Effect of rotational restraint conditions on performance of steel columns in fire

Abstract

This paper presents a parametric analysis about the effect of rotational restraint conditions on the dynamic performance of steel columns in fire. A fine finite element model of restrained steel columns, which adopts an explicit dynamic solver, was developed and validated by test data in literatures. Nine values of rotational restraint stiffness ratio (βR) from 0.0001 to 10.0 were considered. Other considered parameters include the axial restraint stiffness ratio, load ratio and column slenderness ratio. Based on the results, a quantitative criterion of identifying dynamic and quasi-static failures of steel columns in fire was proposed. It is found that βR has a significant effect on the performance of steel columns in fire. With the increase of βR, three failure scenarios about the failure types of steel columns in fire may appear, namely, all the failures are dynamic failures (Scenario I), failures turn from dynamic failure into quasi-static failure (Scenario II), and all the failures are quasi-static failures (Scenario III). In failure scenario I, there exists a βR with which the column shows the minimal dynamic effects. Besides, when βR reaches a critical value (namely βR,cr), the effect of further increasing the value of βR on the response of steel columns becomes slight for all the above scenarios. βR,cr is affected by the axial restraint stiffness ratio, load ratio and column slenderness ratio, and is generally less than 1.5. In fire-resistant design, the steel columns with a βR greater than βR,cr can be considered as rotationally fixed at both ends. Moreover, with the increase of βR, the buckling and critical temperatures of steel columns both increase, and the increase in critical temperature is significantly larger than that in buckling temperature.