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Characteristic values of actions ±q2k for class 90 power car passing under simple horizontal surfaces 4.5 m and 5.0 m above the track, compared with ENV 1991-3:1995, 6.6.3

6.7.1.3 Derailment under structures

1)P Unless otherwise specified by the relevant authority, for supporting structures for new bridges or similar structures constructed over or alongside railway tracks, the following shall be considered.

— Wherever reasonably practicable, supports carrying any structure over or alongside railway tracks shall be placed outside the hazard zone. In general, the hazard zone shall be assumed to extend for a width of 4.5 m from the edge of the outside rails of the nearest operational track.

— Consideration shall be given to extending the hazard zone in the following situations:

— if the support structure is situated within an embankment that carries rail traffic;

— if the support structure is adjacent to the outside of a track curve.

— If supports are placed inside the hazard zone, they should be monolithic piers and not individual columns. All supports located between railway tracks shall be considered to be inside the hazard zone.

— If individual columns are used within the hazard zone, the design of the structure above these shall incorporate a degree of continuity so that removal of any column does not cause the remainder of the structure to collapse under permanent loads together with the appropriate variable traffic loads.

— To provide robustness against the effect of light impacts, all piers and columns and their restraints, within the hazard zone, shall be designed to withstand without collapse a single horizontal design force of 2 000 kN acting at a design height of 1.2 m above the adjacent ground level, and a single horizontal design force of 500 kN acting at a height of 3 m. The two loads may act in any direction but it is not required to consider that they act simultaneously.

— These requirements shall be applied wherever reasonably practicable to new footbridges, taking into account the nature of the rail traffic and the track layout adjacent to the bridge.

— These requirements do not apply to lineside railway infrastructure (e.g. overhead line masts, signal gantries).

— Requirements for particular structures shall be confirmed with the relevant authority.

NOTE The requirements of this subclause are under review.

Reference should be made to ENV 1991-2-7.

Add a new subclause 6.7.4 as follows.

6.7.4 Accidental actions due to rail breakage 1) Actions due to accidental breakage of continuous welded rails on or close to the bridge deck should be considered based on the requirements of 6.5.4.1, and in agreement with the relevant authority. Collapse of a major part of the structure shall not occur as a result of such actions, but local damage is acceptable.

6.8 Assessment of traffic loads on railway bridges

6.8.1 General

1)P Unless otherwise specified by the relevant authority, the minimum spacing between centre lines of the tracks may be taken as the existing spacing or 3 400 mm, whichever is lesser.

NOTE The spacing provided shall be calculated from the dimensions associated with the chosen vehicle kinematic envelope with an allowance made for passing clearances, taking into consideration the effects of track curvature where appropriate. When calculating the required dimension, the expected rail traffic shall be taken into consideration so that the aerodynamic effects can be taken into account.

For bridges that carry more than one track, the checks for the limits of deflection and vibration, particularly with regard to safety, may not be sufficient if only one track is loaded.

6)P Unless otherwise specified by the relevant authority, the checks for the limits of deflection and vibration shall be made with the tracks loaded in accordance with the clauses of this NAD that relate to annex G.3.

6.8.2 Groups of loads: characteristic values of the multi-component action

In Table 6.6 of ENV 1991-3:1995, and Table 6.6(a), the groups of loads identified in Table 6.6(a) by "gr11", "gr12", etc., shall be applied as a single variable action. The c factors given in Tables G1/2(a) and (b) shall be applied to the group of loads as a whole. Unless otherwise specified by the relevant authority, Table 6.6 of ENV 1991-3:1995 shall be replaced by Table 6.6(a). The note at the head of Table 6.6 of ENV 1991-3:1995 shall apply to Table 6.6(a). Values that differ from the boxed values given in Table 6.6 of ENV 1991-3:1995 are shown in bold in Table 6.6(a).

6.9 Fatigue load models

2)P An additional light traffic mix that may be used, subject to agreement with the relevant authority, is given in Table F.3 of this NAD.

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