Structural Peer Review, When A Design Needs One

A structural peer review is a second engineer, independent of the design, checking that the design does what it claims to do. It is not a redesign and it is not a rubber stamp.

Every design that leaves our office has already been reviewed internally by a senior engineer. An independent peer review goes one step further. It brings in someone who had no part in the design, has no stake in defending it, and looks at it cold.

When a design needs one

Not every building needs an external review. Some clearly do.

Complex or unusual structures, where the load path is not obvious. Large transfer structures, long cantilevers, unusual geometry, or a structural system the design team has not used before.

Tall buildings, where wind, earthquake and the lateral system dominate and the analysis model carries a lot of the design. The more a design depends on a computer model, the more value there is in someone checking the model's assumptions.

When someone requires it. A certifier, a council, a financier, an insurer or an asset owner such as a rail or road authority may make a peer review a condition of approval or funding.

When the design is in dispute. A builder proposes an alternative, a value engineering option is on the table, or something has gone wrong on site and the parties need an independent view on the original design.

When an owner simply wants certainty before committing to a large construction contract.

What a reviewer checks

A good review follows the load from the top of the building to the ground, and asks at each step whether the design has accounted for it.

The design basis. Are the loads right under AS 1170, including the importance level, wind region and terrain, earthquake site class, and the live loads for the actual use of each floor? A design built on the wrong loads is wrong everywhere, however carefully the rest is done.

The structural system. Is there a clear, continuous load path for both gravity and lateral loads? Are the cores, walls and diaphragms doing what the designer assumed? The principles are in [understanding load paths in multi-storey buildings](/blog/understanding-load-paths-multi-storey).

The analysis model. Are the assumptions reasonable? Cracked or uncracked stiffness, support conditions, how the slab and walls connect, how the foundations are represented. Most errors in modern design are in the model inputs, not the software, which is the theme of [finite element modelling in structural design](/blog/finite-element-modelling-structural-design).

The critical elements. Transfer beams, heavily loaded columns, punching shear at slab-column connections, and the connections and details that hold everything together. A reviewer checks a selection of these independently, often by hand.

The drawings against the calculations. It is surprisingly common for a calculation to be right and the drawing to show something else. Bar sizes, spacings, laps and cover on the drawings are what the builder builds.

What a review is not

A reviewer is not there to impose their own preferences. If the design is safe, compliant and buildable, a different way of doing it is not a defect.

Good reviews separate their comments into what must change, what should be clarified, and what is a suggestion. A review that mixes all three into one long list slows the project down and does not make the building any safer.

Timing matters

The best time for a peer review is during design development, when the structural system is set but the drawings are not yet issued for construction.

A review at that stage can change the design cheaply. A review after the drawings are issued, or after construction starts, can still find problems, but every change costs more and takes longer. On a project with a complex transfer level, for example, the review should look at the transfer concept before the floors above it are detailed, as covered in [transfer slabs and transfer beams](/blog/transfer-slabs-and-transfer-beams).

Independence

A peer reviewer should have no involvement in the design and no commercial link to the designer or the builder. The value of the review comes entirely from that independence.

The reviewer also needs to be qualified for the type of structure. A review of a 20-storey post-tensioned tower should be done by someone who designs 20-storey post-tensioned towers.

How we approach it

When we carry out an independent structural peer review, we check the design basis, the system, the model and the critical elements, and we give a clear written report that separates what must change from what is optional.

A design that survives an honest review is a design you can build with confidence. One that does not is far cheaper to fix on paper than on site.

ACSES provides structural engineering and independent peer review across Sydney. Talk to us about a project.

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