I found this article really interesting, showing that concentration on connection design could help Steel Entrepreneurs to focus on 50% of their production costs. As a practitioner in this area, I faced many times with unproductive design of connections which resulted in many errors during the design, production and erection phases. Modularized design is one of my solutions in this regard.
COST BASED ENGINEERING AND PRODUCTION OF STEEL CONSTRUCTIONS
H.G.A. EVERS, ICCS bv The Netherlands IR. F. MAATJE, ICCS bv The Netherlands
ABSTRACT
In the last years Steel construction companies in Northern Europe have mainly invested in production machines in the factory: Sawing and drilling machines, punching and shearing machines and Robot flame-cutting. Investments, which reduce the production costs of the Steel structure, looking at the complete development of a building, quit at the end of the whole process. We as ICCS bv state that there are more savings possible if investments are done in the engineering and design, at the start of a project. This will be the subject of our lecture. To know what the possible savings are, the engineer needs to have good knowledge about costs of Steel constructions and software that helps him to make costs clear. In our lecture we will present the state of art of software tools available for the steel construction industry.
WHERE ARE COSTS IN STEEL CONSTRUCTION
In order to be able to reduce costs, it is necessary to know how the costs of creating a steel structure are build up. In regard to this we would like to make the following statement: Approximately 50% of the total costs in a steel structure can be redirected to the connections in the structure.
Roughly, the following cost items in a steel structure can be identified:
1) Design 13%
2) Material 38%
3) Production 27%
4) Coating 10%
5) Erection 12%
COSTS RELATED TO THE CONNECTIONS
Design costs: These can be divided in:
1) Pre-design
2) Detailed design
3) Detailing and work preparation
1) Pre-design: 33% of costs related to connections:
In the pre -design most of the time is spent on main frame design and the stability of the structure. In the pre-design the engineer only has to consider connections that influence the global behaviour of the structure: The so called rigid or semi-rigid connections. Simple calculation rules are available (SG-TCA10a).
2) Detailed design:
55% of costs related to connections: In this phase the engineer has to detail all the connections that influence the behaviour of the structure in detail. When semi-rigid connections are used the behaviour of the steel frame is influenced by these connections.
3) Detailing and work preparation:
77% of costs related to connections: The draftsman spends nearly all his time on detailing connections in the steel structure. Using StruCad, the draftsman spends 10% of the time to set up the steel frame. The rest of the time is spent on detailing the connections and printing and plotting the drawings.
Material costs:
40% of costs related to connections: In normal Steel structure plates contributed approximately 5% of the total weight. Using rigid connections, the field moment will be reduced. The amount of used material can is less. So there is a strong relationship between the type of connection and the amount of material in the structure.
Production costs:
63% of costs related to connections: Nearly all the work in the shop is related to the connections of the steel structure: Prefabricating plates and cleats, the tack welding of the plates to the beams and columns and welding.
Coating costs:
38% of costs related to the connections: The coating of the small parts like plates and cleats of the steel construction takes more time than coating the main beams and columns relatively.
Erection costs:
45% of costs related to the connections: It is clear that on the erection site the connections are fitted together. Easy connections will be less time consuming then difficult connections
This means that approximately 50% of the costs are directly related to the connections in a steel structure. In order to reduce costs in the total process it is of great importance to look at the connections at an early stage. In Dutch practice there are a lot of examples of projects that ended in court due to severe problems with the connections. In frame analysis packages it is very easy to analyze a structure in which all frame elements are rigidly connected. However, in practice, it is (almost) impossible to connect frame elements fully rigid. If it possible, then the costs of that particular connection will be very high.
As many costs are related to the connections, it is fair to say that at the end of the detailing the final price of the structure is determined for approximately 88%. The connections determine the material and hence the production in the shop and on site.
The next figure illustrates this.
How are the costs built up?
On the horizontal axis the progress in the project is shown. The percentages of costs are given along the vertical axis.
The continuous line represents the costs of the wages made during the project. The middle dashed line represents the total costs made during the project. The left dashed line shows the amount of costs that is fixed.
As in the design and detailing phase many costs are fixed. It is very important for an engineer to have a tool with which he can estimate what the financial consequences of his decisions during the design will be.
