INDIRECT HOURS - 30*
CONSTRUCTION EQUIPMENT - 20*
FIELO STAFF " 15%
FIELD OFFICE EXPENSES
100% LABOR COST
designers to more carefully consider the question of "Constructabil-ity." This is the design process of working to construction installation considerations, as well as working to standard design specifications. Constructability considerations can result in significant savings in construction labor. Such considerations are essential in the following types of construction:
• prefabrication and pre-assembly
• offshore hookup work
• site problems of limited access
• lack of resources at the jobsite location
The relationship between home office support services (project management, project control, procurement, computer, clerical, etc.) and engineering is also shown at 40%. This relationship is in manhours.
Figure 6-7 illustrates a typical relationship between construction complexity and labor density. Judgement is required in assessing the appropriate density level for the specific project.
Complexity (manhours/sq. ft.)
Complexity is "automatically" generated by the design specifications. This statistic is based on the number of direct construction manhours (within the plot) divided by the plot area (battery limits). As noted, this assumes that there is no "pre-investment" in the design basis. Pre-investment is a fairly common practice and is carried out when forward company planning has determined that the plant will need to be expanded within a few years. At the moment, the planned (design) capacity is sufficient. The design pre-investment, therefore, usually includes extra area in the plot for future installation of equipment. This "extra" area, open at the moment, would give "false" complexity manhours and density levels. This data can be used to quickly provide a reasonable manhour estimate when only the plot/building area is known. However, good judgment is required in selecting the appropriate manhour/sq. ft. rate.
CONSTRUCTION COMPLEXITY AND LABOR DENSITY
Only applicable ta "complete" Process Unitsi small or large)
0 Assumes an economic design - no "Preinvestment"
Based on "average" US labor productivLtyCCalif ./Union)
COMPLEXITY (direct manhours/sq.ft.)
0 AVERAGE UNIT 6/7
0 COMPLEX UNIT 8/10
Tied to above Complexity Data.
Density data Is based on a Prime EPC Contractor/reimbursable contract. For fixed or unit price contracts, density numbers should be increased by about 5Qsq.ft./man. This reflects the need for lower numbers of men to achieve higher productivity to meet "hard money11 financial requirements.
This statistic is based on the "economic" total number of craftsmen working at peak (supervision is not included). The data is based on historical experience and is tied to the complexity of the area. The more complex, the lower number of men who can work in the area. In practical terms, this means that greater complexity has more equipment (more manhours) per sq. ft., thus taking up space for the men to work in. As with the complexity data, good judgment is essential in selecting the appropriate density level.
Figure 6-8 compares the breakdowns (%) of overall costs and construction manhours for large, grass-roots projects against small, revamp projects. The data for the large, grass-roots breakdown is based on historical experience, whereas the small, revamp breakdown is typical only. As there are wide variations in the EPC makeup of small projects, the "typical breakdown" should be examined very carefully for its application to a specific project.
As with the previous exhibit, these breakdowns/relationships can be helpful in evaluating manhours, schedules and manpower requirements.
Figure 6-15 is a typical breakdown of total home office man-hours for a 'full scope" project. It is based on historical data for small-to-medium sized projects engineered on a reimbursable basis and executed during the period 1955-1975.
Application information can be used to check an estimate or a contractor proposal of home office manhours. It can be used for early evaluations of home office manpower and schedules when only total costs or manhours are available.
1. For a typical project, we can assess the percent piping manhours. This is derived by summing the hours required for piping engineering activities (plant design, 16.4%; piping engineering, 2.1%; bill of materials, 2.1%;and model, 0.4%; giving a total of 21%).
2. As a percent of engineering only, piping becomes 21%/0.67 = 32%. As overall engineering and piping design are often on the critical path, individual evaluations are frequently required. Where information is lacking, use the following:
• Engineering manhours as a percent of total home office: 65%
• Piping manhours as a percent of engineering: 35%
TYPICAL PROJECT COST BREAKDOWN (CONTRACTOR - TOTAL SCOPE PROJECT)
GRASS ROOTS-LARGE ITEM SMALL REVAMP
19 -----CONSTRUCTION INDIRECT---18
DIRECT CONSTRUCTION LABOR HOURS
Engineering Costs Approximately 10%Project Costco,
VARY WITH SIZE AND TYPE JOB
__________ . ÎES,'™:r'.nS cS,t'> 11 averalc FIrctnc of total imial'cd Costs. A, office buildings and laboratories; B. pp'-vsr plaffts. eemenr plants, kiins, and water systems;
C. ba tiiry-hm: ii chemical process plants; D. complex chemical and grits-roots ¿hcrtucal plants and pilot plants.
E ~ small rsvamp/retroflt projects
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