Standard Reference Values #civilengineer

 Standard Reference Values

Height of residential building – 3 m

Height of individual storey – 1.5 m

Width of roads – 3 m (typical minimum lane width; arterial roads are wider)

Height of parapet wall – 1 m

Width of staircase in building – 0.9 m (minimum clear width)

Thickness of one brick cement plaster – 12 mm

Density of cement – 1440 kg/m³

Volume of cement per m³ of 1:5 mortar – 0.167 m³

Quantity of cement bags in 1 m³ of 1:5 mortar – 4.18 bags

Bulk density of cement – 1440 kg/m³

Specific gravity of cement – 3.15

Bulk density of fine sand – 1450 kg/m³

Bulk density of coarse sand – 1600 kg/m³

Size of coarse aggregate – 20 mm

Bulk density of aggregate – 1650 kg/m³

Specific gravity of aggregate – 2.6

Water–cement ratio for plain concrete – 0.45–0.6 (acceptable range)

Rate of water absorption for brick – 20%

Porosity of brick – 25%

Crushing strength of brick – >75 kg/cm² (min. for class designation)

Unit weight of mild steel – 7850 kg/m³

Yield strength of mild steel – 250 MPa

Modulus of elasticity of steel – 200 GPa

Poisson’s ratio for steel – 0.3

Ultimate strength of high‐yield steel – 460 MPa

Minimum reinforcement cover in beams – 25 mm

Minimum reinforcement cover in slabs – 20 mm

Minimum reinforcement cover in columns – 40 mm

Minimum reinforcement cover in footings – 75 mm

Maximum diameter of bars in slabs – 8 mm (or ≤ slab thickness/8)

Maximum diameter of bars in beams – 16 mm

Maximum diameter of bars in footings – 20 mm

Clear cover for RCC elements – 20 mm (depends on exposure)

Water–cement ratio for grade M20 concrete – 0.5 (typical) 

Nominal mix ratio for M20 – 1:1.5:3 

Cement content in M20 – ≈330 kg/m³ 

Maximum aggregate size in M20 – 20 mm

Workability (slump) of M20 – 75–100 mm 

Characteristic strength of concrete at 28 days for M20 – 20 MPa

Autoclave efficiency (for AAC blocks) – 70–75%

Compressive strength of AAC blocks – 3.5–7.5 N/mm²

Dry density of AAC blocks – 600–800 kg/m³

Thermal conductivity of AAC – 0.17–0.21 W/m·K

Minimum number of bars used for square column – 4 bars

Minimum number of bars used for circular column – 6 bars

Maximum diameter of bars used in slabs – ≤ (thickness/8)

Maximum diameter of bars used in each bay – 10 mm

Max cover of reinforcement in RCC pile cap – 50 mm

Dimensional tolerance of cube – ±1.25 mm

Final setting time of cement – ≤10 hours

Initial setting time of cement – ≥30 minutes

Standard consistency of cement – 30% water

Specific gravity of PPC – 2.75

Specific gravity of slag – 2.9

Bulk density of PPC – 1120 kg/m³

Bulk density of slag – 1200 kg/m³

Water demand of PPC – 27%

Water demand of slag – 29%

Yield strength of grade M25 steel – 500 MPa

Compressive strength of grade M25 concrete – 25 MPa

Modulus of rupture of grade M25 concrete – 3.5 MPa

Tensile strength of concrete at 28 days – 2.5 MPa

Elastic modulus of concrete – 25 GPa

Poisson’s ratio of concrete – 0.2

Minimum diameter of bars used in T‐beam flange – 12 mm

Minimum diameter of bars used in T‐beam web – 10 mm

Minimum diameter of bars used in stair slab – 8 mm

Minimum diameter of bars used in raft foundation – 12 mm

Minimum diameter of bars used in strip footing – 10 mm

Minimum diameter of bars used in pile – 16 mm

Minimum number of bars used for square column – 4 bars

Minimum number of bars used for circular column – 6 bars

Maximum diameter of bars used in slabs – ≤ (thickness/8)

Maximum diameter of bars used in each bay – 10 mm

Max cover of reinforcement in RCC pile cap – 50 mm

Minimum tensile strength of steel – 415 MPa

Characteristic strength of steel at yield – 460 MPa

Compressive strength of grade M30 concrete – 30 MPa

Flow of concrete mixture – 60–140 mm (flow table)

Final setting time of PPC – 0.5–2 hours

Initial setting time of PPC – 15–30 minutes

Light sand grading zone for RCC – Zone II

Coarse sand grading zone for plaster – Zone I

Flight height of bucket elevator – not specified

Cement content in M20 is typically 310–330 kg/m³ rather than 403 kg/m³ .

Slump for M20 is 75–100 mm, not 25–75 mm .

Maximum diameter in slabs should reference slab thickness (≤ thickness/8) rather than a fixed 8 mm.

Types of foundation in building

here are some common types of building foundations:

1. **Strip Foundations:** These are long, continuous concrete strips that support load-bearing walls. They distribute the building's load over a larger area, usually used in smaller structures.

Strip foundations are essentially long, continuous concrete structures laid horizontally beneath load-bearing walls. They serve as the primary support for these walls and help distribute the weight of the building evenly across a wider area of the ground. 

These foundations are commonly employed in smaller or medium-sized structures where the load-bearing walls aren't excessively heavy. By spreading the building's weight over a larger surface area, strip foundations help prevent excessive pressure on the soil, reducing the risk of settlement or subsidence.

Their design involves excavation of a trench to a specified depth and width along the perimeter of the building. Reinforcement bars may be added within the concrete to enhance strength. Once poured and set, these strips serve as a stable base for the walls to rest upon, ensuring the structural integrity and stability of the entire building.

2. **Raft Foundations:** Also known as mat foundations, these spread the entire building's load over the entire area of the structure. They are suitable for areas with poor soil bearing capacity.

Raft foundations, often referred to as mat foundations, are extensive concrete slabs that cover the entire footprint of a building. They're employed to evenly distribute the total load of the structure over a large surface area of the ground.

These foundations are particularly useful in areas where the soil's bearing capacity is low or inconsistent. Instead of relying on specific load-bearing points, raft foundations transmit the building's weight uniformly to the soil below, minimizing the risk of differential settlement.

Their construction involves pouring a thick concrete slab that extends beneath the entire building. This slab serves as a unified base for the entire structure, ensuring stability and preventing uneven settling, which could potentially cause structural issues. Raft foundations are commonly used in areas prone to expansive soils or where the underlying soil lacks the necessary strength to support traditional individual point-load foundations.

3. **Pile Foundations:** Utilized in areas with weak soil, these consist of long, slender columns (piles) driven deep into the ground. They transfer the load of the building to deeper, more stable soil or rock layers.

Pile foundations are a type of deep foundation system used in areas where the surface soil is unable to support a structure's weight effectively. These foundations comprise long, slender columns known as piles, which are typically made of materials like concrete, steel, or timber.

These piles are driven deep into the ground, reaching down to layers of soil or rock that can bear the building's load safely. The driving process involves specialized equipment such as a pile driver, which forces the piles into the ground until they reach the desired depth or resistance.

Once installed, the piles effectively transfer the building's weight through friction or end-bearing to the stronger and more stable strata below the weak surface soil. Pile foundations come in various types, such as friction piles (which rely on skin friction along the pile's length) or end-bearing piles (which rely on the load-bearing capacity of the material at the pile's base).

Their design and implementation require careful consideration of factors such as soil conditions, structural loads, and the type of piles best suited for the specific site. Pile foundations are highly effective in stabilizing structures, especially in areas prone to settling or where surface soil lacks the necessary strength to support conventional foundations.

4. **Trench Fill Foundations:** Similar to strip foundations, but instead of a narrow strip, the entire trench is filled with concrete, offering a more uniform support for the building.

Trench fill foundations are akin to strip foundations but with a slight difference in their design and construction. Instead of having a narrow strip of concrete supporting load-bearing walls, trench fill foundations involve excavating a wider trench along the building's perimeter that is then entirely filled with concrete.

This type of foundation provides a more uniformly distributed support for the building compared to traditional strip foundations. By filling the entire trench with concrete, it creates a broader base for the structure to rest upon, dispersing the load over a larger area of the ground.

The process begins with digging a trench that's wider than the typical strip foundation trench. Once the trench is prepared, concrete is poured to fill the entire excavated area. This poured concrete forms a continuous and solid base for the walls to be constructed upon.

Trench fill foundations are particularly suitable for situations where the load-bearing walls demand a broader base of support or when soil conditions necessitate a more uniform distribution of the building's weight. This method helps prevent differential settling and ensures greater stability for the structure.

5. **Pad Foundations:** These are individual footings that support single columns or point loads. They are often used for lighter structures or where strip or raft foundations aren't suitable.

Pad foundations, also known as isolated footings, are individual concrete structures that serve as the base support for single columns, pillars, or point loads within a building. Unlike strip or raft foundations that spread the load over a larger area, pad foundations concentrate the building's weight onto specific points.

These foundations are commonly employed in scenarios where the structure is relatively lighter or where the design or ground conditions make strip or raft foundations impractical or unsuitable. They are ideal for smaller buildings, extensions, or instances where columns support the majority of the load.

The design of pad foundations involves calculating the load-bearing capacity required to support the column or point load. A single pad foundation is typically square, rectangular, or circular in shape, matching the footprint of the supported column or load-bearing point.

During construction, a hole is excavated to the necessary depth, and then concrete is poured into the hole to form the pad. Reinforcement bars may be added within the concrete for added strength and stability.

Pad foundations effectively transfer the building load to the soil underneath, preventing excessive settlement or movement. They are versatile and practical solutions, allowing for individualized support tailored to specific structural requirements within a building.

The choice of foundation depends on factors like soil type, building design, local regulations, and environmental conditions.