**1. Introduction**

Accidents associated with natural events or human actions are a common cause of hydraulic system failure. As a result, unwelcome accidents lead to enormous damage, the destruction of networks and the abruptly stoppage of supply. These events can also be classified as external or internal. External ones may result from extreme events (*i.e*., such as storms, floods, landslides, earthquakes, sudden releases or ruptures) and can be a consequence of structural characteristics, maintenance state, or hydraulic operation devices [1]. Pipe systems, especially those installed above the ground, are under relevant dynamic forces during the occurrence of transients (water-hammer). When these forces are associated with system movement, a fluid structure interaction is generated, which means that the liquid and the pipe must be analysed as a whole [2]. Transient pressures and dynamic vibrations generated by a water-hammer or by the closing of a valve (internal causes) lead to new loads on the system such as internal and external pressures created by the soil and/or through the pipe supports [3].

The vulnerability and susceptibility of a pipeline system can be better understood after the occurrence of accidents. Such hazards may be associated with several factors causing numerous problems, particularly when they are neglected during different design stages: project concept, sizing, implementation and operation [4–7].

Extreme transient pressure variations may cause deformations and displacements in pipes which, in turn, will interact with the hydraulic system, modifying its own active loading and, consequently, its reaction [8,9], resulting in vibration or resonance phenomena that may cause the system to fail. As a consequence, the vibrations can cause the structure to rupture due to fatigue or through the increase of structural deformations. Hence, the structural response under different load combinations is provided by using an FEM representing the characteristics involved in hydraulic systems exposed to external and internal load vibrations [10]. The behaviour of the fluid and the structure can be studied as a whole, with a structural model, if appropriate load combinations are adopted. This approach allows the possible consequences to be shown in terms of displacements and the vulnerability of the pipeline and its supports.

In the classic theory of finite elements it is assumed that movements and deformations are small and the material has a linear elastic behaviour. In some cases this condition cannot be satisfied, leading to the inclusion of non-linearity action/reaction to the model [11]. In this work, the model Robot Autodesk (Autodesk, Inc., San Rafael, CA, USA) is used to study the behaviour of a suspended pipeline under different loads, using nonlinear theory. The results obtained by the computational simulation allow us to verify the adequacy of the supports' design in a presence of transient phenomena. The importance of detailed studies of identical system behaviour for different loads in the infrastructure design is also emphasized.
