ANALYSING THE SEISMIC BEHAVIOUR OF SET BACK BUILDING BY USING E-TABS

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 1, January 2017, pp. 444–451, Article ID: IJCIET_08_01_051

Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication

ANALYSING THE SEISMIC BEHAVIOUR OF SET

BACK BUILDING BY USING E-TABS

Hema Venkata Sekhar

Post Graduate Student,

K. L University, Vaddeswaram-522502, A. P, India

T. Venkata Das

Asst Professor, K. L University, Vaddeswaram-522502, A. P, India

ABSTRACT

Objective: To study building behavior during earthquakes always depends on its

strength, durability, stiffness and adequacy of the regular configuration of the structure.

Methods: The analysis always depends on the forces and importance on the cost of analyzing

the structure. Creating the 3D building model for both linear and non-linear dynamic method

of analyses. Understanding the seismic behavior of Setback buildings and Co-relating the

seismic behavior of the Setback building with that of a building without Setback finally

comparing the seismic behavior of building with a setback at every two levels to that of the

building with a setback at each floor level. Study the influence of vertical irregularity in the

building when subjected to earthquakes. Findings: The present study is limited to reinforced

concrete framed structure designed for seismic loads (DL, LL & EL). The seismic behavior

of three 8-Storied buildings with and without setbacks was studied. The buildings were

analyzed using Time History Analysis and Response Spectrum Method and. Novelty: The

effect of Setback is studied considering the parameters such as Time Period, storey drifts,

Displacements, Storey Shears, Bending Moments and Shear Forces and correlated with the

building without a setback.

Key words: Set Back Buildings, Linear and Non-Linear Analysis, Seismic Loads, IS: 1893-

2002, Dynamic Loads

Cite this Article: Hema Venkata Sekhar and T. Venkata Das, Analysing The Seismic

Behaviour of Set Back Building by Using E-Tabs. International Journal of Civil Engineering

and Technology, 8(1), 2017, pp. 444–451.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1

1. INTRODUCTION

In the last 25years, the globe has experienced many Earthquakes of larger magnitudes leading to

massive loss of lives and extensive physical destruction. Past experiences reveal that for the same

magnitudes of earthquakes, the loss occurred in developing and underdeveloped countries are much

more 1 .This may be attributed to the lack of awareness and technical knowledge related to the aspects

of seismic hazard assessment and mitigation2. Due to recent severe earthquakes, a lot of studies is

required in the development of earthquake resistant structures. Earthquakes present a threat to public

Analysing The Seismic Behaviour of Set Back Building by Using E-Tabs


safety and welfare in the significant portion everywhere. We cannot stop earthquakes but we can

prevent ourselves from them, as earthquakes don’t kill human beings, but the buildings do. In the

past decade, India has seen major earthquakes in the world3.

1.1. GLOBAL DEFICIENCIES

They are broadly classified as plan irregularities and vertical irregularities, as per the Code. Some of

the identified irregularities are as follows4-6:

Plan Irregularities

• Plane symmetry and eccentric mass from water tank crate Torsion irregularity

• Common re-entrant corners.

• Model discontinuity due to large openings or staggered floors, along with the deficiency of collector

elements.

• Out-of-plane offset for columns along the perimeter.

• Nonparallel lateral load resisting systems (not observed in the building studied).

Vertical Irregularities

• Soft storey due to open ground storey. Stiffness irregularity

• The mass irregularity was not observed in building studies.

• Vertical plane geometric irregularity from set-back towers.

• Along the perimeter of the building In-plane discontinuity for columns are observed

• Weak storey due to open ground storey.

The vertical geometric irregularity or set back is shown in Figure 1.

Figure 1 Vertical Geometric Irregularity or Set back

Hema Venkata Sekhar and T. Venkata Das


2. IRREGULARITIES IN STRUCTURES

The configuration of the building is classified as regular or irregular in the mean of size and shape

of the building, the arrangement of structural elements and with respective to weight. Regular

building configurations are almost symmetrical (in plan and elevation) about the axis and have a

uniform distribution of the lateral force-resisting structure such that, it provides a continuous load

path for both gravity and lateral loads 7.

2.1. Reasons for irregularities in buildings

• Construction in Hilly areas

• Modern/new trends in commercial complexes

• Thickly populated areas

2.2. Classification of Irregularities

The structural irregularities are categorized into three types as:

• Plan Irregularities

• Vertical Irregularities

• Other Irregularities

The details of all plans are shown in Figure 2-5.

Figure 2 Plan Irregularities



Figure 3 Code Plan Irregularity

Figure 4 Vertical Irregularities

Figure 5 Code Vertical Irregularity

3. NUMERICAL STUDIES

The regular and irregular buildings are prescribed by the building codes. Roughly all the Indian

standards propose the static analysis for all symmetric structures which were chosen the class of

buildings. Indian standards propose the shape of Buildings with the irregular utilization of static and

dynamic analysis procedures such as Time History Analysis (THA) and Response Spectrum Method

(RSM) 8.



Earthquake-induced deformations are reduced by changing the storey height, which tends to

focus at the flexible/ weak storey of the building. The focus on damage leads to more deformations

in vertical members. The huge deformations in vertical members further lead to the collapse of the

storey of the building.

3.1. DESCRIPTION OF SAMPLE BUILDING

The plan layouts for the building models with and without Setbacks are shown in Figure 6-8.

Figure 6. 3D View of model-1 Building without Setback





Symmetric Building Models

Model 1: Building modeled with Re-entrant corner and without Setback.

Model 2: Building modeled with Re-entrant corner and Setback at every two levels.

Model 3: Building modeled with a Re-entrant corner at Setback at each level.

The Lateral Seismic Shear Forces of View of Building for Model-1, Model-2 and Model-3 are shown

in Table 1.

Table 1 Lateral Seismic Shear Forces of View of Building for Model-1, Model-2 and Model-3

Story (Qi)(KN)

Model-1

(Qi) (KN)

Model-2

(Qi)(KN)

Model-3

8 2223.83 401.33 390.53

7 4135.92 711.45 1137.63

6 5549.19 2444.47 2377.13

5 6526.02 3830.89 3718.51

4 7170.31 5253.79 4890.09

3 7502.84 6111.18 5688.13

2 7627.54 6621.97 6146.57

1 7670 6730 6270

3.2. PERFORMED ANALYSIS IN ETABS

ETABS computer program will do the analysis and design of the building. The following are the

modeling methods:

3.2.1. Equivalent Static Analysis

The normal time period of the structure is ascertained by the expression, T=0.09H/√D given in Indian

Standard code provision 1893-2002, whereas H=height and D= base measurement of the building9.

In this strategy the bearing of vibration and normal periods for every one of the models are same.

The transverse burden count and its appropriation along the tallness are computed according to

Seems to be: 1893-1984.Dead load plus 2.5% of live load is considered as a seismic dead weight/self

weight10.



3.2.2. Response Spectrum Analysis (RSA)

Reaction Spectrum Analysis of the building models is performed in ETABS. The transverse burdens

created by ETABS match to the seismic zone V and the 8% damped reaction range given in IS: 1893-

200211.

3.2.3. Time History Analyses of the Structure

Time History investigation has been done additionally utilizing the Bhuj Earthquake record on

January 26, 2001, otherwise called the seismic tremor in Kutch for acquiring the different floor

reactions12.

3.2.3.1. Time history analysis in ETABS

• It defined as time history adding a command from a file. In this case, Bhuj earthquake records 2001

were applied in this program.

• A separate analysis of the structure within adequate analysis is linked with the appropriate case studies

i.e. linear direct integration time history.

• From the defined time history function earthquake acceleration values are applied.

• By calculating the mass and stiffness proportions the mentioned equations are given in a period of

time with two successive modes of the structure. The program itself calculates the required damping

coefficients from the sources given by the software11-12.

• Direct integration method is to be specified and adopt new mark’s direct integration method to solve

the problem.

• Run the analysis.

The graphical representation of Significant Time History Function (Bhuj earthquake, 2001) in

ETABS was shown in Figure 9.

Figure 9. Significant Time History Function (Bhuj earthquake, 2001) in ETABS



4. CONCLUSIONS

• Generation of all forces due to unequal distribution of mass will be identified by critical setback ratio

along the section of the plan and also in the vertical height of the building.

• The ideal appraisals of basic difficulty proportions are RA and RH. The above evaluation conforms

to the criteria given in gauges for sporadic structures are considered.

• At last, we finish up from the outcomes unpredictable structures are to be treated with appropriate

plan and ought to be trailed by all IS code procurements given the guidelines.

• It can likewise be reasoned that alteration of quake codes geometric horizontal anomalies appear to

be important to determine more preventive ordinates or apply more precise explanatory strategy to

distinguish the seismic execution of difficulty building. Especially for structures with basic difficulty

proportions assumes a critical part.

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