Analysis of Buildings with Varying Percentages of Diaphragm Openings

Download Full-Text PDF Cite this Publication

Text Only Version

Analysis of Buildings with Varying Percentages of Diaphragm Openings

Arya V Manmathan1,

1PG Scholar,

Sree Buddha College of Engineering, Alappuzha/Pathanamthitta cluster of APJ Abdul Kalam Technological University,

Ayathil, Elavumthitta P.O, Pathanamthitta-689625

Aiswarya S2

2Assistant Professor,

Sree Buddha College of Engineering, Alappuzha/Pathanamthitta cluster of APJ Abdul Kalam Technological University,

Ayathil, Elavumthitta P.O, Pathanamthitta-689625

Abstract: The major reasons of structures failure during earthquakes are Irregularities. Damages from earthquake generally initiates at locations of structural weaknesses in multi- storeyed framed buildings. Buildings with openings in slabs are subjected to damages due to the action of lateral loads. Floor and roof systems act as horizontal diaphragms in building structures. They collect and transmit inertia forces to the vertical elements of lateral load resistant systems, i.e. columns and structural walls. They also ensure that vertical components act together under gravity and seismic loads. Diaphragm openings are provided for the purpose of stairways, architectural features or shafts. In this works, openings in slabs are provided at various locations such as centre, at corners and at periphery with buildings having various shaped columns. The effects of size of openings in slabs were investigated. The seismic performance of multistory regular building is determined by Response Spectrum analysis in ETABS software

Keywords: Regular buildings, Diaphragm openings, story drift, Response spectrum analysis, ETABS

  1. INTRODUCTION

    Diaphragm is the structural element that transmits lateral loads to the vertical resisting elements of structure. Excessive openings in diaphragm can results in flexible diaphragm response along with force concentrations and it leads to load path deficiencies at boundaries of the openings. In plan, openings in diaphragms may considerably weaken slab capacities. Discontinuities in the lateral stiffness of the diaphragm are due to openings, cut-outs, adjacent floors at different levels or change in the thickness of diaphragm. The diaphragm of a structure often does double duty as the floor system or roof system in a building, or the deck of a bridge, which simultaneously supports gravity loads. Diaphragms are constructed of plywood or composite metal deck in steel construction; or a concrete slab in concrete construction. Floor diaphragm openings are for the purpose of stairways, shafts or other architectural features. Gravity and earthquake loads flow in a continuous and smooth path through the horizontal and vertical elements of structures and transferred to the supporting ground. Sidestepping and offsetting are vertical discontinuities, leads to unfavourable stress concentrations. In plan, openings in diaphragms weakens the slab capacities. Discontinuities are

    present in plan and elevation. In this work, the effect of diaphragm discontinuity and seismic performance of buildings is done. Response spectrum analysis is used to find the effect of buildings with diaphragm discontinuity. This chapter describes about the diaphragm and diaphragm discontinuity

  2. OBJECTIVES

    • To investigate the seismic performance of a multistory building with slab openings by Response Spectrum analysis

    • To obtain the suitable location of openings

    • To study the effect of size of openings in slab

    • To investigate the effect of shape of column in buildings with diaphragm discontinuity

  3. SCOPE

    The study is limited to

    • 5% slab opening

    • Response Spectrum Analysis

    • columns having rectangular, square and circular shape

  4. LITERATURE REVIEW

    This chapter gives a brief review of previous studies conducted in the field of diaphragm discontinuity

    Momen M. M. Ahmed, Shehata E. Abdel Raheem, Mohamed

    M. Ahmed and Aly G. A. Abdel-Shafy (2016) [1] submitted a paper on Irregularity effects on the seismic performance of l- shaped multi-story buildings. They studied the seismic behaviour of the buildings with irregular plan of L-shape floor plan. Measured responses include inter-story drift; story shear force; overturning moment; torsion moment at the base and along the building height; top floor displacement; and torsional Irregularity Ratio. The models are analysed with ETABS using Equivalent Static Load and Response Spectrum Methods. The results proved that buildings with severe irregularity are more vulnerable than those with regular configuration resulting from torsion behaviour.

    Babita Elizabeth Baby, Sreeja S (2015) [2] published a paper on Analysis of Buildings with Slab Discontinuity. In their work slab openings are provided as discontinuity at different locations such as at centre, at corners and at periphery. A typical multi storeyed building is analysed using the commercial software ETABS for nonlinear static (pushover) and dynamic analysis. This study is done for RC framed multi-storeyed building (G+10) with fixed support conditions. The analyses were performed considering diaphragm discontinuity and results were compared. So, the openings are more effective to be located at periphery. Comparison were done for the linear and nonlinear analysis. Around 4% variation was shown for linear static analysis and response spectrum analysis.

    Md Zibran Pawaar, Khalid Nayaz Khan, Syed Ahamed Raza (2015) [3] published a paper on Performance Based Seismic Analysis of Rc Building Considering the Effect of Dual Systems They analysed and designed the buildings constructed in high seismic zones for the unpredictable earthquakes with unpredictable magnitudes by various lateral load resisting systems. Present study includes linear-static and non-linear static analysis with different shear wall arrangements on dual systems such as flat slabs and shear walls & moment resisting frames and shear walls for different irregular plans using ETABS 9.7.4 software. Parameters such as point displacements, base shears, pushover curves are studied

    Studies have been conducted on the dynamic response of structures with diaphragm discontinuity. But there is no study conducted to investigate the performance of buildings with diaphragm discontinuity as the percentage of discontinuity increases. Therefore, in this study the performance of buildings with increase in percentage of opening and different locations is investigated. Also, performance of buildings having diaphragm discontinuity with different column geometry also investigated

  5. METHODOLOGY

    Methodology employed is response spectrum method of analysis.

    1. Modelling of Building

      This study involves regular building configuration. Here the study is carried out for the behaviour of G+19 Storied Buildings, Floor height provided as 3m and also properties are defined for the building structure.9 models of buildings are prepared in which slab openings are provided at different positions of slab such as centre, corner and periphery with different column geometry such as rectangle, square and circular shape and with 1%,2%, 3%.,4% and 5% opening of floor area. For static behaviour dead load of the building is considered as per IS 875 Part 1and live load is considered as per IS 875 Part II, lateral load confirming IS 1893(part 1)2002.

    2. Building Plan and Dimensions

      The details of frame are obtained from literature review. An ordinary moment resisting framed building of 20 storeys is considered for analysis. The details and diension of the building model is given in Table 1

      Table 1

      Dimensional Details of The Building

      Plan dimension

      20m×20m

      Type of building:

      Ordinary moment resisting frame

      Number of stories

      20

      Floor height

      3m

      Grade of Concrete

      30Mpa

      Grade of steel

      Fe 500

      Beam dimension

      450mm×850mm

      Column dimension

      350mm ×650mm

      Slab depth

      150mm

      Fig.1 Plan of Building

      Fig.2 Elevation of Building

    3. Loads Considered

      Table 2

      Details of Dead Load and Live Load

      Load

      Value

      DL

      1.5kN/m2

      LL

      2kN/m2

      Table 3

      Details of Seismic Load

      Zone

      V

      Soil type

      Type 11

      Zone factor

      0.36

      Importance factor, I

      1.5

      Response reduction factor

      3

    4. Load Combinations

      The following Load combinations have been considered for the analysis

      1. DL

      2. DL+LL

    3. 1.5(DL+LL)

    1. 1.2(DL+LL+ EQX)

    2. 1.2(DL+LL+ EQY)

    3. 1.2(DL+LL – EQX)

    4. 1.2(DL+LL – EQY) 8. 1.5(DL+EQX)

      9. 1.5(DL+EQY)

      10. 1.5(DL- EQX)

      11. 1.5(DL- EQY) 12. 0.9DL+1.5EQX 13. 0.9DL+1.5EQY 14. 0.9DL – 1.5EQX 15. 0.9DL – 1.5EQY

  6. MODELLING

    The building is modelled for the slab openings of 1%,2%,3%,4% and 5% and with rectangular, square and column geometries. The Figure.3 shows1% slab openings at centre, corner and periphery for a building with square column.

      1. Slab Opening at Centre

      2. Slab Opening at Corner

      3. Slab Opening at Periphery

    Fig.3 Plan of building with 1% slab opening and square column

  7. ANALYSIS RESULTS

    The building with three different column geometries is analysed by Response spectrum analysis for slab openings provided at centre, corner and periphery. The maximum storey drifts data is taken for comparison from the analysis results. Storey drift is the displacement of one level relative to other level above or below. The maximum storey drift values are tabulated.

    1. Base Shear

      Table 5

      Slab opening %

      Column geometry

      Slab opening position

      Centre

      Corner

      Periphery

      1%

      Rectangle

      3707.46

      6890.05

      8632.63

      Square

      3274.22

      6134.97

      7964.29

      Circle

      3100.48

      5799.19

      7038.15

      2%

      Rectangle

      7366.04

      7536.34

      8941.67

      Square

      6559.29

      6629.98

      8136.23

      Circle

      6214.38

      6255.18

      7973.54

      3%

      Rectangle

      7478.93

      7935.28

      9009.343

      Square

      6682.31

      6931.64

      8978.579

      Circle

      6284.96

      6560.09

      8013.23

      4%

      Rectangle

      8821.23

      9118.10

      9346.53

      Square

      7442.19

      7893.27

      9153.94

      Circle

      6389.32

      6630.41

      8999.32

      5%

      Rectangle

      8825.71

      9623

      9834.85

      Square

      7947.34

      9219

      9467.93

      Circle

      7032.36

      8317.79

      9013.82

      Base shear(kN) for slab openings at various positions

      1. Storey Drift

    Table 4

    Maximum storey drift for slab openings at various positions

    Slab opening %

    Column geometry

    Slab opening position

    Centre

    Corner

    Periphery

    1%

    Rectangle

    0.001138

    0.002404

    0.00325

    Square

    0.00088

    0.00188

    0.00246

    Circle

    0.00092

    0.001969

    0.00249

    2%

    Rectangle

    0.00229

    0.002574

    0.00360

    Square

    0.00177

    0.002011

    0.00253

    Circle

    0.00185

    0.002102

    0.00262

    3%

    Rectangle

    0.002246

    0.002529

    0.00358

    Square

    0.001768

    0.001978

    0.00237

    Circle

    0.001851

    0.002089

    0.00257

    4%

    Rectangle

    0.004723

    0.00532

    0.00576

    Square

    0.00458

    0.00481

    0.00497

    Circle

    0.00463

    0.00492

    0.0052

    5%

    Rectangle

    0.004723

    0.00532

    0.00576

    Square

    0.004576

    0.00481

    0.00497

    Circle

    0.00463

    0.00489

    0.0052

    The building with three different column geometries is analysed by Response spectrum analysis for slab openings. The Base shear data is taken for comparison from the analysis results. Base shear is an estimate of the maximum expected lateral force that will occur due to seismic ground motion at base of a structure. The base shear values are tabulated.

  8. COMPARISON OF RESULTS

    0.0035

    0.003

    0.0025

    0.002

    0.0015

    0.001

    0.0005

    0

    Rectangle Square

    Circle

    Centre Corner Periphery

    Position of Slab Opening

    Max.Storey Drift

    Fig. 6 Comparison of maximum storey drift for 1% slab openings for building with different column geometry

    Max.Storey Drift

    From Fig.6, it is observed that slab opening at centre has lesser drift value comparing corner and periphery. Square column also has less drift values in comparison with rectangular and circular geometry

    0.005

    0.0045

    0.004

    0.0035

    0.003

    0.0025

    0.002

    0.0015

    0.001

    0.0005

    0

    Rectangle

    Square Circle

    1% 2% 3% 4% 5%

    Slab Opening at Centre

    Fig.7 Comparison of maximum storey drift for slab openings in building with different column geometry

    Base Shear(kN)

    From Fig.7, it is observed that drift value increases 2% opening and it slightly decreases for 3% opening but at 4% and 5% opening, drift values remains constant

    10000

    9000

    8000

    7000

    6000

    5000

    4000

    3000

    2000

    1000

    0

    Rectangle Square

    Circle

    Centre Corner Periphery

    Position of Slab Opening

    Fig. 8 Comparison of Base shear for 1% slab openings for building with different column geometry

    From Fig.8, it is observed that slab opening at centre has lesser base shear value comparing corner and periphery. Square column also has less base shear values in comparison with rectangular and circular geometry

    10000

    9000

    8000

    7000

    6000

    5000

    4000

    3000

    2000

    1000

    0

    Rectangle Square

    Circle

    1% 2% 3% 4% 5%

    Slab Opening at Centre

    Base Shear(kN)

    Fig.9 Comparison of Base shear for slab openings for building with different column geometry

    From Fig.9, it is observed that base shear increased with increase in percentage of opening

  9. CONCLUSIONS

  • The percentage reduction of storey drift for slab opening at centre is 53.02% compared to corner and 64.13% compared to periphery position.

  • The percentage reduction of base shear for slab opening at centre is 46.44% compared to corner and 57.3% compared to periphery position.

  • From Maximum Storey drift and Base shear view, slab openings at centre is found to be more effective in resisting lateral forces.

  • Lateral displacement for slab opening at centre is lesser compared to other positions.

  • The percentage reduction of storey drift for square column is 22.97% compared to rectangular column and 3.38% compared to circular column.

  • The percentage reduction of storey base shear for circular column is 10.12% compared to rectangular column and 7.5% compared to square column.

  • Considering the drift point of view, square column is better and from base shear point of view, Circular column is better

  • The percentage of slab openings at centre, corner and periphery positions in case of storey drift increases up to 2% opening and it reduces for 3% opening. It attains a constant value for 4% and 5% slab opening.

  • As the percentage of slab opening increases, base shear also increases

ACKNOWLEDGEMENT

I am thankful to my guide, Asst. Professor, Aiswarya S in Civil Engineering Department for her constant encouragement and able guidance. Also, I thank my parents, friends etc. for their continuous support in making this work complete.

REFERENCES

  1. Momen M. M. Ahmed, Shehata E. Abdel Raheem, Mohamed M. Ahmed and Aly G. A. Abdel-Shafy, Irregularity Effects on The Seismic Performance Of L-Shaped Multi-Story Buildings Journal of Engineering Sciences Assiut University Faculty of Engineering Vol. 44 No. 5 PP. 513 536, August 2016.

  2. Babita Elizabeth Baby, Sreeja S Analysis of Buildings with Slab Discontinuity International Journal of Science and Research (IJSR) December 2015 ISSN (Online): 2319-7064 Index Copernicus Value (2013): 6.14 | Impact Factor (2015): 6.391

  3. Md Zibran Pawaar, Khalid Nayaz Khan, Syed Ahamed Raza Performance Based Seismic Analysis Of Rc Building International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308, Volume: 04 Issue: 05 August 2015

  4. Mohaiminul Haque, Sourav Ray, Amit Chakraborty, Mohammad Elias, Iftekharul Alam1 Seismic Performance Analysis of RCC Multi-Storied Buildings with Plan Irregularity

    American Journal of Civil Engineering 2015, 4(2): 52-57

  5. Osama Maniar1, Roshni J John2 Effect of Diaphragm Discontinuity on Seismic Response of Multi-storeyed Building International Journal of Emerging Technology and Advanced Engineering, Volume 5, Issue 12, 2015

  6. P.P. Vinod Kumar 1, Dr. V.D. Gundakalle Effect of Diaphragm Openings in Multi-storeyed RC framed buildings using Pushover analysis International Journal of Research Sciences and Advanced Engineering (IJRSAE), Volume 2, Issue 8,2015 pp: 182-192,

  7. Rakesh Sakale1, R K Arora1 and Jitendra Chouhan Seismic Behaviour Of Buildings Having Horizontal Irregularities ASCE Journal of Structural Engineering, Vol. 132, No. 11, 2006, pp. 17321744

  8. S. Varadharajan, V.K. Sehgal, and B. Saini Review of different Structural irregularities in buildings Journal of Structural Engineering Vol. 39, No. 5, December 2012 – January 2013 pp. 393-418

  9. Dr. S.K. Dubey, P.D. Sangamnerkar Seismic Behaviour Of Asymmetric Rc Buildings International Journal of Advanced Engineering Technology E-ISSN 0976-3945,2011

  10. Ravi Kumar C M, Babu Narayan K S, Sujith B V, Venkat Reddy Effect of Irregular Configurations on Seismic Vulnerability of RC Buildings International Journal of Engineering Research & Technology (IJERT), Volume 3 Issue 6, 2009

Leave a Reply

Your email address will not be published.