Numerical Modeling of Spalling in High Strength Concrete at High Temperature

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.