Handbook of Typified Designs for Structures with Steel Roof Trusses (With and Without Cranes) (Based on IS Codes)
1987 Edition

IS SP Part 38 is a specialized publication by the Central Public Works Department (CPWD), New Delhi, targeting focused structural engineering practices.

Highlights:

• Scope: Guidelines for design, execution, and quality assurance of specialized structural elements.
• Objective: To promote uniformity and safety in government infrastructure projects.
• Users: Engineers and architects engaged in public sector construction.

Typical Contents:

• Terminology definitions.
• Fundamental design concepts.
• Material standards.
• Load considerations.
• Safety margins.

Common Equations:

• Load: (P = w \times A), where (w) is load intensity and (A) the area.
• Stress: (\sigma = \frac{F}{A}).
• Relationships for bending moments and shear forces.

Typical Tables:

• Material attributes.
• Load factors and combinations.
• Allowable stress values.

Refer to IS SP Part 38 clauses for detailed formulas and tabulated data.

IS SP Part 38, issued by CPWD, outlines the scope for structural design and detailing related to specific materials and construction methods.

Scope Details:

• Applicability to particular structural types and materials such as steel, concrete, and masonry.
• Design principles emphasizing safety, serviceability, and durability.
• Construction methodologies, load considerations, and material standards.
• Integration with companion IS codes like IS 456 for concrete structures.

Specifications Overview:

Example Load Formula:

[ P_u = 1.5(D + L) ] where (P_u) is ultimate load, (D) dead load, and (L) live load.

For detailed scope, consult the introductory sections of IS SP Part 38.

IS SP Part 38 references load considerations based primarily on the IS 875 series (Parts 1 to 5).

Principal Load Types:

• Dead Loads: Permanent structural and fixed elements.
• Live Loads: Variable loads depending on occupancy and use (IS 875 Part 2).
• Wind Loads: Computed using: [ P = 0.6 , V^2 , k_1 , k_2 , k_3 , A ] where (V) is basic wind speed, (k_1), (k_2), (k_3) are factors for terrain, structure size, and wind direction, and (A) is projected area.
• Seismic Loads: As per IS 1893, considering seismic zones, soil conditions, and structure importance.

Load Factors (Limit State Design):

Summary:

• Adhere to IS 875 for magnitude and combination rules.
• Seismic loads per IS 1893.

Refer to IS 875 and IS 1893 for exhaustive data and calculation procedures.

IS SP Part 38 provides typical design parameters for steel roof trusses used in public constructions.

Design Parameters:

• Span lengths commonly between 6 m and 30 m.
• Truss depth approximately 1/8 to 1/10 of span.
• Number of panels ranges from 6 to 12.
• Member sizing based on axial force calculations following IS 800.

Essential Formulas:

• Axial force in members: [ F = \frac{P \times L}{4 \times \sin \theta} ] where (P) is load, (L) span, and (\theta) member angle.
• Buckling check: [ \sigma_c = \frac{P}{A} \leq f_{cd} ] where (f_{cd}) is design compressive stress.

Typical Truss Types:

• Pratt
• Warren
• Howe

Refer to IS 800 and IS 875 for detailed design and loading.

This part outlines methods for calculating forces in truss members using classical structural analysis.

Methods:

• Method of Joints: Ensures equilibrium at each joint: [ \sum F_x = 0, \quad \sum F_y = 0 ]
• Method of Sections: Cuts through truss to analyze internal member forces: [ \sum F_x = 0, \quad \sum F_y = 0, \quad \sum M = 0 ]
• Member force calculation: [ F = \frac{P \times \text{distance}}{\text{member length}} ]

Design Assumptions:

• Pin-jointed truss members.
• Loads applied only at joints.
• Members resist axial forces only.

Member Considerations:

For in-depth design, refer to IS 800 and IS 875.

This section covers design requirements for purlins and girts in steel structures.

Design Criteria:

• Consider bending, shear, and deflection under lateral support conditions.
• Assess lateral-torsional and local buckling.

Key Equations:

• Bending stress: [ f_b = \frac{M}{Z} ]
• Shear stress: [ f_v = \frac{V}{A_v} ]
• Deflection for uniformly distributed load: [ \delta = \frac{5 w L^4}{384 E I} ]

Specifications:

• Use cold-formed or hot-rolled sections per IS 801.
• Maintain spacing and supports as per IS 800.
• Limit deflection to span/180 or project-specific requirements.
• Provide bracing to avoid buckling.

Refer to IS 800 and IS 801 for detailed sectional properties and design.

Detailed guidance is provided for cantilever column design supplementing IS 456 provisions.

Design Considerations:

• Columns are subjected to axial loads combined with bending moments.
• Lateral buckling effective length is critical.

Important Formulas:

• Ultimate axial load: [ P_u = 0.4 f_{ck} A_c + 0.67 f_y A_s ]
• Slenderness ratio: [ \lambda = \frac{L_{eff}}{r} ]
• Buckling evaluation using Euler’s formula or IS 456 Clause 6.2.3.

Specifications:

• Minimum reinforcement as per IS 456.
• Use grade M20 or above concrete.
• Provide lateral ties to prevent buckling.

Refer to IS 456 interaction curves and IS SP Part 38 for detailed design.

Wind load calculations reference IS 875 (Part 3) and are integrated with IS SP Part 38 design practices.

Wind Pressure Calculation:

[ P = 0.6 \times V_z^2 \times C_d \times C_e \times C_s ] where (V_z) is design wind speed at height, (C_d) drag coefficient, (C_e) exposure factor, (C_s) size factor.

Load Combinations (IS 875 Part 5):

Exposure Categories:

Consult IS 875 for comprehensive parameters and factors.

Guidelines for sizing and choosing structural members emphasize safety and efficiency.

Fundamental Equations:

• Axial capacity: [ P = A \times f_y ]
• Bending capacity: [ M = Z \times f_y ]
• Slenderness ratio for column checks: [ \lambda = \frac{L_{eff}}{r} ]

Typical Section Properties Table:

Design Checks:

• Verify slenderness ratio limits per IS 800.
• Apply interaction formulas for combined axial and bending stresses.

Refer to IS 800 and IS SP Part 38 annexures for detailed data.

This section includes essential formulas for determining reactions and bending moments in beams.

Reaction Forces:

• For simply supported beam with point load (P) at distance (a): [ R_A = \frac{P(L - a)}{L}, \quad R_B = \frac{P a}{L} ]
• For uniformly distributed load (w): [ R_A = R_B = \frac{wL}{2} ]

Bending Moments:

• At distance (x) from left support under point load: [ M_x = R_A x - P (x - a) \quad (x > a) ]
• Maximum bending moments: [ M_{max} = \frac{P L}{4} \quad \text{(point load center)} ] [ M_{max} = \frac{w L^2}{8} \quad \text{(uniform load)} ]

Common Load Cases Table:

Refer to IS 456 and IS 800 for further details.

Key considerations for base plate and column support design include:

Design Parameters:

• Base plate thickness to prevent local buckling.
• Bearing pressure should be within soil/grout capacity.
• Anchor bolts designed for uplift and shear.
• Plate dimensions sufficient to distribute loads evenly.

Important Calculations:

• Bearing pressure: [ q = \frac{P}{A} \leq q_{allow} ]
• Base plate thickness: [ t = \sqrt{\frac{M}{f_y Z}} ]
• Anchor bolt capacity per IS 1367.

Typical Thickness Range:

Specifications:

• Use Fe 410 grade steel.
• Minimum 50 mm bearing beyond flange.
• Grout thickness 10-20 mm.

Refer to IS SP Part 38 for comprehensive guidelines.

IS SP Part 38 supplements IS codes by providing practical design examples and tabulated data.

Features:

• Stepwise solutions for typical structural elements such as beams and columns.
• Tables summarizing material properties, load factors, reinforcement details, and permissible stresses.
• Standardized dimensions and safety factors consistent with government codes.

Sample Table:

Example Flexural Capacity:

[ M_u = f_{ck} \times b \times d^2 \times k ]

Refer to IS 456, IS 800, and IS SP 38 for detailed worked examples.

Guidance on analysis and design approaches includes:

Key Considerations:

• Use suitable analysis methods (elastic, plastic, finite element) depending on complexity.
• Combine loads as per IS 875 (dead, live, wind, seismic).
• Employ characteristic material strengths from IS codes.
• Apply partial safety factors as required.
• Check deflections within permissible limits.
• Verify stability against buckling phenomena.
• Incorporate redundancy and ductility for safety.

Typical Formulas:

• Bending stress: [ \sigma = \frac{M}{Z} ]
• Axial stress: [ \sigma = \frac{P}{A} ]
• Combined axial and bending stress: [ \sigma = \frac{P}{A} \pm \frac{M}{Z} ]

Refer to IS 456 and IS 800 for related tables and values.

IS SP Part 38 serves as a guideline referencing multiple Indian Standards:

Commonly Referenced Codes:

• IS 456: Code of Practice for Plain and Reinforced Concrete.
• IS 800: General Code for Steel Construction.
• IS 1893: Earthquake Resistant Design Criteria.
• IS 875: Design Loads (Dead, Live, Wind, Earthquake).
• IS 13920: Ductile Detailing of Reinforced Concrete.

Referencing Format:

IS <code> : <year> - <title>

Sample Table:

Use latest editions and cross-reference as per project needs.

Annexures in IS SP Part 38 typically contain:

Contents:

• Design formulas and calculation tables.
• Material properties like modulus of elasticity and yield strength.
• Load factors and safety parameters.
• Sectional properties such as moment of inertia and section modulus.
• Detailing requirements including minimum reinforcement and cover.

Example Flexural Design Formula:

[ M_u = 0.87 f_y A_s (d - \frac{a}{2}) ] where (M_u) is ultimate moment, (f_y) yield strength, (A_s) tension reinforcement area, (d) effective depth, and (a) stress block depth.

Refer to the official IS SP Part 38 and CPWD manuals for exact annexure details.