Effect of Shear Wall Location On Seismic Performance of High Raised Buildings

Multi-storey buildings tend to get damaged mainly during earthquake. Seismic analysis is a tool for the estimation of structural response in the process of designing earthquake resistant structures and/or retrofitting vulnerable existing structures. The principle purpose of this work is to analyze and design a building with a shear wall and also to find the appropriate position of shear wall that result in maximum resistance towards lateral forces and minimum displacement of the structure. In this study, a G+7 multi-storey building of 15 m ×20 m in plan area has been chosen and modelled using ETABS. The developed model was validated by solving manually and the results were validated in ETABS. Thereafter, 4 different new plans were modelled in ETABS located in the same earthquake zone area. These plans have shear wall concepts are implemented on the building at four different locations. Seismic, vibration and response spectrum analysis were performed on these structures. Salient parameters such as storey stiffness, storey displacement and storey drift were computed using the ETABS model. These were compared with that of the frame having no shear walls. By comparing the results obtained at different shear wall locations, the best plan with the shear wall having minimum lateral storey displacement and maximum stiffness is suggested for this location.


Introduction
Generally, ground motions occur in a random manner in all directions radiating from hypo center during an earthquake event. These random ground motions can cause structures to vibrate and induces inertial forces in them. If these structures are not designed to resist these additional forces it may fail leading to loss of life and property. Thus, the effects of lateral loads such as earthquake forces, wind loads and blast forces, etc. on the structures are attaining increasing importance. There are many techniques to increase the resistance to lateral load of the structure namely, braced moment resisting frames, frameshear wall systems, framed tubular system, etc. The aim of present work is to study effect of the location of shear wall on lateral capacity resisting of the structure.
Chandurkar [2] did a detailed study to determine the solution for shear wall location in multi-storey building with the help of four different models. The buildings were modeled using software ETABS Nonlinear v 9.5.0. After analyzing ten storey building for earthquake located in zone II, zone III, zone IV and zone V essential parameters like lateral displacement, story drift and total cost required for ground floor were found in both the cases by replacing column with shear wall and conclusion was drawn that shear wall in short span at corner (model 4) is economical as compared with other models. It was observed that shear wall is economical and effective in high rise buildings and providing shear walls at adequate locations substantially reduces the displacement due to earthquake. If the dimensions of shear wall are large then major amount of horizontal forces are taken by shear wall. Varsha R. Harne [3] analyzed a six storey building subjected to earthquake loading in zone II using STAAD Pro and calculated earthquake load using seismic coefficient method (IS 1893 Part II). Four different cases namely a structure without shear wall, structure with L type shear wall, structure with shear wall along periphery and structure with cross type shear wall were analyzed. The lateral deflection of column for building with shear wall along periphery is reduced as compared to other types of shear walls. It was found that shear wall along periphery is most efficient among all the shear walls considered. Similarly, host of other researchers Kameswari et al. In the present work, initially, 15m × 20m size floor plan is taken [1]. Using this as a reference model (model 1), earthquake analysis and response spectrum analysis were done. Base shear, lateral forces are calculated manually and validated with ETABS results, based on this new plan (model 2) is prepared.

A. Description of the Model 1
An eight-storey residential RC building is to be constructed in seismic Zone IV having hard soil. The dimension of the building in planis 15m x 20m with storey height of 3.6m. Using both seismic coefficient and response spectrum approach base shear was calculated. The inter-storey lateral stiffness of floor is taken as k1 = k2 = k3 = k4 = 671.52×10 6 N/m and k5 = k6 = k7 = k8 = 335.76×10 6 N/m. Adead load of 5 kN/m 2 and live load of 1.5 kN/m 2 is considered for roof slab and for floor slab dead load considered was 10 kN/m 2 and live load is taken as 4 kN/m 2 .  Once the base shear calculation is completed, lateral force for individual storey is calculated from the formulas shown in the table 2.
From the table 2, the lateral forces will increase from bottom of the storey till storey number 7 and it was dropped at roof level. The base shear is continuously increases from roof to base of the building.

Effect of shear wall at location 1:
At shear wall location 1, the shear wall is placed at all the corners of the building as shown in figure 3 and further analysis is performed for earthquake and response spectrum analysis. At shear wall location 2, the shear wall is placed at middle of the building as shown in figure 4. Shear wall thickness is considered at 100mm.
At shear wall location 3, the shear wall is placed at C type portion at the middle of the building. It is shown in the red color in the following shown in figure 5.  At shear wall location 4, the shear wall is placed at the L-type portion at the middle of the building as shown in figure 6. Using all 6 models base shear, lateral force, storey displacement, storey drift and storey stiffness are calculated and plotted in the below graph.
The objective of this project is to check and design of the seismic response of multi-storied building using ETABS. For all frame model results are noted from ETABS software. The above figure 7 represents the storey displacement due to Earthquake analysis. The X axis represents storey number and Y axis represents the storey displacement in mm. The color line indicates the location of shear wall. The maximum storey displacement was observed for the shear wall placed at location 2. The above graph represents the storey displacement due to response spectrum analysis. The x-axis represents storey number and y-axis represents the storey displacement in mm. The color line indicates the location of shear wall. At location 2, maximum storey displacement is observed.
The graph (Fig. 9) represents the storey Stiffness due to Earthquake analysis. The x-axis represents storey number and y-axis represents the Storey stiffness kN/m. The color line indicates the location of shear wall. At location 1, maximum storey stiffness is observed. The graph (Fig. 10) represents the storey lateral forces due to Earthquake analysis. The x axis represents storey number and Y axis represents the lateral forces in kN. The color line indicates the location of shear wall. Maxim lateral forces are acting on frame model. The graph (Fig. 11) represents the storey lateral forces due to response spectrum analysis. The x-axis represents storey number and y-axis represents the lateral forces in kN. The color line indicates the location of shear wall.
The graph (Fig. 12) represents the storey drift due to earthquake analysis. The x axis represents storey number and Y axis represents storey drift (unit less). The color line indicates the location of shear wall. The graph (Fig. 13) represents the storey drift due to response spectrum analysis. The x-axis represents storey number and yaxis represents storey drift (unit less). The color line indicates the location of shear wall.

Conclusion
In this paper, a 15×20 m plan area building with G+7 is considered. It was solved and the results are validated, using this methodology a new plan was implemented in same area, as well shear wall concepts are implemented on the building at different locations. By conducting the software analysis for the structures following conclusions are drawn: 1. The displacement is decreased in shear wall structure as compared to framed structure. There is nearly 50% reduction in displacement of structure is obtained when the shear wall is placed at locations 1, 3 & 4 in both Earthquake loading and Response spectrum loading cases. 2. Whereas is no significant reduction in displacement of structure occurred when shear wall is placed at location 2 during application of Earthquake loading and there is 31% of reduction in displacement of structure occurred when shear wall is placed at location 2 during application of response spectrum loading. 3. The story stiffness is increased in greater amount in structure with shear wallwhen compared with frame with no shear walls. The story drift is decreased in shear wall structure than the frame structure. The drift value decreased by 19% in during earth quake loading and 44% during response spectrum loading. 4. The modal period and Earthquake frequency is less in no shear wall frame structure & more in shear wall structure. 5. The performance of shear structure is better than the framed structure. Different locations of shear wall is considered and compared to obtain best suitable location of the shear wall. At location 1 we have minimum lateral storey displacement is observed and we have maximum stiffness at this position. 6. The base shear is observed as 1020.7 kN which results in 11% reduction when compared to framed structure. The cost of the frame structure may be less than the shear structure. The shear structure is suitable in earthquake prone area due to its higher stiffness & less displacement.