Steel frame structures

A frame of pin-jointed beams and columns is a mechanism until you stop it swaying. Lateral stability against wind and notional horizontal loads comes either from bracing, from moment connections, or from a concrete core. The most economical route in most low and medium-rise buildings is vertical bracing in a few bays, cross bracing, K-bracing or a diagonal, that turns wind load into simple tension and compression in the diagonals and carries it to the foundations. Floor plates then act as horizontal diaphragms, tying every column back to the braced bays.

Connections decide how the frame really behaves and where most of the cost and risk sits. Simple, nominally pinned connections use flexible end plates or fin plates and are quick to fabricate and erect. Moment connections, with extended end plates and sometimes haunches, transfer bending between members and let the frame stand without bracing where an open elevation is needed. We design every connection to the Eurocodes and to the Green Book methods, and we set out baseplates, holding-down bolts and the transfer of load into the foundations so the steelwork contractor can fabricate without reworking our intent.

Steel frames suit almost anything that needs long spans, speed on site or heavy loads: warehouses and industrial units, offices, schools, retail, multi-storey residential over a transfer structure, and mezzanines inside existing buildings. Fabrication happens off site while foundations are cast, so erection is fast and weather has less hold over the programme. Openings for services thread through the floor zone, and future change is easier because the frame, not the walls, does the work.

The limits are worth naming plainly. Bare steel loses strength in a fire, so members usually need intumescent coating, boarding or concrete encasement to reach their required fire resistance period. Steel corrodes in wet or coastal conditions and needs galvanising or a paint system where it is exposed. Slender members can buckle before they reach their material strength, so lateral torsional buckling and web stability govern many designs rather than raw yield. We resolve each of these at design stage so the frame that arrives on site is the frame that works.