Seismic Parametric Study on Different Irregular Flat Slab Multi-Story Building

Seismic Parametric Study on Different Irregular Flat Slab Multi-Story Building

Mr. Muralidhara G. B1, Mrs. Swathi Rani K. S1, Mr. Melese Worku2

1 Lecturer, Civil Engineering Department, University of Gondar, Ethiopia

1 Assistant Prof., Civil Engineering Department, East West Institute of Technology, Karnataka, India

2HOD, Civil Engineering Department, University of Gondar, Ethiopia

Abstract With the advancement in the growth of urbanization and for aesthetic requirements, building with irregular structural forms are widely constructed. Irregularity in structures are mainly due to variable distribution of mass, stiffness, and strength or due to irregular geometrical configuration. This present study summarizes the behavior of G+10 irregular Flat Slab building with Vertical irregularity and Plan irregularity under seismicity. Linear static and dynamic analysis of models are performed by using ETABS to determine Earthquake response parameters like Base Shear, Natural Period and Displacement. Conclusions are woven based on the obtained results.

KeywordsUrbanization, Aesthetic, Response, Seismic

1. INTRODUCTION

   Earthquake is one of the natural disasters which the world is facing time to time. Based on previous earthquakes data, loss of human lives and properties which ultimately affects the national economy. The structure should possess, namely simple and regular configuration, adequate lateral strength, stiffness and ductility to accomplish well under Earthquake. Structures with simple regular geometry and uniformly distributed mass and stiffness in plan as well as in elevation are considered to suffer much lesser damage than structures with irregular forms. But nowadays, irregular buildings are preferred due to their functional and aesthetic considerations is evident from examples of realistic existing irregular buildings. As per IS 1893(part1):2002 enlists the irregularity in buildings. These irregularities are categorised as follows [4]:

   1. Vertical irregularities referring to sudden change of strength, stiffness, geometry and mass results in irregular distribution of forces or distribution over the height of the building.

   2. Plan irregularities which refer to asymmetrical plan shapes(L-,T-,U-,F-) or discontinuities in the horizontal resting elements (diaphragms) such as cut-outs, large openings, re-entrant corners and other abrupt changes resulting in torsion, diaphragm deformations and stress concentration.

2. ANALYTICAL MODELLING

   The structure analysed consists of a Multi-storey reinforced concrete flat slab building, characterized by its geometrical irregularity. Our study is restricted to Diaphragm discontinuity and Vertical discontinuity as shown in Fig 2 to Fig 7.

   1. Preliminary data

      • Type of Structure: Multi Storeyed RC Rigid Jointed Flat Plate Frame (Special Moment Resisting Frame)

      • Number of Stories: Eleven (G+10); 35m X 25m

        Data of structural Components:

      • Floor Height: 4m for Ground Floor, 4m for other Floors & 3m below plinth.

      • Grade of Concrete: M40 for Ground, First & Second Floors Columns.

      • M35 for Other Floors Columns

      • M25 for Beams and Slabs

      • Size of Columns: 600mmX600mm

      • Size of Beams: 600mmX300mm

      • Depth of Slab: 200mm thick

      • Thickness of Wall: 230mm

      • Imposed Load: 3.0KN/m2

      • Floor Finish & Partitions: 2.0 KN/m2

      • Specific Weight of RCC: 25 KN/m3

      • Density of brick:18KN/m3

        Earthquake data:

      • Type of Soil: III

      • Seismic Zone: V

      • Importance Factor: 1.5

      • Response reduction Factor: 5.0

      • Structural Software: ETABS Version ultimate 15.1.0

   Fig. 1. Model with Regular plan. (Model 1)

   Fig. 2. Model with Re-entrant corners. (Model 2)

   Fig. 3. Model with Re-entrant corner L-Shape. (Model 3)

   Fig. 4. Elevation of the model with Vertical Irregularity on one side. (Model 4)

   Fig. 5. Elevation of the model with Vertical Irregularity on both side.(Model 5)

   Fig. 6. Model with Rectangle shape as Diaphragm discontinuity. (Model 6)

   Fig. 7. Model with Inverse- T as Diaphragm Irregurality. (Model 7)

3. RESULTS AND DISCUSSIONS

In the present study, the behavior of each models are captured and the results are tabulated in Table-I to Table-V and referring to tables variations are shown in Chart 1 to Chart 4 for Time period, Base shear, eccentricity, top displacements and inter storey drifts in linear analysis.

TABLE I. FUNDAMENTAL NATURAL PERIOD OF VARIOUS STRUCTURE MODELS

TABLE II. BASE SHEAR FOR VARIOUS STRUCTURE MODELS

TABLE III. LATERAL DISPLACEMENT (MM) OF BUILDING MODELS

TABLE IV. ECCENTRICITY OF BUILDING MODELS

TABLE V. STOREY DRIFT (MM) OF BUILDING MODELS

Chart-1: Shows Base Shear of all models

Chart-2: Shows Fundamental natural period of all models

Chart-3: Shows story displacement of all models

Chart-4: Shows story drift of all models

CONCLUSION

1. Computation of fundamental natural period from Equivalent Static method will not contemplate the irregularities in the building. Since, it depends on empirical formula based on height of the building too.

2. All the building models are subjected to displacement in both directions. When load is applied in particular direction which may result in twisting.

3. Inter- story drift is more in Model IV both in 10th floor and Ground floor.

4. When Plan and Vertical building configurations are asymmetric, building will subjected to torsion.

5. Even in the absence of dual systems, the eccentricity between center of mass and center of rigidity differs with respect to plan, vertical and diaphragm irregularities respectively.

6. Base Shear of Model V is less compared to all other models due to reduction in the stiffness of the building also base shear due to Response spectrum is comparatively very low than Equivalent static method.

REFERENCES

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2. J. H. Cassis and E-Cornejo, Influence of Vertical Irregularities in the Response of Earthquake Resistant Structures.

3. IS 456:2000, Plain and Reinforced concrete Code of practice,

   Bureau of Indian Standards, New Delhi.

4. IS 1893-2002(Part-1), Criteria for Earthquake resistant design of structures, General provisions and buildings, Bureau of Indian Standards, New Delhi.

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