Engineering a steel structure

10 March

What is structural engineering and how does it influence your project?

In this episode of our SteelTalk webinar series, structural engineer Julian Luvara talks to Shane and Josh about what structural engineering is, and what is involved in engineering a steel structure for long term performance.

About Julian

Julian Luvara is a director of Eren Engineering and has been working with the Steelcorp team for some time. With nearly a decade of experience behind him, Julian has recently opened his own consultancy with his business partner.

With experience working on everything from residential buildings to hospitals to skyscrapers, Julian’s approach as an independent structural engineer is to work with builders to get the best solutions developed in less time. Following is a summary of our talk with Julian on the ins and outs of structural engineering.

So, what actually is structural engineering?

A structural engineer is responsible for creating the ‘skeleton’ of the client’s vision. In the case of a shed or a large steel structure, the building designer or architect can show you what is required from an aesthetic viewpoint, but it is the structural engineer that brings the design to life.

It’s a common misconception that the architect designs the building, and often if a client has a commercial builder on board in the early stages, they can be shielded from the nuances of this process.

However, although the architect’s job is very important, it is ultimately the engineer that ensures the building will actually stand up.

The 2 key elements of structural engineering: strength design and serviceability

Strength design refers to the design processes that ensure the building remains upright, and it encompasses a wide range of Australian Standards and National Construction Code requirements.

The other side of the coin is the serviceability of the building, sometimes referred to as the performance criteria – this is how the structure feels when you’re standing inside it.

Poor serviceability can feel like movement when the wind hits the structure, vibrations through certain areas, or wobbles on a mezzanine floor. This movement isn’t a strength design issue but it can impact the owner or tenant of the building, so the engineer will work to remove these issues.

In some buildings, the strength design is so prominent in the project that it almost eliminates any change of serviceability issues, for example, if the steel members are very large they will naturally dampen any potential vibration and movement.

Ultimately, your engineer must take serviceability into account not only to make the owner feel safe in their building, but also so that secondary non-load bearing areas such as partitions are not affected.

What is a structural engineer responsible for?

Ultimately the engineer is responsible – and liable – for the building’s structural integrity. They need to ensure the structure is designed to comply with Australian Standards and the National Construction Code, and any other applicable design criteria. This means that responsibility lies with them for any failures or non-compliance in the design.

For example, if a load-bearing concrete column starts to deteriorate and it is determined to be a fault in the structural design, liability rests with the structural engineer.

This is where it’s important to note the difference between engineers: not every engineer can offer a certificate of compliance (also known as a Regulation 126 certificate). Your engineer must be a registered building practitioner with the Victorian Building Authority, a process involving rigorous interviews and screening.

What is involved in engineering a steel structure?

The main aim of the design from an engineering standpoint is to ensure that load travels from the beams in the roof, right down into the ground to the columns and footings. A good design considers loads from the side, which are caused by environmental factors like wind and earthquakes.

As part of the design process, a good engineer will use a combination of analog and digital tools such as fine art 3D modelling, hand design, hand computations and their own experience. Whilst digital designs are a helpful tool, it’s unwise to rely solely on computer models, as getting hands-on early in a project can uncover design challenges that are easily missed when the process becomes too automatic.

Having an engineer on board from day one also allows an additional layer of insight into the project – with a full understanding of the structure, they can provide input as the project progresses which can save time and money down the track.

For our owner-builder or investment clients, it’s doubly important to have the input of a structural engineer from the beginning, as they can help guide your design choices and positively influence the budget.

What impacts the engineering requirements for my structure?

Soil quality

At the end of the day, your structure is sitting on soil, so it’s important to have a full understanding of the soil type.

We’ll often ask for a geotechnical report which involves drilling a few boreholes in the property and analysing the results in a lab. This will allow the structural engineer to get a full understanding of how strong the soil is and how this can impact the design.

If your soil is primarily fill (or disturbed soil) it can be more susceptible to movement, which in turn can affect the design of the footings. Footings are designed to take some load and pressure off the structure, which can lead to design efficiencies in the structure itself, so the right footings are essential, especially on poor soils.

On the other hand, if you have good strong soil, the engineer could look at design efficiencies, such as footings that are 1m deep rather than the standard 2m deep, which can provide significant cost savings.

At the end of the day, $500 – $1500 spent on an initial geotechnical report could save you as much as $30 – $40K down the track so it’s always wise to have one done even before purchasing the land.

Solar panels

Structural engineers are always aiming for the most efficient design – not just for cost-efficiency, but also as an environmentally sound choice, as structures shouldn’t be overengineered unnecessarily.

For this reason, it’s best not to assume that your structure will take solar panels, especially if you are planning a large solar array. This is where getting your engineer involved in the early design is a good idea. An ultra-efficient building design, for example, may not be equipped to take solar panels, air conditioning units or other mechanical units.

Factor in what will need to go on the roof and ensure you advise your engineer.

Geographical location and environmental factors

The location of your building affects its design, so your engineer will take into account environmental factors like the wind (which will impact every structure), earthquakes (which are rare but important to factor in), and snow (which won’t affect every building).

Firstly, wind hits a building from every direction, so a structure needs to consider the forces imposed upon it from every angle. In Australia, winds from the west are strongest so most structures should be oriented so the shorter (gable) side faces west. This serves to lessen the surface area facing the prevailing wind.

If site constraints mean the longer sides have to face west, the columns and other load-bearing structures need to be adapted to ensure the structure can handle the effects of strong winds.

Geographical location is important too: wide-open spaces don’t have the shielding impact of trees or the protection of other buildings, so the shed is likely to need bigger columns and rafters to handle the wind.

Coastal locations experience higher wind pressures, so an engineer will look at your wind region as indicated by the National Construction Code. Salt and corrosion can impact both the steel and concrete components, which is something that has to be managed in the design. Additionally, projects in alpine or subalpine regions need to consider the impacts of heavy snow accumulating on the roof.

An overall understanding of these environmental factors is critical to ensuring your engineer designs the right structure for the site.

Why are connections and fixings so important on a steel structure?

Connection points can be likened to the joints in your body: they don’t work in isolation and need to be designed to handle and transfer loads effectively.

Tension bolts are typically nominated for points where the bolts experience more stress, for example where columns meet rafters. This is in contrast to connections for points that experience shear forces, such as an internal column that supports a mezzanine floor.

In general, the fewer fixings you have in your design, the easier and cheaper it will be, and the fewer potential points of failure. A design with a lot of connections can get quite expensive, primarily due to the volume of steel involved.

A structural engineer will put a heavy emphasis on detailing when they design your steel structure, nominating fixtures in the drawings. The builder will then take these recommendations and detail them to suit the project. It’s common for your engineers and builder to work together so that this critical aspect of the design is fully understood by everyone.

Good to know: where can things go wrong?

If something goes wrong in a steel structure, it will often drag everything down with it. Whether it’s the result of a freak wind event or incorrect fixtures being used, things can sometimes fail in a small number of cases.

In the case of wind damage, structures are designed for 1 in 100-year wind speeds – but freak weather events can happen and sometimes these wind pressures and speeds are exceeded.

With all the safeguards and stringent requirements in the construction industry, failures are rare, but poor detailing is probably the number one thing that leads to issues. If the engineer’s drawings are ambiguous, the building may not end up being built to the engineer’s specifications, so clear communication is essential.

Thankfully, with many sets of hands and eyes on the project, and a building inspector and engineer on-site to inspect the project, 99% of structures remain safe, reliable and structurally sound for decades.

In summary: we recommend finding a structural engineer you trust, getting them on board early in your project, and sharing as many details as possible with them. This approach will give your project the best chance of success and potentially save you serious money and time.

This is a summary of Season 2, Episode 1 of our SteelTalk webinar series. Keen to see all episodes in the series? Visit our SteelTalk page to access all episodes.

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