Numerical modeling of spalling in high strength concrete at high temperature
01 Jan 2019-Vol. 11, pp 431-440
TL;DR: In this paper, a 2D hydrothermal model has been developed for predicting the extent of spalling in high-strength concrete (HSC) buildings, where the model depends on several parameters such as permeability, initial moisture content, and thermomechanical properties.
Abstract: High strength concrete (HSC) is predominantly used in high-rise reinforced concrete buildings. While excellent from strength point of view at room temperature, HSC is known to be prone to spalling, when exposed to high temperatures (e.g., in case of a fire). Fire resistance evaluated from building codes (CEN in Design of concrete structures. Part 1–2: general rules—structural fire design, Eurocode-2, Brussels, 2004; Bureau of Indian Standards in Indian code of practice for fire safety of buildings (General): details of construction code of practice. IS-1641, New Delhi, 1989) [1, 2] and simulation-based studies typically does not consider the effects of spalling. To alleviate these difficulties, a 2-D hydrothermal model has been developed for predicting the extent of spalling in HSC. The numerical model evaluates pore pressure inside the concrete as a function of time using the laws of thermodynamics. Spalling is said to occur when the pore pressure built-up within concrete exceeds its tensile strength. The model depends on several parameters such as permeability, initial moisture content, and thermomechanical properties of concrete. All of these parameters are considered by the model through a two-way coupling between the pore pressure analysis and thermal analysis, both implemented using the finite element method. Validity of the numerical example is established by comparing the spalling predictions obtained from the numerical model against standard experiments available in the literature. Parametric studies have also been performed using the numerical model to quantify the effects of model parameters such as permeability, grade of concrete, and type of fire scenario on the prediction of spalling.
01 Jan 1974
TL;DR: In this article, the authors present a formal notation for one-dimensional elements in structural dynamics and vibrational properties of a structural system, including the following: 1. Isoparametric Elements.
Abstract: Notation. Introduction. One-Dimensional Elements, Computational Procedures. Basic Elements. Formulation Techniques: Variational Methods. Formulation Techniques: Galerkin and Other Weighted Residual Methods. Isoparametric Elements. Isoparametric Triangles and Tetrahedra. Coordinate Transformation and Selected Analysis Options. Error, Error Estimation, and Convergence. Modeling Considerations and Software Use. Finite Elements in Structural Dynamics and Vibrations. Heat Transfer and Selected Fluid Problems. Constaints: Penalty Forms, Locking, and Constraint Counting. Solid of Revolution. Plate Bending. Shells. Nonlinearity: An Introduction. Stress Stiffness and Buckling. Appendix A: Matrices: Selected Definition and Manipulations. Appendix B: Simultaneous Algebraic Equations. Appendix C: Eigenvalues and Eigenvectors. References. Index.
TL;DR: In this article, a computational analysis of hygro-thermal and mechanical behavior of concrete structures at high temperature is presented, and the evaluation of thermal, hygral and mechanical performance of this material, including damage effects, needs the knowledge of the heat and mass transfer processes.
Abstract: A computational analysis of hygro-thermal and mechanical behaviour of concrete structures at high temperature is presented. The evaluation of thermal, hygral and mechanical performance of this material, including damage effects, needs the knowledge of the heat and mass transfer processes. These are simulated within the framework of a coupled model where non-linearities due to high temperatures are accounted for. The constitutive equations are discussed in some detail. The discretization of the governing equations is carried out by Finite Elements in space and Finite Differences in time. Copyright © 1999 John Wiley & Sons, Ltd.
TL;DR: In this paper, a mathematical model for water transfer in concrete above 100°C is developed, and the pore volume available to free water increases as dehydration due to heating progresses and as pore pressure is increased.
Abstract: A mathematical model for water transfer in concrete above 100°C is developed. Drying tests of heated concrete are reported and material parameters of the model are identified from these tests as well as other test data available in the literature. It is found that water transfer is governed principally by the gradient of pore pressure, which represents the pressure in vapor if concrete is not saturated. Permeability is found to increase about 200 times as temperature passes 100°C, which could be explained by a loss of necks on migration passages. The pore volume available to free water increases as dehydration due to heating progresses and as the pore pressure is increased. The temperature effect on pressure-water content (sorption) relations is determined. Thermodynamic properties of water are used to calculate pore pressures. A finite element program for coupled water and heat transfer is developed and validated by fitting test data.
TL;DR: In this article, an experimental study on the optimum amount of polypropylene fibres to be used in lightweight high-strength concrete to prevent spalling when exposed to hydrocarbon fire, taking into consideration the characteristics of the lightweight aggregate, the water-to-cement ratio (W/C) of the mixtures, and the length and thickness of the fibres.
Abstract: This paper presents the results from an experimental study on the optimum amount of polypropylene fibres to be used in lightweight high-strength concrete to prevent spalling when exposed to hydrocarbon fire, taking into consideration the characteristics of the lightweight aggregate, the water-to-cement ratio (W/C) of the mixtures, and the length and thickness of the fibres. Twelve different concrete mixtures were made. One block, 610 × 425 × 770 mm in size, was cast from each mixture and tested for fire resistance under hydrocarbon fire exposure. The temperature in the blocks during the test was recorded. After the test, the condition of the blocks was evaluated, and cores were taken for determining the residual compressive strength of the concrete. Results from the study show that close to 3.5 kg of the 20-mm polypropylene fibres per cubic meter of concrete is required to prevent the spalling of a low W/C lightweight concrete made with a silica fume-blended cement when subjected to hydrocarbon fire but that only 1.5 kg of the finer 12.5-mm fibres per cubic meter is sufficient. The amount of 20-mm fibres required to prevent spalling for a higher W/C of 0.42 is significantly less: of the order of 1.5 kg per cubic meter of concrete. The susceptibility of the concrete to spalling increases with the degree of absorption of the lightweight aggregate used in concrete.
19 Mar 2018