Comparison Of Square And Raft Footing For A Multistory Building Under Static And Dynamic Loads
- 1. Structural Engineering Civil Engineering Department MNNIT ALLAHABAD Supervisor(s) – Dr. L.K. MISHRA Dr. GOUTAM GHOSH Presented By- Lovneesh Modi 2016ST02 A SUMMER PROJECT PRESENTATION On Comparison Of Square And Raft Footing For A Multistory Building Under Static And Dynamic Loads
- 2. List of Contents 1.Introduction 2.Objectives 3.Methodology 4.Problem Definition 5.Results 6.Conclusion 7.Reference
- 3. Introduction Foundation is the structure element that transfers the load from column or load bearing wall to ground. It can be classified as :- 1. Shallow :-Depth upto 2 m 2. Deep :- Depth more than 2m We are focusing on the each of the two types of shallow foundation:- 1. Isolated column footing 2. Mat/Raft foundation Image source:- strucalc.com
- 4. Objectives • To evaluate the Soil Bearing capacity according to IS 6403-1987 and Settlement from the available Bore log data • To identify the suitable type of foundation for given condition • To design the foundations using Staad Foundation advanced
- 5. Methodology • Application of problem formulated by analyzing it in Staad-Pro • Export the reactions from Staad Pro to the Staad foundation Advanced for modeling, analysis and design of the foundations • Comparison of the Results in terms of SBC, Settlement and Quantity of materials
- 6. Problem Definition The dimensions taken are as follows:- • Beams 300x450mm2 and Column 500x500mm2 • Dead load 3.75kN/m2 (assume 150mm slab) • Floor to floor height is 3m and column to column distance is 10m • Live load 2 kN/m2 (according to IS 875 Part2-1987) • Wind load taken according to IS 875 Part3-2015 • Seismic Loads are taken according to IS 1893 Part1-1993
- 7. FOUNDATION DESIGN DEFINE ASSUMPTIONS DESIGN CHECK AND REINFORCEMENT DESIGN STRUCTURAL ANALYSIS PRELIMINARY DESIGN BASED ON SERVICE LOAD Soil Bearing Capacity Depth of footing Water Table Concrete and soil Unit Weight Calculate required foundation dimension based on required area Required foundation area Calculate factored footing pressure Calculate maximum shear Calculate maximum moment Overturning Sliding One way shear Punching shear Choose governing area of steel and determine spacing required CHECK Calculate maximum moment
- 8. Advantages/Disadvantages of the Staad Foundation Advantages Disadvantages Quick and easy assessment of stresses Settlement calculation is not possible Effortless design of footing according to IS 456-2000 Calculation of SBC for isolated column footing is to be manually provided Quick extraction of detail drawing of the structural component(only for isolated and combined footing) Collaboration of model with BIM workflow is yet not possible
- 9. Results Isolated(square) Raft Safe bearing capacity 235 kN/m2 least calculated 476 kN/m2 Settlement 144 mm(allowable 60 mm) 65mm(allowable 75 mm) Maximum dimension 3.85x3.85 - 6.3x6.3 m2 35 x 45 m2 Thickness of footing 450 - 670 mm 600mm Concrete 432m3 945 m3 Steel 33.868x 103 Tonnes 2.921x 103 Tonnes Cost of concrete excluding centering and shuttering(in Rs) 33,64,848(@7789 per m3) 73,60,605(@7789 per m3) Cost of steel (in Rs) 2,16,75,52,000(@ 64 per kg) 18,69,44,000(@64 per kg) Total Cost(in Rs) 2,17,09,16,848 19,43,04,605
- 10. Footing Name Settlement (mm) Square Size(m) X (m) Z (m) SBC(kN/m2) Base Pressure (kN/m2) footing 1 61 5.15 0 0 244 55 footing 2 78 6.15 10 0 252 78 footing 3 78 6.15 20 0 252 70 footing 4 61 5.15 30 0 244 55 footing 25 79 6.1 0 10 251 70 footing26 144 5.75 10 10 248 130 footing 27 144 5.75 20 10 248 131 footing 28 114 4.8 30 10 241 105 footing 49 75 6.3 0 20 253 66 footing 50 139 5.85 10 20 249 126 footing 51 137 5.95 20 20 250 123 footing 52 114 4.8 30 20 241 104 footing 73 79 6.1 0 30 251 70 footing 74 141 5.8 10 30 249 129 footing 75 142 5.8 20 30 249 129 footing 76 112 4.85 30 30 241 103 footing 97 62 5.1 0 40 243 55 footing 98 118 4.7 10 40 240 110 footing 99 116 4.75 20 40 240 108 footing 10097 3.85 30 40 235 94
- 11. The maximum Base pressures or reaction of the mat comes out to be 79 kN/m2and average reaction is 10 kN/m2. The maximum bearing Stresses in mat is 29.5 N/mm2 and average is 3.76 N/mm2
- 12. Conclusion • For the frame structure and given soil type Raft foundation comes out to be most efficient in terms of settlement , strength and economy • Design of bearing stresses being important in Raft for which additional reinforcement in the form of dowel bars should be provided.
- 13. References 1. IS 1893 – 1993Part 1 “Criteria for Earthquake Resistant Design of Structure” 2. IS 1904 – 1986 ”Design and Construction of Foundation in Soils” 3. IS 6403 – 1981 ”Determination of Breaking Capacity of Shallow Foundation” 4. IS 456 -2000 ”Plain and Reinforced Concrete” 5. CPWD Detail Schedule of Rates (2014)