دانلود رایگان مقاله کاربرد و دقت روش طراحی آتش تیرهای فولاد سرد باز

Abstract

This paper presents the results of an experimental and numerical investigation on the structural behaviour of cold-formed steel C and lipped-I beams subjected to uniform temperature distributions under standard fire conditions. A total of 18 specimens divided into four-point bending tests under fire conditions and under 3 different restraining conditions (including no restraints, partial axial restraint to the thermal elongation of the beam and both partial axial and rotational restraints at the beam supports) have been conducted. Local buckling, distortional buckling, lateral-torsional buckling and their interactions were observed in the tests. Then, the tests were modelled by the finite element programme Abaqus and, at the end, the numerical results showed good agreement with the experimental results in terms of axial restraining forces, vertical displacements, critical temperatures and buckling modes. The simulated results were still compared with the predictions from the currently European design rules (EN 1993-1.2:2005), in order to observe if there are safe and consistent regulations for fire design of these members. Finally, the numerical simulations have mainly shown that these design methods for CFS beams may be quite unsafe or over-conservative depending strongly on their boundary conditions.

5. Conclusions

This paper has described a finite element model developed to simulate the fire resistance and behaviour of cold-formed steel C and lipped-I beams under flexural conditions and 3 different restraining conditions (including no restraints, partial axial restraint to the thermal elongation of the beam and both partial axial restraint and partial rotational restraint at beam supports). It was first observed that the model was found to be accurate in predicting the structural behaviour of such beams in fire situation, especially their critical temperatures, with an average difference of not more than 4% when compared with the results obtained from several experimental tests previously performed in Laboratory by the authors [20]. Despite this, the main conclusion of this investigation was that the design rules given in EN 1993-1-2:2005 [15] may not be suitable for designing cold-formed steel flexural members subjected lateral-torsional buckling. It seems that its design methods give too conservative results both for low initial applied loads on the beams and for low slenderness values, while for high slenderness and high initial load levels they appear to be unsafe. On the other hand, these design guidelines did not say anything concerning the fire design of flexural members under different types of restraining conditions (axial and / or rotational restraint), which may also result in overly conservative or quite unsafe design methods. Hence, new simplified calculation methods for fire design of CFS members should emerge. To ensure fire safety of structures, CFS members should be properly designed so that they can withstand unexpected fire situations. Engineers and architects face problems in using cold-formed steel members in structures because of lack of suitable design specifications for fire conditions. This is why there is an urgent and absolute need of finding new fire design methods for CFS members and this research work may be one of the first steps in the right way for solving this problem/need.