Standardization is the key to successful, efficient and economic detailing, the benefits of which are incalculable. It will reduce errors in the workshop and on site during erection and speed up the entire process from concept to commissioning.
There are two main steps to standardization, the first may be outside of the realm of the detailer, but it’s something he or she should be aware of because it will have an impact on how the detailing process is planned and implemented.
The second however is where the steel detailer can make a significant contribution - and make life easier for not only his or herself but for the fabricator and on-site erection team
Make the structure as far as possible, symmetrical by:
- Keeping the column sizes and centers equal – this will promote symmetry for the floor plans
- Keeping the floors and level elevations consistent – it’s not unusual for the first floor elevation above ground level to differ from the general floors, but this is perfectly acceptable.
Maintaining the remaining levels will simplify and enable column splice joints to be standardized together with the vertical stabilizing system (Bracing, Shear-Walls, etc…)
- Reducing the variation of beam sizes and spans – equal column centers will go a long way in achieving this.
For beam sizes, select the worst case and reuse it wherever possible – even if it will be over-designed in some cases, (within reason of course).
Achieving a symmetrical layout may increase the overall weight of the structure especially if some of the members are over-designed, but it must be kept in mind that the lightest possible steel structure is not necessarily the most economical.
The raw materials account for only 30 – 35% of the total project costs, while workshop fabrication can amount to the same. Site erection can account for between 10 and 15%, while coatings, fire protection, transport and engineering services make up the ‘other’ costs.
|Raw Materials||30 - 35%|
|Fabrication||30 - 35%|
|Erection||10 - 15%|
|Other||15 - 30%|
Standardize the Connection Components
Connections, in general, will account for less than 5% of the total tonnage of the structure, but will account for as much as 35% of the fabrication costs – so any advantage gained here will have a significant effect on the financial viability of any project – this is where the detailer comes into his or her own.
The following is a simple guide:
- Limit the connection options. Choose one and stick with it for the entire project, whether it be End-Plates, Cleats, or Fin-Plates. It’s never a good idea to mix-and-match connection types, standardization creates repetition which is beneficial to the fabrication process, it will also go some way in reducing the ‘learning-curve’ apparent at the beginning of the site-erection process. There may be instances where it’s unavoidable or even desirable, but this should be regarded as an exception.
Refer to the Connection Guide which demonstrates the advantages and disadvantages of each of the widely applied connection options, which include:
- Wherever possible, use standard ‘Flats’ for End-Plates and Fin-Plates, meaning they can be simply cut to length, reducing off-cuts and wastage. If the project is detailed using 3D Modelling and Detailing software, then this may not necessarily be a great advantage - the software should be able to optimize the cutting and profiling.
- Choose one bolt-diameter and stick with it as far as possible for the entire project. This will mean the workshop can set-up for production without having to continually stop to change drills or punches, it will also benefit the erector who won’t have to have multiple wrench sizes on-hand in order to tighten joints.
- Never mix Bolt-Grades. It will inevitably mean that at some point the wrong bolt will be placed in the wrong position. Where slip-resistant or HSFG bolts are to be used it’s a good idea to mark the bolt group with a marker or dab of paint being careful not to contaminate the joint mating surfaces.
- Consider using fully-threaded bolts, it will ensure fewer variations on bolt length. Just take into account the thread will be within the Shear-Plane of the joint.
- Standardize the Edge-Distances which are a function of the bolt diameter. For connections designed to resist shear only, the vertical edge distance should not be less than 2 x the bolt-diameter, while the horizontal distance should not be less than 1.5 x the bolt-diameter.
- Standardize the horizontal bolt-hole Pitch, which has been set at - 140 / 90 and 70 mm
- Standardize the vertical bolt-hole pitch, which, like the gauge, is a function of the bolt diameter. For flexible connections it should not be less than 3 x the bolt-diameter
- Standardize the Notch or ‘Cope’ This will enable the determination of the distance between the top of the beam and the first row of bolts. The notch depth and length are a function of the dimensional properties of the supporting beam. (Sometimes but rarely, they may be a function of the connecting beam)
Moment Connections are not quite so straightforward, they will be specified and designed by the responsible engineer – but that’s not to say they cannot be standardized to some extent.
Bracing Connections will depend on the angle of the bracing, but if the structure is set out with symmetry in mind – standardization should be achieved without too much trouble.