Structural Engineering Terminology

Structural Engineering Terminology

An explanation of some of the terms Cornell Engineers use in structural engineering:

Top Plate

The piece or pieces of timber that sit on top of wall studs to make up the top of a timber frame wall. In a timber frame wall top plates are often 1,2 or 3  pieces of 35 x 70 MGP12 or 35 x 90 MGP12. The top plate is the beam that supports the roof trusses or floor joists that sit on the wall frame. Under wind uplift, the top plate is tied down with either steel strap (30 x 0.8 G.I. strap) or steel tie rods (M12 or M16 rods).

6CFW (Continuous Fillet Weld)

Your steel fabricator will understand this terminology. CFW means a continuous (not-ending) fillet (formed between two intersecting pieces of steel) weld (a joint formed by gluing steel together with hot metal known as arc welding).

Double Stud

Double studs” and “Triple studs” are simply 2 and 3 studs placed together to support heavy loads or to provide extra strength beside windows and doors.

MGP Timber

MGP stands for Machine Graded Pine. Sticks of timber used to visually graded and assessed by a person that worked in the sawmill. Now a machine automatically assesses each stick of timber and allocates a grade. Standard MGP grades are MGP10 (normally non-structural timber), MGP12 (structural timber) and MGP15 (more expensive structural timber). The higher the grade, the higher the strength properties of the timber – but also the more expensive it is.

Post Tensioned Slab

A concrete suspended slab that derives most of its strength from high tensile cables that are draped through the slab at special locations and heights. Post tensioned slabs are used in commercial and industrial construction to reduce reinforcement, cracking and concrete thicknesses.

Post tensioned slab with tensioning ducts
Post tensioned concrete suspended slab

Raft Slab

Concrete raft slab
Raft concrete slab

A footing and slab system that gains its strength from a slab with an integral perimeter edge beam and a series of internal strip footings. The strip footings are normally 300mm wide and spaced at up to 6m centres. The edge beam is normally 300mm wide and is excavated into the ground. Strength of the raft slab system comes from steel reinforcement in the edge beam, strip footings and slab and also the depth of the beams. The depth of the edge beam (measured from the bottom of the excavation to the top of slab) gives excellent strength under the perimeter walls keys the slab into the ground. These are the main reasons we prefer raft slabs over waffle slabs.

Shrinkage Cracking

The cracks formed in fresh concrete if the water in the concrete mix evaporates before the hardening process can use it. As water leaves the concrete, the volume of the remaining concrete mix decreases leaving a smaller volume of semi-hardened concrete to fill the same space.


Rectangular Hollow Section (also known as rectangular box section) is a hollow, rectangular cross-section structural steel beam or column. Available from Metalcorp and AustubeMills.

Steel Stud

A stud is normally one of many vertical pieces of timber or steel used in a wall frame to support the roof and internal and external cladding (the wall). Steel studs are folded light gauge galvanised steel made into a “C” shape. They generally come in 70mm high “C” shapes and 90mm high “C” shapes.

Timber Stud

(So tempted to put a picture of Brad Pitt here!) A stud is normally one of many vertical pieces of timber or steel used in a wall frame to support the roof and internal and external cladding (the wall). Timber studs are normally softwood timber measuring 70mm x 35mm or 70mm x 45mm or 90mm x 35mm but hardwood timber can also be used. We prefer using MGP12 softwood but sometimes use MGP15 for heavy loads. MGP10 timber is used for non-loadbearing walls.

Truss Tie Down

More common in cyclonic areas, roof trusses need to be fixed to wall frames with straps or brackets to prevent roofs from lifting off in a cyclone.

Waffle slab (Also known as Waffle Raft)

A waffle slab is constructed on top of firm, flat ground by forming the perimeter with conventional formwork and the internal strip footings with polystyrene void formers. The internal strips of concrete are normally about 110mm wide and are about 1000mm apart. The strength of the waffle slab comes from reinforcement in the bottom of the internal strip footings and the 300mm wide perimeter edge beam (bottom reinforcement) and mesh reinforcement in the slab (top reinforcement) . Extra strength is achieved by increasing the height of the slab above the ground with resultant deeper internal strip footings and edge beams. The advantages of waffle slabs are they are quick and easy to construct. The disadvantages of waffle slabs are that they rely on the ground staying firm and flat (and dry) for best performance.

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