It is not commonly acknowledged that in the design of structures based on a probabilistic approach of the loads, load factors are calibrated against a predefined structure life time (typically 50 years). If your structure has a different life time (say 100 years such as in bridges) then you need to adjust your load factor accordingly. This presentation shows an example on the percentage increase of the load factors based on simplified probabilistic equations and normal distribution of the load. Please note that it exists other methods that would adjust the design load or both (design load and load factor

1. BRIDGE SKILLS
(Dublin, Ireland)
Structure Life Time vs. LRFD (EC)
Laurent Rus (Madrid)
Feb 22, 2013

2. 2
OBJECTIVE
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1. Evolution of Theoretical Design Approach (Allowable Stress Design to Probabilistic
Approach Level I to III)
2. Examples of Probabilistic Measures
3. Definition of Structure Life Time (Design Working Life)
How do we take it into account?
1. Level II: Probabilistic Approach
1. Load Resistance Factor Design Approach (LRFD)
2. Impact of Reliability Index on Partial Factors (Theory and Numerical
Example)
INDEX

3. 3
OVERVIEW OF RELIABILITY METHODS
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Allowable Stress Design Load Resistance Factor Design

4. 4
EXAMPLES OF PROBABILISTIC MEASURES
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5. 5
DESIGN WORKING LIFE
Structural Analysis
• Durability
- Structures shall be designed against deteriorations
• Performance
- Deterioration shall not jeopardize the Structure performance
- => => Global Stability?, => Local Stability?, => Fatigue?
- => Design Supervision (DSL)?,
- => Inspection during Execution (IL)?
- => Inspections?, => Maintenance?, => Monitoring?
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6. 6
DESIGN WORKING LIFE
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7. 7
DESIGN SUPERVISION LEVELS
• Three (3) Design Supervision Levels “during design” related
to the Three (3) Realiability Class
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8. 8
INSPECTION LEVELS
• Three (3) Inspection Levels “during execution” related to the
Three (3) Realiability Class
- These inspections could be linked to a Quality Management
System selected
- Guidance is available for Execution Standards in EN 1992 to
EN 1996 and EN 1999.
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9. 9
CONSEQUENCES CLASSES
• Three (3) Consequences Classes that could be related to the
Three (3) Realiability Class
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10. 10
REALIBILITY INDEX
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MINIMUM VALUES OF “REALIBILTY
INDEX”
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• Note:
- Lognormal or Weibull distributions have usually been used for
material and structural resistance
- Normal distributions have usually been used for self-weight

12. 12
TARGET VALUES OF “REALIBILTY INDEX”
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DIFFERENTIATION COEFFICIENT
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PROBABILISTIC APPROACH
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PROBABILITY OF FAILURE
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Courtesy of EDYCALEST (www.edycalest.es)

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LOAD RESISTANCE FACTOR DESIGN
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17. 17
LOAD RESISTANCE FACTOR DESIGN
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18. 18
CONCLUSION
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