Currently Seismic impacts getting very serious concern when designing multi-storied reinforced concrete structures. Seismic tremors have occurred in numerous parts of the globe. High-rise structures should have proper stiffness to resist lateral loads caused by Earthquakes and Winds. Consequently, Engineers are extremely concerned about finding suitable solution that will allow structures to survive without major damage. Shear walls are structural members which are designed to carry earthquake loads and opposes lateral loads significantly. They are good choice to increase stiffness of high-rise structures. This paper aims to use shear walls in various location of a G+13 multi-storied residential building and to determine the best shear wall placement in high slender building by analyzing storey displacement, storey drift, base shear and fundamental time period in various seismic zones according to IS 1893:2016. Three models are prepared and compared under different seismic zones. Shear walls at core of building, shear walls at four corners of building and the combination of both. Our study's goal is to test a structure's ability to bear lateral load applied to it according to Code and also when it exceeds the limit of allowable deformation. The prepared model for this experimentation is considered to be located on medium soil and wind velocity is high like 148mph. The experiment concluded that, building with shear wall combination of both core and corner will show better result to resist lateral forces though the combination isn’t enough to help withstanding the high slender structure against very powerful earthquake attack like Zone-v.
Research Article
Dynamic Analysis of a G+13 Storey Rcc Building Using Shear Wall in Three Different Location on Various Seismic Zone
https://doi.org/10.21203/rs.3.rs-3885256/v1
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Dynamic Analysis
Shear wall
Response Spectrum Method
Earthquake
Seismic Zone
Earthquake is considered as one of the worst types of natural disaster. In general, design of structure for seismic load is primarily considered with structural safety during any type of major natural ground motions, but economical conditions as well as serviceability should also be major concern. Earthquake can be defined as a natural catastrophic tragedy caused by a rapid release of energy beneath the earth's surface. The vibrations are caused by the energy emitted from the ground and its causes enormous damages to all the internal and external substances within the surface, resulting in loss of life and structural damage. Earthquakes come in a variety of sizes and intensities. Soft stories, mass irregularities, low quality of building materials and improper construction procedures, uneven earthquake response, soil and foundation, and the influence of pounding of nearby structures were identified to be the main causes of the failure of structures. All over world, there is high demand for construction of tall buildings due to increasing urbanization and spiraling population, and earthquakes have the potential for causing the greatest damages to tall structures [1]. As it is seen that earthquake loads are not regular i.e. random in nature as well as unpredictable so the engineering tools must have the ability to account these actions when designing any high rise reinforced concrete structure.
When designing any structure all type of earthquake effects must be considered as dynamic nature. However, for simple regular structures, analysis by equivalent linear static methods is often sufficient [2]. But when deals with high rise building then the equivalent linear static method is not enough. Then the advanced form of analytical system is introduced named Dynamic analysis. During earthquake the gravitational loads are also worked as lateral loads which will produce sway in the real time. When designing any high-rise structure some factors must be considered in terms of earthquake. According to E. Pavan Kumar (2014), The factors are natural frequency of the
structure, damping factor, type of foundation, importance of the building and ductility of the structure [3]. To eliminate most of the failure caused by lateral force, using shear wall is a good option. The thickness of shear wall is also an important parameter for resisting lateral forces. Research shows that, the thickness of the shear wall may differ from 140 mm to 500 mm and the construction method is also too quick when compared to the conventional one [4].
For obtaining the best results as well as to compare the results between the position of shear wall in various location a G+13 storied building model is prepared in this study. The building is comparatively slender and have high torsional affect.
1.1 IMPORTANCE OF SHEAR WALL
Shear wall is a structural system made up of braced panels that is used to counteract the effects of lateral loads on a structure. Shear panels are a type of shear wall. Shear walls are built to withstand wind and earthquake loads. The difference between columns and shear walls are column is mainly compression elements whereas shear wall is compression as well as shear resisting elements [5]. These are provided in addition to slabs, beams and columns in a structure and it provides the required stiffness especially for residential constructions and in general it forms as a case in a structure [6].
N. Karthiga researched on structure with and without shear wall and stated that the location of shear wall will affect the attraction of forces, so that the wall must be placed in proper position [7]. Many researchers carried out their research work to find the optimum location and position of the shear wall in any high-rise structure. In practice shear walls are provided in core section of building as a lift or elevator core which also act as a HVAC transmission system. In this study three model has been prepared with shear wall located accordingly in core, edge portion and both core and edge portion.
1.2. DYNAMIC ANALYSIS
There are two methods of analysis for determining earthquake effects on structures, static method and dynamic method [8]. When subjected to loads or displacements, all real physical structure behave dynamically. In general, dynamic analysis is merely a natural extension of static analysis. Response spectrum analysis or Time History analysis are both used in dynamic analysis. Besides these two major types of analysis there are many other types of earthquake analysis method such as-
A. Equivalent Static Analysis
B. Non Linear Static Analysis
C. Linear Dynamic Analysis
D. Non Linear Dynamic Analysis
The initial stage in dynamic analysis is to create a mathematical model of the structure, which will be used to provide estimations of strength, stiffness, mass, and inelastic member properties. According to I. Hari Krishna (2016), Dynamic analysis is also related to resistance forces developed by the structure, when the structure is excited by sudden dynamic loads [9]. In this study a G+13 RCC multi storied residential building is modeled and analyzed using ETABS v17 software.
1.2.1 RESPONSE SPECTRUM METHOD
Among all the method of dynamic analysis, Response spectrum analysis method is one of the most effective one. According to Bahador Bagheri (2012), response spectrum method is the representation of the maximum response of idealized single degree freedom system having certain period and damping, during earthquake ground motions [10]. Unless it can be demonstrated qualitatively that the second or third mode gives the least response, at least three response modes of the structure should be examined. The response spectrum approach of seismic/earthquake analysis has computational advantages for predicting displacements and member forces in structural systems. From a case study S. Nair (2017) stated that, the main constraint of the Response spectrum analysis is that they are globally suitable to linear systems only [11]. In this experiment, the response spectrum analysis is carried out according to the code IS 1893: 2016 [12].
I. Hari Krishna (2016) have performed a dynamic analysis of G + 14 storied RCC building with shear wall used in core and edge portion of the structure and then compare the results under different Earthquake zones. The study showed that the displacement is reduced when using shear wall in all seismic zones. Similarly, the same amount of shear wall will resist more lateral load when they used in core portion comparing the edge portion.
Shaik Akhil Ahamad (2020) have performed a test on a G+20 storied RCC building and comparing the output of the model using shear wall at two end of the structure and both the four end of the structure. From their research it is observed that shear wall at four end of the building is more effective rather than only two edges of the building. Similarly, for high rise structure shear wall is strongly recommended to avoid torsional irregularities.
N. Karthiga (2019) have studied and published a research output of seismic response analysis in RC framed structure using shear wall and no shear wall by ETABS. From their study we obtained that shear wall plays a vital role to resist later load as well as any type of seismic effects. The study showed that storey drift and lateral displacement of storey is significantly reduced when using shear wall. Also concluded that the position of shear wall plays a vital role in high rise structure.
M. Pavani (2015) have performed a shear wall analysis and design optimization research where it is seen that in case of tall building if shear wall can be provided in possible deflection position of the structure, then it can control the damages occurred due to wind and earthquake forces i.e. lateral and seismic forces. The study was carried out for a G+44 storied high rise building and obtained best result by using shear wall at two core portion of the structure.
1. To analyze the model structure by means of Storey displacement, Storey drift, Storey shear/ Base shear, Fundamental time period in different earthquake zones by dynamic analysis.
2. To locate the best position of shear wall in a multi storied RCC structure so that the structure can minimize the effects of lateral loads.
3. To compare the effects of lateral load on model structure when applying shear wall on three different locations as well as four different seismic zones.
The technical details and information are tabulated below. The 3D model diagram with the plan and dimensions are also shown in this section.
Table1: Location of Shear Wall
|
Identity |
Position |
|
Case A |
Elevator core |
|
Case B |
Four Corners |
|
Case C |
Core + Four Corners |
Table2: Specifications of the Model
|
Description |
Value |
|
Type of the Building |
Residential |
|
Type of Structure |
RC Framed Multi Storied |
|
Storey |
G + 13 |
|
Floor to Floor Height |
12ft |
|
Soil Type |
Type-II (SD) |
|
Damping |
Constant 5% |
|
Importance Factor |
1 |
|
Response reduction factor, R |
5 |
|
Overstrength factor |
5.5 |
|
Exposure Type |
B |
|
Seismic Zones |
Zone II, III, IV and V |
Table3: Properties of Structural Member
|
Description |
Value |
|
Total Building Height |
184ft |
|
Size of Columns |
12X18 inch and 12X20 inch |
|
Size of Beams |
10X17 inch and 10X20 inch |
|
Slab Thickness |
5.5 inch |
|
Strength of Concrete |
4000psi |
|
Strength of Steel |
Grade-60 |
|
Support Condition |
Fixed |
Table4: Load Details
|
Live Load |
40psf |
|
Floor finish |
25pdf |
|
Partition wall load on Beam |
425 lb/ft |
|
Code for Earthquake Load |
UBC 97 |
|
Code used in RSA |
IS 1893:2016 |
The full process of this study is showed in a flow diagram below:
6.1. Floor Plan of the Model:
The ground floor plan (figure1) and floor plan of 1F to 13F (figure2) are shown below.
6.2. DETAILING OF 3D MODEL
6.3 ANALYSIS OF THE STRUCTURE
The maximum storey displacement along both global X direction and global Y direction are plotted in a graph below.
Along global X direction the maximum displacement to be found when shear wall is positioned in core of the structure for all four zones and minimum displacement is found when shear wall is placed in both core of the structure as well as the four corners of the structure.
Same results found for global Y direction also. According to code the maximum permissible displacement is 0.004H i.e. 8.8inch for our structure. In this case the modeled structure with shear wall at core will not survive in earthquake zone IV and V. Same will be happened for the structure having shear wall at four corners of the structure. Only structure with shear wall at both core and corners will withstand in zone IV but unfortunately every model will fail in seismic zone V in terms of maximum displacement analysis.
Same like the pattern of maximum storey displacement, the maximum storey drift is also max for shear wall center of the structure and minimum when shear wall is located in both elevator core and corners of the building. The storey drift in global Y direction is comparatively higher than global X direction. The reason can be written as, our structure is narrow in global Y direction comparing other direction. As a result, when subjected to lateral loads the structure tends to show more deformation in global Y direction.
The maximum storey shear is also known as Base shear. From the graph it is obtained that, the maximum storey shear tends to increase when moving from lower earthquake to higher risky earthquake zone. Similarly, in the same earthquake zone storey share is maximum for Case C (shear wall at both core and corners) and minimum for Case A (shear wall in core only). The Seismic zone factor for these seismic zones is accordingly-
zone-II (0.10), zone-III (0.16), zone-IV (0.24) and zone-V (0.36).
TIME PERIOD & FREQUENCY
The time period obtained from ETABS is plotted in a graph below.
The analysis is done by using Modal case type EIGEN and to confirm highest mass participation 48 number of modes are taken. Hence, this setup confirms 99% of mass participation. In time period analysis it is seen that the fundamental time period remains same even changing the seismic zones for same model. Also the time period tends to decrease when we increased the cross sectional area of the shear wall. The time period is minimum for Case C model and maximum for case A model.
Frequency can be expressed as (1/T) where T is the natural time period of the structure.
After successfully performing the experiment, the results can be concluded as-
- The maximum storey displacement and drift are seen to be higher in seismic zone V. In general, the higher the seismic affect the more displacement will be occurred. Case C has higher Stiffness and show low displacement and storey drift comparing other two cases.
- From the experimentation it is seen that building with both shear wall at core and corners had given better outputs considering storey displacement, drifts, base shear and other parameters.
- The designed model has high slenderness value as a result the structure will fail in zone V for all cases according to IS code. This is due to uneven stiffness as well as low amount of provided shear wall. To make the model more stiff and to withstand it in higher earthquake zone more shear wall should be provided.
- Torsional irregularities are observed when moving higher seismic zones. To avoid the torsional irregularity the shear wall should be provided uniformly all over the structure.
- As last it can be concluded that shear wall at all four corners showed better result comparing only provided in core of the structure. But if shear wall is provided not only in core but also in all four corners of the structure then the structure will give extra stiffness to the structure and help to withstand any highly slender building in high seismic areas.
DECLARATION OF COMPETING INTEREST
The authors declare no conflict of interest that could have appeared to influence the work reported in this paper.
FUNDING
This research did not receive any specific funding.
Author Contribution
Md. Kawsarul Islam Kabbo: Conceptualization, writing original draft, performing analysis, prepared tables and figures
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No competing interests reported.