Nlm

speed in km/h.

V*

resistance of the rail to longitudinal displacement.

Latin lower case letters a distance between rail supports, length of distributed loads (Load

Models SW).

ag horizontal distance to the track centre.

b length of the longitudinal distribution of a load by sleeper and ballast.

c space between distributed loads (Load Models SW).

Cp aerodynamic coefficient.

d regular spacing of axles.

e eccentricity of vertical loads, eccentricity of resulting action (on reference plane).

f reduction factor, force, centrifugal force. g acceleration due to gravity.

h height (general).

hg vertical distance from rail level to the underside of a structure.

k-\ train shape coefficient.

/eg specific factor for slipstream effects on vertical surfaces parallel to the tracks.

/C3 reduction factor for slipstream effects on simple horizontal surfaces adjacent to the track.

/C4 increasing factor of slipstream effects on surfaces enclosing the tracks (horizontal actions).

increasing factor of slipstream effects on surfaces enclosing the tracks (vertical actions).

n0 natural frequency of the unloaded bridge.

<7Aj accidental line load.

Of footpath loading.

qii equivalent distributed loads from slipstream effects.

% vertical distributed load, s gauge.

t twist (changing of cant over 3m).

u cant.

v speed in m/sec.

Greek upper case letters

© end rotation of structure (general).

<t>(<I>2»^>3) dynamic factor for railway loads.

Greek lower case letters a load classification factor;

coefficient for speed.

6 deformation (general); vertical deflection.

6h horizontal displacement.

p density.

a stress.

<p ,(p »,q> " dynamic impact components for actual trains.

Section 2 Classification of actions

2.1 General

(1)P The relevant traffic actions and other specific actions on bridges are classified below in accordance with ENV 1991-1 "Basis of design", section 4 (4.1).

(2)P Traffic actions on road bridges, footbridges and railway bridges consist of variable and accidental actions, which are represented by various models.

(3)P All traffic actions are classified as free actions (see ENV 1991-1, 1.5.1(4) and 4.1 (2)P-ii), within limits specified in sections 4 to 6.

(4) Traffic actions are multi-component actions (see ENV 1991-1, 4.1(7) and 4.8(15)).

2.2 Variable actions

(1) For normal conditions of use (ie. excluding any accidental situation), the traffic and pedestrian loads (dynamic amplification included where relevant) should be considered as variable actions.

(2) The various representative values are :

- characteristic values, which are either statistical, ie. corresponding to a limited probability of being exceeded on a bridge during its normal design working life, or nominal, see ENV 1991-1 clause 4.2(7) ;

- infrequent values ;

- frequent values ;

- quasi-permanent values.

Note : Infrequent values are intended to correspond approximately to a mean return period of one year. Frequent values are intended to correspond approximately to a mean return period of one week.

(3) For verification with regard to fatigue, separate models, associated values and, where relevant, specific requirements are given in 4.6 for road bridges, in 6.9 for railway bridges, and in the relevant annexes.

2.3 Accidental actions

(1) Road vehicles and trains may generate actions due to collision or accidental presence or location. These actions should be considered for the structural design where appropriate protection is not provided.

Note : A protection cannot be considered to be appropriate if the conditions specified by the relevant authority are not satisfied.

(2) Accidental actions described in this Part refer to the common situations. They are represented by various load models defining design values (ie. to be used with ya = in the iorm oi static |oads. The load models and values given in this Part are intended for bridges, and, unless otherwise specified, for retaining walls adjacent to roads and railway lines.

Note : For some models only, applicability conditions are defined in this Part. Complementary conditions, where applicable, should be specified by the relevant authorities, for a particular project or in a more general manner.

(3) Collision forces due to road vehicles under road and railway bridges are defined in 4.7.2 (see 5.6.2 for footbridges).

(4) Collision forces due to boats, ships or airplanes, for road and railway bridges (eg. over canals and navigable water), are not covered by this Part.

Note : These forces should be taken into account, when relevant, as specified or agreed by the relevant authority.

(5) Accidental actions due to road vehicles on road bridges and footbridges are defined in 4.7.3 and 5.6.3 respectively.

(6) Accidental actions due to trains or rail traffic equipment are defined in 6.7.

Section 3 Design situations

(1)P The general format given in ENV 1991-1 for design procedures is applicable.

Note : This does not mean that clauses and values specified for buildings in ENV 1991-1 may be applied to bridges.

(2)P Selected design situations shall be considered and critical load cases identified. For each critical load case, the design values of the effects of actions in combination shall be determined.

(3) Generally, the various traffic loads to be considered as simultaneous are represented by groups of loads (combinations of action components, as given in the following sections); each of which is to be considered in design calculations, where relevant, (see ENV 1991-1, 4.2(15) and annexes C, D and G).

(4)P The combination rules depend on the verification under consideration and shall be identified in accordance with ENV 1991-1 "Basis of design" and in accordance with annexes C, D and G.

(5) Specific rules for the simultaneity with other actions for road bridges, footbridges, and railway bridges are given in annexes C, D and G.

(6)P For bridges intended for both road and rail traffic, the simultaneity of actions and the particular required verifications shall be specified or agreed by the client.

(7) For seismic combinations for bridges and associated rules, see ENV1998-2.

Section 4 Road traffic actions and other actions specifically for road bridges

4.1 Field of application

(1) Unless otherwise specified, this section should be applied only for the design of road bridges with :

- Individual span lengths less than 200 m, and with

- Carriageway widths not greater than 42 m.

For bridges having larger dimensions, traffic loads should be defined or agreed by the client.

Note : For span lengths exceeding 200 m, the main models for characteristic values are considered to be conservative.

(2) The models and associated rules are intended to cover all normally foreseeable design traffic situations (ie. traffic conditions in either direction on any lane due to the road traffic) to be taken into account for design (see however (3) and the notes in 4.2.1).

For bridges equipped with appropriate road signs intended to strictly limit the weight of any vehicle (e.g. for local, agricultural or private roads), specific models may be used.

Load models on embankments are defined separately (see 4.9).

Note : The specific models mentioned above should be defined or agreed by the relevant authority.

(3) The effects of loads on road construction sites (e.g. due to scrapers, lorries carrying earth, etc.) or of loads specifically for inspection and tests are not intended to be covered by the load models and should be separately specified, where relevant.

4.2 Representation of actions 4.2.1 Models of road traffic loads

(1)P Loads due to the road traffic, consisting of cars, lorries and special vehicles (e.g. for industrial transport), give rise to vertical and horizontal, static and dynamic forces.

(2) The load models defined in this section do not describe actual loads. They have been selected so that their effects (with dynamic amplification included unless otherwise specified) represent the effects of the actual traffic. Where traffic outside the scope of the load models specified in this section needs to be considered, then complementary load models, with associated combination rules, should be defined or agreed by the client.

Note 1 : The dynamic amplification factor included in the models (fatigue excepted), although established for a medium roughness of the pavement (see annex B to section 4) and normal vehicle suspension, depends on various parameters. In the most unfavourable cases it may reach 1,7. However still more unfavourable values might be reached for poorer pavement roughnesses, or if there is a risk of resonance. These cases should be avoided by appropriate quality and design measures. Therefore, it is only in exceptional cases, for particular verifications (see 4.6.1.(7)) or for particular projects that an adjustment of the included amplification should be made.

Note 2 : For military convoys, the routes and verification rules for road bridges located on these routes are defined by the relevant authority.

(3) Separate models are defined below for vertical, horizontal, accidental and fatigue loads.

(4) For the sake of simplicity, the load models defined for embankments adjacent to road bridges are intended for the design and verification of abutments. They are deduced from the road traffic models without any correction for dynamic effects (see 4.9).

4.2.2 Loading classes

(1) The actual loads on road bridges result from various categories of vehicles and from pedestrians.

(2)P Vehicle traffic may differ between bridges depending on its composition (e.g. percentages of lorries), its density (e.g. average number of vehicles per year), its conditions (e.g. jam frequency), the extreme likely weights of vehicles and their axle loads, and, if relevant, the influence of road signs restricting carrying capacity.

These differences justify the use of load models suited to the location of a bridge. Some classifications are defined in this section (e.g. classes of special vehicles introduced in 4.3.4). Others are only suggested for further decision (e.g. choice of adjustment factors a and (3 defined in 4.3.2(7) for the main model and in 4.3.3 for the single axle model) and may be presented as loading classes (or traffic classes).

Note : However, because of the variety of parameters, having very different consequences depending on the location of individual bridges (e.g. in urban, rural or industrial areas), a unique set of such classes associated with all aspects should not be decided without a detailed examination of all consequences.

4.2.3 Divisions of the carriageway into notional lanes

(1) The widths w| of notional lanes on a carriageway and the greatest possible whole (integer) number nn\" of such lanes on this carriageway are shown in Table 4.1.

Table 4.1 : Number and width of lanes

Carriageway width V

Number of notional lanes

Width of a notional lane

Width of the remaining area

w< 5,4 m

"i = 1

3 m

w- 3 m

5,4 m < w< 6 m

n\ = 2

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