Basic design decisions may have a significant effect on the overall buildability and cost of a building. The right choices reduce conflict in the construction process reducing the likelihood of post remedial work.

1. Introduction

Design for Fabrication (DFF) and design for assembly (DFA) are the integration of steel structure design and process planning into one common activity. The goal is to make the steel design that is easily and economically manufactured. The importance of designing for manufacturing is underlined by the fact that majority of fabrication costs of a product (cost of materials, processing, and assembly) are determined by design decisions, with production decisions (such as process planning or machine tool selection) responsible for relatively less.

Here are some general design principles that are structured to help the designer for steel construction cost planning.

2. Part Quantity

The reduction of the number of parts is probably the best opportunity for reducing fabrication costs. Less parts implies less purchases, inventory, handling, processing time, development time, equipment, engineering time, quality control, assembly difficulty, inspection testing and etc. In general, it reduces the level of intensity of all activities through the entire life of the steel buildings.

3. Modular and Repetitive Design

The use of modules in design simplifies manufacturing activities such as inspection, testing, assembly, purchasing, redesign, erection, and so on. One reason is that modules simplifies the re-design process, help to standardize fabrication and simplifies erection.

4. Standard Section Utilization

Steel mills tend to overprice less frequent used steel sections, therefore, some steel sections are less expensive than others. Also lead times on frequently used sections are shorter than other sections. As a result, the high availability of the standard sections reduces both procurement lead times and costs. The use of standard sections refers to the production pressure to the fabricator, relieving in part the manufacture’s concern of meeting schedules.

5. Standardized Fasteners

In steel erection, various lengths of same diameter bolts may cause confusion among the erectors and even cause disruption in the erection works. In order to avoid these risks, the designer should try to group the length of the same diameter bolts. This will minimize the risk of using a longer bolt in a connection where shorter bolt should have been used which will later on cause a shortage of the longer bolt to be used where it is required.

6. Design for Hot Dip Galvanization

The design of the metal fabrications should be customized if they are to be galvanized. Hot dip galvanization requires good drainage, good venting, appropriate material combinations, appropriate welding and compatible product dimensions. Early consultation between galvanizer, fabricator and designer is the key to obtaining the best results from the galvanizing process.

7. Wastage Minimization

One of the top priority in the steel structure design is minimising the wastage. The designers should be aware of the potential wastage and should take corrective actions to minimize it. There are various solutions to this problem such as adding more connections to the design or changing the profile section. Each option should be calculated elaborately with the stakeholders in order to come up with the optimum solution for all parties.

8. Conclusion

Selecting the optimum combination between the material and fabrication process will lead to the ideal planning for steel construction. For example bolted connection are generally preferred compared to the welded connection since bolted connection offers simplicity and low cost, on the other hand, welded connections offer higher structural performance.

Rising labour costs steps up the pressure on the fabricators to adapt automation in their workshops. Modern workshops are equipped with various CNC controlled machineries to speed up the fabrication. The designer of the steel structures are expected to be in line with this trend and comply with the fast growing manufacturing technology without compromising the quality and compliance of the steel structure.

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