Comparative Life Cycle Assessment of structural steel and reinforced-concrete frames in residential buildings

Selecting structural materials is critical to reducing the environmental burdens associated with building construction. This study comparatively evaluates structural steel versus reinforced-concrete framing systems in two functionally equivalent three-story residential buildings utilizing identical waffle slab floor configurations in Ahvaz, Iran. The assessment was conducted in SimaPro using the ReCiPe 2016 Endpoint (H) method and was defined as a cradle-to-gate assessment supplemented with end-of-life considerations. The modeled stages encompassed raw-material extraction, material production, transportation, construction-related material flows, and end-of-life treatment and recycling scenarios. To strictly isolate and benchmark the cradle-to-gate and end-of-life embodied impacts of the structural frames independent of envelope physics and operational dynamics, the operational use phase (modules B1–B7) was deliberately excluded from the system boundary. Although the high thermal inertia of concrete relative to steel can significantly influence cooling loads in extreme climates like Ahvaz, dynamic operational simulation (module B6) was defined as beyond the current scope and recognized as a key limitation for future whole-building assessments. The results reveal important environmental trade-offs between the alternatives. The steel-framed building generated a higher total single score than the reinforced-concrete frame building, with scores of 53.59 kPt and 32.61 kPt, respectively, representing a difference of 20.99 kPt. Human health was the dominant damage category in both alternatives. The steel frame recorded 50.83 kPt for human-health damage, compared with 29.87 kPt for the reinforced-concrete frame; calculated relative to the steel alternative, this indicates that the reinforced-concrete alternative had approximately 41% lower human-health damage under the modeled conditions. At the midpoint level, however, the reinforced-concrete building showed an approximately two-fold higher global-warming impact than the steel building, highlighting a significant climate-change trade-off. Regarding the resource-related endpoint, the reinforced-concrete alternative showed a slightly higher score (0.06 kPt) compared to the steel alternative (0.03 kPt), although this difference accounts for only 0.06% of the total score. Crucially, the apparent advantage of the steel alternative in mineral resource conservation is highly conditional, relying on an idealized best-case recycling scenario that presupposes an efficient recovery infrastructure. The difference in ecosystem-quality damage was limited. Furthermore, while the single-score metric indicated an overall higher integrated burden for the steel frame, such aggregated scores carry inherent weighting subjectivity and should not be interpreted as absolute superiority. The findings demonstrate that structural material selection involves multi-dimensional trade-offs that are strongly dependent on local supply chains, operational dynamics, and real-world recycling efficiency.