Collision Force Eurocode

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Note : For the selection of a traffic type, it may broadly be considered that :

- "Long distance" means hundreds of kilometres,

- "Medium distance" means 50 to 100 km,

- "Local traffic" means distances less than 50 km. In reality, mixture of traffic types may occur.

Table 4.8 : Definition of wheels and axles

Load Model Eurocode

4.6.6 Fatigue Load Model 5 (based on recorded road traffic)

(1) Fatigue Load Model 5 consists of the direct application of recorded traffic data, supplemented, if relevant, by appropriate statistical and projected extrapolations. Guidance for a complete specification and the application of such a model is given in annex B.

Note: This model should be used only if specified or agreed by the relevant authority.

4.7 Accidental actions 4.7.1 General

(1)P Accidental loads due to road vehicles are defined in 4.7.2 for road and railway bridges, and in 4.7.3 for road bridges only. They shall be considered, where relevant, during accidental situations as follows :

- vehicle collision with bridge piers or decks,

- heavy wheels on footways (effects of heavy wheels on footways shall be considered for all road bridges where footways are not protected by a rigid safety barrier),

- vehicle collision with kerbs, safety barriers and structural struts (effects of vehicle collision with safety barriers shall be considered for all road bridges where such restraint systems are provided on the bridge deck; effects of vehicle collision with kerbs shall be considered in all cases).

4.7.2 Collision forces from vehicles under the bridge

4.7.2.1 Collision forces on piers and other supporting members

(1) In the absence of an appropriate risk analysis, the force due to the collision of road vehicles with piers or with the supporting members of a portal bridge in the direction of vehicle travel or should be taken as IQOOkN

500 kN

perpendicular to that direction, acting 1,25 m above the level of the adjacent ground surface.

Note : A risk analysis can be considered to be appropriate only if it satisfies the relevant authority. The design load to be taken into account may be differentiated depending on the volume of the traffic expected under the bridge, the presence of protection between carriageway and piers and other particular circumstances. When additional protective measures between carriageway and piers are provided, they should be specified or agreed by the relevant authority.

4.7.2.2 Collision with decks

(1) If relevant the vehicle collision force should be specified for the particular project or, in relation to vertical clearance and other forms of protection, by a more general rule.

Note : This force should be defined or agreed by the relevant authority. Collision loads on bridge decks and other structural components over roads may vary widely depending on structural and non-structural parameters, and their conditions of applicability. The possibility of collision by vehicles having an illegal height should be envisaged, as well as a crane swinging up while a vehicle is moving. Protective measures may be introduced as an alternative to designing for collision forces.

4.7.3 Actions from vehicles on the bridge

4.7.3.1 Vehicle on footways and cycle tracks on road bridges

(1)P If a rigid safety barrier of an appropriate class is provided, consideration of the axle load beyond this protection is unnecessary.

Note : A deformable safety barrier (cable, guard-rail) is insufficient. In particular cases (eg. bridges on rural roads or urban streets), a kerb of 0,25 m or more height can make consideration of the axle load unnecessary, if specified or agreed by the relevant authority.

(2) Where the protection mentioned in (1) is provided, one accidental axle load corresponding to aQ202k (see 4.3.2) should be taken into account. It should be so placed and oriented in the carriageway as to give the most adverse effect adjacent to the barrier as shown in Figure 4.11. This axle load does not act simultaneously with any other variable load on the carriageway. A single wheel alone is taken into account if geometrical constraints make a two-wheel arrangement impossible.

Beyond the barrier, the characteristic variable concentrated load defined in clause 5.3.2(4) is applicable, if relevant, separately from the accidental load.

Parapet

Safety barrier

0,50

0,40

Otg2eac-

1,40

1,40

Carriageway

2,00

Parapet

Parapet

Figure 4.11 : Location of loads on footways and cycle tracks on road bridges

(3) In the absence of the protection mentioned in (1), the rules given in (2) are applicable up to 1 m beyond a deformable safety barrier if it is provided, or up to the edge of the deck in the absence of a safety barrier.

4.7.3.2 Collision forces on kerbs

(1) The action from vehicle collision with kerbs is a lateral force equal to 100 kN acting at a depth of 0,05 m below the top of the kerb.

This force is considered as acting on a line 0,5 m long and is transmitted by the kerbs to the structural members supporting them. In rigid structural members, the load is assumed to have an angle of dispersal of 45°. When unfavourable, the vertical traffic load acting simultaneously with the collision force is equal to OJScxqjQ^ (see Figure 4.12).

Lateral Protection Barriers
Figure 4.12 : Definition of vehicle collision forces on kerbs 4.7.3.3 Collision forces on safety barriers

Note : See also, when available, technical approvals or standards established by CEN/TC 226.

(1) For structural design, an horizontal vehicle collision force transferred to the bridge deck by rigid safety barriers is llOOl kN acting transversely and horizontally 100mm below the top of the barrier or 1,0 m above the level of the carriageway or footway, whichever is the lower. As for kerbs, this force is considered as acting on a line 0,5m long. The vertical traffic load acting simultaneously with the collision force is equal to O^ccq! Q1k.

For deformable safety barriers, the collision force is taken from results obtained for the technical approval of the barriers.

The structure supporting the safety barrier should also be designed to sustain locally an accidental load effect corresponding to |1,25| times the characteristic local resistance of the barrier (e.g. resistance of the connection of the barrier to the structure) exclusive of any variable load.

4.7.3.4 Collision forces on structural members

(1) The vehicle collision forces on unprotected vertical structural end members above carriageway levels are the same as specified in 4.7.2.1-(1), acting 1,25 m above the carriageway level. However, when additional protective measures between the carriageway and these members are provided, this force may be reduced.

Note : Such a reduction should be agreed by the relevant authority.

(2) Unless otherwise specified, these forces are not considered to act simultaneously with any variable load.

Note : For some intermediate members damage to one of which would not cause collapse (eg. hangers or stays), smaller forces may be specified by the relevant authority.

4.8 Actions on parapets

Note : This clause, which has no structural character, might be partially superseded by technical approvals or by standards established by CEN/TC 226.

4.8.1 Definition of actions applicable to parapets

(1) Unless otherwise specified, the action to be considered is a line force of 1,0 kN/m acting, as a variable load, horizontally or vertically on the top of the parapet.

Note : A lower force should be specified only by the relevant authority.

(2) For service side paths, the line force may be reduced to 0,8 kN/m.

Note : Exceptional and accidental cases are not covered by these forces. It is up to the relevant authority to require such cases to be taken into account for the particular projects.

4.8.2 Consideration of the actions

(1) Parapets for footways on road bridges should be designed for the previously defined actions if they are adequately protected against vehicle collision. For the design of the supporting structure, the horizontal actions should be considered as simultaneous with the uniformly distributed actions defined in 5.2.2.(1), unless otherwise specified.

Note : Parapets can be considered as adequately protected only if the protection satisfies the specifications of the relevant authority.

Where they are not so protected, the supporting structure should also be designed to sustain an accidental load effect corresponding to 11,251 times the characteristic resistance of the parapet, exclusive of any variable load. 4.9 Load models on embankments

4.9.1 Vertical loads

(1) Unless otherwise specified for the particular project, the carriageway located behind abutments, wing walls, side walls and other parts of the bridge in contact with earth, should be loaded with the same models as defined in 4.3, corresponding to characteristic loads on carriageways.

Note : Other more general specifications may also be issued by the relevant authority.

For the sake of simplification, the tandem system loads may be replaced by an equivalent uniformly distributed load, noted qeq, spread over a rectangular surface of sides 1,0m x 2,0m.

Note : For the dispersal of the loads through the backfill or earth, see the NAD. In the absence of any other rule, if the backfill is properly consolidated, a dispersal at an angle of 30° from to the vertical may be assumed.

(2) Representative values of the load model other than the characteristic values are not to be considered.

4.9.2 Horizontal force

(1) Unless otherwise specified, no horizontal force should be considered at the coating level of the carriageway over the backfill.

(2) For the design of abutment upstand walls (see Figure 4.13), a longitudinal braking force should be considered. The characteristic value of this force is equal to 0,6ocq; it acts simultaneously with the aQ^^ axle loading of

Load Model Number 1 and with the earth pressure from the backfill. The embankment should be assumed not to be loaded simultaneously.

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