Anatomy of a PEB – all components in one model

Reading a PEB as a system

A pre-engineered steel building is made of a limited number of component families that repeat along the building length. Understanding these families – and how load passes from one to the next – makes it much easier to read a PEB quotation, a set of anchor-bolt and erection drawings, or a bill of materials. This article follows the 3D model on this page from the foundations outwards. Select a component in the model to open its own article.

The components fall into five groups: primary framing, secondary framing, roof and wall cladding, accessories and special structures. The way loads travel through them is described in how a PEB carries loads.

Primary framing

The primary frames are the "skeleton" of the building, spaced at the bay spacing (typically 6–9 m) along its length.

• Rigid frame columns – tapered or uniform built-up columns, pinned or fixed at the base.
• Rafters – tapered roof beams joined to the columns by moment connections at the knee and ridge.
• Tapered built-up members – the welded I-sections from which columns and rafters are made.
• Endwall framing – post-and-beam or rigid endwall frames at the building ends, designed for future expansion if required.
• Bolted end-plate connections – the knee, ridge and splice joints, assembled with high-strength bolts on site.
• Base plates and anchor bolts and the foundation interface – where the steel hands its reactions to the concrete.

Secondary framing

Secondary members span between the frames and give the cladding its support.

• Purlins – Z or C roof members, usually lapped over the rafters for continuity.
• Girts – horizontal wall members spanning between columns.
• Eave struts – the member at the junction of roof and wall, supporting the edges of both claddings.
• Flange braces – small angles from purlins or girts to the inner flange of the frame, controlling lateral-torsional buckling.
• Bracing systems – rod, cable and portal bracing that carry longitudinal wind and seismic loads.
• Sag rods and bridging – restraints that keep purlins and girts straight and stable.

Roof and wall cladding

• Roof sheeting – through-fastened trapezoidal profiles, the most economical roof.
• Standing seam roofs – concealed-clip roofs for low slopes and long sheet runs.
• Wall sheeting – profiled wall cladding, often in a different profile or colour from the roof.
• Insulation – fibreglass or mineral wool blankets, reflective foil or rigid boards.
• Skylights and translucent panels – polycarbonate or GRP sheets matching the roof profile.
• Insulated sandwich panels – factory-bonded panels for cold stores and high thermal performance.

Names and abbreviations on PEB drawings

PEB erection drawings use a compact vocabulary. Frames are identified by grid lines – numbers along the length, letters across the width – and members carry piece marks that match the bill of materials. A few terms describe position rather than member type: the end bay is the bay between an endwall and the first interior frame, the braced bay is any bay carrying rod, cable or portal bracing, and an interior bay is any other bay. Girts are by-pass when they run outside the column flanges, or flush (inset) when they are framed between columns so that the wall finish aligns with the column face.

Definitions of the main dimensional terms – steel line, eave height, clear height, bay spacing and roof slope – are in building dimensions and terminology, and the full list of terms is in the PEB glossary.

Accessories and special structures

Accessories complete the envelope and make the building usable:

• Ridge ventilators and wall louvers for natural ventilation.
• Gutters and downspouts for rainwater drainage.
• Trims and flashings at corners, eaves, rakes and openings.
• Canopies, fascias and parapets for weather protection and architectural finish.
• Doors and framed openings and windows.

Special structures are added when the building has to carry more than its envelope: crane runway beams and brackets for overhead cranes, and mezzanine floors for offices or storage above ground level.

World Steel supplies every group shown in the model as one coordinated package, with anchor-bolt plans, erection drawings and a part-marked bill of materials – see WSC pre-engineered buildings.