4.2.1. Load Combinations

The primary pipe loading on the bridge structure is the pipe dead load which includes the weight of the pipe, the water inside the pipeline, pipe accessories (*i.e*., expansion joints, couplings), and the pipe support system. Other loads that should be considered are wind, earthquake and impact. In the present study, only an internal load is evaluated: the water-hammer phenomenon.

In limit states, the loads are multiplied by safety factors and grouped into load combinations. For different codes (e.g., BSI 8010 UK; ASME B31.4 US; ISO 13623), different combinations of loads are established. The general requirement is that the defined load combination should be appropriate to the ultimate limit state. The Canadian code CSA-Z662 (1996) uses the following general equation for calculating the load combinations (*i = 1, 2, 3, ...*):

$$\text{Lci} = \alpha \left( \gamma\_G G + \gamma\_Q Q + \gamma\_E E + \gamma\_A A \right) \tag{1}$$

where, 9 = safety factor class; *γG*, *γQ*, *γE*, *γA* " loading factors (Table 2) for *G* = permanent loads (*i.e*., weight of the water inside the pipeline); *Q* = operational loads (overloading, *i.e.*, internal pressure during normal conditions); *E* = environmental loads (*i.e*., seismic load); *A* = live loads (*i.e*., transient events).



Note: \* For a faulted combination, the condition is associated to fault fluid transients resulting from an earthquake [27].

For each load combination, its effects are calculated as the level of stress and deformation. The resulting value of these effects is compared with the threshold value, to determine if the limit state is respected.

The safety factor class depends on the risk to which the structure is subjected. In the case of pipelines the safety factor is 2.0. According to the case study, two types of combinations were selected and applied as presented in Table 3.

**Table 3.** Selected combinations.


Note: \* The performed simulations do not take into account seismic events.
