Structural Eng 7-12-06

By: Shihab W. ABDALLA

STRUCTURAL DEPT.

(OFFSHORE STRUCTURES)


Structural engineering is a field of engineering that deals with the design of any structural system(s), the purpose of which is to support and resist various loads.




• Offshore platforms are constructed to produce the hydrocarbons oil and gas. The contribution of offshore oil production in the year 1988 to the world energy consumption was 9% and is estimated to be 24% in 2000.


Basic Types of Offshore Platforms

1. Piled-jacket with deck structures



2. gravity concrete structure



3. FPU / FPSO


Other Types of Offshore Platforms


While the design of buildings onshore is usually influenced mainly by the permanent and operating loads, the design of offshore structures is

dominated by environmental loads, especially waves, and the loads arising in the various stages of construction and installation.

• The loads for which an offshore structure must be designed can be classified into the following categories:– Permanent (dead) loads. – Operating (live) loads. – Environmental loads including earthquakes. – Construction - installation loads. – Accidental loads.

Analysis and Design of Offshore Platforms


IN-PLACE ANALYSIS• The static in-place

analysis is the basic and generally the simplest of all analyses. The structure is modelled as it stands during its operational life, and subjected to pseudo-static loads.


LOAD-OUT ANALYSIS

• For load-out to the transport barge, the jacket is put on skids sliding on a straight track of steel beams, and pulled onto the barge.


LIFT ANALYSIS

• In a direct lift the jacket or topsides is lifted off the barge completely in air.

• A second form of lift is the buoyancy assisted lift. In this case the barge is flooded and hence submerged. This results in part of the jacket being buoyant, reducing hook loads. Buoyancy tanks may be added to the jacket if required.


TRANSPORTATION (TOWING) ANALYSIS• The transportation of heavy components from a

fabrication yard to the offshore site is a critical activity. • The behaviour of the unit usually influences the

verification of barge strength, the design of seafastenings, and indeed the design of the unit itself.

• Also there are the practical aspects of tug selection, tow route, etc. to be considered.


LAUNCHING ANALYSIS



UPENDING ANALYSIS


FLOAT-OVER ANALYSIS

Float-over procedure involves separation of the barge from the deck after load transfer and then removal of the barge from the

mating slot .


FATIGUE ANALYSIS• A fatigue analysis is performed for those structures sensitive to the action of

cyclic loadings such as:– wave (jackets, floating structures). – wind (flare booms, stair towers). – structures under rotating equipments.

EARTHQUAKE ANALYSIS• Earthquake analyses distinctive feature is that they represent essentially a base

motion problem and that the seismic loads are therefore dependent on the dynamic characteristics of the structure.

BLAST ANALYSIS

BARGE IMPACT ANALYSIS


1. MODELLING

2. LOAD APPLICATION

3. ANALYSIS

4. DESIGN

WHAT STUCTURAL ENGINEERS DO?


THANK YOU

Documents

Structural Eng 7-12-06