Limit state, working stress, ultimate load method - Detailed Concept
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The document discusses various design philosophies in structural engineering, including the Working Stress Method (WSM), the Ultimate Load Method (ULM), and the Limit State Method (LSM). It explains the assumptions and limitations of each method, with a focus on how LSM combines the strengths of WSM and ULM to ensure safety and serviceability. Ultimately, it emphasizes the importance of designing structures to withstand loads throughout their lifespan while considering durability and performance.
Limit state, working stress, ultimate load method - Detailed Concept
- 2. Table of Content What are the Various Design Philosophies? Working Stress Method Assumptions of Working Stress Method Limitations of Working Stress Method Ultimate Load Design Assumptions of Ultimate Load Method Limitations of Ultimate Load Method Limit State Method What are the different types of limit state of design? Assumptions of Limit State Method
- 3. Introduction Whereas Ultimate Load Method was developed in the 1950s as a alternative to Working Stress Method. ULM got accepted as an alternative to WSM in ACI code in 1956 and in British code in 1957. ULM was based on the ultimate load carrying capacity of reinforced concrete on collapse.
- 4. What are the Various Design Philosophies? Working Stress Method Ultimate Load Method limit State Method
- 5. Working Stress Method Working Stress Method was the traditional method of design for RCC structures, steel structures, and timber structures also. The basic concept of working stress method is adequate safety can be achieved by restricting the stresses in the material due to working loads on the structures, if we assume that structural materials in a linear elastic manner.
- 6. Assumptions of Working Stress Method • The plane section before bending remains plane after bending at any cross-section. • • • σ
- 7. Limitations of Working Stress Method • The assumption that the stresses under working loads can be kept within permissible stresses is unrealistic or not practical. • •
- 8. Ultimate Load Design The ultimate load design method also termed as load factor method or the ultimate strength method. This method was developed in the 1950s with overcoming shortcomings of WSM and introduced in the USA in 1956, the UK in 1957, and also in 1964 revision of IS 456. In the ultimate load method, the nonlinear stress-strain curves of steel and concrete also the stress conditions just before the collapse are considered so as to avoid the problems arisen due to the imaginary concept of modular ratio (m).
- 9. Assumptions of Ultimate Load Method • Stress in reinforcement varies linearly with strain up to specified yield strength. • •
- 10. Limitations of Ultimate Load Method • Performance under normal service load is not considered, that is why it was realized that the design approach that combines the very best features of the working stress method and the ultimate load method will result in better structural stability and performance. • •
- 11. Limit State Method In the limit state method of design, the structure should be designed to withstand safely all the loads acting on it throughout its life. Also, the structure should satisfy the serviceability requirements, like limitations of deflection and cracking. WSM was based on calculations on service load conditions only, ULM was based on calculations on ultimate load conditions only and now LSM provides comprehensive and rational solutions to the design problems by considering safety at ultimate loads and serviceability at working loads.
- 12. WHAT ARE THE DIFFERENT TYPES OF LIMIT STATE DESIGN? 1 COLLAPSE 1.2 DURABI LI T Y 1.3 SERVI CEABI LI T Y 1.1.A F L E X URE 1.3.A DE F L E CT I O N 1.1.B CO MP RE S S I O N 1.3.B CRA CK I NG 1.1.C S HE A R 1.1.D TO RS I O N LIMIT STATE OF 1.1 WWW. CI V I L I NS IDER. CO 1.4 FI RE RESI STANCE
- 13. Assumptions of Limit State Method • A section that is plane normal to the axis of structural components remains plane after bending. • •
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