Loadout Analysis

LOADOUT ANALYSIS AN OVERVIEW OF LOADOUT OF STRUCTURAL SYSTEMS.

PRESENTED BY

OLASUNKANMI ARIYO

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 Questions & Answers

Objectives 

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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

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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:

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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.

Loadout Skidway

Loadout Skidway

Loadout by Skidding

Barge Transportation

Loadout by SPMT

Loadout by Lifting

Why Loadout? 

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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 

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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 the barge by shore-based or floating crane

Importance of Loadout Analysis 

To assess and design the structure for installation stresses.

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Provides a better idea of structural layout in terms of weight distribution and overall weight control.

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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.

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To capture fabrication tolerances in terms of eccentricities when finally built.

Some of the Component for Loadout;  

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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 model)

Dry Loads considered are:    

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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 reinforcement required (above and below deck)

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, additional piping, etc.)

Analysis

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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: • Same contingency as in weight report if the weight

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 shall be reinforced accordingly if required.

Analysis Cont’d (TOTAL) 

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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  

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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 successively released (no support) or a

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) 

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Another Method is the Skew Method where it is assumed 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 Guidelines for Loadout.

Post Processing 

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Check and ensure that displacement forces are applied as defined by the specification being used. Perform code check for primary and secondary members appropriately as stated in API RP-2A

PRACTICAL

Questions & Answers