Design Optimization of X-Bracing using SAP2000

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Design Optimization of X-Bracing using SAP2000

Priya Venugopal¹, Revathy Parameshwaran2, Sruthy K. P3, Wilfred James4,

1,2,3,4UG students, Department of Civil Engineering, Mangalam College of Engineering

Ettumannoor, Kottayam

Sankar Bose5 5Assistant Professor,

Department of Civil Engineering, Mangalam College of Engineering, Ettumannoor,

Kottayam

Abstractthis paper focuses on design optimization by studying the performance vs cost relationship of X-bracings using SAP2000 for an open ground storey structure during seismic loading. Bracings are provided to arrest lateral stress and prevent swaying of the given structure. The open ground storey creates a soft storey condition.

KeywordsOpen ground storey; soft storey; bracing; lateral stress, cost.

  1. INTRODUCTION

    Steel braced frame is one of the structural systems used to resist earthquake and wind loads in multistoried buildings. Many existing reinforced concrete buildings need retrofit to overcome deficiencies to resist seismic loads. The use of steel bracing systems for strengthening or retrofitting seismically an inadequate reinforced concrete frame is a viable solution for enhancing earthquake resistance. Steel bracing is economical, easy to erect, occupies less space and has the flexibility to design for meeting the required strength and stiffness. Table 2 shows the position of steel bracing.

  2. MODELLING

    The building used for analysis is a four-storied RC building with a floor height of 3m as shown fig 1. The building is assumed to be located in a seismic zone V and the earthquake zone is plotted using fig 5. The table 1 provides data regarding the G+3 storey building.

    Table 1. Design data of G+3 storey building

    Sr.No.

    Content

    Description

    1

    No. of Storey

    G+3

    2

    Floor Height

    3m

    3

    Material

    Concrete(M25) & Reinforcement (Fe415)

    4

    Size of Column

    C1=300mm×300mm All column of G.F & Outer column

    C2=280mm×280mm Interior column for Ist & IInd Floor

    C3=250mm×250mm Interior column for IIIrd floor

    5

    Size of Beam

    230mm×450mm

    Fig 1: Base model of G+3

    Fig 1 shows a G+3 Storey building with 5 bays in X & Y directions. Fixed restrains are provided at the bottom.

    Table2. Different cases of providing bracing.

    Sr.No.

    Designation

    Position of bracing

    1

    Model 01

    Without Bracing

    2

    Model 02

    Bracing throughout

    3

    Model 03

    Storey (1+2+3)

    4

    Model 04

    Storey (2+3)

    5

    Model 05

    Storey (3)

    6

    Model 06

    Storey (1+3)

    7

    Model 07

    Storey (G+2)

    8

    Model 08

    Alternative direction

    The X-bracings are provided at the exterior parameter of the structure. Soil conditions are considered medium stiff and a damping ratio of 5% and the importance factor taken is 1. The loads are provided as per IS 1893:2002 (Part 1). The structural data is the same for all the structures.

    1. Models considered

      Fig 2: Model 02, 03, 04 & 05

      Fig 3: Model 06 & 07

      Fig 4: Model 08

      • Fig 2, 3 & 4 shows the models of steel bracing provided.

      • In model 08, the bracings are provided for G&2 storey in X-Z plane and for 1 & 3 storey in Y-Z plane.

      • The bracing used in the model is made of steel.

    2. Seismic zone in India

    Fig 5: Major Zonation and Intensity map in India

    Table 3. Region-wise major Earthquakes in India.

    Seismic Region

    No. of Earthquakes of Magnitude

    Return period

    5.0-5.9

    6.0-6.9

    7.0-7.9

    8.0+

    Kashmir & Western Himalayas

    25

    7

    2

    1

    2.5-3 yrs.

    Central Himalayas

    68

    28

    4

    1

    1 yrs.

    North East India

    200

    128

    15

    4

    <4 months

    Indo-Gangetic Basin and Rajasthan

    14

    6

    5 yrs.

    Cambay and Rann of kutch

    4

    4

    1

    1

    20 yrs.

    Peninsular India

    31

    10

    2.5-3 yrs.

    Andaman & Nicobar

    80

    68

    1

    1

    <8 months

    Table 3 provides information regarding the No. of Earthquakes of Magnitude 5.0- 8.0+ & their return period.

  3. METHODOLOGY

    In this study 8 models are considered with different bracing combinations as shown in fig 2, 3 & 4. The position combination of X-bracings is entered into the design evaluation of SAP2000. By comparing all the results to the cost parameter the optimal selection of the position of X- bracing is verified. Accodingly, minimum lateral drift is achieved.The procedure is shown in fig 6.

    Bracing type: X-bracing

    Bracing type: X-bracing

    Position: External Parameter

    Position: External Parameter

    Diaplacement in X- direction

    Diaplacement in X- direction

    0.002

    0.0015

    Graph of EQ-x

    M1

    M2 M3

    M4

    M5 M6 M7

    M8

    M1

    M2 M3

    M4

    M5 M6 M7

    M8

    Criteria: Lateral Drift

    Criteria: Lateral Drift

    Without bracing frame

    Design & Analysis

    Compare Compare

    Bracing Cost

    0.001 0.0005

    0

    217 218 219 220

    Joint No:

    Fig 7: Displacement in X-direction vs Joint No:

    Model

    Joi

    nt No:

    No

    217

    218

    219

    220

    M1

    0.0008

    0.0015

    0.0017

    0.0017

    M2

    0.0006

    0.0009

    0.001

    0.0009

    M3

    0.0008

    0.0013

    0.0015

    0.0014

    M4

    0.0009

    0.0015

    0.0017

    0.0017

    M5

    0.0008

    0.0015

    0.0018

    0.0018

    M6

    0.00018

    0.0013

    0.0015

    0.0014

    0.0006

    0.0011

    0.0013

    0.0012

    M8

    0.0008

    0.0013

    0.0015

    0.0014

    Model

    Joi

    nt No:

    No

    217

    218

    219

    220

    M1

    0.0008

    0.0015

    0.0017

    0.0017

    M2

    0.0006

    0.0009

    0.001

    0.0009

    M3

    0.0008

    0.0013

    0.0015

    0.0014

    M4

    0.0009

    0.0015

    0.0017

    0.0017

    M5

    0.0008

    0.0015

    0.0018

    0.0018

    M6

    0.00018

    0.0013

    0.0015

    0.0014

    M7

    0.0006

    0.0011

    0.0013

    0.0012

    M8

    0.0008

    0.0013

    0.0015

    0.0014

    Table 5. Displacement in Y-direction (EQ-y)

    Optimal Bracings position

    Optimal Bracings position

    Fig 6: Selection of the optimal bracings position

    Fig 6 show how the optimal bracing position is selected by comparing braced frame with G+3 without bracing frame & Bracing cost.

    Table 5 Represents the displacement in Y-direction. The values are given for EQ-y and they are in meters. The values are plotted as graph in fig 8.

  4. RESULTS AND DISCUSSIONS

    Model No

    Joint No:

    217

    218

    219

    220

    M1

    0.0008

    0.0014

    0.0016

    0.0016

    M2

    8.159E-05

    0.0002

    0.0003

    0.0004

    M3

    0.0009

    0.001

    0.0011

    0.0011

    M4

    0.0008

    0.0015

    0.0015

    0.0016

    M5

    0.0008

    0.0014

    0.0017

    0.0017

    M6

    0.0009

    0.0009

    0.0012

    0.0012

    M7

    7.255E-05

    0.0007

    0.0008

    0.0009

    M8

    7.309E-05

    0.0007

    0.0008

    0.0009

    Model No

    Joint No:

    217

    218

    219

    220

    M1

    0.0008

    0.0014

    0.0016

    0.0016

    M2

    8.159E-05

    0.0002

    0.0003

    0.0004

    M3

    0.0009

    0.001

    0.0011

    0.0011

    M4

    0.0008

    0.0015

    0.0015

    0.0016

    M5

    0.0008

    0.0014

    0.0017

    0.0017

    M6

    0.0009

    0.0009

    0.0012

    0.0012

    M7

    7.255E-05

    0.0007

    0.0008

    0.0009

    M8

    7.309E-05

    0.0007

    0.0008

    0.0009

    Table 4. Displacement in X-direction (EQ-x)

    Displacement in Y-

    direction

    Displacement in Y-

    direction

    0.002

    0.0015

    0.001

    0.0005

    0

    Graph for EQ-y

    M1 M2 M3

    M4

    M5

    M6

    M7

    M8

    M1 M2 M3

    M4

    M5

    M6

    M7

    M8

    217 218 219 220

    Joint No.

    Table 4 Represents the displacement in X-direction. The values are given for EQ-x and they are in meters. The values are plotted as graph in fig 7.

    Fig 8: Displacement in Y-direction vs Joint No.

    • By comparing the above plots, the addition of X- bracing to open ground storey structure improves the performance of the building to some extent.

    • For the nonlinear static analysis, from table 4 it is clear that M2, M7& M8 are producing minimum displacement in X-direction. Fig 7 shows the graphical representation of displacement in X- direction vs joint no. and the models are plotted inside the graph.

    • Table 5 shows that M2, M7 & M8 are producing minimum displacement in Y-direction. Fig 8 shows the graphical representation of displacement in Y-

      direction vs joint no. and the models are plotted inside the graph.

      • By comparing the displacement parameter with cost parameters, we could conclude that M7 and M8 provides better performance than other models. The displacement parameters values are taken from fig 7 & fig 8.

  5. CONCLUSIONS

    In this study, the analysis and design software, SAP2000 is utilized to develop a numerical model of G+3 storey structures as shown in fig 1. Standard bracings are provided at the external parameter. From the study, we can conclude that in M2, minimum deflection is obtained which results in lower chances of failure of the structure during an earthquake. Providing bracings throughout the section is not feasible, M7 and M8 can be considered economical and still provide less lateral deflection. The model considered here is symmetrical, Further studies can be carried on unsymmetrical models.

  6. REFERENCES

[1]. Shemin T John, Pradeep Sarkar, Deepak Kumar Sahu,Enhancement of the seismic performance of an open ground storeyed building using X-bracings,Journal of IOP Conference series Material Science and Enginerring, Vol.936, pp.757-899 October 2020.

[2]. Bush T. D., Jones E. A. and Jirsa J. O.,, Behaviour of RC frame strengthened using structural steel bracing, Journal of Structural Engineering, Vol.117, No.4, April,1991.

[3]. Marc Badoux and James O. Jirsa,Steel bracing of RC frames for seismic retrofitting, Journal of Structural Engineering, Vol.116, No.1, January 1990.

[4]. IS 1893:2002 Indian Standard Criteria for Earthquake Resistant Design of structures Part1 General Provision and Buildings. (Bureau of Indian Standard: New Delhi)

[5]. Jain S k, Review of Indian seismic code IS 1893(Part1) 2002 Indian Concrete Journal.pp.1414-1422.

[6]. Sujeesh S., Shemi T. John., Enhancement of seismic performance of soft storeyed buildingsInternation Journal of Engineering and Advanced Technology, Vol.7, pp. 152-157, December 2017.

[7]. Sarita Singal, Megha Kalra, Rahul Kalra, Taranjeet Kaur.,Behaviour of RC Framed Building with Different Lateral bracing Systems,Internation Conference in Civil Engineering ,pp. 151-155, August 2012.

[8]. Chiral S Modi, Jasmin A. Gadhiya, Aditya Bhatt Pushover Analysis of a G+3 Storey building with Vertical Irregularity by SAP2000, International Journal of Innovative Science and Research Technology, Vol.2, Issue 5, pp.822-827, May-2017.

[9]. https://nidm.gov.in/images/safety_eq3.jpg

[10]. https://nidm.gov.in/images/safety_eq1.jpg

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