For the purposes of this guide we define hybrid construction as systems that include a combination of hot rolled and cold rolled steel. This is generally in areas where additional hot rolled elements are required to enhance the performance of the structure.
LSF is a supremely efficient load-bearing solution and in lower rise structures where there is a full alignment of load paths from roof to substructure, a fully cold rolled structure can be highly efficient. However, in higher structures and those where set-backs and insets are formed, it is rare that the structure of a building would be formed purely from LSF. In reality most of these structures exhibit varying degrees of a hybrid approach:
Hot rolled steel (HRS) is present in varying proportions in every LSF building. HRS is used to break up areas of large span, with LSF doing the work in between. HRS is also introduced to cater for areas of more concentrated load, such as from stairs, lift shafts or to provide cantilevered support for balconies. External structural features, outside the line of the warm frame, are also most commonly formed in HRS.
Concrete
Concrete, in the form of composite metal deck intermediate floors is a very common companion.
In addition, concrete is by far the most common foundation layer for LSF systems.
Timber
Timber – duo-pitch, cold roofs are frequently formed in timber trusses supported on LSF walls. And on occasion CLT, or glulam timber components, which rely on steel to create their joints, are also integrated with LSF components forming external walls – where timber is no longer permitted in buildings >18m.
In reality there is spectrum between LSF and HRS, with simple low-rise structures (houses) being potentially 100% LSF, with higher and more complex structures having a greater proportion of HRS, with eventually higher structures having all load-bearing via HRS, with LSF purely acting as infill within the primary structure.
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Image credit: Reading Gateway - Kier
