铝合金板式节点的等效计算方法研究及应用

Research and Application on Equivalent Method of Aluminum Alloy Gusset Joints

基于板式节点的单层铝合金网壳被广泛应用于大跨空间结构。目前在进行板式节点单层铝合金网壳分析和计算时,均采用弹簧单元法模拟该节点的力学性能。弹簧单元法虽然准确,但建模方法较为复杂,并不便于工程师使用。为此,以板式节点的等效方法为研究对象,采用等效梁单元来模拟板式节点的力学性能,给出了该等效方法的计算公式,并通过数值模拟和拟静力试验验证了该方法的有效性。然后使用该方法分析了节点域长度和起拱高度对板式节点的影响。通过前期的抗压及抗弯试验发现,在轴力和弯矩作用下板式节点的荷载-位移曲线包含4个阶段:弹性阶段、螺栓滑移阶段、孔壁承压阶段及失效阶段。因此,在弯矩或轴力作用下,板式节点的荷载-位移曲线近似为四折线模型。若采用弹簧单元法固然可实现四折线模型,但同样存在计算繁琐、建模困难的问题。为简化计算,采用等效梁单元来模拟板式节点,并按照屈服荷载等效及屈服位移等效的原则,将四折线模型转换为双折线模型。基于板式节点的变形机理推导其在轴力和弯矩单独作用下的变形机理,并基于等效原则提出了等效梁单元的计算方法。在单层铝合金网壳中,节点往往同时承受轴力和弯矩(偏心力)的作用。为验证等效方法在偏心力工况下的有效性,建立了板式节点及对应等效梁单元模型,然后施加相同的偏心力。分别提取了板式节点模型及对应等效模型的轴力-轴线变形曲线和弯矩-转角曲线。通过对比两个模型的曲线发现,不同偏心力作用下的等效梁轴向变形及弯曲变形,均与板式节点非常吻合。同时,为验证该等效方法在拟静力荷载工况下的准确性,引用一组拟静力试验的结果,并建立对应的等效分析模型。通过对比二者所得的荷载-位移滞回曲线,发现该等效方法可用于模拟板式节点在往复荷载作用下的力学性能。即该方法可用于模拟不同工况下的板式节点。使用该等效方法建立数值分析模型,分析节点域长度和起拱高度对板式节点的影响。结果显示:1)节点域长度的增加对于结构整体刚度有一定削弱作用,且削弱作用在逐渐降低,但对承载力的影响很小;2)随着起拱高度的增加,节点的受力状态发生变化,承载力和刚度均显著提高。在对板式节点单层铝合金网壳进行结构设计时,应合理选择节点域长度及起拱高度。

Single layer aluminum alloy reticulated shells based on gusset joints are widely used in long-span spatial structures.At present,the spring element method is used to simulate the mechanical properties of the gusset joint single-layer aluminum alloy reticulated shell.Although the spring element method is accurate,the modeling method is complex and not easy for engineers to use.Therefore,this paper takes the equivalent method of gusset joints as the research object,uses the equivalent beam element to simulate the mechanical properties of gusset joints,gives the calculation formula of the equivalent method,and verifies the effectiveness of the method through numerical simulation and quasi-static test.Then using this method,the effects of the length of the joint domain and the camber height on the slab joints are analyzed.Through the early compression and bending tests,it is found that the load displacement load-displacement curve of gusset joints under the action of axial force and bending moment includes four stages:elastic stage,bolt slip stage,hole wall pressure stage and failure stage.Therefore,under the action of bending moment or axial force,the load displacement load-displacement curve of gusset joints is approximately a four fold line model.Although the four fold line model can be realized by using the spring element method,it also has cumbersome calculation and difficult modeling.In order to simplify the calculation,the equivalent beam elements are used to simulate the gusset joint,and the four fold line model is transformed into the double fold line model according to the principle of equivalent yield load and equivalent yield displacement.Based on the deformation mechanism of gusset joints,the deformation mechanism under the separate action of axial force and bending moment is deduced,and the calculation method of equivalent beam element is proposed based on the equivalence principle.In single-layer aluminum alloy reticulated shells,the joints often bear the effects of axial force and bending moment(eccentric force)at the same time.In order to verify the effectiveness of the equivalent method under eccentric force,the gusset joint and the corresponding equivalent beam element model are established,and then the same eccentric force is applied.The axial force axis deformation axial force-axial deformation curve and moment rotation moment-rotation curve of the gusset joint model and the corresponding equivalent model are extracted respectively.By comparing the curves of the two models,it is found that the axial deformation and bending deformation of the equivalent beam under different eccentric forces are very consistent with the gusset joints.At the same time,in order to verify the accuracy of the equivalent method under quasi-static load conditions,a group of quasi-static test results are quoted,and the corresponding equivalent analysis model is established.It is found that the equivalent displacement curve of the two gusset joints can be used to simulate the hysteretic load it is found that the equivalent method can be used to simulate the mechanical properties of gusset joints under reciprocating load.In conclusion,this method can be used to simulate gusset joints under different working conditions.Using this equivalent method,a numerical analysis model is established to analyze the effects of joint domain length and camber height on slab joints.The results show that:1)the increase of joint domain length has a certain weakening effect on the overall stiffness of the structure,and the weakening effect is gradually decreasing,but has little effect on the bearing capacity.2)With the increase of camber height,the stress state of the joint changes,and the bearing capacity and stiffness are significantly improved.In the structural design of single-layer aluminum alloy reticulated shell with gusset joints,the length of joint area and camber height should be reasonably selected.