Modeling And Programming Of Reinforced Concrete Structures Exposed To Fires

The high temperatures resulting from building fires have a significant influence on the strength and deformation characteristics of various reinforced concrete structural elements such as beams, columns, slabs, walls etc. Because of the high cost of fire testing facilities and of the fire tests it is becoming considerably important to develop computer software based on prior experimental data to model the thermal and structural response of individual members and structures in fire environments. In addition, advances in fire science and technology have fostered a movement in some industrialized countries developing performance-based fire safety design method. This transition toward performance-based method has made computer software become a predominant tool for fire design and analysis. Without computer software, it is impractical to investigate the response of a large variety of structural elements under differing restraint, loading, and fire conditions.This dissertation comprises two parts. The first part deals with nonlinear finite element models related to the thermal and structural responses of reinforced concrete structures during the course of a fire. The second part is about the development of computer software. The main contents studied in this dissertation may be summarized as follows.(1) The analysis formulations and models predicting the temperature history of cross-sections of structural members exposed to fires are presented. The fire boundary conditions of temperature field are simplified. Elements for temperature analysis are developed, in which the thermal properties of concrete and steel are considered as temperature dependent. Parametric studies of thermal response are conducted and some new conclusions are drawn.(2) A new orthotropic nonlinear elastic constructive model for concrete under high temperature and biaxial stress state is established based on the ideas originated from Ottosen. The complex features of concrete such as crack and crush etc. are considered in the new model. This model makes it possible to analyze the structural response of planar reinforced concrete structures exposed to fire. Layered plane stress concrete element and bar element that are used to model concrete and reinforced steel respectively are developed.(3) The constructive model of concrete under ambient temperature and triaxial stress state suggested by Guo is improved, and a new orthotropic constructive model of concrete under elevated temperature and triaxial stress state is suggested. An attempt is made to calculate three-dimensional behavior of reinforced concrete members in fire conditions.(4) Scientific visualization is studied systemically. A new method for plotting colored patterns of finite element results called SPEM (Scan Parent Element Method) is described. This method is simple, straightforward, accurate, and easily implemented.(5) A computer software package called STRUFIRE is developed which can be used to determine the internal temperature distribution, displacements, deformations, stress in concrete and steel reinforcement, cracking and crushing of concrete elements at any time interval after being exposed fires. The user-friendly interface, graphical pre- andpostprocessors make it easy to use. STRUFIRE is validated against available test data and fairly good accuracy is found.The study on modeling and programming of the responses of reinforced concrete structures in fires relates many fields such as combustion, heat transfer, engineering mechanical, engineering mathematics, finite element method, software engineering, computer graphics etc. Thus, more analytical, experimental, and programming work is needed before STRUFIRE can be used as calculation and design tool by practicing engineers.