Finite element modelling of concrete at elevated temperatures

• Main Author: Cotton, John
• Published: Cardiff University 2003
• Subjects: 620.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.630477

This thesis presents a new plastic damage constitutive model for concrete subjected to elevated temperatures. The proposed Cardiff Concrete Temperature (CARCOT) model combines the original theory presented by Lubliner et al. (1989) with newly derived temperature dependent material parameters developed for normal and high strength concrete. The temperature dependent material parameters have been obtained from a laboratory based experimental study conducted by the author. The CARCOT model has been implemented into the finite element code LUSAS after a successful validation programme using a single point constitutive driver. The overall aim of the CARCOT model is to accurately represent the non-linear behaviour of concrete in both tension and compression for temperatures up to 600· C with a single set of constitutive equations. This is achieved by using the Lubliner yield surface to asses the current stress level and the Mohr Coulomb surface to control the change in volume caused by plastic deformation, i.e. a non associated flow rule is adopted. The proposed model also incorporates the comer indicators proposed by Crisfield (1987) to assess the comers present on the yield surface. Depending on the current stress level and its position on the yield surface a multi vector return algorithm is employed to bring the stress increment back to the yield surface. The thermal damage mechanisms are dealt with in a staged approach in which the temperature damage effects are accounted for at the start of every load increment of finite element computations by a subroutine incorporating the temperature dependent functions.