Unbraced composite structures in fire (UCoSiF) : final report

Designers paid to date little attention to unbraced composite frames as a structural system for buildings. Two main reasons hindered a more frequent application. First, normative regulations lack simplified methods for the fire design of unbraced composite frames. This can be attributed to their sway and the linked P-Δ-effects that complicate the design compared to non-sway structures. Second, it is demanding to construct external composite joints for the regarded one-bay frames. Thus, even in composite constructions external joints are mostly constructed as mere steel joints. Nevertheless, unbraced composite frames offer important advantages. These include increased usable space, fast construction times, and inherent fire resistance. Thus, these frames are particularly interesting for one-bay office buildings with three storeys at most, where most European building codes require the fire rating R60. To meet these requirements, a design concept for fire-exposed unbraced composite frames was established in this project. This concept was verified by test series on columns, joints, and frames at both room temperature and under fire-exposure. Accompanying numerical studies further deepened the understanding of the frames' fire performance. Overall, results showed that unbraced composite frames are a serious alternative to traditional load-bearing structures in low- and medium-rise buildings. In this project, technical foundations were laid for a new type of construction for office buildings with one to three storeys. Aiming at high share of prefabrication of the frames, the proposed design concept results in fast, economical, and reliable construction times.