Steel Buildings in Europe

Part 2: Concept Design 2 - 28 4.3.1 Rigid frames For buildings up to four storeys high, ri gid frames may be used in which the multiple beam to column connectio ns provide b ending resistance and s tiffness to resist horizontal loads. This is ge nerally only possible where the beam s are relatively deep (400 mm to 500 mm) and where the column size is increased to resist the applied moments. Full depth end plate connections generally provide the necessary rigidity. 4.3.2 Braced frames For buildings up to 12 storeys high, braced steel frames are commonly used in which cross , K or V bracing is used in th e walls, gener ally within a cavity in the façade, or around stairs o r other se rviced zones. Cross b racing is designed in tension only (the other m ember be ing redundant). Cross bracing is often simple flat steel plate, but angle s ections and channel sections m ay also be used. When bracing is designed to work in com pression, hollow sections are often used, although angle sections and channel sections may also be used. A steel braced frame has the two key advantages:  Responsibility for temporary stability lies with one organisation  As soon as the steel bracing is connected (bolted), the structure is stable. 4.3.3 Concrete or steel cores Concrete cores are th e most practical sy stem for buildings of up to 40 storeys high, but the concrete core is generally constructed in advance of the steel framework. In this form of construction, the beams often span directly between the columns on the perim eter of the bu ilding and the concrete core. S pecial structural design considerations are required for:  The beam connections to the concrete core  The design of the heavier primary beams at the corner of core  Fire safety and robustness of the long span construction. Special attention must be paid to the connections between the steel beams and the concre te cores allow ing f or adjustment, anticipating that the core may be out of position. The connection itse lf m ay not be com pleted until in situ concrete ha s cured, or until elements have been welde d, so attention to temporary stability is important. A typical layout of beam s around a conc rete core is shown in Figure 4.3, showing the use of heavier beams at the corner of the core. A double beam may be required to minimise the structural depth at the corner of the cores.