METHODS TO REDUCE THE COST OF STEEL FRAME
The steel frame has many advantages, but it is traditionally considered that the cost is not one of them.
The cost can be affected by certain negative factors that can be avoided.
The purpose of this article is to consider methods to reduce construction costs and the main ways to improve the efficiency of the project for the customer.
The article "Steel Construction Economy" considers this issue in terms of a comprehensive assessment of the project cost and how the use of steel frame can reduce the cost of the life cycle of the building (as opposed to the standard assessment of the cost of structures only).
The purpose of this article is to consider methods to reduce construction costs and the main ways to improve the efficiency of the project for the customer. The latter can be divided into 3 main groups:
Architectural and layout
Organizational and technical.
Architectural and layout methods
In many cases, the material of structures (steel or concrete) for its most effective use requires different types of layout. Therefore, considering different options for a frame in terms of the use of structures, it would be rational to consider different options for the horizontal and vertical layout of the building. The expected effect of the right choice can provide 10-30% savings.
The design decisions made at the stage of development of the design documentation of MS (metal structures) largely determine the economic efficiency of the entire facility. A low-quality design will entail extra financial and time costs for the elimination of deficiencies or errors on the project. A low-quality design can entail extra costs associated with the overuse of building materials due to poor optimization in the calculation of load-bearing structures, the use of "extra" stocks and the use of non-optimal design solutions.
As metal structures are more "sensitive" to design errors than reinforced concrete, high-quality MS design is the cornerstone of an economically attractive steel frame. Moreover, design costs usually account for 2-5% of the total object cost, so savings on design can be considered useless.
The following methods can be used to implement an effective project:
Clarification of the constructive scheme. Clarification of loads, purpose of elements, places of transfer of loads, supports and bases (approximately 5-20% savings).
Multi-optional design. Consideration of many options of constructive schemes results in additional time costs, and, as a result, allows to determine the rational scheme with such types of joints, spacing and type of elements which provides the maximum economic efficiency.
BIM modeling technologies. BIM is the process of creating and processing data of 3D model of a building. The use of BIM reduces design errors, inconsistencies with other sections of the design, which entail extra costs. A BIM model provides accurate specification and list due to automation.
High strength steels. For structures for which the limiting states of the first group (in terms of strength) are decisive, it is advisable to use high strength steels. Currently, the difference in the cost of a sheet of strength class C245 compared to sheet C355 is about 8%, although the difference in the design resistance is ~ 31%. Therefore, the expected economic effect of its use is about 20%. Also, additional advantages can be the reduction of dimensions of section and the area of application of fire protection means.
Reinforced concrete structures. These structures include combined elements consisting of concrete (or reinforced concrete) and steel section combined with each other by means of special connections (anchors, supports, etc.). The inclusion of concrete in the work of the structure allows to reduce the cross sections of steel elements. The main types of such elements are beams and columns. Reinforced concrete beams should be used in case of high imposed loads as the concrete part of the section is engaged in the work already at the stage of operation. In the case of large spans, it may be necessary to install temporary supports under the beam for the period of concrete strength development or to make beams with a construction lift. Reinforced concrete columns are effective in multi-storey buildings as they provide the required strength with the minimum dimensions of the columns, and the fire protection cost is significantly reduced or may be zero due to the concreting of steel sections.
Use of domestic rolled products and welded sections. If the design includes an assortment of products that are not produced by domestic manufacturers and that are absent in warehouses, it results in an increase in the project cost and time. Such products have to be ordered abroad or the design has to be changed. Often the limited assortment can be compensated by the use of welded sections that allow to optimally design the structure. To analyze the available products, you can visit the relevant page on the USCC website – an assortment of available rolled metal products.
Structures with variable section. Beams, frames, mainly industrial, exhibition, trade, warehouse facilities with spans over 12 m. Savings of 5-15% through reduction of metal consumption.
Perforated solutions. They can be used as walls of beams with regular perforation intervals and as single cuts. This solution allows to reduce steel costs and provide the possibility of laying utility lines through the beam.
Construction lift. For structures with significant spans, for which the limit states of the second group (i.e. deformation) are decisive, it is advisable to consider the use of a construction lift. Also, this constructive method can be effectively used in conjunction with the use of high-strength steels or for reinforced concrete beams.
LGSF. For structures without significant requirements for fire resistance (e.g., joists, facades, frameless buildings), the use of LGSF is usually the most economical solution.
Differentiated fire protection. Due to the application of a differentiated approach — calculation of critical temperatures of the load-bearing structures of the building, the fire protection cost can be significantly reduced (approximately 30% with the use of fire protective paints). Also in case of application of the design and architectural solution regarding decorative finishing of columns and elements of the covering (cladding of columns, finishing of the ceiling, etc.), the fire protection costs for these elements can be significantly reduced.
Other methods. For example, small element solutions, lowering the joist, rational unification of elements, calculation according to Eurocodes, corrugated walls of beams and columns, etc.
Organizational and technical methods
In order to achieve the best economic efficiency of a facility with a steel frame, it is necessary to ensure a high quality of manufacture and installation of structures in addition to a high-quality design. One of the main factors is the rational parallelization of processes, simultaneous design and manufacture, as well as simultaneous production and installation. Other organizational and technical methods include the breakdown into initial grades, choice of rational methods and means of transporting structures to the construction site, optimization of production processes, organized designer's and technical supervision, etc. It should also be noted that if there are existing metal structures, they can be reused.