Multicriteria Decision Analysis of Steel and Mass Timber Prototype Buildings in the Pacific Northwest

This study used multicriteria decision analysis to quantitatively compare two prototype buildings, both designed using equivalent mass timber and steel structural systems across four decision criteria of seismic resiliency, global warming potential, superstructure cost, and durability. The 5-story and 12-story prototype buildings were both located at an arbitrary site in Seattle, WA. The first three decision criteria were quantitatively measured for each prototype building and durability was assumed to be equivalent between the alternatives. Seismic resiliency was measured using the median expected annual loss calculated using as a percentage of predicted building replacement cost using a procedure in line with FEMA P-58. The global warming potential was measured over the production, construction, and end-of-life stages using the life-cycle analysis program Athena Impact Estimator for Buildings (IE4B). The superstructure cost was calculated as the average cost per square meter using 10 estimating variations that attempt to account for uncertainty in market rates of material, labor, and mass timber design efficiency. Five decision-maker scenarios were analyzed that span the practical range of decision-maker priorities, as informed by discussions with architects and engineers active in the Pacific Northwest. Results from this study showed that for decision-maker cases where the global warming priority was low, steel buildings were the preferred choice. For cases with moderate to high global warming priority and low priority on cost, mass timber buildings were the preferred choice. However, for decision-maker scenarios with moderate priority on both global warming potential and cost, the steel and mass timber buildings were approximately equivalent. Finally, a hybrid steel–timber alternative was presented as a possible sweet-spot solution that merged the benefits of each building material and minimized their drawbacks, making it the most-preferred solution for the case of moderate priority on both cost and global warming potential. The hybrid case was also close second in ranked choice for all other scenarios examined.