An embedded FE model for modelling reinforced concrete slabs in fire

Abstract

It is evident from a series of tests on simply supported reinforced concrete slabs that the failure of the slabs at large deflections is due to the formation of individual large cracks. This failure mode was also observed in the Cardington full-scale fire tests. Previous research indicates that the global behaviour of concrete slabs subject to large deflections can be well predicted by the smeared cracking model; however, the model cannot quantitatively predict the openings of individual cracks within the slabs at large deflection. For the discrete approach it is usually assumed that the cracks are formed along element edges, therefore continuous re-meshing is required during the analysis.Consequently, the results are mesh-dependent and the computing cost is high. In recent years, mesh independent finite element procedures, such as embedded (EFEM) and extended (XFEM) approaches, were widely used for modelling of the crack initiation and growth in structural members. However, most of the meshless models developed are either based on in-plane loading conditions or confined to thin shells with assumed full-depth cracks, which form apparent displacement jumps within an element.For a reinforced concrete slab, out-of -plane load causes coupled stretching and bending of the slab, cracks are usually initiated at discrete positions and then propagated, until at last some individual full-depth cracks are formed. Pure stretching or assumed full-depth cracking is inadequate for modelling this kind of failure. Therefore, in this research, a non-linear layered procedure with embedded weak discontinuity is developed to quantitatively model the progressive tensile failure of reinforced concrete slabs subjected to large deflections. The current model inherits the advantage of smeared approach, and at the same time, introduces the opening width of crack explicitly by taking the advantage of the better description of the kinematic characteristics of EFEM approach. A series of validations have been conducted against test data at both ambient and elevated temperatures, and as well as to identify the occurrence and severity of crack failure in reinforced concrete slabs subjected to extreme loading conditions, such as fire.

Progressive collapse analysis of steel structures under fire conditions

“…For example, Wang and Moore [2] built a three dimensional model of a steel frame with semi-rigid connection to study the structural behaviour in fire. A computer program Vulcan has been developed at the University of Sheffield for three-dimensional modelling of steel, steel-framed composite and reinforced concrete buildings in fire [3][4][5][6][7]. The computer program FEMFAN from the Fire Engineering Research Group at Nanyang Technological University has been used by Tan et al [8][9][10][11], to study the behaviour of a number of steel frames under fire conditions.…”

Integrated nonlinear structural simulation of composite buildings in fire

“…Nevertheless, caution must be advised when interpreting the damage parameter results as they can only give a general idea of the expected damage pattern at a particular layer. Tracking the coalescence, and propagation of through depth cracks, and even discrete surface cracks, requires more sophisticated approaches that employ the extended finite element method [60] or other advanced implementations and solvers.…”

“…The column bases were assumed to be fixed. The fine mesh used here was chosen to allow the distribution of concrete damage to spread in a more natural manner reducing the meshdependency reported for distributed cracking methods [60]. As per the workflow of the ISE, at each thermocouple location an appropriate HT analysis was performed, and the results were then automatically applied to the correct mesh elements.…”

Advanced computer model for analysis of reinforced concrete and composite structures at elevated temperatures

“…This line of research requires a knowledge of the numerical solution procedures, physical-mathematical models and characteristics of the studied physical phenomenon, enabling a wide understanding of the physical behavior of the problem [7]. Computational models able to describe the behavior of structures in fire have been developed considering different physical-mathematical approaches, such as the use of the direct stiffness method based on the stability and bowing functions [8], the approach of the embedded and extended finite element model [9], [10], the use of customized beam finite element with skeletal structures [11] and among other methodology and analysis models [12], [13], [14].…”