Figure 4.10 : Fatigue Load Model 3

(2) The maximum and minimum stresses and the stress ranges, ie. their algebraic difference, resulting from the transit of the model along the bridge should be calculated.

4.6.5 Fatigue Load Model 4 (set of "standard" lorries)

(1) Fatigue Load Model 4 consists of sets of standard lorries which together produce effects equivalent to those of typical traffic on European roads. Unless otherwise specified, a set of lorries appropriate to the traffic mixes predicted for the route as defined in Tables 4.7 and 4.8 should be considered.

Note : This model, based on five standard lorries, simulates traffic which is deemed to produce fatigue damage equivalent to that due to actual traffic of the corresponding categoiy defined in Table 4.5.

It is up to the relevant authority, if necessary, to specify or agree other standard lorries.

(2) Each standard lorry is defined by :

- The number of axles and the axle spacing (Table 4.7, columns 1+2),

- The equivalent load of each axle (Table 4.7, column 3)

- The wheel contact areas and the transverse distances between wheels, in accordance with column 7 of Table 4.7. and Table 4.8.

(3) Unless otherwise specified:

- The percentage of each standard lorry in the traffic flow should be selected from Table 4.7. columns 4, 5 or 6 as relevant.

- The total number of vehicles per annum to be considered for the whole carriageway SA^ is obtained from 4.5.1-(4).

- Each standard lorry is considered to cross the bridge in the absence of any other vehicle.

(4) The stress range spectrum and the corresponding number of cycles due to the successive passage of individual lorries across the bridge should be used with the Rainflow or the Reservoir counting method to determine the fatigue damage rate.

Table 4.7 : Set of equivalent lorries

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