By the end of this chapter, you will be able to:
Mastering these skills will help you create precise and trustworthy cost plans, which are essential for successful project management in the construction trade.
Preparation of Specifications is a critical step in producing accurate and comprehensive bills of quantities (BoQ) in civil engineering projects in Kenya. It involves detailing the quality, workmanship, and materials to be used, ensuring all project requirements are clearly communicated to contractors and stakeholders. This process is guided by standardized methods such as the Standard Method of Measurement (SMM) and the Civil Engineering Standard Method of Measurement (CESMM), which promote consistency and transparency. Cross-referencing specifications with drawings and designs ensures alignment between the documented requirements and the physical project scope.
Specification preparation in civil engineering is the detailed documentation of requirements for materials, workmanship, and quality standards to be used in a construction project. This ensures all parties have a clear understanding of expectations, reducing ambiguity and potential disputes during execution. The preparation process involves several key steps to develop clear, measurable, and enforceable specifications that align with project objectives.
$$\text{Specification} = \text{Material Requirements} + \text{Workmanship Standards} + \text{Quality Criteria}$$
Example 1: Prepare a specification for concrete mix to be used in the foundation of a hospital building with a compressive strength of 25 MPa.
Given: Required compressive strength = 25 MPa
$$\text{Specification requirement} = \text{Concrete mix design with } f_c = 25 \text{ MPa}$$
Answer: Specify concrete mix with minimum compressive strength of 25 MPa at 28 days curing.
Example 2: Specify the type of reinforcement steel for beams in a retail complex requiring yield strength of 500 MPa.
Given: Yield strength = 500 MPa
$$\text{Specification} = \text{Use of high yield deformed bars with } f_y = 500 \text{ MPa}$$
Answer: Reinforcement steel specified as high yield deformed bars with yield strength of 500 MPa.
Example 3: Prepare a workmanship specification for block laying in a county government office construction to ensure alignment and bonding.
Given: Workmanship criteria includes verticality tolerance ±3 mm per meter.
$$\text{Specification} = \text{Block laying with verticality tolerance} \pm 3 \text{ mm/m}$$
Answer: Blocks to be laid with verticality tolerance not exceeding ±3 mm per meter length.
Example 4: Specify the curing period for concrete slabs in a school construction project.
Given: Minimum curing period = 7 days
$$\text{Specification} = \text{Curing of concrete slabs for a minimum of 7 days}$$
Answer: Concrete slabs to be cured for at least 7 days to achieve required strength.
Example 5: Prepare a specification for waterproofing treatment on a hotel basement wall.
Given: Waterproofing membrane with minimum thickness 1.5 mm
$$\text{Specification} = \text{Application of waterproofing membrane with } t = 1.5 \text{ mm}$$
Answer: Basement walls to receive waterproofing membrane of minimum 1.5 mm thickness.
The Standard Method of Measurement (SMM) and Civil Engineering Standard Method of Measurement (CESMM) are essential frameworks that standardize how quantities and specifications are prepared in civil engineering projects. SMM is primarily used for building works, while CESMM applies to civil engineering works such as roads, drainage, and earthworks. Adhering to these standards ensures uniformity, reduces errors, and facilitates fair tendering and contract administration.
$$\text{Quantity Measurement} \xrightarrow[\text{SMM or CESMM}]{} \text{Standardized Bill of Quantities}$$
Example 1: Using SMM, measure the quantity of 200 mm thick concrete wall with dimensions 5 m length and 3 m height.
Given: Thickness = 0.2 m, Length = 5 m, Height = 3 m
$$\text{Volume} = \text{Length} \times \text{Height} \times \text{Thickness}$$
$$= 5 \times 3 \times 0.2$$
$$= 3 \text{ m}^3$$
Answer: Concrete wall volume = 3 m³ according to SMM.
Example 2: Apply CESMM to measure earthworks excavation for a trench 10 m long, 1.5 m wide, and 2 m deep.
Given: Length = 10 m, Width = 1.5 m, Depth = 2 m
$$\text{Volume} = 10 \times 1.5 \times 2$$
$$= 30 \text{ m}^3$$
Answer: Earthworks excavation volume = 30 m³ per CESMM.
Example 3: Calculate the quantity of reinforcement steel bars measured in kilograms for a beam requiring 100 meters of 16 mm diameter bars.
Given: Length = 100 m, Diameter = 16 mm
Density of steel = 7850 kg/m³
Cross-sectional area \(A = \pi \times \frac{d^2}{4} = 3.1416 \times \frac{(0.016)^2}{4} = 0.000201 \text{ m}^2\)
Weight per meter \(= A \times \text{density} = 0.000201 \times 7850 = 1.577 \text{ kg/m}\)
Total weight
$$= 1.577 \times 100$$
$$= 157.7 \text{ kg}$$
Answer: Reinforcement steel weight = 157.7 kg.
Example 4: Using SMM, measure external wall plastering area for a wall 6 m long and 3 m high.
Given: Length = 6 m, Height = 3 m
$$\text{Area} = 6 \times 3$$
$$= 18 \text{ m}^2$$
Answer: Plastering area = 18 m².
Example 5: Measure the volume of concrete for a column 0.4 m by 0.4 m cross-section and 3 m height using CESMM.
Given: Width = 0.4 m, Depth = 0.4 m, Height = 3 m
$$\text{Volume} = 0.4 \times 0.4 \times 3$$
$$= 0.48 \text{ m}^3$$
Answer: Column concrete volume = 0.48 m³.
Cross-referencing specifications with drawings and designs is essential to verify consistency and completeness in civil engineering projects. This process ensures that the quantities and descriptions in the bill of quantities accurately reflect the project scope as depicted in the technical drawings. It involves systematic comparison and validation between the specification document and the design documents.
$$\text{Accuracy} = \text{Specifications} \cap \text{Drawings and Designs}$$
Example 1: Verify wall length specified in the BoQ matches the drawing dimension of 8 m.
Given: Drawing length = 8 m, BoQ length = 7.5 m
Check: \(8 \text{ m} \stackrel{?}{=} 7.5 \text{ m}\)
Difference \(= 8 - 7.5 = 0.5 \text{ m}\)
Answer: Discrepancy of 0.5 m, update BoQ to match drawing length of 8 m.
Example 2: Confirm concrete slab thickness in specification is consistent with design drawing of 150 mm.
Given: Drawing thickness = 150 mm, Specification thickness = 140 mm
Difference \(= 150 - 140 = 10 \text{ mm}\)
Answer: Specification thickness is 10 mm less than design; revise to 150 mm.
Example 3: Cross-check reinforcement spacing specified in BoQ with design drawing showing 200 mm centre-to-centre spacing.
Given: BoQ spacing = 250 mm, Drawing spacing = 200 mm
Difference \(= 250 - 200 = 50 \text{ mm}\)
Answer: BoQ spacing does not conform; adjust to 200 mm as per design.
Example 4: Validate the window opening dimensions in specifications against architectural drawings: 1200 mm width and 1500 mm height.
Given: Drawing width = 1200 mm, height = 1500 mm; Specification width = 1200 mm, height = 1500 mm
Check: Dimensions match.
Answer: Specification dimensions match drawings; no change required.
Example 5: Check the quantity of bricks specified for a wall of 10 m length, 3 m height, and 230 mm thickness against drawing dimensions.
Given: Wall dimensions same as above; Brick size 230 mm × 110 mm × 75 mm
Calculate wall volume
$$= 10 \times 3 \times 0.23 = 6.9 \text{ m}^3$$
Brick volume
$$= 0.23 \times 0.11 \times 0.075 = 0.0018975 \text{ m}^3$$
Number of bricks
$$= \frac{6.9}{0.0018975} = 3634 \text{ bricks}$$
Answer: Quantity of bricks required is approximately 3634, ensure BoQ matches this.
Prepare specifications for a 150 mm thick plaster on internal walls with a surface area of 200 m², including material and workmanship requirements. (10 marks)
Using CESMM, calculate the volume of earthworks excavation for a rectangular pit measuring 6 m by 4 m by 2.5 m depth. (8 marks)
Verify and correct the specification of a reinforced concrete column with a cross-section of 0.5 m x 0.5 m and height 4 m if the drawing shows a height of 4.2 m. Calculate the volume difference. (10 marks)
Cross-reference the specification for a window frame of 1.2 m by 1.5 m with the architectural drawings showing 1.1 m by 1.5 m. Identify the discrepancy and suggest corrective action. (7 marks)
Calculate the weight of reinforcement steel bars required for a beam of length 12 m using 20 mm diameter bars, given the density of steel is 7850 kg/m³. (10 marks)
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Create a free accountThis chapter covers the essential steps in preparing a bill of quantities, beginning with the development of clear and detailed specifications. It emphasizes the importance of defining material requirements and workmanship standards while adhering to SMM and CESMM guidelines. The preparation process includes thorough cross-referencing with drawings and designs to ensure accuracy. Next, the chapter addresses the calculation of schedule of rates by abstracting quantities, applying standard costing methods, and adjusting rates to reflect specific project conditions. Accuracy and adherence to costing guidelines are highlighted as critical for reliable estimates. Finally, the compilation of the bill of quantities is discussed, focusing on using working drawings, maintaining comprehensiveness, following standard formats, and reviewing the document to ensure consistency with the prepared specifications. This systematic approach ensures that the bill of quantities is a precise and dependable document for project costing and management.
A concrete slab requires 5 m³ of concrete. The specification states the material cost for concrete is Ksh 8,500 per m³. Calculate the total material cost for the concrete. (2 marks)
A wall plastering job covers 50 m². The workmanship rate is Ksh 300 per m². Calculate the total workmanship cost. (2 marks)
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