14

6 Actions (loading)

Figure 6.1Diagrammatic representation of constituent

components of a temperature profile.

(a) A uniform temperature component, ∆Tu

(b) A linearly varying temperature difference component about the z–z axis, ∆TMY

(c) A linearly varying temperature difference component about the y–y axis, ∆TMZ

(d) A non-linear temperature difference component, ∆TE. This results in a system of self-equilibrated stresses which produceno net load effect on the element

The residual stresses are the stresses resulting from the temperature change remaining after the uniform and linearly varying stresses are subtracted from the original temperature distribution.

Before traffic loading can be applied to the model of the structure, the carriageway must be divided into notional lanes as specified in BS EN 1991-2, Table 4.1. For widths of 6.0 m and above, the carriageway is divided into an integer number of 3.0 m wide lanes. Any excess width is known as the ‘remaining area’.

For the analysis of the bridge, the positioning of the notional lanes does not have to correspond to the position of the actual lane markings on the bridge. Instead, the lanes and the remaining area are positioned so as to create the most severe load effects for each element being considered. Similarly, the numbering of the notional lanes is not related to their position. Instead, the lane producing the most unfavourable effect on the element being considered is ‘lane 1’, that producing the second most unfavourable effect is ‘lane 2’, and so on.

6.3 Traffic loads6.3.1 Notional lanes