The spectral density <1>(Q) is given by :

For a rough and quick estimation of the roughness quality, the following guidance is given :

- actual roadway layers, such as, for example, asphalt or concrete layers, can be assumed to have a good or even a very good roughness quality ;

- old roadway layers which are not maintained may be classified as having a medium roughness;

- roadway layers consisting of cobblestones or similar material may be classified as medium ("average") or bad ("poor", "very poor").

(2) Unless otherwise specified, the wheel contact areas and the transverse distances between wheels are assumed as described in 4.6.5, if relevant.

(3) If the data are recorded on one lane only, assumptions should be made concerning the traffic on other lanes. These assumptions may be based on records made at other locations for a similar type of traffic.

(4) The stress history should take into account the simultaneous presence of vehicles recorded on the bridge in any lane. A procedure should be developed to allow for this when records of individual vehicle loadings are used as a basis.

(5) The numbers of cycles should be counted using the rainflow method or the reservoir method, so that the stress range histogram can be obtained.

(6) If the duration of recordings is less than a full week, the records and the assessment of the fatigue damage rates may be adjusted taking into account observed variations of traffic flows and mixes during a typical week. An adjustment factor should also be applied to take into account any future changes on the traffic

Note: The adjustment factor should be specified or agreed by the relevant authority.

(7) The cumulative fatigue damage calculated by use of records should be multiplied by the ratio between the design working life and the duration considered on the histogram.

Basis of design - supplementary clauses to ENV 1991-1 for road bridges

Note : This annex is intended, at a later stage, to be incorporated into ENV 1991-1 "Basis of design".

C1 - General

(1) This annex gives rules on partial factors on actions (^factors), and on combinations of traffic loads on road bridges with permanent actions, quasi-static wind, snow and temperature actions, and the relevant y-factors. If other actions need to be considered (e.g. mining subsidence, instability due to wind, water, floating debris and ice pressure for some verifications relating to foundations), the combinations should be supplemented to take them into account. It should also be supplemented and adapted for the erection phases (see the relevant design Eurocodes) and for some particular categories of road bridges (eg. moving bridges and roofed bridges).

C2 - Ultimate limit states (fatigue excluded)

C2.1 Simultaneity of load models with other actions

C.2.1.1 Models of variable actions

(1)P When relevant, the road traffic, pedestrian (or cycle) and crowd actions shall be considered as groups of loads as given in 4.5. These groups differ depending on the representative values and on the design situations being considered.

For any combination of traffic loads together with actions specified in other parts of ENV 1991, any such group shall be considered as one action.

(2) The characteristic wind action on road bridges may be assessed in ENV 1991-2-4 either as characteristic force FWk or as nominal force

Note : The choice of a sufficiently high value for FWn (boxed in ENV 1991-2-4) may make it possible to simplify calculations by considering significant wind action and traffic action as not simultaneous.

When considering combinations of road traffic actions with wind action, the maximum wind force compatible with road traffic should also be considered.

This force Fyy is associated with a wind speed equal to I 231 m/s at the level of the deck.

(3) For combinations of wind and traffic actions, the reference area Aref x defined in ENV 1991-2-4 should be increased by adding | 2,00 \ m to the deck thickness from the level of the carriageway, without adding it with the additional depth of parapets, safety barriers, noise barriers etc., defined in ENV 1991-2-4. The wind pressure on vehicles should be considered on the unfavourable length independently of the length of application of vertical loads.

(4)P The forces and constrained deformations resulting from relevant permanent and variable actions on bridges specified in other Parts of ENV 1991 shall be considered in combinations of actions simultaneously with the traffic loads where relevant.

(5) Unless otherwise specified, Load Model 2 (defined in 4.3.3.) and the concentrated load Qfwk on footways (defined in 5.3.2.(4)) should not be combined with any other variable non-traffic load.

(6) Unless otherwise specified, and with the exception of roofed bridges, neither snow nor wind should be combined with :

- special vehicles (Load Model 3, see 4.3.4) or the associated group of loads gr5 (see 4.5.1),

- crowd loading on road bridges (Load Model 4, defined in 4.3.5) or the associated group of loads gr4 (see 4.5.1),

- braking and acceleration forces on road bridges (see 4.4.1) or the centrifugal forces (see 4.4.2) or the associated group of loads gr2 (see 4.5.1),

- loads on footways and cycle tracks or with the associated group of loads gr3 (see 4.5.1)

(7) Snow loads should not be combined with the main loading system (Load Model 1) or with the associated group of loads gr1.

Note : Snow load is therefore not mentioned in the following Tables. It may however have to be considered during some transient situations.

(8) No wind action greater than the smaller of Fw and Vo/=Wk (or Vo^n)

should be combined with the main loading system (Load Model 1) nor with the associated group of loads gr1.

(9) Unless otherwise specified, for road bridges, wind and thermal actions should not be taken into account as simultaneous actions.

C2.1.2 Models including accidental actions

(1) Where an accidental action is to be considered, no other accidental action nor wind nor snow actions should be considered to occur simultaneously.

(2) The simultaneity of accidental actions with variable traffic actions is defined below where the relevant individual accidental actions are defined.

(3) When collisions due to traffic running under the bridge are considered (forces defined in 4.7.2, 5.6.2 and )P), the frequent loads due to the traffic running on the bridges should be introduced as accompanying actions in the combinations, unless otherwise specified.

(4) When accidental actions due to traffic running on the bridge are considered (loads defined in 4.7.3 and 5.6.3), all accompanying road traffic actions should be neglected, unless otherwise specified.

Note : When other accidental actions on bridges have to be considered, rules on simultaneity with traffic actions shall be specified.

C2.2 Combinations of actions

(1)P For each critical load case, the design values of the effects of actions shall be determined by combining the values of actions which occur simultaneously. ENV 1991-1, 9.4.2 applies.

C2.3 Partial factors for road bridges (fatigue excluded)

(1) For verifications governed by the strength of structural material or of the ground, the partial factors on actions for ultimate limit states in the persistent, transient and accidental design situations are given in Table C.1.

Note : For bridge design Table C.l and the following notes cover cases B and C specified for buildings in Table 9.2 of ENV 1991-1. For case A, see (2) below.

Table C.1 : Partial factors on actions : ultimate limit states for road bridges




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