Jean-Baptiste Schleich

A Simple Model for the Fire Resistance of Axially-Loaded Members According to Eurocode 3

A general model, i.e. a non-linear computer code, has been extensively used to determine the buckling load of axially-loaded members according to the hypotheses of Eurocode 3, Part 10 or Part 1.2. Two yield strengths, two buckling axes, six ultimate temperatures and 10 different lengths have been considered for 339 different steel H-sections. The numerical results have been statistically sorted and compared to the simple models presented in Eurocode 3, Part 10 and Eurocode 3, Part 1.2. The simple models that have been proposed up to now can lead to different safety levels when compared to the general model, the safety level depending mainly on the buckling length. A new proposal has thus been made for a simple model that systematically ensures a conservative result when compared to the general model.

A Simple Model for the Fire Resistance of Axially Loaded Members - Comparison with experimental results

Abstract A general model, i.e. a non linear computer code, has been extensively used to determine the buckling load of axially loaded members, considering that the material model behaves at elevated temperatures according to the hypotheses of Eurocode 3 Part 1.2, and the main results of this numerical investigation are summarised in this paper. The main parameters and the results of 59 experimental tests found in the literature are reported, as well as the results of 21 original tests made within this research project. Those test results are used to evaluate the severity factor of the analytical formula deduced from the numerical simulations. This factor is chosen in order to obtain an analytically calculated ultimate load which is, in the average, the same as the experimental load. The ultimate load or ultimate temperature can be determined by the proposed analytical formula or directly by interpolation in tables which give the ratio between the ultimate load and the plastic load at room temperature.

Effect of reinforced concrete between the flanges of the steel profile of partially encased composite beams

Abstract During the last 20 years composite structures have been built in increasing numbers. Composite steel concrete constructions are able to take full advantage of the respective properties and performance of both materials and lead to building with the following advantages: easy prefabrication, building time reduction, extremely reduced cross-sections, flexibility, fire resistance.... However in the last version of the Eurocode 4 (pr ENV 1994-1-1/April 1992)/§4.12(2)) it is not allowed to take into account reinforced concrete between the flanges of the steel beams with concrete-encased steel webs for the load bearing capacity and for the deflection calculation. The reinforcing bars and the concrete may be assumed to contribute only to resistance to local buckling or lateral-torsional buckling. From this point of view this version of the Eurocode 4 is too conservative. Indeed 13 tests, performed in 1991 and 1992 in the University of Bochum (Institut fur konstruktiven Ingenieurbau), have indicated the importance of the reinforcing bars and the concrete between the flanges for the calculation of the ultimate bending moment, the ultimate shear force and the deflection. From these tests were deduced methods taking into account the increase in the bearing capacity and in ridigity due to the reinforced concrete. This research has already provoked changes in the Eurocode 4 and will be an important data source for writing the annex of EC4 dealing with partially encased composite beams.

A Comparison Between Five Structural Fire Codes Applied To Steel Elements

A comparison program has been established concerning the simulation of the static behaviour of steel columns submitted to fire [I]. The stress strain relationships in steel are those recommended in EC3, part 10 121. The five numerical codes used in this comparison are briefly described, namely CEFICOSS, DIANA, LENAS, SAFIR and SISMEF. A description of 8 tests is given: Lees frame at ambient and at elevated temperatures, an eccentrically loaded column at ambient temperature, at uniform elevated temperature and under I S 0 heating and finally an axially loaded column in the same three cases ( ambient, uniform and ISO). The evolution of the horizontal displacement is graphically given for each test, as well as a table summarising the results in term of ultimate resistance. The five programs compare reasonably well when the final resistances are considered, which would be the case in a situation of design for a real structure. In all the tests, the maximum difference between two different programs is 6%. Differences may occur in the evolution of displacements, mainly due to the way that the residual stresses are considered. or to the fact that the non uniform temverature distribution has sometimes been replaced by a uniform temperature equal to the average value of the non uniform distribution.

Numerical simulations of fire resistance tests on steel and composite structural elements or frames

A computer program for the analysis of steel and composite structures under fire conditions is presented. It is based on the finite element method using beam elements with subdivision of the cross section in a rectangular mesh. The structure submitted to increasing loads or temperatures is analyzed step-by-step using the Newton-Raphson procedure. The thermal problem is solved by a finite difference method based on the heat balance between adj acent elements. Comparisons are made between full scale tests on steel and composite structural elements and frames and the results given by the numerical simulations. The agreement appears to be quite good. Furthermore are discussed the new possibilities given by this numerical computer code.