Best practice guidance is given below on the key factors, together with information on “lead times”, erection times and typical prices.
Commercial Factors
The following are profitable factors that should be considered when estimating the cost of steel construction project:
This is often left far too late for the good of the project.
In order to fully obtain the experience and expertise of the steelwork contractor and the benefits of value engineering, the steelwork contractor should be engaged at the earliest possible opportunity.
While delivery periods of 12-14 weeks or less are usually achieved, it frequently leaves less time than is desirable for the consultants, the contractor and the steelwork specialist to jointly review the design and construction methods and agree the very best solutions to be used. Earlier involvement will also increase the levels of understanding and project knowledge of all concerned and reduce the probability of variations and and/or delay.
Contract Conditions
Comparatively cruel terms and conditions will result in higher prices from specialist contractors such as steelwork, which requires significant investment in materials and fabrication processes before any completed work arrives on site.
Making interim payments for work and materials in the process of being fabricated but not yet delivered or erected, will often lower the overall steelwork costs and improve contingency planning. The Client also has the benefit of knowing that his steelwork has been ordered and paid for and that the risk of material availability is not a threat to his program.
Similarly, the system of deduction of cash retentions is incompetent and is no longer operated in a number of areas of specialist contracting, including steelwork.
Market Conditions
Current order levels and mix of work/fabrication shop loading characteristics will affect price levels.
When conferring with or inviting possible steelwork contractors for a particular project, ascertain how busy they are in terms of their total design, detailing, fabrication and erection capacity when the work is to be placed.
Complete “Frame Package”
Many steelwork contractors are able to undertake additional work packages, for example concrete work, fire protection, decking and cladding. Also the larger the project the greater the scope is for economies of scale, for example a special production line can be set up for repetitive components.
Site Organization
Good site co-ordination will ease a smooth running project. “Closed” sites in central city locations, as well as remote sites, necessitate premiums caused by transport and logistics. Ensure that there is adequate access for steel transportation, unloading and erection, both on the site as well as on surrounding or adjoining access roads.
Ensure that there is enough well prepared level ground that
is adequate to take the requisite wheel loads.
Ensure that everyone is aware of the need to comply with the BCSA Safe Site Handover Certificate and maintain its provisions.
Ensure that pre-site co-ordination is defined and that where the crane is to be supplied by others, it will always be available in accordance with the agreed erection schedule. Ensure that all foundation work will be completed within the agreed schedule and that all anchor bolts will be set in place within the specified tolerances, free from damage and contamination. All work to be connected to or needy upon the steelwork needs to be properly identified as to whether the steelwork contractor is responsible for supplying and/or installing it, or it is the responsibility of others.
TECHNICAL FACTORS
There are a number of general "technical" factors that apply to most projects. Some relate to the difficulty of the particular project, whilst others are specific to the type of project, e.g. multi-storey, portals, trusses.
Specification
Conformance with the National Structural Steelwork Specification for Building Construction (NSSS) will reduce uncertainty; more demanding tolerances or testing than that specified in the NSSS will increase costs.
Bay Size
Structural steelwork prices are influenced by both the size and quantity of pieces used in the frame. (i.e. number of pieces per ton). This in turn is largely dependent on bay size. Consider larger bay sizes, where the extra weight due to longer spans may be totally offset by the reduced price per ton and the saving in number of columns and related workmanship. Also the resultant column – free space generally adds value to a project.
Structural steel frames must have the required degree of lateral resistance to wind loads. This can be provided by a stiff core or by the frame itself - diagonal steel bracing is usually a less expensive solution than moment frames.
Complexity
Modern CNC fabrication equipment can cope with complex individualistic designs but, in general, the more compound the fabrication required the greater the cost. Fabrication is more economic with:
Wherever possible, leave the choice of the connection detail to the steelwork contractor as the type and design of connections directly influences the total frame cost.
Rationalize the range and tonnages of section sizes used.
Complex individualistic designs are going to cost more per ton even with modern CNC
Materials
Avoid mixing steel grades where possible and rationalize the range of section sizes/tonnages used in order to minimize cost, lead times and shop handling. In general steel grade S275 will be adequate, unless the strength requirements of grade S355 are essential.
Ensure that the most appropriate sections are specified for the particular application. “I” sections are usually most economical in conventional framing, while tubular sections are a possible alternative for columns as well as for long span trusses. While tubular sections are higher in first cost than “I” sections, their lower overall gross weight required to perform the same function can largely offset this, often with an “aesthetic bonus”. Asymmetric beams are often used as part of a reduced construction depth floor system. Plate is usually used to fabricate economic “I” sections for longer spans and in connections, stiffeners and base plates.
Architectural Influence
Ensure that unnecessary finishing is not specified and that any applied corrosion resistant coating is suitable for the environmental conditions to be encountered. Grinding of welds is usually only necessary for exposed steel in close proximity to a building's occupants.
Quality of Engineering and Documentation
Completeness and accuracy of information are very important for a steelwork contractor to be able to properly assess the work involved.
Where the steelwork is pre-designed, ensures that all member sizes are shown and that the connection forces are shown or is available.
LEAD TIMES
Steel construction "lead time" figures of, say, 10 to 12 weeks are often quoted in journals.
The figures usually quoted are in fact "length of order book".
The information that specifiers really need to know is the elapse time from placing an order to the time of start of delivery of steelwork to site and commencement of erection. Obviously this varies depending upon the size and complexity of the project, but for relatively straightforward projects the period from receipt of order with full information to start of delivery can be typically around 6 to 8 weeks.
Similarly erection times can differ depending upon location and complexity of the project, but for, an 8-storey office building, are typically around 1,500 m² of floor area per week, using two hoists.