- Author
-
Holmberg, S.
|
Anderberg, Y.
- Title
- Computer Simulations and Design Method for Fire Exposed Concrete Structures.
- Coporate
- Swedish Fire Research Board, Stockholm, Sweden
- Report
-
Document 92050-1; FSD Project 92-50
September 27, 1993
36 p.
- Keywords
-
simulation
|
computers
|
structures
|
concretes
|
columns
|
thermal properties
|
steels
|
mechanical properties
|
design applications
|
thermal analysis
|
concrete columns
- Abstract
- The design methods for the fire exposed concrete columns presently used in Sweden are not considered to be sufficiently differentiated. Therefore, further developments of these are necessary. The purpose of this report is to improve the present design method. Tests performed at Statens Provningsanstalt in Sweden, National Research Council in Canada, and Technische Universitat Braunschweig have been used as references. Computer-simulations have been made using the programs SUPER-TEMPCALC, for thermal analysis and CONFIRE for structural analysis. The simulations repordice the tests in an acceptable way, the differences observed between theory and experiment were due to insufficient information provided on the properties of the materials and the geometry of the columns. With the computer programs a parametric study has been performed to identify important factors influencing the fire resistance. The basis for the design method is to reduce the cross-section by using two isotherms, 400 deg C and 600 deg C. The quartzite concrete with temperatures lower than 400 deg C is assumed to possess 90% of its strength at room-temperature and the concrete with temperatures between 400 and 600 deg C 70%. Above 600 deg C the strength is assumed to be zero. The strength of the reinforcement is reduced according to the temperature in the bars, the strength curve used is basedon 0.5% residual strain. The study shows that the location of the reinforcement is more important than former design methods have suggested. Due to the thermal expansion, the tensile stresses in the corner bars are considerably reduced and even turn into compression. It therefore becomes feasible to make a reduction of the reinforcement area. For columns with reinforcement in the corners of the cross-section, a reduction factor of only 0.5 is appropriate. For columns with more bars, the bars in the corners will not contribute significantly to the fire resistance of the column. Furthermore the behavior of steel at high temperatures has to be considered more accurately. The proposed design method, while not too complicate, still provide satisfactory fire resistance.