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我们在垂直升船机的闸首和渡槽设计中,曾遇到这样一个问题:一个直接支承在地基上的“?”型刚架,它的支座约束性质是固接还是铰接呢?应该如何考虑才不致在设计中造成浪费或安全度不足。实际上把支座约束看成是固接的假定只有当地基很坚硬且基础底惯矩较大时才比较合理;而铰接的假定也只有当地基很软弱且基础底惯矩较小时才比较合理。一般情况下,刚架支座是属于弹性约束,即刚架在受荷时,其支座相对于地基有一弹性变形。这种变形对于刚架的内力分布有很大影响。因此,本文将研究支座为弹性约束时刚架内力的计算方法。一、弹性约束系数及其关系式的推导图1表示一支座为弹性约束的“?”型刚架。当考虑刚架支座的弹性约束影响时,是利用图2的带有虚拟梁的刚架来代替的。虚拟梁与实梁相对抗弯劲度之比假定为“λ”,称为弹性约束系数。现取图3刚架杆件ab来研究,当a端转动一角度时,杆ab的应力与变形值均将随λ的大小而改变。现按一
In the design of the head and the aqueduct of a vertical shiplift, we encountered the question of whether a “?” Type frame rigidly supported on a foundation and its bearing restraint is of a fixed or hinged nature? Consideration will not result in the design of waste or lack of safety. In fact, the assumption that the bearing restraint is fixed is only reasonable when the foundation is very hard and the base moment of inertia is relatively large. However, the assumption of articulation is only reasonable when the foundation is weak and the base moment of inertia is small . In general, rigid frame supports are elastic restraints, that is, the rigid frame is under load and its support has an elastic deformation relative to the foundation. This deformation has a great influence on the internal force distribution of rigid frame. Therefore, in this paper, we will study the calculation method of internal forces of rigid frame when the support is elastic constraint. I. The Derivation of Elastic Constraints and Their Relationships Figure 1 shows a “?” Type frame with an elastic constraint. When considering the elastic restraints of frame supports, the rigid frame with virtual beams in Fig.2 is used instead. The ratio of the relative bending stiffness between the virtual beam and the solid beam is assumed to be “λ”, which is called the elastic constraint coefficient. Now take Figure 3 rigid frame member ab to study, when the a-end rotation angle, the rod ab stress and deformation values will change with the size of λ. Now click one