Construction - Multi-Storey Building Form.

A period of around 8–12 weeks is usual between placing a steel order and the arrival of the first steel components on site. Site preparation and foundation construction generally take a similar or longer period (see Fig. 2.11). Hence, by progressing fabrication in parallel with site preparation, significant on-site construction time may be saved, as commencement of shop fabrication is equivalent to start-on-site for an in situ concrete-framed building. By manufacturing the frame in a factory, the risks of delay caused by bad weather or insufficient or inadequate construction resources in the locality of the site are significantly reduced.

 Typical progress schedule (in weeks)
Fig. 2.11 Typical progress schedule (in weeks)

Structural steel frameworks should generally be capable of being erected without temporary propping or scaffolding, although temporary bracing will be required, especially for welded frames.This applies particularly to the construction of the concrete slab,which should be self-supporting at all stages of erection. Permanent metal or precast concrete shutters should be used to support the in situ concrete.

In order to allow a rapid start to construction, the structural  steelwork frame should commence at foundation level, and preference should be given to single foundations for each column rather than raft or shared foundations (Fig. 2.12).

Columns on large diameter bored piles
Fig. 2.12 Columns on large diameter bored piles

Speed of erection is directly linked to the number of crane hours available. To reduce the number of lifts required on site, the number of elements forming the framework should be minimized within the lifting capacity of the craneage provided on site for other building components. For similar-sized buildings, the one with the longer spans and fewer elements will be the fastest to erect. However, as has been mentioned earlier, longer spans require deeper, heavier elements, which will increase the cost of raw materials and pose a greater obstruction to the distributionof building services, thereby requiring the element to be perforated or shaped and hence increasing the cost of fabrication.

Columns are generally erected in multi-storey lengths: two is common and three is not unusual. The limitation on longer lengths is related more to erection than to restrictions on transportation, although for some urban locations length is a major consideration for accessibility.

To provide rapid access to the framework the staircases should follow the erection of the frame. This is generally achieved by using prefabricated stairs which are detailed as part of the steel frame.

The speed of installation of the following building elements is hastened if their connection and fixing details are considered at the same time as the structural steel frame design. In this way the details can be either incorporated in the framework or separated from it, whichever is the most effective overall: it is generally more efficient to separate the fixings and utilize the high inherent accuracy of the frame to use simple post-fixed details, provided these do not require staging or scaffolding to give access.

Finally, on-site painting extends the construction period and provides potential compatibility problems with following applied fire protection systems. Painting should therefore only be specified when absolutely necessary.

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