Scenario:

We need to replace a 10mm diameter distribution bar with a 12mm diameter bar due to non-availability.

Given Data:

• Original bar diameter (D₁) = 10mm
• Spacing of 10mm bar (S₁) = 150mm (center-to-center)

Objective:

To calculate the required spacing (S₂) for the 12mm diameter replacement bar.

Step 1: Calculate New Spacing

The formula used for spacing adjustment is:

Where:

• D₁ = Diameter of the original bar (10mm)
• D₂ = Diameter of the replaced bar (12mm)
• S₁ = Spacing of the original bar (150mm)
• S₂ = Spacing of the replaced bar (to be determined)

Thus, the 12mm bars should be placed at 216mm center-to-center.

Note:
The new spacing should not exceed the maximum allowable spacing as per the design criteria.

Step 2: Verify the Total Weight of Steel Used

Even though the bar diameter is increased, the total steel weight remains almost the same.

For 10mm bars:

Number of distribution Bars Required

For 10mm bars:

= 17.67

Rounded off to 18 bars.

For 12mm bars:

Number of distribution Bars Required

= 12.57

Rounded off to 13 bars.

Step 3: Compare the Total Weight

Steel weight per meter:

• 10mm bar = 0.62 kg/m
• 12mm bar = 0.88 kg/m

Total weight for 10mm bars = 18 × 0.62 = 11.16kg 

Total weight for 12mm bars = 13 × 0.88 = 11.4kg

Since 11.4 kg ≈ 11.16 kg, the weight of steel remains nearly the same.

Conclusion:

• Replacing a 10mm bar with a 12mm bar does not increase the cost because the total weight of steel used remains the same.
• Spacing should be adjusted accordingly to maintain the same reinforcement area and structural strength.

This method ensures efficient material utilization while maintaining structural integrity.

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