正六边形孔蜂窝组合梁腹板纯弯屈曲研究

Study on Pure Flexural Buckling Behavior of Web of Castellated Composite Beams with Regular Hexagonal Hole

蜂窝构件具有承载力高、抗弯刚度大和方便穿越管线等优点,近年来广泛应用于各类高层建筑和大跨度结构中。对于蜂窝构件来说,腹板的局部屈曲是其主要破坏模式之一,屈曲会导致腹板局部变形的急速增加,直至退出工作,并可能导致构件整体失稳及结构上的连锁反应。在传统钢结构设计中通过对腹板高厚比进行限制来避免腹板局部屈曲的发生,而蜂窝构件相比于实腹构件受力更加复杂,孔间墩板及其桥板都有可能发生局部屈曲。目前对于蜂窝构件局部稳定问题的研究大多围绕着纯钢蜂窝梁开展,对于蜂窝组合梁的研究较少。因此有必要对蜂窝组合梁的纯弯屈曲开展研究。在已有2个纯钢蜂窝梁的基础上,设计并制作了两个简支蜂窝组合梁,对这两根蜂窝组合梁在四分点处施加集中力进行静力加载试验研究,通过观察钢梁上屈曲发生位置及混凝土裂缝开展的位置及形态,对腹板屈曲性能、承载力和蜂窝孔应变等进行分析,与纯钢蜂窝梁进行对比,研究混凝土板和腹板间加劲肋的设置对蜂窝钢梁试件破坏形态、应力分布及承载力的影响。利用有限元软件ABAQUS建立模型进行数值模拟,将试验结果与有限元模拟结果进行对比,发现模型结果与试验结果较为吻合。以试验模型为基础,分析纯弯作用下,高厚比和开孔率的改变对蜂窝组合梁的纯弯屈曲和极限承载力的影响规律,得到蜂窝组合梁发生强度破坏和屈曲破坏的临界值。研究表明:纯钢蜂窝梁在上翼缘及相应桥板屈曲,组合梁试件在桥板和墩板屈曲,混凝土板可以有效提高组合梁的屈服荷载和极限荷载,提高试件延性,有效避免局部屈曲的发生;组合梁腹板间设置加劲肋可以提高对腹板的约束作用,减弱孔角处应力集中,避免孔间墩板屈曲失稳;组合梁共出现两种屈曲模式,均为孔间墩板发生半波形平面外失稳,区别在于平面外位移分布方式;第一种屈曲模式位移相对跨中呈对称轴分布,第二种屈曲模式位移相对跨中呈中心对称分布。高厚比是影响组合梁破坏模式和纯弯屈曲的决定性因素,高厚比小于80时,发生强度破坏,高厚比大于80时,发生屈曲破坏,减小腹板高厚比可以有效提高组合梁屈曲荷载,提高试件抗屈曲能力;开孔率是影响组合梁破坏模式和纯弯屈曲的重要因素,在一定范围内增大开孔率可以提高试件屈曲荷载。

Castellated components have been widely used in high-rise buildings and long-span structures in recent years because of their advantages such as high bearing capacity, great bending stiffness and convenient crossing pipelines. For the castellated component, the local buckling of the web is one of its main failure modes, and the buckling will cause a rapid increase of the local deformation of the web until the work is terminated, which may result in the overall instability of the components and the structural chain reaction. In the traditional steel structure design, the local buckling of the web is avoided by limiting the height to thickness ratio of the web. In the castellated component, the inter-hole pier and its bridge are likely to have local buckling problems, which is more complicated than the solid member. At present, most of the researches on the local stability of castellated beam members are carried out around pure steel castellated beams, and there are few studies on castellated beams considering concrete slabs. Therefore, it is necessary to study the pure flexural buckling of castellated composite beams. On the basis of the two pure steel castellated beams, two simply supported castellated composite beams were designed and fabricated. The static test of these two castellated steel beam-concrete composite beams was carried out at the four points. By observing the location of buckling on the steel beam and shape of the cracks in the concrete slab, the web buckling performance, bearing capacity and hole angle strain were analyzed, and compared with the pure steel castellated beams, in order to study the effect of the stiffening rib between the floor and web on the failure pattern, stress distribution and bearing capacity of castellated steel beam specimens. The finite element software ABAQUS was used to establish the model to carry on the numerical simulation, by comparision between the test result and the finite element simulation result, the model result is consistent with the test result.Based on the experimental model, the influence of height to thickness ratio and the opening ratio on the pure flexural buckling and the ultimate bearing capacity of castellated composite beams was analyzed. It shows that pure castellated beams buckle at the upper flange and the corresponding bridge plate, and the composite beams buckle at the pier plate and bridge slab. Concrete slab can effectively improve the yield load and ultimate load of composite beams, improve the ductility of specimens, and avoid the occurrence of local buckling. Setting stiffeners between the webs of composite beams can reduce the stress concentration at the corner of the holes and avoid buckling of the pier plates between the holes. There are two buckling modes of the composite beams, both of which are the semi-wavy out-of-plane instability of the piers between holes. The difference lies in the out-of-plane displacement distribution.The displacement of the first buckling mode centrosymmetric distributes with respect to the middle of the beam span and the displacement of the second buckling mode centrosymmetric distributes with respect to the middle of the beam span.The height to thickness ratio is a decisive factor affecting the failure mode and pure flexural buckling of composite beams. When the height to thickness ratio is less than 80, strength failure occurs. When the height to thickness ratio is greater than 80, buckling failure occurs. Reducing height to thickness ratio of web can effectively improve the buckling resistance of specimens and increase the buckling resistance of specimens. Opening ratio is an important factor affecting the failure mode and pure flexural buckling of composite beams. Increasing the opening ratio within a certain range can increase the buckling load of specimens.