Study On Robust Characteristics Of End-plate Joint In Steel Structure Exposed To Post-earthquake Fire

The semi-rigid joint with extended end-plate is a typical semi-rigid beam-tocolumn connection that has a good hysteretic properties for structures resisting a moderate earthquake.However,many components,affect the seismic behavior together,in an end-plate joint,such as column stiffness,beam scales,end-plate thickness and bolt diameters.Some earthquakes would induce post-earthquake fire that normally acted a significant damage for structural safety.During an earthquake,a joint will develop the plastic deformations and the impact always causes some interior damage and some surface cracks.At this time,the fire resistance of the joint decreases due to the increase of the damage.However,most of studies still only consider the fire resistance of non-damage joints.The damage caused by different levels of earthquake is different.In some views,the bearing capacity and fire resistance times are different between damaged joints and non-damaged joints.The paper is based on the data and results of the end-plate joints tested by Shi G.Firstly,a model,built by finite element software ABAQUS,is compared with the experimental results in this paper.It can be find that the method of analysis is right and feasible.Then,the method is used to analyze the mechanical properties of the same type joints with different geometrical scales.The material nonlinearity,geometric nonlinearity and state nonlinearity are all considered in the three-dimensional finite element model in ABAQUS.The main job and the conclusions are listed in the below:(1)Firstly,the damage properties and stress distributions in end-plate joint subjected to an earthquake are analyzed.The moment rotation(M-?)and hysteretic curve are fulfilled via the result.The effects of column section scales,end-plate thickness and bolt diameters on the hysteretic behavior of joints are studied.The results showed that monotonous loadings and column section scales could improve the bearing capacity,but the increases are limit.While,the increment of a bolt diameter has a significant effect on the bearing capacity of the joint.The impact of an end-plate thickness is less than bolt diameter.At the same time,the hysteretic performance of the joint is better when the end-plate thickness is 13 mm compared to15 mm.Therefore,it is suggested to improve the bearing capacity of the joint by lifting bolt diameter.Under earthquakes,the bolts at both sides play major roles thanother bolts.The bolt arranged in the middle have little effect on the performance of the joint,hence it is reasonable for the arrangement of the bolt in four rows.(2)The damage characteristics of end-plate joint under earthquake,the stress distribution and failure mechanism the post-earthquake fire are analyzed by some comparisons.The effects of the each parameter to the robustness are also discussed.The results show that the lower level of earthquake,which is helpful to release the initial stress and the initial defect,which can improve the fire resistance of the joint.The damage temperature is increased about 5 degrees.The improvement of the ratio of column stiffness to beam stiffness is helpful to enhance the fire resistance of the joint.The effect,however,is very little when the ratio more than 3:1.Considering the safety of the structure and material cost,the reasonable ratio of column stiffness to beam stiffness is 3:1.(3)The thickness of the end-plate has a certain influence on the failure temperature,but the effect is not very large.This paper found the enhancement of thickness of end-plates would improve the failure temperature of 2-11 ?.The bolt diameter have a large impact to failure temperature of the joint,the failure temperature are lifted about 8-22?.It is useful to use the larger diameter of the bolt in the design process.The joint will not failure in the cooling process as long as it don't failure in the heating process.The circulating load have little effect on the fire resistance of the joint if only take the deformation in consider,the strength of material plays a leading role absolutely.However under cyclic loading,it is crucial to keep the joint far away from breakages of cracks.In the mechanical analysis of end-plate joint exposed to post-earthquake fire,the improvement of bolt diameters reduced the damage of the joint relatively under earthquake.It improves the fire resistance limit of joints,prolongs the failure time,and plays an important role in improving the robustness of the joints.The improvement of the size of column has a great influence to the changes of the internal force,while it has little influence on the ultimate temperature.It also has little influence on the robustness of the joint;the improvement of the end-plate has a certain significance for improving the robustness of the joints.