**Global conventional and extreme loads on conical and vertical**

**constructions:** sheet and rafted ice; ice ridge compression; ultimate moving force (ice field crowding force); global (abnormal loads); ice islands (stopped by a construction).

**Local ice pressure (for vertical and inclined surfaces):** solid ice area; and ice fragments area.

**Ice loads dynamics:** shock actions and interaction "ice—construction" (selfexcited); ice load change in time; fatigue ice impact; ice grinding impact; and regelation.

#### **Figure 6.**

*Types of sea platforms dependent on the sea depth (for standard soil conditions): (a) the artificial pad, depth is up to 5 m; (b) the caisson-island fixed along contour, depth up to 15–20 m; (c) the monopod or monokone, depth is up to 25–30 m; (d) shell support; and (e) the truss-shell type supports, depth 25–30 m and more.*


• develop the concept of consideration of engineering-geological conditions;

• provide consideration of the level, nature and duration of dynamic impacts;

• formulate additional requirements to be imposed on sea engineering surveys;

• justify the range of design cases for assessment of bearing capacity and stress-

The analysis of threats for off-shore oil and gas production platforms is the first stage of the accidents' risks analysis for the specified objects and provides estimation of their safety level [1, 2]. The threat for SP is the probabilistic characteristic defining a possibility of the impact of affecting factors of specific type, intensity and duration in response to some dangerous (extreme) event that can take place both in the territory of the object and in the external environment. Therefore, the analysis of threats for SP has to be preceded by assessment of dangerous events

The secondary dangers occur and provoke secondary affecting factors when some object's process modules – SP parts are damaged. The possibility of initiation of these secondary threats will be defined by vulnerability of an object in relation to the primary threats. Thus, the analysis of threats has to be made in an agreement with assessment of vulnerability of the SP parts in relation to the affecting factors

The danger to SP is defined by the pattern of random events or processes (*Th*): extreme external natural and technogenic impact, wrong personnel actions and operating conditions of the object technical systems having the potential which can lead to accident. Examples of such events are: seismic activity, extreme wave or ice loads (external dangers), loss of the oil tank containment or of fatigue damages accumulation (internal dangers). The danger of an extreme event is a random variable which, in the simplest case, can be characterized by the probability of occurrence of an event *P Th* ð Þ during a certain period (1 year) or the during the

Threats for SP are characterized by impacts on an object of the affecting factors of dangerous events. The threat is also a random event (process) *H*, which

*Presentation of accident occurrence and development as a complex event. (a) Probabilities of the elementary events are described with the help of point estimations, and (b) probabilities of the elementary events are*

**2.5 The analysis of external and internal factors and threats for safety of sea**

deformed state of the system "construction—foundation."

*Hybrid Modeling of Offshore Platforms' Stress-Deformed and Limit States…*

*DOI: http://dx.doi.org/10.5772/intechopen.88894*

which can initiate impact of the affecting factors on platforms.

and

**platforms**

acting on them.

**Figure 7.**

**83**

platform's operational lifetime (**Figure 7**).

*described with the help of probabilistic determination.*
