LOADOUT ANALYSIS
AN OVERVIEW OF LOADOUT OF STRUCTURAL SYSTEMS.
PRESENTED BY
Topics for Discussion
What is Loadout and Loadout Analysis?
Why Loadout?
Type of Loadout
Importance of Loadout analysis.
Components used for Loadout
Loads
Loadout Procedure
Analysis.
Post processing
Practical
Objectives
To highlight the purpose of Loadout and
component used for Loadout.
To give an overview into the various criteria
considered in Loadout Analysis and to
interprete results.
What is Loadout and Loadout Analysis?
By loadout, we mean the process of moving a
structure from a set of skidways, crane on the land to a cargo barge.
Loadout Analysis is the analysis performed to determine the state of stress in the structural
member when loading out as a result of loss of one or more support and also to determine the best
approach to loadout considering safety
Normally, the barge is placed some fixed distance
away from the land skidway and the structure is
skidded along the land skid. At some point, part of the structure will cantilever over the gap between the barge and the land. The structure is moved further until part of it is over the barge.
At this time, the barge ballast is changed so that
the barge partially supports the structure. Now, the structure is skidded further off of the land and onto the barge. Throughout this process two things are important:
The ballast in the barge, and The stresses in the structure.
These two things are intimately related . Even if
the structure is completely on the barge, it is possible to ballast the barge so that the
structure becomes overstressed .
Loadout Analysis is the analysis performed to
determine the state of stress in the structural member when loading out as a result of loss of one or more support and also to determine the best approach to Loadout considering safety.
Why Loadout?
Aid installation of offshore structures such as
jackets, topsides, decks, modules, etc.
Convenience in installation, cost–effective and
clean.
The structure of the vessel has to be investigated
to find out constraints affecting the integration of
the structure during such load-outs and explore
ways to improve and optimize it.
Loadout Methods
Loadout by Skidding
- Where the structure is
lifted onto the barge by means of skid beams
from the fabrication yard onto the barge.
Loadout by Trailer
-Where the structure is lifted
onto the barge by means of Self Propelled
Modular Trailers(SPMT)
Lifted Loadout
-Where the structure is lifted onto
Importance of Loadout Analysis
To assess and design the structure for
installation stresses.
Provides a better idea of structural layout in
terms of weight distribution and overall weight
control.
Loadout—on many occasions—is known to be
one of the critical pre–service conditions in
terms of member and joint stresses.
Importance of Loadout Analysis Contd?
To capture changes in layout post-design stage
tolerances.
To capture fabrication tolerances in terms of
Some of the Component for Loadout;
Skid rail or Skid beam
Padears/ Padeyes
Slings
Shackles
Spreader Bars
Cranes
Winches
Jack.
Pulling Cable
Loads
All dry weights are considered with proper
contingencies (Contingencies are those multiplying
factors that capture the non-modeled items in a
Dry Loads considered are:
Self weight
Non modeled dead loads
Architectural dry loads ( if any) .
Equipment dry loads.
Piping dry loads
Electrical and instrument dry loads
etc
Loadout Procedure
Procedures:
The load-out procedure shall also be submitted to COMPANY's approval at least one month prior to load-out. In particular, this procedure shall define:
• The method selected for loading • The mooring system of the barge
• The draft of barge when fully loaded
• The water depth and the pier configuration • The current and wind conditions
• The material and equipment planned to be used
• The loading scenario, back up equipment and contingency plan • The calculation note to demonstrate the acceptability of loads generated in the barge structure, and any corresponding
Loadout Procedure-Cont’d
• The behaviour of the cargo barge shall be considered for one (or more) sudden mistake during loading (mechanical break down of ballast pump, free surface effect during
ballasting, etc.)
• The procedure shall show any additional reinforcement or modification of the barge (surelevation of manholes,
Analysis
There are different known methods of loadout analysis that are actively performed by design engineers. These are based on individual company’s specification. An
example is the one given below:
The variation of the calculated location of the centre of
gravity within a rectangle whose sides are equal to 5 % of the overall width and length for the jacket and 10 % of the overall width and length, but not less than within a 2 m x 2 m square area, for a deck.
The weight contingencies to be applied to derive the
loaded weights shall be as follows:
Analysis Cont’d
report is the reference for the load cases (maximum expected weight)
• A contingency equal to the weighing precision with a minimum of 3 % if a weighed weight is the reference for the load-cases.
Whenever the results of a weighing (if any) would show a weighed weight greater than the maximum expected weight and/or an excessive COG shift, the loading-out calculations shall be revised to consider the weighed weight and COG, and the structures
Analysis Cont’d (TOTAL)
Normal case: a vertical displacement equal to ±
30 mm shall be imposed to each structure support points. These elementary support point
deflections shall then be combined to cover any situation that can be met during load-out. The
member stresses resulting from this analysis shall be compared to basic allowable stresses without 1/3 increase.
• Extreme case: each structure support shall be
successively released (no support) or a maximum displacement of ± 60 mm shall be applied (three
Analysis Cont’d
ANOTHER EXAMPLE: (CHEVRON)
Normal case: a vertical displacement e.g equal
to ± 30 mm shall be imposed to each structure support points. These elementary support point deflections shall then be combined to cover any situation that can be met during load-out. The member stresses resulting from this analysis shall be compared to basic allowable stresses without 1/3 increase.
• Extreme case: each structure support shall be
Analysis Cont’d
maximum displacement e.g of ± 60 mm shall be
applied (two adjacent supports for a four point
Loadout arrangement and one row unsupported for a multipoint load-out arrangement); the member
stresses resulting from this analysis shall be
compared to the basic allowable stresses with 1/3 increase.
Analysis Cont’d-Skew Method(Pulling)
Another Method is the Skew Method where it isassumed that 75% of the Pulling load is rested on one leg and the remaining 25% on the other leg.
The pulling load is load = vertical load or gravity
load x 0.75(or 0.25) x 0.3
*Steel to Steel 0.3(max. typical friction factor -
Post Processing
Check and ensure that displacement forces
are applied as defined by the specification
being used.
