so sánh WSD & LRFD, ưu điểm và nhược điểm

Bác nào có tài liệu về so sánh 2 phương pháp luận thiết kế theo Ứng suất cho phép (WSD) và theo trạng thái giới hạn ( LRFD) thì cho em xin với. Em xin chân thành cảm ơn các Bác!
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Choosing Between WSD and LRFD for Offshore Structural Design
Selecting the appropriate design methodology is crucial for ensuring both the safety and efficiency of offshore platforms. Should designers continue with the proven Working Stress Design (WSD) approach or adopt the more modern and probabilistic Load and Resistance Factor Design (LRFD) philosophy?
A - Working Stress Design (WSD) / Allowable Stress Design (ASD)
A.1 Pros:
1. Simplicity & Familiarity: Straightforward to apply and widely understood by engineers.
2. Proven Track Record: Extensively used in offshore projects for decades (e.g., API RP 2A–WSD).
3. Intuitive Checks: Compares calculated stresses directly with allowable limits.
4. Reliable for Conventional Structures: Performs well in less complex or well-understood design scenarios.
A.2 Cons:
1. Single Safety Factor: Applies one overall factor that combines all uncertainties into a single margin.
2. Less Rational Safety Treatment: Fails to differentiate between the variability of different load types (e.g., Dead vs. Wave).
3. Potential Overdesign: Can produce heavier and more costly structures due to conservative assumptions.
B - Load and Resistance Factor Design (LRFD)
B.1 Pros:
1. Rational Safety Basis: Separates load and resistance factors based on statistical reliability and uncertainty.
2. Consistent Reliability: Ensures a uniform safety level across all components and limit states.
3. Optimized Material Usage: Enables lighter, more efficient, and cost-effective designs.
4. Modern Standard: Aligns with probabilistic-based global codes (e.g., ISO 19902).
5. Differentiated Load Treatment: Assigns higher safety margins for unpredictable loads such as environmental or accidental events.
B.2 Cons:
1. Greater Complexity: Involves multiple factors and requires understanding of reliability theory.
2. Less Intuitive Application: Compares factored loads with factored strengths rather than direct stress limits.
3. Data Sensitivity: Requires reliable statistical data for accurate load and resistance calibration.
Summary
While WSD remains a simple and familiar approach with a long history of safe use, LRFD offers a more rational, reliability-based framework that provides consistent safety and improved material efficiency. In modern offshore design practice, LRFD is generally preferred for new developments—though WSD may still be used for brownfield or conventional cases where historical design continuity is a priority.
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There is another two cons of WSD or ASD:1-It assumes that any cross section has no stress in the beginning, but in fact all hot rolled sections/thin walled sections have locked stresses crom cooling down which are all highly unpredictable. You can assume the same for soils which have stress history already.2-It usually tend to treat materials as linear which is not applicable for wood and concrete. It was invented basically for steel.Finally, it is always better saying that this bridge will fail with probability 1 in 10,000 in a design life of 75 years, than this bridge has a safety factor of 2.