دانلود رایگان مقاله انگلیسی ستون های فولادی در آتش و یخ زدگی - امرالد 2017

Abstract

Purpose – The use of cold-formed steel members has increased significantly in the past few years; however, its design is only briefly addressed in the current design codes, such as the EN 1993-1-3. To evaluate the compressive behavior of single and built-up cold-formed steel members, at ambient and simulated fire conditions with restrained thermal elongation, experimental and numerical tests were undertaken. Design/methodology/approach – Four cross-section shapes were tested, namely, one single (lipped channel), one open built-up (I) and two closed built-up (R and 2R), considering two end support conditions, pinned and fixed. Two test set-ups were specifically developed for these tests. Based on the experimental results finite element models were developed and calibrated to allow future parametric studies. Findings – This paper showed that increasing the level of restraint to thermal elongation and the initially applied load led to lower critical temperatures. Increasing the level of restraint to thermal elongation, the failure is governed by the generated axial restraining forces, whereas for lower levels of restraint to thermal elongation, the failure is controlled by the temperature increasing. Originality/value – This paper is a contribution to the knowledge on the behavior of cold-formed steel columns subjected to fire, especially on the ones with a built-up cross-section, where results on thermal restrained ones are still scarce. It presented a set of experimental and numerical results useful for the development of numerical and analytical analysis concerning the development of new simplified calculation methods.

5. Conclusions

In this paper, a large experimental campaign on CFS columns at both ambient temperature and simulated fire conditions with restrained thermal elongation is reported. The developed finite element model is also described and the final results regarding the calibration process are presented. In the buckling tests at ambient temperature, the advantage of using built-up members was clear since the increase in the buckling load was significant. In terms of the design predictions according to EN 1993-1-3 (2004), it was observed that increasing the number of profiles the design predictions become unsafe.

In the fire resistance tests, it was found that the interaction between the initial applied load and the imposed level of restraint to thermal elongation significantly influence the behavior of isolated CFS columns under fire conditions. When some level of restraint exists, additional forces are generated, which may lead to premature collapse and consequently to lower critical temperatures. It seems that increasing the level of thermal restraint the failure of the columns may be controlled by the generated axial restraining forces, whereas for lower levels of thermal restraint, the failure is controlled by temperature increase and consequent degradation of the mechanical properties of the S280GD þ Z steel. It seems that the higher reductions on critical temperature, because of restraint, occur for lower values of ak.