The Structural Engineer's Corner

Eng. Onorio Francesco Salvatore

Traffic loads on road bridges: the Traffic Load Models

Written By: Lexatus - Nov• 10•13

Traffic loads 2 - Onorio

In the Eurocodes there are four Traffic Load Models to be used for the determination of road traffic effects associated with Ultimate Limit and Serviceability Limit States.

These load models for vertical loads represent different traffic effects. In short:

LOAD MODEL 1 (LM1): implies concentrates and uniformly distributed loads which cover most of the effects of the traffic of lorries and cars. This model has to be used for general and local verifications.

LOAD MODEL 2 (LM2): implies a single axle load applied on specific tyre contact areas which covers the dynamic effects of the normal traffic on short structural members. The LM2 can be predominant in the range of loaded lengths up to 3 m to 7 m.

LOAD MODEL 3 (LM3): implies a set of assemblies of axle loads representing special vehicles (e.g. for industrial transport) which can travel on routes permitted for abnormal loads. It is intended for general and local verifications.

LOAD MODEL 4 (LM4): implies a crowd loading, intended only for general verifications. This load model is particularly relevant for bridges located in or near towns if its effects are not covered by Load Model 1.

The Code (Eurocode in this case) requires to apply the Load Models 1, 2 and 3, where relevant, for any type of design situation (e.g. for transient situations during repair works). The Load Model 4 should be used only for some transient design situations.

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Eng. Onorio Francesco Salvatore

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