ISO 10721-1:1997 鉄骨構造—パート1：材料と設計 | ページ 6

Limit states

The states beyond which the structure no longer satisfies the design requirements.

Ultimate limit state

The limit states corresponding to the maximum load carrying resistance (safety related).

Serviceability limit state

The limit states related to normal use (often related to function).

Specified life

The time the structure is to be used under the given design assumptions.

Direct action

One or a set of concentrated or distributed forces acting on the structure, such as selfweight, imposed specified actions, wind, etc.

Indirect action

The cause of imposed or constrained deformations in the structure, such as temperature effects, settlements, creep etc.

Nominal action

The numerical value of an action either defined by the authorities or by the contract documents. When this value corresponds to a specified probability to be exceeded within a specified reference time, it is called characteristic action, and it is calculated in accordance with ISO 2394.

Design action

Actions used in calculations. The design action is the nominal action multiplied by its partial safety factor γ_f, or it is the combination of nominal actions, each multiplied by its partial safety factor γ_f for the relevant limit state.

Shake down

The process of local yielding due to the initial applications of variable actions, leading to a condition of residual stress where all further applications can be sustained elastically (applies particularly to the formation of plastic hinges).

Variable action

Action which is unlikely to act throughout a given design situation or for which the variation in magnitude with time is not monotonic nor negligible in relation to the mean value.

Repetetive action

Design action which involves stress fluctuations leading to possible fatigue effects, i.e. it is the design action to be used for checking the fatigue limit state.

Characteristic material property

The value of material properties established by its specified occurrence taking account of control conditions and statistical variability.

Design material property

The value of material properties obtained by dividing the characteristic property by a partial material safety factor.

Nominal strength or resistance

The strength or resistance value based on specified characteristic material and geometric properties.

Design strength or resistance

The nominal strength or resistance divided by the appropriate partial safety factor for resistance, γ_r.

Normal use

Normal use is that which conforms to the loading and performance intended by the designer, or as specified in codes of practice, or by other relevant requirements.

Fatigue

Damage, by gradual crack propagation in a stuctural part, caused by repeated stress fluctuations.

Fatigue loading

A set of typical load events described by the position of loads, their intensities and their relative occurence.

Loading event

A defined loading sequence applied to the structure and giving rise to a stress history variation.

Equivalent fatigue loading

A simplified fatigue loading representing the fatigue effects of all loadings events.

Stress history

A record or a calculation of the stress variation at a particular point of a structure during the load event.

Stress range

The algebraic difference between two extrema of the stress history ( ). This difference is usually identified by a stress cycle counting method.

Nominal stress

A fatigue design stress in the parent material adjacent to potential crack location calculated in accordance to simple elastic strength of materials theory. For the purpose of fatigue assessment of a particular class of constructional detail, the design stress is either the normal stress (axial and bending stress) or/and the shear stress. Where there is a geometric discontinuity, not taken into account in the classification of the constructional detail, the nominal stress shall be modified by the use of stress concentration factors.

Geometric stress

A fatigue design stress, adjacent to the weld toe, defined as the extrapolation of the maximum principal stresses. The geometric stress takes into account the overall geometry of the constructional detail, excluding local stress concentration effects due to weld geometry and inherent defects in weld and adjacent parent metal. (The geometric stress is often referred in the litterature as the"hot spot stress").

Cycle counting

A particular method used for counting the number of stress cycles and related stress ranges from a stress history.

Stress-range spectrum

Histogram of the frequency of occurrence for all stress ranges of different magnitudes recorded or calculated for a particular loading event.

Design spectrum

The total of all stress spectra relevant to the fatigue assessment.

Equivalent stress range

The constant-amplitude stress range that would result in the same fatigue life (number of cycles of stress ranges) as for the spectrum of variable amplitude stress ranges based on a Miner's summation.

Miner's summation

A cumulative linear damage calculation based on the Palmgren-Miner rule.

Constant amplitude fatigue limit

The limiting stress range value above which a fatigue assessment is necessary.

Detail category

The designation given to a particular welded or bolted detail, in order to indicate which fatigue strength curve is applicable for the fatigue assessment.

Fatigue strength curve

The quantitative relationship between stress range and number of stress cycles to fatigue failure (selected on the basis of a statistical analysis of available test data of a constructional detail).

Design life

The reference period of time for which a structure is required to perform safely with an acceptable probability that failure by fatigue or cracking will not occur.

Cut-off limit

Limit below which stress ranges of the design spectrum do not contribute to fatigue damage.

Groove (butt) weld

A weld made in a preparation to receive weld metal. (Also referred to as a butt weld).

Fig. 3.1 — Fatigue strength curve definitions