Variable Load Distribution

Poutanen, Tuomo

doi:10.1061/9780784413609.100

Cited by 3 publications

(2 citation statements)

References 6 publications

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“…A feasible solution is that the target reliability is lowered to about β 50 = 3.2 when the reliability calculation for timber and concrete approximately remains unchanged but the material safety factor of steel γ M = 1.0 should be increased considerably. The authors also suggest that the load distribution of the variable load should be changed from Gumbel to modified Gumbel [17] where the upper tail of the distribution is removed which would mitigate the changes.…”

Section: Discussionmentioning

confidence: 99%

Combination of Permanent and Variable Load Is Dependent

2021

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This study concerns the combination of the permanent and the variable loads in the structural design. The Eurocodes are used as a reference. Three new findings are presented: (1) In each physical structure, and in every load pair of the permanent load and the variable load, the maximum variable load is the service time load, the 50-year load, i.e., the high value of the variable load. Therefore, no load reduction should be applied in the combination. (2) The governing hypothesis is the independent load combination (ILC) with random load pairs and random single loads. However, the load pairs are not independent as normally one variable load occurs simultaneously in multiple structures and in multiple load pairs inducing correlation between the loads, ultimately full correlation, and the dependent load combination (DLC). (3) In the current Eurocodes, the design load combination applies to one load pair only. However, one design load combination virtually always applies to multiple load pairs which demands using the DLC. The authors have explained earlier that the permanent and variable loads should be combined dependently as the ILC contradicts the physics. The new findings support this conclusion. Changing the current codes towards the DLC approach would simplify them and eases their use in the structural design work.

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Section: Discussionmentioning

confidence: 99%

Combination of Permanent and Variable Load Is Dependent

2021

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“…In the calculation above, the variable load distribution is assumed to be Gumbel. This distribution has a robust upper tail that makes the distribution excessively safe [21], which especially applies to steel.…”

Section: Discussion On the Steel Reliabilitymentioning

confidence: 99%

Code Calibration of the Eurocodes

Poutanen

2021

Applied Sciences

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This article addresses the process to optimally select safety factors and characteristic values for the Eurocodes. Five amendments to the present codes are proposed: (1) The load factors are fixed, γG = γQ, by making the characteristic load of the variable load changeable, it simplifies the codes and lessens the calculation work. (2) Currently, the characteristic load of the variable load is the same for all variable loads. It creates excess safety and material waste for the variable loads with low variation. This deficiency can be avoided by applying the same amendment as above. (3) Various materials fit with different accuracy in the reliability model. This article explains two options to reduce this difficulty. (4) A method to avoid rounding errors in the safety factors is explained. (5) The current safety factors are usually set by minimizing the reliability indexes regarding the target when the obtained codes include considerable safe and unsafe design cases with the variability ratio (high reliability/low) of about 1.4. The proposed three code models match the target β50 = 3.2 with high accuracy, no unsafe design cases and insignificant safe design cases with the variability ratio 1.07, 1.03 and 1.04.

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Combination of Variable Loads in Structural Design

Poutanen

2024

Applied Sciences

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This study delves into the intricacies of variable load combination factors (ψ) within structural codes under fundamental design scenarios, with Eurocodes serving as the primary reference. Currently, variable loads are combined by adding one load, the leading load with its full value, and the other load, the accompanying load, with a reduced value multiplied by a combination factor ψ. This approach employs an independent load combination methodology, utilizing hypothetical reference materials. In contrast, this paper advocates for a shift towards dependent load combination, anchored in the use of actual reference materials. Specifically, it is proposed that imposed loads be combined without the combination factor, i.e., ψ = 1. Given that combination factors are in approximate unity or pertain to infrequent load cases, this research recommends the elimination of ψ from codes altogether. This recommendation stems from the recognition that the current combination factor calculation excels in cases with approximately equal loads with a significant reliability gain, while more frequent unequal loads introduce a minor reliability gain and harmful unsafe errors. Despite the overall minor safety advantage of about 2–3% being negligible considering unavoidable safe errors of about 7% in codes, this simplification significantly reduces code complexity, enhances user-friendliness, and substantially decreases the workload associated with design processes.

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Variable Load Distribution

Cited by 3 publications

References 6 publications

Combination of Permanent and Variable Load Is Dependent

Combination of Permanent and Variable Load Is Dependent

Code Calibration of the Eurocodes

Combination of Variable Loads in Structural Design

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