دانلود رایگان مقاله انگلیسی رفتار ستون های فولادی با استحکام بالا در دمای بالا - الزویر 2018

abstract

High strength steel has been widely used in various types of structures due to its merits of high strength and good ductility. However, high strength steel structures are vulnerable to fire hazards as the strength and stiffness of the steel deteriorate rapidly at elevated temperature. Presented in this paper are the investigations on the behaviour of restrained high strength steel columns at elevated temperature obtained from full-scale fire tests and finite element analyses. In the fire tests, applied load and restraint stiffness are two key factors to be examined. Column responses such as the axial displacement, deflection at column middle height and axial force induced by thermal expansion associated with temperature evolution were reported. Column buckling and failure temperatures were determined based on the criteria of the axial displacemen t and lateral deflection of the specimens at elevated temperatures. The test results show that both the applied load and restraint stiffness have considerable influences on fire resistances of high strength steel columns. It was observed that the columns with only axial restraints failed by flexure buckling about the weak axis whereas the columns with both axial and rotational restraints and subjected to large magnitude of the applied load failed by flexural torsional buckling. Finite element analyses were conducted to simulate the fire responses of the test specimens and the obtained numerical results are found to be reasonably agree with the test data. Parametric studies via finite element analysis were carried out to quantitatively determine the effect of applied load, restraint stiffness and slenderness ratio on fire resistance of high strength steel columns.

5. Conclusions

Based on the aforementioned experimental and numerical investigations on the fire behavior of restrained high strength Q460 steel columns, the following conclusions can be drawn:

(1) Restrained high strength Q460 steel columns without fire protection are quite sensitive to the elevated temperature even though the applied axial load is relatively small and the columns can only survive approximately 20 min in fire scenario of ISO-834.

(2) Applied load ratio is a critical factor to influence the fire resistance of the restrained high strength steel column.

(3) For the columns subjected to the same magnitude of the applied load, the one with the larger axial restraining stiffness would result in a lower buckling temperature. In addition, the columns with the lager axial restraining stiffness, the corresponding post buckling stage is prolonged and the columns can survive a longer in fire duration.

(4) At the same condition, the fire performance of the restrained high strength steel columns is better than that of mild steel columns.

(5) When the rotational restraint ratio is less than 1.0, the higher value of the rotational restraint ratio would result in a higher buckling temperature. But the efficiency of the rotational restraint ratio on buckling temperature becomes less effective if the ratio exceeds 1.0.

(6) For the axially restrained high strength steel column with smaller slenderness ratio, the axial force drops slowly after the column bucked which consequently results in a larger difference between the buckling and failure temperatures for the column with slenderness ratio less than 60. There is a minor influence on the difference between the buckling and failure temperatures when the slenderness ratio ranged between 60 and 90. Once the slenderness ratio exceeds 90, the difference between the buckling and failure temperatures increases as the increase of the slenderness ratio.