Code of practice for construction with large panel prefabricates

IS 11447: Scope - Key Specifications & Symbols

This standard defines letter symbols and tolerances for plain and reinforced concrete structural elements.

Key Letter Symbols (Clause 3.1)

Permissible Tolerances (Clause 4.3.1)

• Length/Breadth: ±0.1% (max +5 mm or -10 mm)
• Thickness: ±2 mm (up to 300 mm), ±3 mm (>300 mm)
• Bow to straightness: 1/750th of larger dimension (max +5 mm)
• Squareness: Max +2 mm / -5 mm deviation at ends (Fig. 2)
• Twist in plane: Max ±1/500th dimension or ±5 mm (smaller value) (Fig. 3)

Summary Diagram of Tolerances

graph LR
A[Length/Breadth] -->|±0.1%| B[Max +5mm/-10mm]
C[Thickness] -->|±2mm (≤300mm)| D[±3mm (>300mm)]
E[Bow to Straightness] -->|1/750th| F[Max +5mm]
G[Squareness] -->|+2mm/-5mm| H[At ends]
I[Twist in Plane] -->|±1/500th or ±5mm| J[Smaller value applies]

This scope ensures consistent definitions and acceptable dimensional tolerances for concrete elements, critical for design accuracy and quality control.

IS 11447: Definitions and Symbols (Clause 3.1) - Key Points

Important Formulas (Selected)

• Load Bearing Capacity of Plain Concrete Walls:

[ R = f_{ck} \times A_w \times Q \times Y_m ]

Where:

• ( R ) = Load bearing capacity

• ( f_{ck} ) = Characteristic compressive strength

• ( A_w ) = Area of wall panel

• ( Q ) = Coefficient (from Table 1)

• ( Y_m ) = Partial safety factor for material

• Coefficient (K_1) for Wall Panels Stiffened Along Edges:

[ K_1 = \begin{cases} 1.0 & \text{if } l_w < b_w \ 1.0 & \text{if } b_w < l_w < 2b_w \ 1.4 - 0.4 \frac{l_w}{b_w} & \text{if } l_w > 2b_w \end{cases} ]

IS 11447: Materials and Concrete Strength Requirements

Key Concrete Strengths

• Reinforced Concrete Floors: Minimum grade M20.
• Prestressed Concrete Floors:
  • Post-tensioned: Minimum M35
  • Pretensioned: Minimum M40
• Concrete Panels with Deformed Bars: Lower strength may be allowed with designer approval.
• Filler Blocks (Cellular/Clay): Minimum strength 5 N/mm².

Symbols (Selected)

Load Bearing Capacity (Plain Concrete Walls)

[ R = f_{ck} \times A_w \times Q \times \gamma_m ]

• (R): Load-bearing capacity
• (f_{ck}): Characteristic compressive strength
• (A_w): Cross-sectional area
• (Q): Coefficient from Table 1 (depends on panel geometry)
• (\gamma_m): Partial safety factor for material

Coefficients for Wall Panels (K1)

• For panels stiffened along one vertical edge:

  • (K_1 = 1.0) when (l_w < b_w)
  • (K_1 = 1.4 - 0.4 \frac{l_w}{b_w}) when (b_w < l_w < 2b_w)
  • (K_1 = \sqrt{1 + 0.5 \frac{l_w}{b_w}}) when (l_w > 2b_w)

• For panels stiffened along both edges:

  • (K_1 = 1.0) when (l_w < 0.5 b_w)
  • (K_1 = 1.5 - \frac{l_w}{b_w}) when (0.5 b_w < l_w \leq b_w)
  • (K_1 = 1 + \left(\frac{b_w}{l_w

IS 11447: Structural Requirements & Design Principles - Key Points

1. Symbols & Dimensions (Clause 3.1)

• b = Breadth of beam/shorter column dimension
• D = Overall depth of beam/slab or column dimension
• d = Effective depth of beam/slab
• bf, bw = Effective flange/web widths
• fck = Characteristic compressive strength of concrete
• fy = Characteristic strength of steel
• M = Bending moment
• V = Shear force
• La = Development length
• LL, WD = Live load, Dead load
• Z = Section modulus
• m = Modular ratio (Es/Ec)

2. Structural Requirements (Clause 4.9.5)

• Tie-beams required along external edges (vertical & horizontal) for prefabricate interaction.
• Floor and wall panels must have keys and continuous reinforcement.
• Minimum reinforcement in tie-beams: 4.0 cm³.
• Connections by loops or welding; no overlapping.

3. Design Principles (Clause 5.1)

• Design for limit state of collapse ensuring:
  [ \text{Design Strength} \geq \text{Design Load} ]
• Use characteristic values & partial safety factors per IS 456:1978.
• Additional safety factors (Y_s) applied for wall panels.

4. Earthquake & Diaphragm Action (Clause 4.9.6)

• Follow IS 1893 (Part 1): 2002 and IS 4326:1993 for earthquake resistance and diaphragm action.

Typical Design Formulae (from IS 456 & IS 11447 context):

• Flexural Strength:
  [ M_u \leq 0.87 f_y A_{st} (d - d') ]

• Shear Strength:
  [ V_u \leq V_c + V_s ]

• Modular Ratio:
  [ m = \frac{E_s}{E_c} ]

Diagram: Tie-beam & Panel Connection Concept

IS 11447: Building Stability & Safety Checks - Key Points

1. Stability Systems (Clause 4.1.2)

• Stability ensured by frames, shear walls, shear cores, or other systems.
• Shear walls should be evenly distributed vertically & horizontally to reduce torsion.
• Shear walls must extend from foundation to top to avoid floor torsion.

2. Loads for Stability (Clause 5.2)

• Consider lateral loads: wind (IS 875-1964) & earthquake (IS 1893-1975).
• Base shear ( V_b ) from IS 1893-1975 increased by 5% per storey beyond 5th, max 25%.

[ V_b = V_{base} \times \left(1 + 0.05 \times \text{(storeys - 5)}\right) ]

3. Tie-Beams & Connections (Clause 4.9.5)

• Tie-beams along external edges vertically & horizontally.
• Minimum reinforcement in tie-beams: 4.0 cm³.
• Connections by loops or welding, no overlapping.

4. Important Symbols (Clause 3.1)

5. Stability Check Summary

• Use shear walls/cores + horizontal diaphragms for lateral load resistance.
• Calculate lateral forces per IS 875 & IS 1893.
• Increase earthquake base shear for tall buildings.
• Provide continuous tie-beams with minimum reinforcement.
• Ensure proper connections with welding/loops.

flowchart TD
    A[Building Stability] --> B[Frames]
    A --> C[Shear Walls]
    A --> D[Shear Cores]
    B & C & D --> E[

IS 11447: Permissible Tolerances for Prefabricated Panels

Key Tolerances as per Clause 4.3.2 (Erection Tolerances):

Notes:

• These tolerances ensure proper fit and structural integrity during erection.
• Accumulated deviations should be controlled to avoid misalignment over larger panel assemblies.
• Always verify tolerance compliance during site inspection.

flowchart TD
    A[Prefabricated Panels] --> B[Level Differences ±5mm]
    A --> C[Plumb Lines ±5mm]
    A --> D[Bearing ±5mm]
    A --> E[Joint Dimensions ±5mm]
    A --> F[Accumulated Deviation ≤ ±20mm]

This concise table and diagram summarize the permissible erection tolerances critical for quality control in large panel prefabricated construction.

IS 11447: Key Points on Floor Panel Design and Construction

1. Floor Panel Types & Thickness (Clause 4.9.2)

• Use solid concrete panels in high seismic zones.
• For ribbed panels:
  • Flange thickness ≥ 50 mm.
  • Joints only between ribs.
• Continuous reinforcement over supports:
  • Projected bars top & bottom.
  • Minimum cross-sectional area: 1.5 cm²/m length.
  • Bars can be welded or loops.
• Edges have castellations for keyed joints.

2. Longitudinal Joint Design (Clause 4.4.9)

• Joints resist differential loads and shear.
• Minimum gap: 40 mm.
• Joint depth: ≥ 75% of panel thickness.
• Screeding concrete (optional) with positive joint connection or minimum reinforcement of 0.5 cm²/m.
• Joint filled with cement mortar of one grade higher strength.

3. Design Moments for Floor Panels (Clause 5.4.2)

• ( l ) = span length.
• ( q_1 ) = load before connecting reinforcement.
• ( q_2 ) = load after connecting reinforcement.
• For continuous floors with spans differing ≤15%, use longest span ( l ).

Summary Diagram: Floor Panel Joint

flowchart LR
   

IS 11447: External Wall Panel Requirements - Key Points

1. Classification & Thickness (Clause 4.5.1.1)

• External walls: homogenous or non-homogenous (sandwich or framed infill).
• Thickness depends on structural needs & water tightness.
• Sandwich panels:
  • Min. external concrete layer thickness:
    • 40 mm if movement constrained.
    • 60 mm if free movement, connected by clips allowing movement.

2. Joints (Clauses 4.6.1 & 4.8)

• Joints must resist forces without excessive deformation/cracking.
• Accommodate dimensional deviations during production/erection.
• Horizontal joint load-bearing capacity may require empirical determination if not per Table 2.
• For battery moulds with external vibrators, reduce R in Eq. 22 by 10%.

3. Structural Design - Zone 1 (Clause 5.5.2)

• Wall supported on horizontal edges or vertical edges (Fig. 18).
• Eccentricity for external walls: [ e = 0.20 \times t_w, \quad \text{max } 30 \text{ mm} ]
• Eccentricity for internal walls: [ e = 0.15 \times t_w, \quad \text{max } 20 \text{ mm} ]
• Effective height of wall: [ l_{wd} = K_1 \times l_w ] where (K_1) depends on stiffening along vertical edges.

4. Stiffening (Clause 5.5.2b)

• Wall edge stiffened if connected to perpendicular stiffener ≥ ¼ panel depth.
• Stiffening reduces effective height, improving stability.

Summary Table: Minimum Thickness for Sandwich Panels

flowchart LR
    A[External Wall Panel] --> B{Type}
    B --> C[Homogenous]
    B --> D[Non-Homogenous]
    D --> E[Sandwich Panel]
    D

IS 11447: Joint Design and Sealing - Key Points

1. Joint Design Requirements (Clause 4.1.5)

• Joints must accommodate shrinkage, temperature changes, and other movements.
• Vertical joints between external wall panels must ensure:
  • Water tightness
  • Structural integrity
• Consider:
  • Capillary action prevention
  • Rain pressure
  • Shrinkage allowance
  • Use of external sealants, water barriers, vertical drainage canals.

2. Joint Types and Sealing (Clause 4.6.5)

• Two main joint types:
  • Filled joints: Use flexible sealants (e.g., polysulphide compounds) to absorb cyclic movements and prevent water ingress.
  • Open joints: Must be wide enough for panel movement; may be protected or unprotected from water entry.
• Ensure continuity of waterproof membranes through joints.

3. Minimum Joint Width and Reinforcement (Clause 4.6.5)

• In-situ joints require:
  • Minimum width for concreting.
  • Loops/projecting reinforcements from side panels.
  • Vertical bars in joints.

4. Structural Joint Resistance Formula (Clause 9.5)

For grooved joints:

[ R_j = 0.02 \times O_{KC} \times (A_j + A_{ct}) ]

Where:

Typical Joint Components (Fig. 1 & 10)

• Membrane waterproofing
• Compressible packing
• Flexible sealants

flowchart LR
    A[External Wall Panels] --> B[Vertical Joint]
    B --> C{Joint Type}
    C --> D[Filled Joint]
    C --> E[Open Joint]
    D --> F[Flexible Sealant (Polysulphide)]
   

IS 11447: Tie-Beams and Connections - Key Specifications & Formulas

1. Tie-Beams Location & Purpose

• Provided at each floor level along all structural walls and building perimeter (Clause 4.7.1, 2.7).
• Ensures monolithic action of walls and floors and limits progressive collapse.

2. Reinforcement Requirements

• Reinforcement must be placed near supports/edges within 500 mm from ends (Clause 4.7.2).
• Reinforcement should be continuously connected (no lap splices; use loops or welding) (Clause 4.7.2, 4.9.5).

3. Connection Details

• Tie-beams along external edges must connect floor and wall panels with keys and continuous reinforcement (Clause 4.9.5).
• Minimum reinforcement in tie-beams and connections: 4.0 cm².
• Connections by loops or welding, not by overlapping.

Summary Formula for Minimum Reinforcement Area (As):

[ As = \begin{cases} 2.5 \text{ cm}^2 & \text{if } d \leq 4.5 \text{ m} \ 4.0 \text{ cm}^2 & \text{if } 4.5 < d \leq 6.0 \text{ m} \end{cases} ]

Where:

• (d) = distance between internal longitudinal structural walls.

flowchart LR
    A[Structural Walls] --> B[Tie-Beams at floor levels]
    B --> C[Continuous Reinforcement near supports]
    C --> D[Connections by loops/welding]
    D --> E[Monolithic action of walls

IS 11447: Loads and Structural Analysis - Key Points

1. Symbols & Parameters (Clause 3.1)

• b = Breadth of beam or shorter side of rectangular column
• bw = Breadth of web or rib
• D = Overall depth of beam/slab or diameter of column
• d = Effective depth of beam/slab
• fck = Characteristic compressive strength of concrete
• fy = Characteristic strength of steel
• LL = Live load
• EL = Earthquake load
• M = Bending moment
• V = Shear force
• La = Development length
• K = Stiffness of member
• Ym, Yl = Partial safety factors for material and load

2. Load Considerations (Clause 5.2)

• Wind and earthquake loads per IS 875-1964 and IS 1893-1975 respectively.
• Increase earthquake base shear by 5% per storey beyond 5th storey, max 25%.

3. Load Bearing Capacity for Walls

• Plain concrete walls:

[ R = 0.4 \times f_{ck} \times A_w / \gamma_m ]

Where:

• (R) = Load bearing capacity

• (A_w) = Cross-sectional area of wall

• (\gamma_m) = Partial safety factor for material

• Reinforced concrete walls: As per IS 456-1978 with strength reduction factors.

4. Effective Width of Wall Panels (bw)

• (bw = lw) if panel stiffened along vertical edge
• (bw = 1.0,m) if unstiffened
• (bw) < width of strips between openings

5. Tie Beams & Connections (Clause 4.9.5)

• Tie beams along edges with minimum 4 cm³ reinforcement.
• Connections by loops or welding, not overlapping.

Summary Table: Load Bearing Capacity of Plain Concrete Walls

IS 11447: General Load Design Principles - Key Formulas & Specs

1. Load Factors (Clause 1.05)

• Design Dead Load (D):
  [ D = 0.95 F_d \quad \text{or} \quad 1.05 F_d ]
• Design Imposed Load (I):
  [ I = 0.35 F_i \quad \text{or} \quad 1.05 F_i \quad \text{(for permanent imposed loads)} ]
• Design Wind Load (W):
  [ W = 0.35 F_w ] Where (F_d, F_i, F_w) are characteristic dead, imposed, and wind loads respectively.

2. Load Distribution on Floor Panels (Clause 5.4.4)

• Load on panel (W_1) calculated as:
  [ p = \text{load other than dead load} ] [ W_1 = p \times \frac{x_i}{\sum x_i} ] where (x_i) = percentage load transferred by the panel.

3. Wall Panel Stiffness Factor (K_1) (Clause 1.0)

• For panels stiffened along one vertical edge: [ K_1 = 1.0 \quad \text{if } l_w < b_w ] [ K_1 = 1.0 \quad \text{if } b_w < l_w < 2 b_w ] [ K_1 = 1.4 - 0.4 \frac{l_w}{b_w} \quad \text{if } l_w >

IS 11447: Wind and Earthquake Load Considerations

1. Wind and Earthquake Loads

• Use IS 875 (Part 3) - 1964 for wind loads.
• Use IS 1893 - 1975 for earthquake loads.
• For earthquake base shear, increase by 5% per storey beyond 5th storey, max 25%.

2. Panel Stiffness Factor (K1)

For panels stiffened along vertical edges:

For panels stiffened on both edges:

(lw = length of wall panel, bw = breadth of wall panel)

3. Load Bearing Capacity (Plain Concrete Walls)

[ R = O k_c A_w Q Y_m ]

• (O, k_c, Q, Y_m) = coefficients/factors per IS 11447.
• (A_w) = cross-sectional area of wall panel.

For non-uniform loads (e.g., wind), assume uniformly distributed load over width (b_w):

• (b_w = l_w) if panel stiffened along vertical edge.
• (b_w = 1.0,m) if panel unstiffened.

4. Load Sharing in Open Layout Buildings

[ \text{Load on wall } i = \frac{r_i^2}{\sum r_j^2} \times \text{Total lateral load} ]

• (r_i) = distance of wall i from center of rotation.
• Use flexibility coefficients (a_i) and coordinates (x_i, y_i

Serviceability and Deflection Checks (IS 11447: Clause 5.4)

Key Points:

• Deflection checks are essential at the serviceability state to avoid cracking in walls, cladding, and finishes.
• Allowable deflections and span-to-depth ratios must comply with IS 456-1978.
• Load distribution for deflection checks is given in Fig. 17 (serviceability state), where load sharing among floor panels depends on the number of panels (n).

Load Distribution for Deflection (Serviceability State)

• Load on considered panel (W_1) is calculated as:

[ W_1 = p \times \frac{x_i}{\sum_{i=1}^k x_i} ]

where:

• (p) = load other than dead load,
• (x_i) = percentage load transferred by the panel,
• (k) = number of panels.

Span-to-Depth Ratio (IS 456-1978 Reference)

Deflection Formula (Approximate)

For simply supported beams/slabs under uniform load (w):

[ \delta_{max} = \frac{5 w L^4}{384 E I} ]

• (w) = load per unit length,
• (L) = span,
• (E) = modulus of elasticity,
• (I) = moment of inertia.

Summary Diagram of Load Distribution for Deflection Check

graph LR
A[Load on Panel 1] -->|60%| B[Panel 1]
A -->|25%| C[Panel 2]
A -->|10%| D[Panel 3]
A -->|5%| E[Panel 4]

References:

• IS 11447

IS 11447 – Accidental Forces & Progressive Collapse Prevention

Key Points from Clauses:

• Clause 5.6.1: Structures must resist accidental loads beyond normal use without disproportionate collapse.
• Clause 2.8: Progressive collapse is triggered by local failure causing widespread failure over multiple floors.
• Design should ensure residual stability after loss of a load-bearing element.
• Use tensile ties or alternative methods to prevent collapse spread.

Design Concepts & Specifications:

Typical Design Approach:

1. Identify critical elements whose failure could cause progressive collapse.
2. Apply accidental load factors (often 1.5 to 2 times normal loads) on these elements.
3. Check alternate load paths to redistribute loads if an element fails.
4. Design tensile ties to transfer loads and prevent disproportionate collapse.

Formula for Alternate Load Path (Simplified):

[ P_{acc} = \alpha \times P_{normal} ]

• (P_{acc}) = Accidental load on element
• (\alpha) = Factor (1.5 to 2.0, per design judgment)
• (P_{normal}) = Normal design load

Summary Diagram:

graph LR
A[Normal Load] --> B[Critical Element]
B -->|Failure| C[Load Redistribution]
C --> D[Tensile Ties]
D --> E[Residual Stability]
E --> F[Prevent Progressive Collapse]

Recommendations:

• Follow IS 11447 Clause 5.6 for accidental load design.
• Provide adequate ductility and redundancy in structure.
• Use detailed connection design for tensile ties.
• Evaluate progressive collapse via nonlinear analysis or simplified methods.

This ensures safety against accidental forces and prevents disproportionate failure per IS 11447.