The logic of portal frame halls

The elements of the system

Portal frames

The main members: column and rafter joined with a rigid haunch. They give the large, column-free space.

Purlins

The members running between the frames and carrying the roof covering. These are typically cold-formed sections: Z or C profiles.

They have a double role: they carry the covering and they restrain the rafter laterally.

Wall framing

The framing of the side walls, also often from cold-formed members.

Bracing

Longitudinal stability of the hall from diagonal bracing or braced bays.

Where thin-walled steel appears

This structural type is a good example of the two technologies working together:

• the long-span main frame is hot-rolled,
• the purlins, the wall framing and the secondary structure are thin-walled,
• and the enclosing build-up follows light gauge steel logic.

The characteristic design questions

Wind load

On a large-area, light structure, wind suction and uplift can govern. Wind load and terrain category.

Snow load and drifting

On a large roof the drift locations — steps, rooftop structures, valleys — have to be examined separately. Snow load in Hungary.

The double role of the purlin

If the purlin also restrains the frame, its continuity and connections have to be designed for that.

Continuity of the bracing

Longitudinal stability rests on the braced bays — and their position is constrained by the plan and the openings.

What to watch in the build-up

A heated hall raises the same building-physics questions as a dwelling: thermal bridging, vapour control, airtightness — only over a larger area, and often with stricter fire requirements.

The point

A hall is the textbook mixed structure: the long span comes from the hot-rolled frame, everything else from cold-formed members. Where the boundary lies is a design decision.