Centre line method of estimating a building — key rules: Identify the correct statements about using the centre line method to compute quantities for walls and associated items in a building.
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AProduct of the total centre line length and the item's cross-sectional area gives the total quantity of that item
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BCentre line lengths are worked out separately for different wall thicknesses or sections
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CAt junctions, centre line length is adjusted by half the thickness of the main wall meeting a partition wall
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DAll the above
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E—
Answer
Correct Answer: All the above
Explanation
Introduction / Context:The centre line method is a fast and reliable estimating technique for buildings with repetitive wall geometry. Instead of measuring each wall face separately (long-wall/short-wall), quantities are obtained using the total centre line length multiplied by item-specific cross-sections, with careful junction corrections.
Given Data / Assumptions:
- Rectangular/symmetric planning so that junction corrections are systematic.
- Different wall thicknesses (e.g., main wall vs. partition) may exist.
- Items measured include excavation, foundation concrete, brickwork, and DPC where applicable.
Concept / Approach:
For any layer having uniform cross-section, quantity = centre line length * cross-sectional area. When wall thickness changes or walls intersect, the centre line length requires adjustments (usually by half the meeting wall thickness at each junction) to avoid double counting.
Step-by-Step Solution:
1) Compute centre line lengths for each distinct thickness section.2) Apply junction corrections: subtract or add half the meeting wall thickness as per layout.3) Multiply corrected centre line by item cross-section (e.g., t * depth for masonry).4) Sum over all layers/items (excavation, PCC, footing, brickwork, DPC).Verification / Alternative check:
Cross-check with long-wall/short-wall method on a small bay; both should match within rounding if junction corrections are applied properly.
Why Other Options Are Wrong:
- Options (a)–(c) are individually correct; hence “All the above” is the right consolidated choice.
Common Pitfalls:
- Forgetting to recompute centre line for different wall thicknesses and offsets.
- Omitting half-thickness deductions at T-junctions and cross-junctions, causing quantity inflation.
Final Answer:
All the above.