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Figure 6.10: Factors f for Load Model 71

(7)P In addition, for bridges located in a curve, the case of the loading specified in 6.3.2 and, if applicable 6.3.3, shall also be considered without centrifugal force

(8)P Centrifugal forces shall be determined from equation (6.5) using classified vertical loads (see 6.3.2 (3)P) with:

The centrifugal forces depend on the maximum speed specified for the rail line and are decreased by the reduction factor f as given by equation (6.6).

6.5.2 Nosing force

(1)P The nosing force shall be taken as a concentrated force acting horizontally, at the top of the rails, perpendicularly to the centre-line of track. It shall be applied on both straight track and curved track.

(2)P The characteristic value of the nosing force shall be taken as Q^ = 100 kN. It shall not be multiplied by the factor a (see 6.3.2 (3)P) or by the factor f (see 6.5.1 (6)P).

(3)P The nosing force shall always be combined with a vertical load.

6.5.3 Actions due to traction and braking

(1)P Traction and braking forces act at the top of the rails in the longitudinal direction of the track. They shall be considered as uniformly distributed over the influence length L, of the action effect of the structural element considered.

(2)P Their characteristic values shall be taken as follows:

Traction force: Qtek = 33[ kN/m] L[m] * 1000[kN] for Load Model 71 (6.7)

and Load Models SW

Braking force: Qlbk = 20[ kN/m] L[m] s 6000[kN] for Load Models 71 (6.8)

and SW/O

Note: For Load Models SW/O and SW/2 only those parts of the structure which are loaded according to Figure 6.3 and Table 6.1 shall be taken into account

(3) These characteristic values are applicable to all types of track construction, i.e. long welded rails or jointed rails, with or without expansion devices.

(4) For lines carrying special traffic (restricted to high speed passenger traffic for example) the traction and braking forces may be taken as equal to 25% of the sum of the axle-loads (actual train) acting on the influence length of the action effect of the structural element considered, with a maximum value of 1000 kN for Qtak and 6000 kN for Qlbk.

(5)P Traction and braking forces shall be combined with the corresponding vertical loads.

(6) When the track is continuous at one or both ends of the bridge only a proportion of the traction or braking force is transferred through the deck to the bearings, the remainder of the force being transmitted through the track where it is resisted behind the abutments. The proportion of the force transferred through the deck to the bearings is given in 6.5.4.4.

6.5.4 Application of longitudinal actions 6.5.4.1 General and principles

(1) Where the rails are continuous between a bridge and the embankment at one or both ends of the structure, longitudinal actions due to traction or braking will be resisted partly by the earthworks behind the abutment where the rails are continuous and the remainder through the bridge bearings. Also, where the rails are continuous and provide restraint against the free movement of the bridge deck, any thermal variations between the rails and the bridge deck, or movement of the bridge deck, will produce an indirect longitudinal action at the bridge bearings.

(2)P The longitudinal actions from 6.5.4.1(1) shall also be taken into account for the design of the bearings and the substructure. In the same way, longitudinal actions will need to be taken into consideration when designing the superstructure.

(3)P The following cases shall be considered in the calculation of the longitudinal actions:

- traction and braking of trains

- thermal effects

- deformation of the structure due to vertical actions

- shrinkage and creep of concrete structures

(4)P Where the track is provided with an expansion device at each end of the structure, all the longitudinal actions shall be resisted at the bearings (and the substructure).

(5) Rail carrying structures may generally be classified as follows:

(a) structures consisting of a single span or continuous spans with a fixed bearing at one end,

(b) continuous span structures where the fixed bearing is not located at the end,

(c) structures consisting of a succession of simply supported spans, each with a fixed bearing at one end.

(6)P The values of the longitudinal actions transmitted to the structure shall be calculated taking account of the resistance to longitudinal movement of the track and the structure stiffness using a similar model to that shown in Figure 6.11. The values of the track resistance and the additional rail forces to be used shall be specified, together with the maximum relative displacement permitted between the rails and the deck.

Note: The different values to be used shall be specified by the relevant authority.

(7) The structure stiffness defines the total resistance to the longitudinal displacement of the deck which can be mobilised by the substructure at the bearings. It shall take account of flexure and translation of the support beneath the bearing and rotation of the foundation.

Figure 6.11: Model for structures defined in (5)(a) 6.5.4.2 Assessment of longitudinal actions

(1)P For the classes of structures defined in (5)(a) and (5)(b) an assessment of the actions transmitted to the structure shall be based on:

- coefficients given in Table 6.4 for traction and braking,

- equations 6.10, 6.11 or 6.12 for thermal effects, where the conditions specified in 6.5.4.2(2)P apply.

For the class of structure defined in (5)(c) a particular calculation of the longitudinal forces as described in 6.5.4.1 (6)P will be required.

(2)P The specified conditions are:

(a) If the track is continuous (i.e. without an expansion device), the expansion length of the structure shall be limited as follows:

- 60 m for steel structures supporting ballasted track,

- 90 m for concrete or composite structures carrying ballasted track.

The expansion length (LT) is the distance between the thermal centre and the opposite end of the deck (for class (5)(a) structures this is generally the overall length of the structure with the thermal centre being close to the fixed bearing).

(b) Unless otherwise specified the minimum value of track stiffness to be taken into account is 12 kN/m for unloaded track and 25 kN/m for loaded track.

Note: This track stiffness refers to track with rail sections conforming to UIC 54 or UIC 60. The relevant authority may give other specifications.

(c) The temperature variations related to an initial temperature of 10 °C do not exceed ± 35 °C for the deck and ± 50 °C for the rails and the temperature difference between the deck and the rails does not exceed ± 20 °C.

(d) The displacement of the deck shall be limited to 5mm under traction or braking actions multiplied by the factors given in Table 6.4. Where the track has an expansion device at each end of the bridge, the displacement shall be limited to 30mm.

6.5.4.3 Longitudinal actions due to temperature variation

Note: These actions are not "traffic actions"; they will be developed in ENV 1991 Part 2.5; they have been introduced in the present clause as a simplification.

(1 )P For bridges carrying ballasted track which is continuous over both ends of the deck and in which the fixed bearing is at one end, the characteristic value of the longitudinal action which is to be taken into account at the bearing level is given by:

for class (5)(a) structures where:

Lr is the expansion length in m as defined in 6.5.4.2(2)P(a).

For bridges carrying ballasted track which is continuous over both ends of the deck and in which the fixed bearing is not located at one end, the characteristic value of the action which is to be taken into account at the bearing level is given by:

for class (5)(b) structures where:

L1 and L2 according to Fig. 6.12

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