Search for: All records

The resistance of thin-walled steel beams in fire is governed by a complex interaction between the buckling of the plates and the lateral-torsional buckling (LTB) of the member, combined with the temperature-induced reduction of steel properties. Besides, in many applications, steel beams are subjected to non-uniform thermal exposure which creates temperature gradients in the section. There is a lack of analytical design methods to capture the effects of temperature gradients on the structural response, which leads to overly conservative assumptions thwarting optimization efforts. This paper describes a study on the strength of thin-walled steel beams subjected to constant bending moment in the major-axis and thermal gradients through analytical and Machine Learning (ML) methods. A parametric heat transfer analysis is conducted to characterize the thermal gradients that develop under three-sided fire exposure. Nonlinear finite element simulations with shells are then used to generate the resistance dataset. Results show that the use of the Eurocode model with a uniform temperature taken as the hot flange temperature severely underestimate the moment strength with an R^2 of 0.61. The ML models, trained using physically defined features, are far superior to the Eurocode methods in predictive capacity. The ML-based models can be used to improve existing design methods for non-uniform temperature distributions. 

Cold-formed steel assemblies are commonly used for partition walls in buildings, playing a critical role for fire compartmentation, and are also increasingly used as load-bearing structural systems due to their high strength-to-weight ratio and suitability for off-site prefabrication. This evolution leads to a need to characterize the behavior of these systems under the combined action of loading and fire. The objective of this paper is to provide a review of experimental studies on cold-formed steel members and assemblies at elevated temperatures. A comparative overview of testing methods is presented with a focus on the heating and loading procedures, temperature distributions, and end boundary conditions. The review covers experimental tests on lipped channels and built-up sections in compression and flexure, and wall and floor assemblies. The impact of elevated temperature on material properties and member strength is explored. Drawing on data from 30 experimental studies, the review examines the effects of end boundary conditions, section shape, temperature distribution, gypsum sheathing, and internal insulation on the stability and strength of the thin-walled members. Recommendations for future research include member experiments with non-uniform section temperatures and under localized fires, comparisons of steady-state and transient tests, and studies on lipped channel joists. By synthesizing key findings and identifying research gaps, this review aims to guide future experimental studies and support the advancement of building codes and performance-based fire design methods for cold-formed steel structures. 

This paper describes an experimental study on the behavior of load-bearing cold-formed steel (CFS) members under elevated temperatures from fire exposure. A custom-built electrical furnace with six independently controlled heating zones was installed in a loading frame, enabling testing of CFS members under uniform or non-uniform elevated temperatures. The ability to precisely control temperature gradients between the flanges allows testing a single member to failure under thermal conditions representative of a wall assembly exposed to fire on one side, capturing the effect of thermal gradient on the buckling behavior. Steady-state tests on short (18 in.) 600S200- 54 lipped channels in compression were conducted at temperatures up to 600 °C, including tests with uniform temperatures and tests with 100°C gradient between the two flanges. Coupon tests were also conducted to characterize the material properties at elevated temperatures. The members lost about 23% of their strength at 400°C and 66% at 600 °C. For these short specimens under nonuniform heating, with one flange 100°C hotter than the other, the member strength fell between the strengths associated with the temperatures of the hot and cold flanges, with limited asymmetric effect on the local buckling response. This experimental data can support the development of design methods for CFS members in fire, enabling performance-based fire design. 

The objective of this paper is to investigate the post-earthquake thermal-mechanical response of cold-formed steel (CFS) members. A 10-story cold-formed steel building (CFS-NHERI) will undergo seismic tests, followed by post-earthquake live fire tests. To support the fire test setup, computational models are developed to simulate the impact of varying post-earthquake damage levels on the fire response of the structure. As a panelized system, damage to different finish and nonstructural systems significantly affects the thermal behavior and load-bearing capacity of the CFS components. The computational models integrate the modeling capability in CUFSM and SAFIR for the elastic buckling, heat transfer, and transient structural analysis under fire. A parametric analysis considering different seismic damage levels is conducted to study the buckling and strength behavior of the CFS members under fire-induced nonuniform temperature fields. These pre-test models inform the duration and severity of the fire tests to maintain structural stability while achieving substantial thermal loading on the CFS load-bearing system. They also provide guidance for the sensor layout plan for the fire tests. This study advances methods for fire resilience of thin-walled CFS structures under multi-hazard scenarios.