THUMB RULES FOR CIVIL ENGINEERS
As a civil engineer, there are several thumb rules that can be helpful in estimating, designing, and executing various construction activities. These thumb rules are quick calculations based on experience and are commonly used in the industry. However, it’s important to note that these rules are approximate and should be used with caution, as each project may have unique requirements. As a civil engineer, there are several thumb rules that can help you make quick estimates and approximate calculations on construction sites. While these thumb rules can provide rough estimates, it’s important to note that they should not replace detailed engineering calculations and analysis.
Here are some commonly used thumb rules for civil engineers:
- Concrete:
- 1 part cement: 2 parts sand: 4 parts coarse aggregate (by volume) in concrete mix.
- 0.0347 cubic meters (1.23 cubic feet) of cement bags required per square meter (10.76 square feet) for plastering.
- The approximate amount of concrete required for a structure can be calculated using the rule: 1 cubic meter of concrete per 10 square meters of area.
- The ratio of cement, sand, and aggregate in a concrete mix is typically 1:2:4.
- Reinforcement:
- Approximate steel quantity for RCC (Reinforced Cement Concrete) structures is 1-2% of the volume of concrete.
- 0.4 kg of steel reinforcement per cubic meter of concrete for residential buildings.
- 0.5 kg of steel reinforcement per cubic meter of concrete for commercial buildings.
- For mild steel reinforcement in RCC (Reinforced Concrete) structures, the thumb rule is to use 0.8% to 1% of the concrete volume.
- For steel bars, the weight can be estimated by using the formula: D^2/162, where D is the diameter of the bar in millimeters.
- Brickwork:
- 500 modular 19cm x 9cm x 9cm bricks are required per cubic meter (35.3 cubic feet) of brickwork.
- 393 bricks of size 4.5″ x 3″ x 9″are required per cubic meter (35.3 cubic feet) of brickwork.
- 7 bags of cement (50 kg each) are required per 1000 bricks for mortar.
- The number of modular bricks required for a wall can be estimated using the rule: 500 bricks per 100 square feet of wall area.
- The cement mortar required for brickwork is typically 1:6 (1 part cement to 6 parts sand).
- Excavation:
- Approximate soil weight is 1.8-2.2 tons per cubic meter (varies depending on soil type and moisture content).
- Approximate soil removal during excavation is 25-30% more than the volume of earthwork required.
- The approximate volume of excavation can be estimated using the rule: 1 cubic meter of loose soil or 1.25 cubic meters of compacted soil per 10 square meters of area.
- Slopes and Gradients:
- Maximum slope angle for earthwork stability is 1:1.5 (horizontal:vertical) for loose soil and 1:2 (horizontal:vertical) for stable soil.
- Minimum slope angle for safety in excavation is 1:1 (horizontal:vertical) or flatter.
- For road gradients, a common thumb rule is a 1:20 slope, which means a 1-meter rise in elevation for every 20 meters of horizontal distance.
- Column Reinforcement:
- Minimum 4 bars of 12mm diameter for a column size of 300mm x 300mm.
- Shuttering:
- 0.02 cubic meters (0.71 cubic feet) of timber required per square meter (10.76 square feet) of formwork.
- 0.006 cubic meters (0.21 cubic feet) of plywood required per square meter (10.76 square feet) of formwork.
- The approximate quantity of timber required for formwork can be estimated using the rule: 0.1 cubic meter of timber per square meter of formwork area.
- The quantity of nails required is roughly 2 kg per cubic meter of timber used for formwork.
- Water Supply:
- Water requirement for domestic use is approximately 135-150 liters per person per day.
- Water storage capacity in overhead tanks is usually calculated as 150 liters per person for one day.
- The water demand for residential buildings can be estimated at 135 liters per person per day.
It’s important to note that these thumb rules may vary based on local construction practices, codes, and project specifications. They should be used cautiously and in conjunction with professional engineering judgment. These thumb rules can serve as a starting point for initial estimations, but it’s crucial to consult with relevant codes, standards, and engineering calculations for accurate and safe design and construction.
