From construction to reuse: How structural BIM software enables sustainable building design
Structural engineers play an important role in reducing the embodied-carbon footprint of the construction industry. Trimble Business Development Manager Sakari Lahti explains how small decisions on the desktop can have a massive impact on our planet.
One of my interests as a structural engineer is to help other engineers design buildings that are more sustainable. My work is particularly focused on concrete, as this is where our industry has excellent opportunities to make carbon reductions in design, material engineering, and during the construction phase.
I joined Tekla in 2013 as an application manager focused on growing our global precast business. With sustainability becoming a more pressing issue, I soon saw that optimising a building to minimise its embodied carbon is done with similar mechanisms to those used for calculating material costs. I thus had the idea of making embodied carbon a design parameter in our software, so we validated the need and proceeded with development.
Over the past decade I’ve seen that not everyone in our industry is familiar with the benefits of Building Information Modelling. The BIM methodology is essentially about improving the entire construction process, with data as the value-adding factor.
This was not understandable enough in the early days of BIM. For example, just saying ‘a thicker wall has higher volumes and you can export all this information to a spreadsheet’ does not really help the designer to understand the impact of making that wall thicker. The benefit of BIM becomes much clearer when you can dynamically see both the cost and the embodied-carbon impact of a proposed design decision.
Why is this important?
As structural engineers we have the power to make a massive positive impact on minimising CO2. Our professional decisions have a far greater impact than any we make in our private lives.
For example, if I choose not to take a flight from my home in Finland to a city in Italy, I will save approximately 300 kg of CO2. If I go on a plant-based diet, then I may save 500 kg of CO2 each year. Driving a hybrid car may save 600 kg over a year, while going completely car free could double that.
Every bit helps, but the point is that these numbers are miniscule compared to the impact a structural engineer can make by optimising the materials used to construct a building – particularly when it comes to concrete.
More than 950 tons of concrete are poured globally every single second, while some 350 tons are destroyed at the same rate. When we think of all the emissions generated from this concrete, we need to understand that very small percentage changes in certain parameters can make a huge difference to embodied carbon. This is why our profession can have such a profound impact.
From the point of view of the contractor and the fabricator, standardising and repeating a building’s concrete design may make sense in terms of getting the job done quickly. Even though the loads on different floors and walls vary greatly, the structural designer may be asked to use the same columns and slabs for the ground floor, the top floor, and all the floors in between.
However, as end-customer awareness of embodied carbon increases and the cost of materials rises, contractors and fabricators are becoming more interested in optimising utilisation ratios.
A standard utilisation ratio is approximately 80%. But with just a few optimisations you can easily get this up to 90%. Optimising a design not only reduces the materials used in the fabrication stage, it also reduces the CO2 generated from transportation.
Sometimes optimisation can simply mean using less concrete than needed in walls and slabs, or converting some elements to a more efficient geometry. Just changing a bearing direction, for example, can often lead to a higher utilisation ratio. Parameters such as wall or slab thickness, materials used, and type of reinforcement can all have an impact on embodied carbon. The earlier in the design process you start to optimise, the greater the impact can be.
Determining the optimal combination of these parameters is challenging without a tool like the embodied-carbon calculator we’ve built into Tekla. By enabling engineers to easily compare the environmental impact of different design iterations, we’re encouraging the industry to make sustainability a key factor in the decision-making process.
Optimising for disassembly and reuse
There’s also a future-proof dimension to using Tekla tools for calculating embodied carbon.
Tekla is highly customisable software that’s designed for adaptation to the fast-evolving regulations and requirements of the circular economy. There is now increasing emphasis on designing buildings that are easy to take apart at their end of life, so that the constituent materials can be reused in new constructions.
This departure from the demolition practices of the past requires rethinking certain details within a structure. Among other things, I foresee changes to connections and increases in prefabricated construction.
We need to be sure that BIM software is able to keep up with this evolution, as detailed BIM data is of great value to the building owner when considering the materials in a building at the end of its life. This is an area that’s now getting a lot of attention, with Trimble involved in some important research aimed at finding the way forward.
I expect to be able to share some news on this work during 2023.