Russian Federation
Objective: to investigate the influence of non-stationary (cyclic) temperature exposures on the stability of a frame rod system in progressive collapse calculations. The relevance of the work is driven by the need to ensure the safety of buildings operating under extreme climatic fluctuations, particularly in the Far North regions. Methods: the study is based on numerical modeling using the finite element method in the LIRA-SAPR software package. A spatial kinematic scheme of a frame consisting of cross beams and columns was analyzed. The calculation was performed using a quasi-static method, considering the combined effect of a constant vertical load and a cyclic temperature field defined by a symmetric harmonic law with specified amplitude and period. A comparison of results for steady-state and non-steady-state thermal regimes was conducted, as well as for scenarios with thermal exposure on all elements and only on the beam grid elements. Results: it was found that accounting for the non-stationary (cyclic) nature of temperature leads to a significant change in the stability safety factor compared to the steady-state regime. During the cooling phase, the stability margin is on average 12 % lower, and during the heating phase, it is 13 % higher than under constant temperature exposure. The maximum overall reduction in the safety factor under cyclic exposure reaches 14-16 %. Meanwhile, direct thermal exposure on the columns has a lesser effect (difference up to 7 %). The minimum safety factor value (64.2) was recorded for load combination No. 6, considering cyclic temperature on all elements. Practical significance: the results demonstrate the significance of variable temperature factors for the accurate assessment of structural stability in progressive collapse. A conclusion is drawn about the necessity to develop and supplement current calculation methodologies (including regulatory documents) to account for non-stationary cyclic thermal exposures. This is particularly important for designing reliable buildings and structures in northern latitudes, as well as for industrial facilities with technological thermal cycles.
progressive collapse, buildings and structures, variable temperature effects, stability
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