Reference vs Proposed Structural Designs

[Max4067]

Dear eTool,

have a question on reference vs proposed structural designs. Hypothetically, if we are working on a project where the major structural element is CLT, we are given a bill of quantities based on the CLT. But, our reference design assumes conventional standard practice (e.g. reinforced concrete and steel). But, we don’t have the quantities for those materials since our building is built with a different material.

My question regards how we model the reference design:
– The CLT is being used in lieu of conventional concrete and reinforcing steel.
– But we would model our reference design with concrete and reinforcing steel (or whatever standard practice materials are used)
– Based on BoQ, we don’t have what the hypothetical quantity of concrete and steel so how do we go about quantifying these materials in our reference design? Can we use the quantity of CLT as a estimate (even though, the quantity of CLT would be different if the building were built using concrete and reinforcing steel)

Wondering, in any other such cases, what other people have done in modelling their reference design, or vice versa modelling their improved design to inform design decisions (in instances where project may wish to use CLT)

[Fei Ngeow]

Hi Max,

Thanks for the great question! Usually our users would seek the advice of their structural engineers to give them an estimate on quantities of concrete/steel used for a similar project.

If the project is only at design review stage and if for some reason an estimate is unobtainable at the time of assessment, you may consider taking on the assumption that the CLT is replaced by the same volume of reinforced concrete. Typically you’ll need less concrete (in volume) than CLT for the equivalent structural integrity. Therefore please bear in mind the GWP savings may be overstated with this assumption if you’re using it for any point/credit calculation predictions.