A two-scale method to include essential screw connection behaviour in two-way coupled fire-structure simulations

Abstract

PurposeSimulations exist for the prediction of the behaviour of building structural systems under fire, including two-way coupled fire-structure interaction. However, these simulations do not include detailed models of the connections, whereas these connections may impact the overall behaviour of the structure. Therefore, this paper proposes a two-scale method to include screw connections.Design/methodology/approachThe two-scale method consists of (a) a global-scale model that models the overall structural system and (b) a small-scale model to describe a screw connection. Components in the global-scale model are connected by a spring element instead of a modelled screw, and the stiffness of this spring element is predicted by the small-scale model, updated at each load step. For computational efficiency, the small-scale model uses a proprietary technique to model the behaviour of the threads, verified by simulations that model the complete thread geometry, and validated by existing pull-out experiments. For four screw failure modes, load-deformation behaviour and failure predictions of the two-scale method are verified by a detailed system model. Additionally, the two-scale method is validated for a combined load case by existing experiments, and demonstrated for different temperatures. Finally, the two-scale method is illustrated as part of a two-way coupled fire-structure simulation.FindingsIt was shown that proprietary ”threaded connection interaction” can predict thread relevant failure modes, i.e. thread failure, shank tension failure, and pull-out. For bearing, shear, tension, and pull-out failure, load-deformation behaviour and failure predictions of the two-scale method correspond with the detailed system model and Eurocode predictions. Related to combined load cases, for a variety of experiments a good correlation has been found between experimental and simulation results, however, pull-out simulations were shown to be inconsistent.Research limitations/implicationsMore research is needed before the two-scale method can be used under all conditions. This relates to the failure criteria for pull-out, combined load cases, and temperature loads.Originality/valueThe two-scale method bridges the existing very detailed small-scale screw models with present global-scale structural models, that in the best case only use springs. It shows to be insightful, for it contains a functional separation of scales, revealing their relationships, and it is computationally efficient as it allows for distributed computing. Furthermore, local small-scale non-convergence (e.g. a screw failing) can be handled without convergence problems in the global-scale structural model.

A pyrolysis model for steel‐insulation sandwich building façade systems under fire

“…A fire-structure simulation starts with an FDS fire dynamics simulation, whereafter the AST data are rewritten by the reWriteAST2py program to a format that can be read by the HT model (itself updated by upGeomHT). During the HT analysis, the pyrolysis model, implemented by the user subroutines UMATHT and USDFLD in Abaqus [12], is involved in giving a more accurate prediction for the temperature distribution within the structure. Subsequently, the resulting temperature data is transferred to the SR model (as updated by upGeomSR) for the SR analysis, in which material properties depend on their pyrolysis level).…”

“…For e.g. sandwich panels with PIR insulation, properties can be used as given in [12]. The following boundary conditions are used: The thin-walled steel faces have a convection coefficient equal to 25 [W/(m 2 K)] and an emissivity coefficient of 0.8.…”

“…Panels show a complex mechanical response (e.g. deformations), further elaborated in [12]. Figure 6(b) shows the number of failed panels vs. simulation time for the complete TWC simulation.…”