Methods for Determining Ultimate Bearing Capacity of Steel Beam-Column Joints Based on Moment-Rotation Curves
首先总结了现有规范及相关研究中,钢管结构梁柱节点极限位移的取值方法。主要包括两类,一是通过主管位移取值,另一是通过支管位移取值。通过主管位移取值的方法主要有:CIDECT法,即以主管变形量为其直径的3%时作为极限状态;Lu方法,对 CIDECT法进行改进,即引入了主管变形量为其直径 1%时对应的荷载,将该荷载与 3%所对应的荷载进行比较,当 3%对应荷载大于 1%对应荷载的 1. 5倍时,取 1%对应荷载的 1. 5倍作为极限荷载,反之则取 3%对应荷载作为极限荷载;二倍刚度法(TEC),即过原点作斜率为初始刚度一半的直线,其与曲线的交点即为极限点。通过支管位移取值的方法主要有 Yura法,该方法将支管看作施加均布荷载的简支梁,以梁跨中处应变达到材料屈服应变的 4倍时作为极限状态。其次,针对 Yura方法未在规范中采用的情况,通过圆钢管节点试验和有限元模拟进行该方法的验证。最后以方钢管柱-工字梁节点为例探究了以上 4种不同取值方法的应用效果,设计了 4组试验并进行了相应的有限元模拟。在比较试验和模拟结果以确定模拟的可靠性后,基于有限元模拟结果对以上不同方法的极限转角取值进行分析。
结果表明:Yura方法在钢管柱-工字梁节点中应用具有可行性;对于钢管柱 -工字梁节点,Lu方法得出的结果相对保守,且操作复杂;二倍刚度法需要节点具有完整的弯矩 -转角曲线,且同样操作复杂,并容易出现误差,因而适用性有限;CIDECT和 Yura方法相对而言操作简便,只要确定主管或支管的直径即可估算出极限位移,且这两种方法得出的极限转角差异较小。因而,建议用这两种方法计算其各自对应的极限转角,取其中较小的转角来确定极限承载力。Abstract: For beam-column steel joints,the moment-rotation curve is an important criterion of the ultimate bearing capacity,as well as an essential criterion for the design of joints.Generally,the moment-rotation curve of a joint has both ascending and descending range,therefore,the ultimate bearing capacity of the joint can be captured intuitively by the peak point of the curve.However,for some curve which is monotone increasing without an obvious peak point,the detemination of the ultimate bearing capacity needed to be further studied.Based on this issue,methodology of deformation limit will be discussed,in order to determine the ultimatate capacity.
Firstly,current codes as well as corresponding researches on methods of displacement limit calculation are summarized.These methods can be classified in two types,one is through the displacement of the chord,and another is through the brace.CIDECT method belongs to the type of chord,which takes the value of chord deformation in 3% of chord diameter as the ultimate deformation limit.Lu's method,as an improvement of CIDECT method,considering the relationship of load between the deformation of 1% and 3% of chord diameter,when the load of 3% is higher than 1.5 times load of 1%,and then the value of 1.5 times load of 1% is taken as the ultimate bearing capacity,otherwise,the value of 3% is taken as the ultimate point.TEC (Twice Elastic Method) is also belongs to the type of chord,which draws a straight line that the slope is half of the initial stiffness through the origin,and the intersection between the line and the curve is the ultimate point.Yura's method belongs to the type of brace,in which the brace is regarded as a simply supported beam with uniform load,when the strain in the middle of the beam span is 4 times the yield strain of the material,it is considered to reach the limit.Secondly,in view of situation that Yura's method is not adopted in codes,a series of steel circular tubular joint tests as well as finite element analysis are carried out to verify the method.Finally,the application of methods above were explored by taking the example of joints with square steel tubular column and H-shaped beam.Four groups of tests were designed and corresponding finite element simulation was carried out.After comparing the experimental and simulation results which verified the reliability of the simulation,the ultimate rotation angles of the above different methods are evaluated based on the finite element simulation results.
Results indicated that the application of Yura's method for joints of steel tubular column and H-shaped beam is feasible.The results obtained by Lu's method are relatively conservative and the operation is complicated.TEC method requires complete moment-rotation curves of joints,and is also complex to operate and prone to errors,so its applicability is limited.CIDECT and Yura's methods are relatively easy to operate,as the ultimate deformation can be estimated as long as the diameter of the chord or brace is determined,and the difference of the ultimate rotation obtained by these two methods is minor.Therefore,this research suggests to use these two methods to calculate the corresponding ultimate rotation,and take the smaller as the ultimate limit.
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