Handbook on Structures with Steel Lattice Portal Frames (Without Cranes)

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Load Considerations from IS SP 47 (S&T) : 1988 & IS 875:1964

1. Live Load (I.L) Calculation (Clause 58.13):
[ \text{Live Load} = 58.13 \times \frac{2}{3} \times 6 = 232.52 \text{ kg/m} = 2350 \text{ N/m (approx.)} ]

2. Basic Wind Load (Note 3(a), IS 875:1964):
[ P = 0.75 \times 100 \times 6 = 450 \text{ kg/m} = 4500 \text{ N/m} ]

Key Wind Load & Foundation Forces Tables (Selected Extracts)

IS SP 47 (S&T) : 1988 provides detailed analysis and design guidance for Steel Lattice Portal Frames (without cranes). Below are key points and formulas:

1. Design Load Combination

• For Dead Load (DL) + Wind Load (WL), multiply design forces by 1.33 to account for increased allowable stresses:

  [ F_{design} = 1.33 \times (DL + WL) ]

2. Typical Frame Geometry (Clause 6.0)

• Column Height (H): 6.0 m
• Frame Spacing (S): 6.0 m
• Lacing Sections: Commonly 40×40 mm or 60×60 mm angles with 6 mm thickness
• Lacing Spacing: As per design tables, typically between 500 mm to 900 mm depending on member size and buckling length

3. Structural Analysis Notes

• Use moment distribution or matrix stiffness methods for frame analysis.
• Lattice members are designed for axial forces; bending moments in chords are generally small.
• Stability is ensured by proper lacing spacing and member sizing.

4. Sample Table Extract (Lacing Section & Spacing)

5. Design Checks

• Axial Load Capacity:

  [ P_u = A \times f_y / \gamma_m ]

  Where:

  • (A) = Gross cross-sectional area
  • (f_y) = Yield strength
  • (\gamma_m) = Partial safety factor (typically 1.5)

• Buckling Check:

  [ \sigma_{design} \leq \frac{f_y}{\text{Buckling Reduction Factor}} ]

6. Visualization of Lattice Portal Frame

graph TD
    A[Base Plate] -->|Column 6m|

IS SP 47 (S&T): 1988 - Design of Steel Lattice Portal Frame Members

Key Notes (Clause 1.33)

• For DL + WL load combination, multiply design forces by 1.33 to account for increased allowable stresses.
• For DL + W'L combination, multiply design forces by 1.33 similarly.
• For other combinations, multiply by 1/1.33 as applicable.

Member Design Parameters (From Tables 12, 15, 17)

Design Force Adjustment Formula

[ F_{design} = F_{analysis} \times 1.33 \quad \text{(for DL + WL or DL + W'L)} ]

[ F_{design} = \frac{F_{analysis}}{1.33} \quad \text{(for other combinations)} ]

Typical Member Section Selection (Example for 1/3 Roof Slope, 150 kg/m² Wind)

Key Specifications for Eaves Beam Design (IS SP Part 47)

Clause 5.6 Highlights:

• Eaves beams run along the building length at stanchion-rafter junctions.
• Maximum slenderness ratio ≤ 250.
• Recommended sections:
  • ISMB 200 for frame spacing 4.5 m.
  • ISMB 250 for frame spacing 6.0 m.
• Connection: One ISA 90×90×6 web framing angle with 3 or 4 numbers of 16 mm dia block bolts.
• Eaves beams can be hot-rolled or built-up lattice sections.

Slenderness Ratio Formula:

[ \text{Slenderness Ratio} = \frac{l}{r} \leq 250 ]

• (l) = effective length of beam (mm)
• (r) = radius of gyration of the section (mm)

Typical Eaves Beam Section Selection:

Load & Moment Data (Example from Clause 9.0 for 9m span, 4.5m spacing):

IS SP 47 (S&T) - Foundation Forces and Design Key Points

Foundation Forces (Clause 4.1)

• Forces due to Dead Load (DL), Live Load (LL), and Wind Load (WL) are presented separately.
• Two base conditions:
  • Fixed base: Use only if foundation ensures fixity (e.g., stiff soil with isolated footing).
  • Hinged base: For foundations not providing fixity.
• Design forces can be combined for Working Stress or Limit State Design.
• When using DL + WL, multiply forces by 1.33 (Clause 1.33) to increase allowable stresses.

Foundation Design Types

• Spread footings, pile foundations, or caisson foundations depending on soil and support conditions.
• Typical foundation design shown in Clause 6.

Tables for Foundation Forces

• Tables 25 to 48: Critical foundation forces for various frame configurations.
• Tables 50 to 73: Design results including member sizes, depths, and weights for different spans, heights, slopes, wind zones, and support conditions.

Typical Formula for Foundation Design Forces Combination:

[ F_{design} = 1.33 \times (DL + WL) \quad \text{(if DL + WL governs)} ]

Summary Table Extract (Example from Tables 25-48):

Conceptual Diagram of Load Transfer to Foundation

flowchart TD
    A[Dead Load (DL)] --> F[Foundation]
    B[Live Load (LL)] --> F
    C[Wind Load (WL)] --> F
    F --> G[Soil Bearing]

Note: Refer to IS SP 47 Tables 25-73 for precise force values and member sizing based on your frame parameters.

Wind Load Conditions & Effects (IS SP 47)

Key Parameters (Clause 18.435)

Typical Wind Load Effects (from Clause 12.0 & 18.0 Tables)

Note: Negative axial indicates compression.

Wind Load Calculation Formula (General IS Code Practice)

[ P = 0.6 \times V^2 \times C_d \times C_e \times C_s ]

Where:

• (P) = Wind pressure (N/m²)
• (V) = Basic wind speed (m/s)
• (C_d) = Drag coefficient (depends on shape)

Earthquake Load Considerations — IS SP 47 (S&T) : 1988

Key Points:

• IS SP 47 primarily provides wind and load effects on lattice portal frames; earthquake loads are considered similarly as lateral loads.
• Design forces for DL + WL are multiplied by 1.33 to account for increased allowable stresses (Clause 1.33).
• Earthquake load effects can be approximated by equivalent lateral forces similar to wind loads but adjusted per seismic zone and dynamic factors (refer IS 1893 for seismic coefficients).

Typical Load Parameters from SP 47 Tables (for portal frames):

Earthquake Load Estimation (General):

• Use Equivalent Lateral Force Method (IS 1893):

  [ F = \alpha \times W ]

  Where:

  • ( F ) = design lateral force
  • ( \alpha ) = seismic coefficient (depends on seismic zone, soil, importance factor)
  • ( W ) = seismic weight of the structure

• Apply forces at column bases and joints similar to wind loads in SP 47 tables.

Design Recommendations:

• Use SP 47 load tables for axial, shear, and moment under lateral loads.
• Multiply DL + WL forces by 1.33 for stress increase (Clause 1.33).
• Refer to IS 1893 for seismic coefficients and dynamic factors.
• Consider frame slope and span effects on lateral forces (see tables in Clauses 9.0, 12.0, 18.0).

graph LR
A[Seismic Weight (W)] --> B[Seismic Co

IS SP 47 (S&T): 1988 — Allowable Stresses & Load Combinations

Key Points from Clause 1.33:

• When design is governed by Dead Load (DL) + Wind Load (WL), multiply design forces by 1.33 to increase allowable stresses.

Allowable Stress Checks (Combined Axial & Bending):

For axial compression + bending:

[ \frac{f_u}{F_c} + \frac{M_c}{F_{be} Z} \leq 1.0 ]

For axial tension + bending:

[ \frac{f_u}{F_u} + \frac{M_t}{F_{be} Z} \leq 1.0 ]

Where:

• ( f_u ) = actual axial compressive/tensile stress
• ( F_c, F_u ) = allowable stresses under axial compression/tension
• ( F_{be} ) = allowable bending stress
• ( M_c, M_t ) = bending moments with compression/tension
• ( Z ) = section modulus

Load Combination Factor:

Summary Table (Allowable Stresses):

flowchart LR
    A[Design Forces] --> B{Load Combination?}
    B -->|DL + WL| C[Multiply forces by 1.33]
    B -->|Others| D[Use forces as is]
    C --> E[Check Allowable Stresses]
    D --> E
    E --> F{Stress Check}
    F -->|Axial Compression + Bending| G[\( \frac{f_u}{F_c} + \frac{M_c}{F_{be} Z} \leq 1 \)]
    F -->|Axial Tension + Bending

IS SP 47 (S&T) : 1988 – Connection Details Summary

1. Haunch and Crown Connections (Clause 5.2.2, Table 75)

2. Lacing Connection Details (Table 74)

• Rod Lacing Sizes: 8mm to 18mm diameter rods.
• Angle Lacing Sizes: 4040 × 6 mm to 110110 × 10 mm.
• Fillet Weld Sizes: 3 mm to 6.5 mm with lengths proportional to member size.
• Gusset Plate Thickness: 8 mm to 12 mm depending on lacing size.

3. Base Plate Connection Details (Table 76)

IS SP 47 (S&T) - Design Examples Key Points

1. Design Force Adjustment (Clause 1.33)

• When design is controlled by Dead Load (DL) + Wind Load (WL), multiply design forces by 1.33 to account for increased allowable stresses.

  [ F_{design} = 1.33 \times (DL + WL) ]

2. Design Tables (Clause 3.3.4)

• Tables 50 to 73 provide design results for lattice portal frames:
  • Varying span, length, column height, frame spacing
  • Two support conditions: hinged & fixed
  • Three roof slopes and wind zones
• Tables include:
  • Overall depth & width of lattice members
  • Sizes of corner legs and intersections
  • Total frame weight per unit area (excluding purlins, bracings)

3. Sample Table Format (from Table 17)

4. Foundation Forces

• Use the multiplied design forces (DL + 1.33WL) for foundation design.

Summary for Practical Use:

• Multiply DL + WL by 1.33 for design forces.
• Refer to Tables 50-73 for member sizing and forces based on span, slope, and wind zone.
• Use given member depths, moments, axial forces, and weights for design checks.
• Foundation forces are derived from these amplified loads.

flowchart TD
    A[Loads: DL + WL] --> B[Multiply by 1.33]
    B --> C[Design Forces]
    C --> D[Select Table (50-73) based on span, slope, wind zone]
    D --> E[Member sizes, moments, axial forces]
    E --> F[Design Members & Foundation]

This approach ensures safe and optimized lattice portal frame design per IS SP 47

Development Length of Anchor Bolts (IS SP Part 47)

From the provided context:

• Clause 133.4:
  Development length required = (133.4 , \text{N/mm}^2 \times 24 , \text{mm} = 601 , \text{mm})
  (Here, 24 mm is likely the bolt diameter or an effective length parameter.)

• Anchor Bolt Specification:

  • Use 12 bolts of 20 mm diameter for anchorage as per Clause 5.3 and Table 76.
  • Bolt diameter (d = 20 , \text{mm})
  • Development length (l_d = 601 , \text{mm}) (minimum embedment length into concrete for full strength)

• Base Plate & Anchorage:
  Design must ensure that the anchor bolts develop the required tensile strength without pullout or yielding, considering forces from DL + LL and DL + WL cases.

Summary Table

Key Formula for Development Length (Generalized)

[ l_d = \frac{T_{bolt}}{\tau_{concrete} \times \pi \times d \times \text{embedment depth}} ]

Where:

• (T_{bolt}) = tensile force in bolt
• (\tau_{concrete}) = allowable shear stress of concrete (e.g., 133.4 N/mm² here)
• (d) = bolt diameter

flowchart TD
    A[Anchor Bolt] --> B{Development Length}
    B --> C[Embedment in Concrete]
    B --> D[Base Plate Connection]
    C --> E[Resists Tensile Force]
    D --> F[Transfers Load to Foundation]

Note: Always verify development length with actual forces and concrete strength per IS 456 and IS 800 for steel-concrete interaction.

IS SP Part 47: Key References Summary

The code provides detailed tables for steel lattice portal frames without cranes, covering various parameters:

1. Frame Parameters (Clauses 1.7, 4.5, 9.0, 24.0)

• Span: 9 m to 24 m
• Column Height: 4.5 m to 9.0 m
• Frame Spacing: Typically 4.5 m
• Roof Slopes: 1/3, 1/4, 1/5
• Basic Wind Pressure: 100, 150, 200 kg/m²

2. Member Forces and Moments

• Compression and Tension Forces (kN)
• Moments at Haunch, Base, Crown (kN·m)
• Shear Forces (kN)
• Sway (cm)

3. Typical Data from Tables

4. Design Notes:

• Use fixed or hinged base conditions as specified.
• Forces and moments vary with wind pressure and roof slope.
• Sway values indicate lateral displacement under load.

Formula for Wind Load on Frame (IS 875 Part 3):

[ W = p_z \times A ]

• (W) = Wind force (kN)
• (p_z) = Design wind pressure (kN/m²)
• (A) = Projected area (m²)

Visualization: Frame Load Components

graph TD
    A[Wind