Fire resistance tests and analysis of plasterboard-encased steel columns under standard conditions
Octavian Lalu, Tom Lennon, Thomas GernayPurpose
This study investigates the fire performance of Type F plasterboard-encased steel columns under standard fire exposure conditions, addressing a research gap regarding fall-off behaviour in column protection systems. Six full-scale 203 × 203 × 52 kg/m steel columns, three with single-layer 15 mm protection (60-min target) and three with double-layer 30 mm protection (120-min target), were tested under sustained axial loading. The research quantifies fall-off temperatures and times for Type F plasterboard, providing empirical data to support advanced numerical modelling and structural fire engineering design calculations.
Design/methodology/approach
Six full-scale steel column specimens from three manufacturers were tested in a column furnace under ISO 834 standard fire exposure with sustained axial loading (60–66% of ambient capacity). Columns were 3.4 m tall and box-encased in Type F plasterboard, using proprietary steel framing systems. Temperature measurements included thermocouples in the furnace, on the steel surface, and on the plasterboard rear face. The tests measured heat transfer, mechanical stability, fall-off time/temperature, and failure mechanisms.
Findings
Single-layer systems (15 mm Type F) achieved fire resistance exceeding 60 min, with plasterboard fall-off at 785–795 °C after 81–94 min. Double-layer systems (2 × 15 mm Type F) exceeded 120-min targets, with first-layer fall-off at 755–790 °C after 135–155 min. Load-bearing failures occurred before fall-off in all cases, with steel temperatures ranging from 570 to 620 °C. Therecommended design limiting temperature of 550 °C was exceeded in every specimen prior to structural failure, demonstrating the conservatism of simplified design methods. Fall-off resulted from coupled thermal degradation and mechanical deformation of loaded columns, distinguishing columns from wall/ceiling assemblies.
Research limitations/implications
The testing programme was limited to a single column section (203 × 203), reducing applicability to other sizes; smaller sections would heat faster due to higher surface area-to-volume ratios and may require separate analysis. Load ratios (0.60–0.66) represent standard fire scenarios but do not explore the effects of eccentricity or second-order effects. Temperatures between plasterboard layers were not measured due to concerns regarding system protection. Validated finite element models could enable extrapolation to untested configurations and design optimisation tools.
Practical implications
The research provides fire engineers with evidence-based fall-off temperature ranges for Type F plasterboard, enabling them to calibrate advanced numerical models with greater confidence. Designers can now account for realistic protective performance durations in structural fire design calculations. Single-layer 15 mm Type F systems reliably exceed 60-min ratings; double-layer systems exceed 120 min, offering flexibility in retrofit and lightweight construction applications. The findings validate that conservatism in simplified design methods (using 550 °C critical temperature) remains justified. Practitioners could reference these benchmarks when developing system-specific fire-resistance performance predictions for commercial applications.
Social implications
Understanding the performance of plasterboard-encased columns at elevated temperatures improves the overall building fire safety. More accurate fire-resistance predictions enable safer, code-compliant design of steel-frame buildings, particularly in mid-rise residential and commercial construction. The research supports evidence-based regulatory standards and performance-based design approaches, allowing for protection optimisation and cost reduction while maintaining adequate safety margins.
Originality/value
This research provides the first comprehensive experimental quantification of fall-off temperatures for Type F plasterboard-encased steel columns under sustained axial loading, a critical gap in the literature. Previous studies have largely focussed on the fire performance of light steel frame wall and ceiling assemblies. This work demonstrates that protection failure is a coupled thermo-mechanical phenomenon influenced by structural deformation. The empirical dataset from six full-scale specimens across three manufacturers provides robust benchmarks for validating advanced numerical models. The findings advance structural fire engineering beyond simplified design methods by characterising realistic protective performance, enabling more accurate fire resistance predictions and supporting evidence-based regulatory standards for steel-frame construction.