The Concept of Moving Loads Based on Eurocode ③

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The Concept of Moving Loads Based on Eurocode ①

1. What is moving load?

2. Various types of loads to be aware of for moving load design

The Concept of Moving Loads Based on Eurocode ②

3. What is EUROCODE?

4. Calibration of the main Load Models (LM)

5. Horizontal forces - Characteristic values

Braking Force

A braking force, Q_1k, shall be taken as a longitudinal force acting at the surfacing level of the carriageway. The characteristic value of Q_1k limited to 900 kN for the total width of the bridge, should be calculated as a fraction of the total maximum vertical loads corresponding to the Load Model 1 likely to be applied on Lane Number 1, as follows:

Q_1k​=0.6a_Q1​(2Q_1k​)+0.10a_q1​q_1k​w₁​L

180a_Q1(kN)≤Q_1k≤900(kN)

*L is the length of the deck or of the part of it under consideration.

*The upper limit (900 kN) is normally intended to cover the maximum braking force of military vehicles.

Acceleration Force

Acceleration forces should be taken into account with the same magnitude as braking forces, but in the opposite direction.

Centrifugal Force

The centrifugal force Q_tk should be taken as a transverse force acting at the finished carriageway level and radially to the axis of the carriageway.

where:

r is the horizontal radius of the carriageway centreline (m)

Q_v is the total maximum weight of vertical concentrated loads of the tandem systems of LM1

6. Groups of traffic loads on road bridges

The simultaneity of the loading systems defined in 4.3.2 (Load Model 1), 4.3.3 (Load Model 2), 4.3.4 (Load Model 3), 4.3.5 (Load Model 4), 4.4 (horizontal forces) and the loads defined in section 5 for footways should be taken into account by considering the groups of loads defined in Table 4.4a.

* Dominant component action (designated as component associated with the group)

^a May be defined in the National Annex (for the cases mentioned).

^b May be defined in the National Annex. The recommended value is 3 kN/m².

^c See 5.3.2.1-(2). One footway only should be considered to be loaded if the effect is more unfavourable than the effect of two loaded footways.

^d This group is irrelevant if gr4 is considered.

Group of loads gr1a

The carriageway is loaded with LM1 (characteristic values), the footways are loaded with a ‘combination’ value. This value is determined by national choice, but the recommended value is 3.0 kN/m2.

Group of loads gr2

This group is based on the characteristic values of horizontal forces due to braking/acceleration and due to centrifugal effects (in case of curved bridge). Vertical forces due to LM1, taken with the frequent values, are applied simultaneously with horizontal forces. It has to be noted that forces due to breaking (or acceleration) and centrifugal effects, which are independent variable actions, are simultaneously taken with their characteristic values only for simplicity for designers.

Group of loads gr3

This consists of Load Model 4 and is applied to the footways only; it is not combined with any other load model. The UDL may be applied to one or both of the footways so as to achieve the worst load effect.

Group of loads gr4

This consists of Load Model 4 and is applied to the footways, carriageways and central reserve; it is not combined with any other load model.

Group of loads gr5

This group of loads is based on the consideration of special vehicles. The condition of taking account of these special vehicles on bridge decks, and particularly their simultaneity with normal road traffic, are defined at the national level.

Examples of Groups of Moving Loads (UK)

gr1a

Load Model 1 is combined with footway loading. The footway loading is reduced to 3kN/m². The diagram below illustrates Group gr1a for a single span two lane carriageway with two footways. gr1a is a case where footways/cycle tracks are considered, and the load on the pedestrian bridge is said to be a crowd load of 5kN/m², but it is stated that the load may be reduced if the length is more than 10m. 5kN/m² is further reduced for loaded lengths greater than 10m. And the traffic load on each lane can be calculated by placing them where the worst load occurs.

gr1b

This consists of the 400kN axle shown in Load Model 2 and is not combined with any other load model.

• Load Model 2 consists of a single axle load β_QQ_ak

• Q_ak = 400kN

Therefore, it becomes 400kN.

gr2

The diagram illustrates Group gr2 for a single 10m span deck with a two lane carriageway. Although the axle loads and UDL values have been shown as reduced by Ψ₁ it is usually more convenient to apply the 0.75 factor to the load effects rather than the loads.

^a The recommended values of Ψ₀, Ψ₁ for gr1a and gr1b are given for roads with traffic corresponding to adjusting factors α_Qi, α_qi, α_qr and β_Q defined in the NA to BS EN 1991-2:2003.

^b The frequent values of load groups gr4 and gr5 do not need to be considered in accordance with BS EN 1991-2:2003, 4.5.2.
NOTE The Ψ₀ factors specified for a group of loads apply to all the component actions in that group, except for gr1a where they are individually specified. The Ψ₁ and Ψ₂ factors always apply to individual components of loading and the values for a given component are the same in all load groups in which the component occurs.

Topics

Moving Load

Eurocode

Dynamic Force

Vehicle Load

Load Model

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