Miss S. S. Nibhorkar 1 1 M. E (Structure) Scholar,

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1 Volume, Special Issue, ICSTSD Behaviour of Steel Bracing as a Global Retrofitting Technique Miss S. S. Nibhorkar M. E (Structure) Scholar, Civil Engineering Department, G. H. Raisoni College of Engineering and Management, Amravati, Maharashtra, India Abstract- Recent earthquakes in India have shown that not only non-engineered but also engineered buildings in our country are susceptible even to moderate earthquakes. Indian Standard IS 89 is revised in. A number of buildings those were designed as per the previous code may not comply with the present code. Therefore evaluating seismic performance of a building and proposing suitable retrofit measure is an important area of study in this context. In many cities it has been observed that the residential parking space is provided in the building itself by utilizing open ground storey. Past earthquake in India shows that open ground storey structure is vulnerable in earthquake and most of the failures occur in open ground storey causes total collapse. To prevent failures in such type of buildings we have to choose appropriate technique for retrofitting of those structures. Less amount of work is done towards the study of performance of steel system as a global retrofitting technique. The study on retrofitted open ground structure by using system in ETAB software is presented in this paper. For this purpose three dimensional models of open ground structure were developed to understand and study the behaviour and performance of system. Comparative results are presented in graphical form to justify the potential in chosen global retrofitting technique. Keywords: Retrofitting technique, Bracing System, Equivalent Static Analysis, Response Spectrum Method. I. INTRODUCTION Earthquake is a natural phenomenon, which is generated in earth s crust. Duration of earthquake is usually very less. Due to this earthquake we are loose thousands of people. Building collapse or damages are the major loss due to earthquake ground motion. In an earthquake, the building base experiences high-frequency movements, which results in inertial forces on the building and its components. The force is created by the building's tendency to remain at rest, and in its original position, even though the ground beneath it is moving. The assessment of the seismic vulnerability of structures is a very complex issue due to the non-deterministic characteristics of the seismic action and the need for an accurate prediction of the seismic responses for levels beyond conventional linear behavior. Lateral stability has always been a major problem of structure in earthquake and for minimizing that problem we have to develop any system. Bracing system is one of the good techniques to resist lateral forces. Inelastic performance is one of the main factors influencing the choice of systems. The system that has a more plastic deformation before collapse can absorb more energy during the earthquake. Seismic Analysis is a subset of structural analysis and is the calculation of the response of a building (or non-building) structure to earthquakes. It is part of the process of structural design, earthquake engineering structural assessment and retrofit in regions where earthquakes are prevalent. Providing strength, stability and ductility are major purposes of seismic design. There are three sources of deficiencies in a building, which have to be accounted for by the retrofitting engineer: Inadequate design and detailing Degradation of material with time and use Damage due to earthquake or other catastrophe. The three sources, suggest a retrofit scheme to make up for the deficiencies and demonstrate that the retrofitted structure will be able to resist the future earthquake forces expected during the lifetime of the structure. In this paper we have studied behaviour of system as a retrofitting technique in existing open ground building located in Amravati region. Now a day a common trend that is followed by most the builders and developers to utilize ground floor as parking space for tenants of building which is an example of open ground structure, vulnerable in the event of earthquake. To understand and study the potential of system as a global retrofitting technique present research is dedicated. 97

2 Volume, Special Issue, ICSTSD II. BRACING SYSTEMS In a multi-storey building, the beams and columns are generally arranged in an orthogonal pattern in both elevation and on plan. In a braced frame building, the resistance to horizontal forces is provided by two orthogonal systems like horizontal and vertical system. III. TYPES OF BRACINGS There are two types of systems. A. Concentric Bracings Concentric s increase the lateral stiffness of the frame thus increases the natural frequency and also usually decreases the lateral storey drift. However, increase in the stiffness may attract a larger inertia force due to earthquake. Further, while the s decrease the bending moments and shear forces in columns and they increase the axial compression in the columns to which they are connected. B. Eccentric Bracings Eccentric Bracings reduce the lateral stiffness of the system and improve the energy dissipation capacity. The lateral stiffness of the system depends upon the flexural stiffness property of the beams and columns, thus reducing the lateral stiffness of the frame. IV. SYSTEM DEVELOPMENT In recent years, the topic of analyzing buildings with considering infill walls have been increased due to largely increasing population growth and land acquisition structures have to be designed to solve various issues including parking at base. For solving such problems I choose open ground structure which is vulnerable under earthquake forces, and hence if we are providing outer system as a retrofitting of structure then it is a good solution. In this research I have analysed three buildings (D models) G+ buildings (actual structure, retrofitting using system at outer to open ground storey and retrofitting using system at outer + middle at some location). I have performed equivalent static analysis initially before response spectrum analysis to calculate point displacement, storey drift and storey shear of building by using software E-tab. Details of building like load data, seismic definitions and geometric data are as follows. Table Load Data Live Load kn/m Roof Live Load kn/m Floor Finished Load kn/m Table Seismic Definitions Earthquake Zone III Damping Ratio % Importance Factor Response Reduction Factor (OMRF) Type of Soil Medium Soil Type of Structure RC Structure Time Period User Calculated from IS 89- Table Geometric and Material data Density of RCC Considered kn/m Density of infill Considered 8 kn/m Thickness of Slab mm Dimension of Beam mm x 8 mm Dimension of Column mm x mm Exterior wall mm Interior wall mm Poisson s Ratio of infill. Conc. Cube Comp. Strength, N/mm fck Bending Reinforcement yield strength, fy Shear Reinforcement yield strength, fys N/mm N/mm The plan and elevation of three models which we are studied are as follows: Fig : Plan of Existing Building 98

3 Volume, Special Issue, ICSTSD A. Model of actual existing structure by considering infill effect Fig : Elevation of Existing Building (Infill Model Actual) B. Model of Retrofitting Using Bracing System V. Performance Analysis In this area I have compared point displacement, storey drift and storey shear for three models with respective each other in software. By comparing the result one can easily observe the performance of structure and can predict the behaviour of structure Fig : Elevation of Existing Building (Retro Bracing Model) 99 which performs against earthquake forces. Detailed study of each graph is shown below, I have retrofitted an existing structure using steel as retrofitting technique but as we know that available technique must not hamper the normal dwelling of the tenants. I tried for various locations of which would not obstruct the parking problem. To overcome this problem I have modeled various options by trying various locations of

4 International Journal of Innovative and Emerging Research in Engineering Volume, Special Issue, ICSTSD and find out the best location for the existing structure. c infill v B....8 Point Displacement. X (m) C infill c B... Storey Drift. Y (m) Fig 7: Storey Drift in Y Direction (Retro Bracing) Fig : Point Displacement in X Direction (Retro Bracing... Point Displacement Y (m) c Storey Shear X (kn) c M too infill C B Fig : Point Displacement in Y Direction (Retro Bracing Fig 8: Storey Shear in X Direction (Retro Bracing.. Storey Drift. X (m) C infill c B Fig : Storey Drift in X Direction (Retro Bracing c infill C B Storey Shear Y (kn) Fig 9: Storey Shear in Y Direction (Retro Bracing Above graph of point displacement in X and Y direction shows that point displacement of

5 Volume, Special Issue, ICSTSD using outer + middle satisfy permissible limit as per [] Murty CVR, (), quantitative approach to seismic strengthening Of RC frame building, Seminar on IS 89. Above graph of storey drift in X and Y seismic assessment and retrofitting buildings, pp 9-7. direction shows that storey drift of using outer + middle satisfy permissible limit as per IS 89, hence we choose outer + middle appropriate location for existing structure by using as a retrofitting technique. Above graph of storey shear in X & Y direction shows that location of outer + middle attracts more storey shear than other. After studying different location I found that appropriate location for providing X system which came out to be considering at outer + mid too. By adopting this option we have achieved successes in solving the parking problem more effectively. When storey drift is lesser then bending moment, shear force and axial force are also lesser and hence it achieves economy with serviceability. Conclusion Effects on chosen models have been shown in the form of graphs in part of performance analysis; by comparing various parameters such as point displacements, storey drift and storey shear. Hence from the obtained results we conclude that the effect of point displacement, storey drift and storey shear are more in case of bare frame which is analysed using effect of infill i.e. it is not within permissible limit as per IS 89- hence there is need of retrofitting. By considering steel as a global retrofitting I have studied the behaviour of chosen system.. When I studied behaviour of all parameters like point displacement, storey drift and storey shear by providing system in different location then I had found that the best location for existing structure. It shows that system is a good global retrofitting technique in case of open ground storey. Consideration of infill wall in analysis of earthquake resistance structure achieves economy with serviceability. References [] S Krishnan (8) Modeling Steel Moment Frame and Braced Frame Buildings in Three Dimensions Using Frame D The th World conference earthquake engineering October -7 Beijing China. [] Mohammed Idrees Khan et al () Seismic Analysis Of Steel Frame With Bracing Using Pushover Analysis International journal of advanced Technology in engineering and science vol issue No. 7. [] Manish S. Takey& prof. S. S. Vidhale() Seismic Response of Steel Building with Linear Bracing System (A software approach) International journal of Electronics and soft computing Science and Engineering ISSN , vol, Issue