Handbook on Structures with Reinforced Concrete Portal Frames (Without Cranes)

Scope of IS SP 43 (Part 43) - Portal Frames Design Handbook

This code covers the analysis and design of portal frames with the following key specifications:

• Span: Up to 30 m
• Frame Spacing: 6 m and 12 m
• Column Height: 5 m to 12.5 m (includes 0.5 m embedded length)
• Roof Slopes: 1:3, 1:4, 1:5
• Support Conditions: Fixed and hinged
• Wind Zones: I, II, III
• Seismic Zones: I to V

Key Features:

• Design based on stiffness method of analysis (computer program).
• Internal pressure/suction as per IS 875-1964 for normal permeability (±0.2).
• RCC design per IS 456-1978 using M25 (portal frames, 6m purlins) and M40 concrete (12m prestressed purlins).
• Prismatic rafters; prismatic columns for fixed base, non-prismatic for hinged.
• Includes design of purlins, cladding runners, lugs, brackets, eaves beams.
• Bracing and foundation design examples included but not typified.
• Detailed design examples provided for practical use.

Summary Table (Typical Parameters)

Design Notes:

• Column height includes 0.5 m embedment below ground.
• Use M25 concrete for portal frames and 6 m RCC purlins.
• Use M40 concrete for 12 m prestressed concrete purlins.
• Analysis considers both wind and seismic forces per relevant IS codes.

IS SP Part 43: Materials - Key Specifications & Tables

1. Material Grades

• Concrete: M25 (Characteristic compressive strength = 25 MPa)
• Steel: Fe 415 (Yield strength = 415 MPa)

2. Design Tables (Clause 4.1 & 6.5)

• Quantities of steel and concrete are tabulated for various frame types (e.g., gable frames with hinged bases).
• Example from Clause 6.5 Table for Gable Frames:

  Parameter	Value
  Column Height (H)	9.5 m
  Span	12 m
  Bays	3
  Steel Quantity (kg/m²)	4.444 to 6.079
  Concrete Volume (m³)	0.024 to 0.077
  Support Condition	Hinged Bases

3. Purlin Spacing & Numbers (Clause 6.5 & 24.0)

• Exterior and interior rafter purlins spacing varies with slope:

  Slope	Exterior Purlins	Spacing (mm)	Interior Purlins	Spacing (mm)
  1:3	6	1306	5	1416
  1:4	6	1276	5	1381
  1:5	6	1262	5	1365

4. Support Conditions

• Hinged bases for all wind and seismic zones.
• Foundation details and forces per analysis tables (e.g., Table 104, 91).

Summary Diagram: Material Specification Flow

flowchart TD
    A[Frame Type] --> B[Select Support Condition]
    B --> C[Choose Material Grade]
    C --> D[Concrete: M25]
    C --> E[Steel: Fe 415]
    B --> F[Determine Frame Dimensions]
    F --> G[Refer Design Tables for Quantities]
    G --> H[

IS SP Part 43: Loads and Load Combinations - Key Data

1. Design Ultimate Forces (Clause 9.5 & 18.0)

• Forces are tabulated for various Section Designations (A, B, C, ...).
• Parameters include:
  • Bending Moment (Hogging & Sagging) in kN·m
  • Compressive Force in kN
  • Shear Force in kN

2. Foundation Forces at Service Load Stage

• Forces due to Dead Load (DL), Live Load (LL), Wind Load (WL)
• Includes Bending Moment, Axial Force (Compressive/Tensile), Shear Force

IS SP Part 43 — Design Forces Summary

Key Tables of Design Forces (kN, kN.m)

(Values vary by span, load stage, and ultimate/service load conditions)

Design Force Types:

• Bending Moment (BM): Hogging (negative) and Sagging (positive) moments in kN·m
• Axial Force: Compressive or Tensile forces in kN
• Shear Force: In kN

Typical Load Combinations (Service Stage):

Important Notes:

• Support condition: Hinged
• Roof slopes: 1:3, 1:4, 1:5
• Frame spacing and column height vary (e.g., 6m, 12m spacing; 5m height)
• Design ultimate forces are higher than service load forces (factored loads)

Formula for Design Ultimate Forces (General):

[ \text{Design Ultimate Force} = 1.5 \times \text{DL} + 1.5 \times \text{LL} + 1.5 \times \text{WL} ]

Visualization of Force Types on a Section

flowchart LR
    A[Section] --> BM[Bending Moment]
    A --> AF[Axial Force]
   

Structural Analysis Key Data from IS SP Part 43 (1987)

1. Design Ultimate Forces (Clause 9.5, Tables 19, 20, 22)

• Parameters:

  • Span: 9.0 m
  • Frame spacing: 12.0 m
  • Column height: 5.0 m
  • Roof slopes: 1:3, 1:4, 1:5
  • Support: Hinged
  • Wind/seismic zones: All

• Design Forces at Critical Sections (kN, kN.m):

2. Foundation Forces at Service Load Stage

• DL: Dead Load, LL: Live Load, WL: Wind Load

3. Design Notes:

• Values are valid for

Design of Principal Rafters (IS SP Part 43 - Clause 6.4.1 & Related)

Given:

• Cross-section: 400 mm × 800 mm
• Concrete: M25
• Steel: Fe 415
• Bar diameter: 20 mm
• Effective depth, ( d = 800 - 25 - 10 = 765 ) mm
• Factored hogging moment, ( M_u = 422 ) kN·m (from Table 11)

Key Formula for Flexural Design:

[ M_u = 0.36 f_{ck} b x_u (d - 0.42 x_u) ]

Where:

• ( f_{ck} ) = characteristic compressive strength of concrete (25 MPa)
• ( b ) = width of rafter = 400 mm
• ( d ) = effective depth = 765 mm
• ( x_u ) = depth of neutral axis (to be found iteratively or from IS 456/ SP:16 Table D)

From SP:16 Table D (for Fe 415 & M25):

Use these to find required steel area ( A_s ):

[ A_s = \frac{M_u \times 10^6}{0.87 f_y (d - 0.42 x_u)} ]

Purlin Spacing & Number (Clause 6.5 & 12.5)

Design of Columns as per IS SP Part 43 (Summary)

1. Column Dimensions & Heights

• Typical column sizes: 300 × 400 mm
• Column height includes 0.5 m embedded below ground
• Heights vary with span (e.g., 5.0, 6.5, 9.5 m for spans 9m, 12m, 18m)

2. Support Conditions

• Columns designed for Fixed and Hinged supports
• Design forces differ based on support type

3. Design Forces (Clause 6.5, Table 57 & 82)

• Forces vary with wind/seismic zones I to V and frame spacing (6m or 12m)

4. Key Formula for Ultimate Moment (Example)

[ M_u = 1.4 \times 6 \times 8.52 \times 8 \times 1.5 = 113.8 \text{ kN·m} ]

5. Design Checks

• Axial load + bending moment combined design per IS 456
• Shear design as per IS 456 or relevant clauses
• Use interaction curves for combined axial and bending

Quick Reference Table: Column Design Forces for Span 18m, Frame Spacing 6m, Hinged Support

IS SP Part 43: Bracing and Stability - Key Points & Formulas

1. Purpose of Bracing (Clause 5.4)

• Bracing ensures longitudinal stability against wind forces on gable ends and roof drag.
• Provided at rafter level and between columns in vertical planes.
• Usually placed at end bays, and intermediate bays if building length is large.
• Bracing members can be steel or concrete.

2. Design Parameters

• Horizontal forces depend on:
  • Gable end area
  • Roof surface area
  • Wind zone (I, II, III)
• Bracing design varies with:
  • Building length, span, spacing, height, wind zone.
• No fixed typification due to variability.

3. Bracing Types (Clause 39.4)

• Compression diagonal
• Tension diagonal
• Vertical bracing

4. Typical Bracing Spacing & Frame Details (Clause 6.0)

5. Basic Wind Force Calculation (for bracing design)

[ F_w = C_s \times A \times P ]

Where:

• (F_w) = total horizontal wind force on bracing (N)
• (C_s

Foundation Forces per IS SP Part 43 (Clause 9.5 & 4.1.2)

Key Points:

• Foundation design uses axial force, bending moment, and shear force at service (working) load stage.
• Ultimate design forces are provided for different sections (A to E) and support conditions.
• Forces vary by load types: Dead Load (DL), Live Load (LL), Wind Load (WL).
• Design tables provide hogging/sagging moments, compressive/tensile axial forces, and shear forces.

Typical Design Forces Table Format (Example: Section A)

Important Notes:

• Ultimate forces are higher and used for strength design.
• Service load stage forces are used for foundation bearing capacity checks.
• Foundation design must consider support conditions and wind/seismic zones.
• IS SP 43 tables (e.g., Tables 19, 20, 22, 86) list detailed forces for each section.

Summary Formulae for Foundation Design:

• Factored Axial Load:
  ( N_u = \sum \gamma_i N_i )
  Where (\gamma_i) = load factor, (N_i) = axial loads from DL, LL, WL.

• Factored Bending Moment:
  ( M_u = \sum \gamma_i M_i )

• Shear Force:
  Consider max shear (V_u) from combined loads.

flowchart TD
    A[Load Types: DL, LL, WL] --> B[Calculate Service Load Forces]
    B --> C[Determine Axial Forces (Comp/Tensile)]
    B --> D[Determine Bending Moments (Hogging/Sag

IS SP:43 Part 43 (1987) - Detailing Requirements for Precast Structures (12.0 m Span)

Key Detailing Specifications:

• Eaves Beam Reinforcement:

  • Provide 8#ST stirrups @ 100 mm spacing or at H/6 or effective depth (d), whichever is greater.
  • ST = Stirrups; d = Effective depth.

• Development Length (Ldt):

  • As per IS 456 and IS 13920 for tension bars ensuring ductility.

• Holes for Handling:

  • Indicated holes for transportation and erection as per Drg. No. 149 & 150.
  • Distances 'a' and 'b' for holes refer Table No. 141.

• Connections:

  • Use mechanical connections (pins, lifting eyes, cast-in studs) for slender units (Drg. No. 151).
  • Lap welding of longitudinal reinforcement in rafters with M.S. cover plates (Drg. No. 153).

• Bracing Details:

  • Steel bracing with gusset plates and back-to-back ISAs (Drg. No. 155).
  • RCC bracing details also provided.

Typical Reinforcement Detailing Formula:

Summary Table for Purlin & Rafter Spacing (Example from Clause 6.20 & 6.5)

IS SP 43 (S & T):1987 — Key Points for Precast & Cast-in-Situ Construction

1. Precast Eaves Beams (12.0 m span) — Clause 12.0 (b)(ii)

• Stirrups spacing:
  [ \text{Spacing} = \max\left(\frac{H}{6}, D\right) ] Where:
  • (H) = Overall depth of beam
  • (D) = Effective depth
  • Use 8#ST stirrups at spacing ≤ 100 mm or > 100 mm as per design
• Refer Drawing No. 149 for ductility detailing.

2. Joint & Lifting Details

• Holes for transportation & erection as per Drawings No. 149, 150.
• Use through holes for pins and lifting eyes/cast-in studs for safe handling (Drawing No. 151).
• Refer to Table No. 141 for distances 'a' and 'b' related to hole locations.

3. Precast Column to Cast-in-Situ Foundation (Drawing No. 152)

• Use cement mortar 1:3 grout for bedding.
• Reinforcement: 4-12#4 or 6-12#4 bars depending on fixed or hinged base.

4. Rafter Connections (Drawing No. 153)

• Lap weld longitudinal reinforcement bars.
• Use M.S. cover plates and rods welded for mechanical connections.
• Concrete grade: M25 for in-situ joints.

5. Bracing Details (Drawings No. 154, 155)

• Steel bracing: Use M.S. plates (e.g., 150x70x10 mm), L-angles, gusset plates (10 mm thick).
• RCC bracing details also provided for stability.

6. General Guidelines (Clause 5.1)

• Joint location and detailing critical for full moment and shear capacity development.
• Consider crane lifting capacity and erection methods in design.

Summary Table: Stirrup Spacing for 12m Span Eaves Beam

IS SP Part 43 - Key Formulas & Tables for Roof Slopes and Frame Spacing

1. Roof Slopes (Clause 6.5)

• Standard roof slope:
  [ \text{Slope} = \frac{1}{3} \approx 18.435^\circ ]
• Other slopes considered: 1 in 4, 1 in 5.

2. Frame Spacing (Clause 6.0)

• Typical frame spacing: 6.0 m and 12.0 m.
• Spans considered: 9.0 m, 12.0 m, 18.0 m, 24.0 m, 30.0 m.
• Column heights: 5.0 m, 6.5 m, 9.5 m, 12.5 m.
• Support types: Fixed and Hinged.
• Wind zones: I, II, III.
• Seismic zones: I to V.

3. Purlin Number and Spacing (Fixed Support, All Wind/Seismic Zones)

• H1, H2: Heights related to column and frame geometry.
• R: Ridge height.

4. Additional Notes

• Distance of nearest purlin lug from:
  • External column face = 100 mm
  • Ridge =

IS SP 43 Part 43: Support Conditions Summary

Key Support Conditions (Clause 6.5 & 9.5):

• Support Types:

  • Fixed Support: For all wind and seismic zones (typical for columns with heights 5.0m to 6.5m)
  • Hinged Support: For taller columns (e.g., 9.5m height) in wind/seismic zones

• Materials:

  • Concrete: M25
  • Steel: Fe 415

Typical Parameters (Referencing Tables 66, 68, 69, 80, 104)

Purlin Layout (No. & Spacing)

Important Notes:

• All dimensions in mm.
• For foundation forces, refer to respective Analysis Tables (66, 69, 80, 104).
• Support conditions are designed considering all wind and seismic zones.
• Typical three-link extra details and reinforcement bars (e.g., 1-16#07) are specified per drawing/table.

IS SP Part 43 – Examples and Illustrative Designs: Key Points

• Design Tables (Clause 4.1):
  Provide bending moments, shear forces, and axial forces at critical sections of portal frames and at foundation level.
  These tables allow adaptation for different materials (e.g., M20 concrete) or slight section dimension changes, provided the section properties (area, moment of inertia) do not vary significantly.

• Design Drawings (Clause 4.2):
  Detailed drawings ready for fabrication and erection based on fixed assumptions of material and section properties.

• Usage:

  • Use tables for preliminary design or when deviating from base assumptions.
  • Adopt drawings directly when assumptions match.

Typical Design Parameters Covered:

• Frame span and height
• Section dimensions (beam, column)
• Material properties (concrete grade, steel grade)
• Load combinations

Example Table Format (simplified):

Design Adaptation Formula:

If using alternate section with properties ( A' ), ( I' ), approximate moments and forces can be scaled as:

[ M' \approx M \times \frac{I'}{I}, \quad V' \approx V \times \frac{A'}{A}, \quad N' \approx N \times \frac{A'}{A} ]

Where:

• ( M, V, N ) = original moment, shear, axial force
• ( A, I ) = original section area, moment of inertia
• ( A', I' ) = new section area, moment of inertia

flowchart LR
  A[Extensive Analysis] --> B[Design Tables]
  A --> C[Design Drawings]
  B --> D[Preliminary Design]
  C --> E[Fabrication & Erection]
  D -->|Adjust for material/section| F[Modified Design]

Summary: IS SP Part 43 provides detailed design tables and drawings for portal frames

IS SP Part 43 - References and Appendices Key Points

1. Design Tables (Clause 4.1)

• Frame spacing: 6.0 m and 12.0 m

• Roof slopes: 1 in 3, 1 in 4, 1 in 5

• Span and column height combinations:

  Span (m)	Column Height (m)	Bays (1 to 4)
  9.0	5.0, 6.5	Available
  12.0	5.0, 6.5, 9.5	Available
  18.0	6.5, 9.5, 12.5	Available
  24.0	9.5, 12.5	Limited
  30.0	9.5, 12.5	Limited

• Support types: Fixed and hinged

• Wind zones: I, II, III

• Earthquake zones: I to V

2. Design Specifications

• RCC design per IS 456-1978, using:
  • M25 concrete for portal frames and 6m span purlins
  • M40 concrete for 12m span prestressed purlins
• Portal frames use prismatic rafters; columns are prismatic if fixed base, non-prismatic if hinged.
• Internal pressure/suction per IS 875-1964 considered.
• Analysis via stiffness method computer program.

3. Design Forces (Sample from Table 19)

4. Estimation of Materials (Sample from Clause 6.5)

• Steel and