Dominant component action (designated as component associated with the group).

O Unless otherwise specified in design codes or other standards

(**) See One footway only should be considered to be loaded if the effect is more unfavourable than the effect of two baded footways.

(***) This group is irrelevant if gr4 is considered.

4.5.2 Other representative values of the multi-component action

Note : For the individual components of the traffic action, these representative values are defined in annexes C and D. Infrequent values of the multi-component action

(1) The same rule as in 4.5.1 is applicable by replacing all characteristic values in Table 4.4 by infrequent values defined in annex C, without modifying the other values mentioned in the Table.

Note : It has been considered that the infrequent group gr2 is practically irrelevant for road bridges. Frequent values of the multi-component action

(1) Unless otherwise specified, the frequent action consist only of, either the frequent values of the main loading system or the frequent value of the single axle model, or the frequent values of loads on footways or cycle-tracks (taking the more unfavourable), without any accompanying component.

Note: For quasi-permanent values (generally equal to zero), see annex C.

4.5.3 Groups of loads in transient situations

(1) The rules given in 4.5.1 and 4.5.2 are applicable with the following modifications.

(2) Unless otherwise specified, for verifications in transient situations the characteristic values ocQj Qik (tandem system) are taken equal to the infrequent values defined in annex C, and all other characteristic, infrequent, frequent and quasi-permanent values and the horizontal forces are as specified for persistent situations without any modification (i.e. they are not reduced proportionally to the weight of the tandems).

Note : In transient situations due to road or bridge maintenance, the traffic is commonly concentrated on smaller areas without significant reduction, and long lasting traffic jams are frequent However, more reductions may be applied if agreed by the relevant authority, in the cases where the heaviest lorries are diverted by appropriate road signs.

4.6 Fatigue load models 4.6.1 General

(1)P Traffic running on bridges produces a stress spectrum which may cause fatigue. The stress spectrum depends on the geometry of the vehicles, the axle loads, the vehicle spacing, the composition of the traffic and its dynamic effects.

(2) In the following, five fatigue load models of vertical forces are defined. Horizontal forces usually need not be considered.

Note 1 : Centrifugal forces may occasionally need to be considered in conjunction with the vertical loads.

Note 2 : The use of the various Fatigue Load Models is defined in the relevant ENV 1992 to 1994.

(a) Fatigue Load Models 1, 2 and 3 are intended to be used to determine the maximum and minimum stresses resulting from the possible load arrangements on the bridge of any of these models ; in many cases, only the algebraic difference between these stresses is used in ENV 1992 to 1994.

Fatigue Load Models 4 and 5 are intended to be used to determine stress range spectra resulting from the passage of lorries on the bridge.

(b) Fatigue Load Models 1 and 2 are intended to be used to check whether the fatigue life may be considered as unlimited when a constant stress amplitude fatigue limit is given. Fatigue Load Model 1 is generally conservative and covers multi-lane effects automatically. Fatigue Load Model 2 is more accurate than Fatigue Load Model 1 when the simultaneous presence of several lorries on the bridge can be neglected for fatigue verifications. If that is not the case, it should be used only if it is supplemented by additional data.

Fatigue Load Models 3,4 and 5 are intended to be used for fatigue life assessment by reference to fatigue strength curves defined in design Eurocodes. They should not be used to check whether fatigue life can be considered as unlimited. For this reason, they are not numerically comparable to Fatigue Load Models 1 and 2. Fatigue Load Model 3 may also be used for the direct verification of designs by simplified methods in which the influence of the annual traffic volume and of some bridge dimensions is taken into account by a material-dependent adjustment factor Xq .

Fatigue Load Model 4 is more accurate than Fatigue Load Model 3 for a variety of bridges and of the traffic when the simultaneous presence of several lorries on the bridge can be neglected. If that is not the case, it should be used only if it is supplemented by additional data, specified or agreed by the relevant authority.

Fatigue Load Model 5 is the most general model, using actual traffic data.

c) For fatigue verifications, the required design working life of bridges as indicated in ENV 1991-1 (100 years) is applicable, unless otherwise specified for certain categories of bridges.

(3) The load values given for Fatigue Load Models 1 to 3 are appropriate for typical heavy traffic on European main roads or motorways (traffic category Number 1 as defined in Table 4.5).

Note : The relevant authority may modify values of Fatigue Load Models 1 and 2 when considering other categories of traffic. In this case, the modifications made to both models should be proportional. For Fatigue Load Model 3 a modification depends on the verification procedure.

(4) A traffic category on a bridge should be defined, for fatigue verifications, at least, by:

- the number of slow lanes,

- the number of lorries per year per slow lane, observed or estimated, A/obs.

Unless otherwise specified, the numerical values of A/obs given in Table 4.5, corresponding to a slow lane, should be adopted for using Fatigue Load Models 3 and 4.

Table 4.5 : Number of lorries expected per year and for a slow lane

Traffic categories

Nobs per year and per slow lane

1 : Roads and motorways with 2 or more lanes per direction with high flow rates of lorries

2,0 x106

2 : Roads and motorways with medium flow rates of lorries

0,5 x106

3 : Main roads with low flow rates of lorries

0,125 x106

4 : Local roads with low flow rates of lorries

0,05 x106

On each fast lane, additionally, 10% of A/obs should be considered.

Note 1: Table 4.5 is not sufficient to characterize the traffic for fatigue verifications. Other parameters to be considered may be :

- percentages of vehicle types (see, e.g., Table 4.7), which depend on the "traffic typeM,

- parameters defining the distribution of the weight of vehicles or axles of each type.

Note 2 : There is no general relation between traffic categories for fatigue verifications, and the loading classes and associated (X factors mentioned in 4.2.2 and 4.3.2.

Note 3 : Intermediate values of N^ are not excluded, but are unlikely to have very significant influence on the fatigue life.

(5) For the assessment of general action effects (e.g. in main girders) all fatigue load models should be placed centrally on the notional lanes defined in accordance with the principles and rules given in 4.2.4(2) and (3). The slow lanes should be identified in the design.

(6) For the assessment of local action effects (e.g. in slabs or orthotropic decks) the models should be centered on notional lanes assumed to be located anywhere on the carriageway. However, when the transverse location of the vehicles for Fatigue Load Models 3, 4 and 5 is significant for the studied effects, a statistical distribution of this transverse location should be considered, unless otherwise specified, in accordance with Figure 4.8.

of centre line of vehicle

(7) Fatigue Load Models 1 to 4 include dynamic load amplification appropriate for pavements of good quality (see annex B). An additional amplification factor Acpfat should be considered near expansion joints, as shown in Figure 4.9, to be applied to all loads as a function of the distance of the considered cross-section from the expansion joint.

Note : A conservative, often acceptable, simplification may consist of adopting A<P^=13 for any cross-section within 6m from the expansion joint.

4.6.2 Fatigue Load Model 1 (similar to main loading system)

(1) Fatigue Load Model 1 has the configuration of the main loading system (characteristic Load Model 1 defined in 4.3.2) with the values of the axle loads equal to 10,710^ and the values of the uniformly distributed loads equal to

|0,3|qh and (unless otherwise specified) [0,3|qrk.

Note : The load values for Fatigue Load Model 1 are similar to those defined for the Frequent Load Model. However adopting the Frequent Load Model without adjustment would have been excessively conservative by comparison with the other models, especially for large loaded areas. For particular projects, may be neglected.

(2) The maximum and minimum stresses (ol^^x and cy^m) shou,cl be determined from the possible load arrangements of the model on the bridge.

4.6.3 Fatigue Load Model 2 (set of "frequent" lorries)

(1) Fatigue Load Model 2 consists of a set of idealised lorries, called "frequent" lorries, to be used as defined in (3) below.

(2) Each frequent lorry is defined by :

- the number of axles and the axle spacing (Table 4.6, columns'!+2),

- the frequent load of each axle (Table 4.6, column 3),

- the wheel contact areas and the transverse distance between wheels (column 4 of Table 4.6 and Table 4.8).

(3) The maximum and minimum stresses should be determined from the most severe effects of different lorries, separately considered, travelling alone along the appropriate lane.

Note: When some of these lorries are obviously the most critical, the others may be disregarded.

Table 4.6 : Set of "frequent" lorries

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