Project 1

To create the 3D STAAD Pro model of the underground water tank based on the provided data and requirements.

1. Calculate Total Water Demand

Flats & Occupants:

• 2BHK: 200 flats × 3 persons = 600 persons

• 3BHK: 100 flats × 4 persons = 400 persons

• Total = 1000 persons

Water Usage Per Person:

Activity	Litres/person/day
Drinking	5
Cooking	45
Bathing	30
Toilet Flushing	25
Cloth Washing	35
Miscellaneous	10
Total	150 L/day

Total Demand:

$$1000 \times 150 = \boxed{150,000 \, \text{L/day}} = 150 \, \text{m}^3/\text{day}$$

Assume 2 days storage for emergencies → Storage Volume = 300 m³

2. Tank Sizing Based on Site Constraints

Width ≤ 6 m (due to road width)

Assume:

• Length = $L$, Width = 6 m, Depth = $D$

Using volume = L × B × D

$$300 = L \times 6 \times D \Rightarrow L \times D = 50$$

Let's trial:

• Depth = 5.0 m → $L = 10 \, \text{m}$

• Provide freeboard = 0.5 m, effective water depth = 4.5 m

→ Final Dimensions (Inner Clear):

• L = 10 m

• B = 6 m

• D = 5 m (including freeboard)

3. Structural Elements

Element	Thickness/Size	Notes
Base slab	500 mm	As per best practice
Walls	300 mm	RCC, M25
Top slab	500 mm	Spans ≤ 4 m
Beams (if needed)	500×900 mm	Used if top slab spans > 4 m

4. Material Properties

Material	Grade	Notes
Concrete	M25	fck = 25 MPa
Rebars	Fe500	fy = 500 MPa
Water	γ = 10 kN/m³
Soil (saturated)	γ = 18 kN/m³

5. STAAD Pro Modeling (Key Points)

➤ Modeling Method:

• Use centerline approach (model slab/wall centerlines)

• Use plate elements for slabs and walls

• Use beam elements for slab stiffening beams if required

➤ Mesh Size:

• Use an average mesh size of 500 mm

➤ Supports:

• Fixed supports at base (soil contact)

• Use plate mat or spring supports with appropriate subgrade modulus

➤ Loading:

1. Dead Load (DL):

• Self-weight of structural elements (automatically applied)

2. Live Load (LL):

• 15 kN/m² on top slab (input as floor load)

3. Superimposed Dead Load (SDL):

• 3 kN/m² on top slab

4. Water Pressure:

• Hydrostatic load: 0 at top, 45 kN/m² at base (triangular load)

• Apply as pressure on inner walls and base

5. Soil Pressure (Outside walls):

• Consider saturated backfill → 18 × 5 = 90 kN/m² at base

• Triangular load applied externally

6. Soil Pressure & Foundation

Depth	S.B.C (t/m²)	kN/m²
3 m	7.5	75
4 m	8	80
5 m	8.5	85

Use 5 m founding depth → SBC = 85 kN/m²

Apply spring support with subgrade modulus derived from:

$$k = \frac{\text{SBC}}{\text{Settlement}} = \frac{85}{0.025} = 3400 \, \text{kN/m}^3$$

7. Final STAAD Setup Checklist

• Geometry via centerline modeling

• Define materials (M25, Fe500)

• Define thicknesses: 500 mm base/top, 300 mm walls

• Plate mesh: 500 mm

• Apply all applicable loads

• Apply fixed or spring supports

• Define load combinations (DL+LL+Hydrostatic)

• Ensure no modeling errors or warnings

• Use proper naming & units