Hệ số tổ hợp tải

Có khá nhiều tiêu chuẩn và tài liệu liên quan tới việc lấy các hệ số này, dưới đây là một ví dụ trong tài liệu weight control report.
1.1 DEFINITION OF WEIGHTS

Base Weight	:	The base weight of any individual item or collection of items is specified to a Functional Weight Condition (refer to section 3.1) and is, at the time of estimating, the best available estimate of weight for that item or collection of items exclusive of allowances and contingencies.
Factored Weight	:	The factored weight of any individual item is characterized by its Base Weight multiplied by the product of all relevant allowances. The factored weight of an item or collection of items is obtained as below: Factored Weight = (1+IAA+DCA+FCA)
NTE Weight	:	The maximum design weight which under no circumstances shall be exceeded, i.e. not-to-exceed weight.

1.2 FUNCTIONAL WEIGHT ALLOWANCE

LOAD-OUT	:	is that condition which exists during the activity of loading the structure out from the fabrication facility onto the transportation barge.
LIFT	:	is that condition which exists during the lifting of the structures. The lift weight shall be deemed to include the weight of the structure together with the weight of all equipment and bulks actually being lifted. It shall include all temporary lifting accessories such as lifting slings, shackles and lifting frames, tie-down and support beams and, any shipped-loose items temporarily placed on the structure/module during lifting, but exclude hook-up spools, in fill steel or other items which are to be lifted separately.
DRY	:	is that condition in which a single weight item or a collection of items is characterized by its dead weight alone. This condition shall typically exclude any operating fluids/supplies, spares, maintenance, tools, packing, temporary transportation materials, etc. However, the recorded dry weight of that equipment delivered with lubricants or coolants or the like pre-installed shall be deemed to include such additional weights.
OPERATING	:	is that condition which exists when all equipment and bulks, contain all relevant fluids and supply weights which occur under normal operating conditions.
HYDROTEST	:	is that condition which generally occurs during topsides hook-up and commissioning and includes weight contributions from all permanent and temporary facilities together with all weight elements associated with hydro testing.

1.3 ALLOWANCE DEFINITION
An amount, expressed in terms of a percentage of Base Weight, which experience of past projects has shown to be consumed during the various phases of project execution. Allowance shall comprise 3 components i.e. item accuracy allowance (IAA), design change allowance (DCA) and fabrication change allowance (FCA). The following definitions apply:
1.3.1 Item Accuracy Allowance (IAA)
This allowance represents the anticipated weight growth of each individual item, or collection of items, resulting from inaccuracies inherent in the method of establishing the base weight. The value of the IAA is dependent on the degree of definition of each individual item, or collection of items and the level of confidence in the weight estimate at any particular time. Four categories apply:
· Estimating Allowance
· Calculation Allowance
· Material Take-off Allowance
· Weighing Allowance
The IAA should, for most items, change from an estimating to a calculation allowance throughout conceptual design, followed by a reduction to the material take-off allowance at completion of detailed design.
1.3.2 Design Change Allowances (DCA)
This allowance provides for changes to design during the engineering phase. These design changes are a normal part of the design activity and represent the anticipated weight growth of each individual item resulting from the development of the design
1.3.3 Fabrication Change Allowance (FCA)
This allowance provides for changes to design during the fabrication phase. These changes are a normal part of the fabrication activity and represent the optimization of the design in satisfying previously unidentified constraints arising during the fabrication phase. Examples are steel section substitutes and pipe work, cable work or duct work rerouting, over-rolling of plates, weld metal and paint.
2.0 ALLOWANCES
The weight contingencies shall be as per the PTS 34.19.10.30, Jan 2010 – Design of Fixed Offshore Structure and is reproduced below:

IAA	Vendor Catalogue	15%	5%
[C] vendor Data/Quotation	10%
[D] Calculated MTO	15%
DCA	5%	5%
FCA	5%	5%

Note:
1) IAA = Item Accuracy Allowance.
2) DCA = Design Change Allowance.
3) FCA = Fabrication Change Allowance.
The allowances used for this revision of report are summarized in the Table below:

Item accuracy allowance (IAA)	5%	10%	15%	15%
Design change allowance (DCA)	5%	5%	5%	5%
Fabrication change allowance (FCA)	5%	5%	5%	5%
Contingency Factor	1.15	1.20	1.25	1.25

Note: Contingency Factor = 1+(IAA+DCA+FCA).