt truss system eliminate the direct connections to the building core walls with outer columns. As shown in figure (Fig.2) below.

V. ACKNOWLEDGMENT

I would like to acknowledge my deep sense of gratitude to Prof. K. R. Ghadge & Prof. D. B. Saruk Sir, my dissertation Guide, Department of Civil Engineering, Sanmati Engineering College, Washim, SGBA University, Amravati for his guidance and encouragement. They gladly accepted all the pains in going through my work again and again and gave me opportunity to learn essential research skills. This dissertation would not have been possible without his insightful and critical suggestions, his active participation in constructing right models and a very supportive attitude. I will always remain grateful to him forgiving right direction to my study.

Conclusion

A study has been carried out to determine the optimum configuration of a twenty-five story building by changing outrigger location. Seven different cases of outrigger position for a twenty-five storey building have been analyzed by Response Spectrum analysis as a space frame system using a standard package ETAB subjected to lateral and gravity loading. The typical shear wall and X bracing is also used in considered cases. This study leads to following conclusions: 1) The X-braced and shear wall Outriggers is very much effective; as it shows minimum lateral displacement as compared to without Outriggers provision. 2) The Outriggers provided with X Bracing at core area were less effective in reducing lateral displacement compared with Shear wall by a small margin, hence it can be employed as the cost effective construction. It is observed that 30% more top storey displacement of Model 6 as compared to Model 7. 3) And relatively comparison of all the similarly located outrigger system like in Model 2 with Model 3, Model 4 with Model 5 has experienced less displacement variation. It is observed that 3.5% more top storey displacement of Model 2 and Model 4 as compared to Model 3 and Model 5 respectively. 4) Lateral displacement values obtained from analysis indicate that numbers of outrigger provisions increases along longitudinal and transverse directions are effective in reducing the displacement values in the same directions. 5) The absolute lateral displacement obtained from analysis of regular building Model 1 at respective nodes is found to be greater at less storey stiffness. The reason for high storey displacements in buildings is that the overall stiffness of the building decreases due to attract maximum lateral forces. Due to decreasing stiffness, the flexibility increases and strength decreases resulting in high displacements. 6) Building Models7 with outrigger as an shear wall have maximum base shear about 11% when compared to building Model 6 where outrigger as an X bracing. Similarly all the models having outrigger as an shear wall is found more base shear value as compared to similarly located outrigger as an X bracing. Indicating these models are stiffer than without shear wall model. 7) From analysis, shorter fundamental periods is obtained in the form of seconds for shear wall building models that means to attract higher forces than the without shear wall model. So it concludes that these building models have more strength against the lateral loads to stable the structure. The analysis proves that without outrigger system structures may exhibit poor performance during a strong shaking, as far as possible without outrigger provision in a high-rise building must be avoided. Therefore building provided with outrigger provision have to be introduced for reducing vulnerable response of building, they must be analyzed and designed properly following the conditions of IS 1893-part-1: 2002 and IS- 456: 2000, and joints should be made ductile as per IS 13920:1993. Now a day, complex shaped high-rise buildings are getting popular, but they carry a risk of sustaining damages during earthquakes. Therefore, such buildings should be designed properly taking care of their dynamic behavior.

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Copyright

Copyright © 2023 Prof. K. R. Ghadge, Prof. D. B. Saruk, Lavanya V. Ghongade. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.