Study Of The Maximum Displacement Of A Fixed Supported Steel Beam With Non-uniform Longitudinal And Transverse Temperature Distributions

Nowadays steel constructions are widely used, especially in high-rise buildings and big-span, large-load structures, for its high strength, light weight, material uniformity, high level of industrialization, short construction period. However, the poor fire-resistance ability is the main weakness of steel structure. So far, numerical simulation studies of steel beam designed by worldwide scholars were assumed uniform longitudinal temperature distributions, which was very different from the characteristics of the real fire environment. Therefore, it is necessary to study the response characteristics of steel beam in the enviroment which is close to real fire.Fixed supported steel beam, a common steel structure, with a length of 12m, is used as the object of the study. The study considers the maximum displacement, and compares the results with the maximum displacement in uniform longitudinal temperature distributions, using ANSYS, a software for finite element analysis, to analyse the fire response characteristics in non-uniform longitudinal and transverse temperature distributions. And then to analyse the effects of temperature and fire loads on the maximum displacement of steel beam, together with the analysis of the limits of safety. The following content are mainly considered:1)Solid modeling uses Fire Dynamics Simulation(FDS) to obtain the indoor temperature rise by positioning thermocouples, comparing to ISO-834 standard and natural fire-BFD curve of temperature rise. Results indicate: all three are close to each other and this study uses the ISO-834 standard curve of temperature rise, considering it's commonality and authority.2)Using ANSYS, this study obtains the maximum displacement in uniform longitudinal, non-uniform longitudinal and uniform transverse, non-uniform longitudinal and transverse temperatue distributions and compares the results with each other, ensuring T_max=688.4℃, T_min=352.7℃and q=64.8kN/m. Results indicate: the maximum displacement is declining with an abrupt increase at 1/4 location from the end; The maximum displacement is declining in the order of uniform longitudinal, non-uniform longitudinal and transverse, non-uniform longitudinal and uniform transverse temperature distributions.3)Using ANSYS, this study analyses the influnce of temperature loads on maximum displacement by changing the temperture difference, on the basis of T_max=688.4℃and q=64.8kN/m. Results indicate: the larger temperature difference, the smaller the maximum displacement in the non-uniform longitudinal temperature distributions; the declining is even faster in the non-uniform longitudinal and uniform transverse temperature distributions, and the difference between the maximum displacement is enlarging with the temperature difference increasing; the temperature difference in non-uniform longitudinal and transverse temperature distributions makes a grater contribution, that is to say, the smaller temperature difference makes the larger maximum displacement.4)Using ANSYS, This study analyses the influnce of fire load on maximum displacement, keeping T_max=688.4℃a nd T_min=352.7℃. Results indicate that in uniform longitudinal temperature distributions: the decreasing rate of maximum displacement is decreasing when fire force decreases, correspondinglly the fire resistance period is increasing; the beam won't fail when q≤32.4kN/m. And in non-uniform longitudinal temperature distributions: the maximum displacement is increasing with fire load increasing, the increasing rate of the maximium displacement is higher in non-uniform longitudinal and transverse temperature distributions at first and made a reverse after q=64.8kN/m; the maximum displacement is larger all the time, the difference between them increases firstly and then decreases with fire load increasing; fire load in non-uniform longitudinal and transverse temperature distributions makes a grater contribution, that is to say, the smaller fire load makes the larger maximum displacement.5)This study analyses the limits of the safety considering temperature and fire loads. regarding the critical point(X,Y), in non-uniform longitudinal temperature distributions,we can conclude: X↑,Y↓, the steel beam is safe; X↓,Y↑; the steel beam will fail; But when X↑, Y↑or X↓, Y↓, more computational analysis is needed to determin whether temperature or fire load contributes to the maximum displacement more.