elevated temperatures

Monther's picture

Hydrothermal Model for Predicting Fire Induced Spalling in Concrete Structural Systems

Journal Title, Volume, Page: 
Fire Safety Journal Volume 44, Issue 3, Pages 425–434
Year of Publication: 
2009
Authors: 
M.B. Dwaikat
Department of Civil and Environmental Engineering, Michigan State University, 3580 Engineering Building, East Lansing, MI 48824-1226, USA
Current Affiliation: 
Building Engineering Department, Faculty of Engineering and Information Technology, An-Najah National University, Nablus, Palestine
V.K.R. Kodur
Department of Civil and Environmental Engineering, Michigan State University, 3580 Engineering Building, East Lansing, MI 48824-1226, USA
Preferred Abstract (Original): 

A one-dimensional numerical model to predict fire-induced spalling in concrete structures is presented. The model is based on pore pressure calculations in concrete, as a function of time. Principles of mechanics and thermodynamics are applied to predict pore pressure in concrete structures exposed to fire. An assessment of the possibility of tensile fracture is made by comparing the computed pore pressure with temperature-dependent tensile strength. The pore pressure calculations are coupled with heat transfer analysis to ensure that the loss of concrete section, resulting from spalling, is accounted for in subsequent heat transfer analysis. The validity of the numerical model is established by comparing temperature, pore pressure, and concrete spalling predictions with results from fire tests. The computer program is applied to conduct case studies to investigate the influence of concrete permeability, tensile strength of concrete, relative humidity in concrete, and heating rate on fire-induced spalling in concrete members. Through these case studies, it is shown that permeability, tensile strength of concrete, and heating rate have a significant influence on fire-induced spalling in concrete. It is also shown that relative humidity has a marginal influence on fire-induced spalling in concrete.

Mahmud's picture

Strength Design Criteria for Steel Beam-Columns with Fire Induced Thermal Gradients

Journal Title, Volume, Page: 
Engineering Journal, AISC
Year of Publication: 
2011
Authors: 
M.M.S. Dwaikat
Civil and Environmental Engineering Department, Michigan State University, East Lansing
Current Affiliation: 
Department of Civil Engineering, An-Najah National University, Palestine
VKR Kodur
Civil and Environmental Engineering Department, Michigan State University, East Lansing
Preferred Abstract (Original): 
When exposed to fire, restrained steel members develop significant internal forces, and these forces transform their behavior from beams or columns to that of beam-columns. The current provisions for fire-resistance assessment of such beam-columns through P-M interaction equations are an extension to the ambient interaction equations. These fire design equations take into consideration the reduction in the capacity arising from temperature-induced degradation of strength and stiffness properties but do not take into account the effect of other critical factors, such as thermal gradient, end restraints and realistic fire scenarios (with cooling phase). In this study, the different fire design equations for steel beam-columns are compared against results from nonlinear finite element simulations. Results from the analysis show that fire-induced thermal gradient leads to not only a reduction in the P-M diagrams, but also a noticeable distortion in the shape of the P-M diagrams. Therefore, modifications are proposed to the current design interaction equations for steel beam-columns at elevated temperatures. The modified P-M design equations are validated against results from fire tests and from finite element analysis and then illustrated through a design example. The proposed approach requires minimum computational effort and provides better assessment of beam-columns under fire when compared to current provisions.
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