Posted: May 27th, 2021
EVALUATION OF SEPERATION GAP BETWEEN MULTISTOREY BUILDINGS SUBJECTED TO DYNAMIC SEISMIC LOAD
Dr. G Sridevi1*(0000-0002-5922-3132), Mr. Umesh Biradar 2(0000-0003-0087-9433), Mr. G Sudarshan 3(0000-0002-5129-5465) and , Mr. A Shivaraj 4(0000-0002-7437-1256) 1234 B V Raju Institute of Technology, Narsapur, India Abstract : When structures are under earthquake forces, adjacent structure may collide with each other due to different dynamic characteristics. When building vibrates out of phase and separated gap between buildings are not sufficient to accommodate their relative motions, this can cause severe damage to the structures and it is known as seismic pounding.
Most of the time it is not possible to maintain sufficient pounding gap between adjacent buildings. Present work evaluate the minimum separation gap required between high-rise building models considered. Two high-rise building of 10 storey and 15 storey are modelled and analysed for dynamic time history analysis for the EI Centro ground motions and minimum pounding gap between buildings has been discussed.Keywords : Seismic Pounding, RC Building, ETABS, Time History Analysis.
Because of expanding population and land esteems, structures are being built to close to each other. During a quake it is expected that, they will pound against each other. This repeated collision activity is referred as seismic pounding. Pounding of structures could have cause severe damage, as neighbouring structures with various dynamic attributes vibrate out of phase and there is inadequate separation gap to accommodate the relative movements of adjacent structures.
This highly congested construction system in the metropolitan cities is the major concern for the seismic pounding. The most simple and viable method for controlling the issue and diminish the harm caused by it is to give enough separation gap between the adjacent structures.
Shehata (2006) examined structure pounding response and proper seismic hazard dissipation technique. Three categories of recorded earthquake excitation are used for input. The effect of impact is studied using linear and nonlinear contact force model for different separation distances and compared with nominal model without pounding consideration. And it is concluded that, an increasing gap width is likely to be effective to minimize the effect of seismic pounding.
Mizam Dogan et.al (2009) carried stress examinations on outline models for various effect focuses and investigation on pounding. It is concluded that pounding forces are not totally absorbable on account of their high esteems but rather their consequences for structure can be decreased by setting versatile materials between adjacent structures or by strengthening basic frameworks.Pushover is a static nonlinear analysis method to estimate seismic structural deformations. It gives force displacement relationship of a structure or structural element. Horizontal load is applied in a specified pattern in increments and for a given applied shear force, associated displacement is found until it reaches its maximum capacity of deformation.
As the storey drift increases the columns are subjected to additional moment leading to the failure of the structure. A B Kawade et.al studied the minimum gap to be provided between the adjacent buildings using push over analysis. Response spectrum analysis was carried out by taking the data of EI Centro earthquake on different models. The results indicated that the acceleration and shear force produced because of pounding varies with the storey height and peak storey drift depends on the ground excitation characteristics.
The effect of pounding is observed to be more predominate when floor levels of adjacent building are different constructing separate buildings with equal floor heights is one of viable solutions to prevent seismic structural pounding. It was also observed that the separation distance to be maintained increases with the increase in peak ground acceleration values.Jeng-Hsiang Lin et.al (2002) investigated the seismic pounding probability of buildings in the Taipei metropolitan area.
Detailed procedures of the analytical method are presented. And concludes that pounding probability of adjacent buildings is found to be significantly affected by the natural period of individual buildings and the period ratio of the adjacent buildings. Due to the lack of proper treatment of the vibration phases of adjacent buildings, it is found that the method used in the current Taiwan Building Code (TBC’97) provides poor estimates for the required building separation distance and produces a non-uniform risk for all the cases investigated in this study.
MOTIVATION AND OBJECTIVES OF STUDY
To Study the Dynamic Behaviour of Tall Structures.To Evaluate Seismic Pounding Effect of Adjacent Buildings with Consideration of Vertical Geometrical Irregularity.To Study the Influence of Shear Walls on Seismic Pounding Effect.
In Present Study Total 3 Models have been Modelled to Evaluate Dynamic Behaviour of High Rise Buildings by Considering Vertical Geometrical Irregularities.Model 1 : A Plan which consists adjacent multi storey buildings one is 10 Storey and the other one is 15 Storey with a separation of 100mm with Masonry infill walls.Model 2 : A Plan which consists adjacent multi storey buildings one is 10 Storey and the other one is 15 Storey with a separation of 100mm in this particular model all infill walls are modelled and designed as shear walls.-47625012700Fig 1 : Plan View of the Buildings1219200176530Fig 2 : Isometric View of ETABS Model1104900191770Fig 3 : Elevation of ETABS Model
The principle objective is to evaluate the effects of seismic pounding between two closely spaced multi-storey buildings, to understand the minimum seismic gap between the buildings, modelling is done to study the response of buildings under pounding during EI Centro earthquake.In order to observe pounding effect between adjacent buildings, two RC buildings of 10 and 15 storey are considered. Both buildings have been modelled and analysed in ETABS 2015 software. Based on the analysis results the clear separation distance is provided. all 3 models have been analysed for nonlinear time history analysis to study dynamic behaviour of buildings.
The output results were obtained.In Time History Analysis the ground motion records are given as input. The time history analysis has the ability to perform linear as well as non linear analysis . The ability of this method to account for bidirectional effects by applying three components of ground motion helps in predicting the response more precisely. In a Linear analysis, it is assumed that the displacement of whole structure does not exceed elastic limit under the application of design forces. when the structure deforms more than elastic limit, non linearity of the structure in terms of geometry or material are to be considered.
Bureau of Indian Standards clearly gives in its code IS 4326, that a Separation distance is to be provided between buildings to avoid collision during an earthquake. The IS code provisions are mentioned in following Table.Fig 4 : Gap Width for Adjoining Structure as per IS 4326 ( Table 1 )Table 1 : Seismic ParametersSoil Type MediumResponse Reduction Factor, R 5Importance Factor, I 1.5Zone IVTable 2 : Material PropertiesConcrete cube strength, fck30 N/mm2 (M30)Characteristics strength of reinforcing steel, fy415N/mm2(Fe 415)Modulus of elasticity of concrete, E 29.5 kN/mm2Unit weight of concrete 25 kN/m3
Table 3 : Sectional PropertiesName of the Element Size in mmBeam 1 300 * 400Beam 2 300 * 500Beam 3 350 * 600Column 1 300 * 300Column 2 300 * 400Column 3 300 * 500Column 4 300 * 600Column 5 300 * 700Slabs 125Exterior walls,w1 300Interior walls,w2 230 6. RESULTS AND DISCUSSIONS Dynamic Time History Analysis of considered models have been performed in ETABS Software. EI Centro Ground Motions were considered as Input Data for Analysis.
Effect of Pounding is studied with a reference to storey displacement. The Storey Height Vs Storey Displacement graph has been plotted to understand the dynamic behaviour of Structure.Fig 2 : Storey Displacement Curve for Model 1Fig 2 : Storey Displacement Curve for Model 2Fig 3 : Storey Displacement Curve for Model 37. CONCLUSION :Stiffness of building has got a great influence on displacements in respective directions.
In Model – I separation gap between adjacent buildings are 100 mm. Displacement observed was 509.883 mm in X direction and 31.881 mm in Y direction. When masonry wall are replaced with shear wall, lateral displacement has reduced in considerable amount to 36.74 % and 80.8 % in X and Y direction respectively.Effect of pounding can be reduced by providing safe separation gap. By the result of Model – I we can conclude that minimum safe separation gap between building is 540 mm.Stiffness of building can be enhanced by adopting shear wall to reduce the pounding effect
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