M

Pressure change across base aqd --- 0kPa

Combination 2 (leading variable = imposed, accompanying = wind) O Permanent vertical action is unchanged

Design vertical action Vd = yg x ( Wgk + Vgk) + yq x 1.0 x VQk = 5964 kN Design horizontal action Hd = yQ x ^0w x HQk = 187.5kN Design moment Md = yq x ^0w x (MQk + HQk x d) = 1275 kNm

Average bearing pressure qd av = ——— = 372.8 kPa

12Md

Pressure change across base aqd --- 119.5 kPa w

Combination 3 (leading variable = wind, accompanying = none) O Permanent vertical action is unchanged

Design vertical action Vd = yg x ( Wgk + Vgk) + yq x 0kN = 3564 kN Design horizontal action Hd = yQx 1.0 x HQk = 375 kN Design moment Md = yq x 1.0 x (MQk + HQk x d) = 2550kNm

Average bearing pressure qd av = ——— = 222.8 kPa

12Md ~ Pressure change across base aqd --- 239.1kPa

Combination 4 (leading variable = wind, accompanying = imposed) O Permanent vertical action is unchanged

Design vertical action Vd = Yg x i(N&k + ^Gk) + yQ x ^0i x VQk = 5244 kN Design horizontal action Hd = yQx 1.0 x HQk = 375 kN Design moment Md = yq x 1.0 x (MQk + HQk x d) = 2550kNm

Average bearing pressure qd av = ——— = 327.8 kPa

12Md

Pressure change across base Aqd --- 239.1 kPa

© In Combination 3, wind is leading = 1) and the imposed action is ignored = 0).

& As wind is included at its full characteristic value, the moment causes greater variation than in Combination 2.

© In Combination 4, wind is leading (^ = 1) and the imposed action is accompanying (^0 = 0.7).

© The variation in bearing pressure due to wind is the same as in Combination 3.

2.15.2 Elevated bridge deck

Example 2.2 looks at combinations of actions on a pile foundation beneath the elevated bridge deck shown in Figure 2.24.13

Permanent actions on the foundation include the self-weight of the bridge deck, the pier head, and the pier itself; any superimposed weight; and the

Figure 2.24. Typical viaduct substructure (based on the Dubai Metro)

vertical force due to settlement. The pre-stress in the deck produces an uplift on the foundation. Variable actions include temperature effects, wind on the deck and pier, and traffic actions. Possible accidental actions are from vehicle impact and seismic events.

The tables that follow give the characteristic actions from each of these sources, in the longitudinal (x), transverse (y), and vertical (z) directions defined on Figure 2.24. For simplicity, moments have been ignored.

Separate tables are shown for different design situations: persistent and transient at the ultimate limit state (ULS); accidental ULS; seismic ULS; and characteristic at the serviceability limit state (SLS).

The tables give the combination factor ^ and partial factor yf for each action, together with their relevant values taken from Eurocode 1.

Finally, the design actions in the x-, y-, and z-directions are calculated from the equation:

The sum of the Fx, Fy, and Fz components are given at the bottom of the each table.

Notes on Example 2.2

O Self-weight is a permanent action and hence ^ is omitted.

© The pre-stress attracts a combination factor ^ = 1.0 and (because it produces a favourable effect) a partial factor YP,fav = 1.0 also.

© This is the leading variable action in this combination, so ^ = 1.0.

© This is an accompanying variable action that, in this combination, uses ^ = W

© One of the rules for bridges is that wind and temperature actions do not have to be considered together. Hence this action is ignored.

© This action does not occur in this particular combination.

© For accidental design situations, all partial factors yf = 1.0.

Example 2.2 Combination of actions for ULS persistent and transient design

situation (leading variable

= traffic, accompanying = wind)

0 0

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