Different_Design_Philosophies_of_RCC_Design_Comparison.pptx

WSM/LSM

1. Different Design Philosophies of RCC Design – Comparison Presented by: [Your Name] Subject: Reinforced Cement Concrete

2. Introduction RCC design ensures safety, serviceability, and economy. Main RCC Design Methods: 1. Working Stress Method (WSM) 2. Ultimate Load Method (ULM) 3. Limit State Method (LSM)

3. Working Stress Method (WSM) • Based on Elastic Theory. • Stress ∝ Strain. • Permissible stresses not exceeded under service loads. • Safety ensured by Factor of Safety. • Used before 1960s.

4. Ultimate Load Method (ULM) • Based on ultimate strength of materials. • Designed for ultimate loads. • Load Factor = Ultimate Load / Working Load. • More economical, less serviceability. • Obsolete now.

5. Limit State Method (LSM) • Combines WSM & ULM advantages. • Considers ultimate and serviceability limit states. • Uses partial safety factors. • Ensures safety and serviceability. • Adopted by IS 456:2000.

6. Comparison of RCC Design Philosophies Feature | WSM | ULM | LSM Basis | Elastic theory | Ultimate strength | Both elastic & plastic behavior Safety | FOS on stresses | Load factor | Partial safety factors Economy | Conservative | Economical | Balanced Serviceability | Controlled | Poor | Controlled Use | Old | Obsolete | Present standard

7. Advantages & Limitations WSM: Simple but conservative. ULM: Economical but neglects serviceability. LSM: Comprehensive and balanced, but complex.

8. Practical Example Beam design differs: • WSM – Based on permissible stresses. • ULM – Based on ultimate load capacity. • LSM – Checks both limit states. (Use bending stress diagram for illustration.)

9. Code Provisions WSM: IS 456:1978 LSM: IS 456:2000 Design aids: SP-16 and SP-34

10. Summary • WSM: Safe but uneconomical. • ULM: Economical but lacks serviceability. • LSM: Balanced approach. Conclusion: Limit State Method is most rational and widely used.

11. References • IS 456:2000 • SP 16 – Design Aids for RCC • N. Krishna Raju – Design of RCC Structures • S. Unnikrishna Pillai & Devdas Menon – RCC Design