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A Comparative Analysis on Absolute and SRSS Methods of Response Spectrum using STAAD-PRO


Call for Papers Engineering Journal, May 2019

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A Comparative Analysis on Absolute and SRSS Methods of Response Spectrum using STAAD-PRO

A Comparative Analysis on Absolute and SRSS Methods of Response Spectrum using

STAAD-PRO

1A. Eugene Victor

UG Scholar, Department of Civil Engineering

Sri Muthukumaran Institute of Technology, Chennai, India

2S. Yokesh

UG Scholar, Department of Civil Engineering

Sri Muthukumaran Institute of Technology, Chennai, India

3K. Preethi

Assistant Professor, Department of Civil Engineering Sri Muthukumaran Institute of

Technology, Chennai, India

Abstract Here is the present study, describes the effect of earthquake load which is one of the most important dynamic loads along with its consideration during the analysis of the structure. In this Comparative study, the seismic response of the structures is investigated under ABSOLUTE AND SRSS methods of dynamic analysis and earthquake excitation expressed in the form of member forces, joint displacement, support reaction, and story drift. The response is investigated for G+5 Educational building structures by using STAAD PRO designing software. We observed the response reduction of cases ordinary moment resisting frame. In this case, we have taken earthquake zone 5, Response factor 5 for ordinary moment resisting frame and Importance factor 1.5. A comparison is done between the response spectrum methods, the results such as story drift, average Displacements, Mode shapes are observed, compared and summarized for Beams, Columns, and Structure as a whole during both the analysis.

Keywords Dynamic analysis, Response spectrum method, ABSOLUTE Method, SRSS Method, Joint displacement, Story drift, STAAD PRO Analysis, STAAD Generic Method.

  1. INTRODUCTION

    Analysis and design of buildings for static forces is a routine affair these days because of the availability of affordable computers and specialized programs which can be used for the analysis. On the other hand, dynamic analysis is a time- consuming process and requires additional input related to the mass of the structure, and an understanding of structural dynamics for the interpretation of analytical results. Reinforced Concrete (RC) frame buildings are a most common type of constructions in urban India, which are subjected to several types of forces during their lifetime, such as static forces due to dead and live loads and dynamic forces due to the earthquake. Here the present study describes the effect of earthquake load which is one of the most important dynamic loads along with its consideration during the analysis of the structure.

    STAAD.Pro is structural engineering software widely used for the design of multistoried buildings. It is comprehensive structural engineering software that addresses all aspects of structural engineering including model development, verification, analysis, design and review of results. It includes advanced dynamic analysis and push over analysis for wind load and earthquake load. STAAD.Pro is a comprehensive, integrated design and finite element analysis tool. The exponential growth of India, as well as the global construction

    industry, has directly impacted the demand for structural engineers. It has become important for civil design engineers to be well equipped with structural software like STAAD.Pro, since most of the companies are using STAAD as a tool for designing massive structures, it is imperative that professionals should get trained in this field too to gain an advantage in the highly competitive construction market. Its a known fact that computers reduce man-hours required to complete a project, and knowledge of STAAD will ensure fast and efficient planning as well as accurate execution. The commercial version STAAD.Pro is one of the most widely used structural analysis and design software. It supports several steel, concrete, and timber design codes. It can also make use of various forms of dynamic analysis from modal extraction to time history and response spectrum analysis.

    The detailed comparative study on dynamic analysis is been made to ensure the seismic design for major and frequent shaking intensity without any damage, To eliminate the problem faced by the unsigned Response Spectrum and SRSS method in STAAD- pro due to the interaction of axial force with its corresponding bending moment. This Study Will provides complete guidelines for STAAD-Pro software analysis to give the accurate results for dynamic analysis of response spectrum in absolute and SRSS methods, to show joint displacements, support reactions, Member forces, base shear, and lateral load.

  2. METHODS OF ANALYSIS

    STAAD-based procedure for seismic analysis

    Main features of the seismic method of analysis based on Indian standard 1893(Part 1): 2002 are described as follows

    1. Equivalent static lateral force method

      All design against seismic loads must consider the dynamic nature of the load. However, for simple regular structures, analysis by equivalent linear static methods is often sufficient. This is permitted in most codes of practice for regular, low-to medium-rise buildings. It begins with an estimation of base shear load and its distribution on each story calculated by using formulas given in the code. Equivalent static analysis can, therefore, work well for low to medium-rise buildings without significant coupled lateral-torsional effects, are much less suitable for the method, and require more complex methods to be used in these circumstances

    2. Response Spectrum Analysis method

      This approach permits the multiple modes of response of a building to be taken into account (in the frequency domain). This is required in many building codes for all except for very simple or very complex structures. The response of a structure can be defined as a combination of many special shapes (modes) that in a vibrating string correspond to the "harmonics". Computer analysis can be used to determine these modes for a structure. For each mode, a response is read from the design spectrum, based on the modal frequency and the modal mass, and they are then combined to provide an estimate of the total response of the structure. In this, we have to calculate the magnitude of forces in all directions i.e. X, Y & Z and then see the effects on the building.

      Combination methods include the following:

      • Absolute – peak values are added together

      • Square root of the sum of the squares (SRSS)

      • Complete quadratic combination (CQC)

      In this Study, the result of a response spectrum analysis was analyzed using the Absolute and SRSS Generic methods, and the results were compared.

  3. MODELING AND ANALYSIS

    These buildings were designed in conformity to the Indian Code of Practice for Earthquake load (Seismic) Resistant Design of Buildings. The buildings were assumed to be fixed at the base. The buildings were modeled using software STAAD Pro. Models were studied in 5th zones comparing lateral displacement and story drift for all structural models under consideration.

    TABLE I. GENERAL DIMENSIONS OF THE BUILDING

    S.NO

    PARTICULAR

    DIMENSION

    1

    Length of building

    79.857m

    2

    Width of building

    46.939m

    3

    Height of building

    21m

    4

    Typical story height

    G+5

    5

    Live load on te floor

    4kN/m2

    6

    Wall load

    18.6kN/m2

    7

    Floor finishing

    1kN/m2

    8

    Density of concrete

    25kN/m3

    9

    Density of wall

    20kN/m2

    10

    Grade of concrete

    M30

    11

    Grade of steel

    Fe500

    12

    Thickness of slab

    220mm

    13

    Zone

    V

    Zone factor

    0.36

    Response Reduction factor

    5

    Importance Factor

    1.5

    Type of soil strata

    medium

    Damping ratio

    0.05

    TABLE II. SEISMIC LOAD PARAMETERS

    Fig. 1. plan of the Model

    Fig. 2. Rendered View of the Model

    Fig. 3. Bending Moment of the Critical Beam

    Fig. 4. Mode Shapes

  4. RESULT

    By performing different methods of Analysis in STAAD PRO, the results are obtained for different parameters, which are discussed below.

      1. Average Displacement

        2.3329

        2.7293

        2.564

        2.998

        TABLE III. COMPARISON OF AVERAGE DISPLACEMENT

        S.NO

        STORY

        AVG. DISP (CM)

        SRSS

        ABSOLUTE

        X

        Z

        X

        Z

        1

        0

        0.2091

        0.0353

        0.2445

        0.0584

        2

        4

        0.7953

        0.1374

        0.9302

        0.2279

        3

        8

        1.4134

        0.2473

        1.6533

        0.412

        4

        12

        1.9438

        0.3407

        2.274

        0.5707

        5

        16

        2.3329

        0.4068

        2.7293

        0.6867

        6

        20

        2.564

        0.4443

        2.998

        0.7567

        AVERAGE DISPLACEMENT

        0

        4

        8

        12

        16

        20

        STORY

        AVG. DISP (CM) SRSS X AVG. DISP (CM) SRSS Z

        AVG. DISP (CM) ABSOLUTE X AVG. DISP (CM) ABSOLUTE Z

        DISPLACEMENT (CM)

        0.2091

        0.0353

        0.2445

        0.0584

        0.7953

        0.1374

        0.9302

        0.2279

        1.4134

        1.6533

        0.2473

        0.412

        1.9438

        2.274

        0.3407

        0.5707

        0.4068

        0.6867

        0.4443

        0.7567

        Fig. 5. Average Displacement Comparison

      2. Story Drift

        S.NO

        STORY

        DRIFT (CM)

        SRSS

        ABSOLUTE

        X

        Z

        X

        Z

        1

        0

        0

        0

        0

        0

        2

        4

        0.5862

        0.1021

        0.6857

        0.1695

        3

        8

        0.6181

        0.11

        0.7231

        0.184

        4

        12

        0.5304

        0.0933

        0.6207

        0.1587

        5

        16

        0.3891

        0.0662

        0.4553

        0.116

        6

        20

        0.231

        0.0375

        0.2705

        0.0701

        TABLE IV. STORY DRIFT COMPARISON

        0

        4

        8

        STORY

        12

        16

        20

        DRIFT (CM) SRSS X

        DRIFT (CM) SRSS Z DRIFT (CM) ABSOLUTE X DRIFT (CM) ABSOLUTE Z

        DRIFT

        DRIFT

        0

        0

        0

        0

        0.5862

        0.6857

        0.1021

        0.1695

        0.6181

        0.7231

        0.11

        0.184

        0.5304

        0.6207

        0.0933

        0.1587

        0.3891

        0.4553

        0.0662

        0.116

        0.231

        0.2705

        0.0375

        0.0701

        Fig. 6. Story Drift Comparison

      3. Base Shear Comparison

        TABLE V. BASE SHEAR COMPARISON

        Total Seismic Weight of the Building

        Base Shear in X Direction

        Base Shear in Z direction

        Manually Calculated

        235000kN

        28224.5 kN

        28224.5 kN

        Equivalent static lateral force method

        445085kN

        19095.04 KN

        17235.17 KN

        SRSS

        Method

        445085kN

        15506.86 KN

        14624.63 KN

        ABSOLUTE

        Method

        445085kN

        16311.91 KN

        14802.52 KN

      4. Quantity Take-off Comparison

        Fig. 7. The quantity of Steel Take- off by SRSS

        Fig. 8. The Quantity of Steel Take- off by Absolute

      5. STAAD Design Comparison

    Fig. 9. Column Design by SRSS Method

    Fig. 10. Column Design by Absolute Method

    Fig. 11. Beam Design by SRSS Method

    Fig. 12. Beam Design by Absolute Method

  5. CONCLUSION

The aim of this study is to design and to perform the comparative analysis of response spectrum methods for the economic design for the seismic building, and the results are discussed below,

  1. Short term deflection of all horizontal members is within 5 mm.

  2. The structural components of the building are safe in shear and flexure.

  3. AVERAGE DISPLACEMENT AND STOREY DRIFT is minimum in SRSS method than ABSOLUTE method.

  4. BASE SHEAR is minimum in SRSS method than ABSOLUTE method.

  5. Amount of steel provided for the structure is economic in SRSS METHOD only.

Hence, it is safer and economic to construct any Aseismic structure by designing in SRSS method.

REFERENCES

[1] IS 1893 (Part 1):2002, Criteria for earthquake resistant design of structures, Bureau of Indian standards, New Delhi, 2002.

[2] IS: 456-2000 (Indian Standard Plain Reinforced Concrete Code of Practice) Fourth Revision.

[3] IS: 875-1987 (part-1) for Dead Loads, code of practice of Design loads (other than earthquake) for buildings and structures.

[4] IS: 875-1987 (part-2) for Live Loads or Imposed Loads, code of practice of Design loads (other than earthquake) for buildings and structures.

[5] IS: 875-1987 (part-3) for Wind Loads, code of practice of Design loads (other than earthquake) for buildings and structures.

[6] Dr. S.K Duggal, Earthquake Resistance Design of Structure.

[7] Use of Signed response quantities in Response Spectrum Analysis, Sanjib Das (2014)

[8] Dynamic Seismic Analysis of RCC Building as per IS 1893:2002 by Using STAAD-Pro, Hiteshkumar D. Mishra, Prof. D.L.Budhlani (2017).

[9] Study of Comparison of Applying Modes in Response Spectrum Analysis, Kiran Somasundar M, Rahul Leslie, Belarmin Xavier (2018).

[10] STAADPro2004 v8iGetting started & tutorials- Published by: R .E.I. [11] STAADPro2004v8iTechnical reference manual- Published by:

R.E.I.

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