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本文对周边支承的蜂窝形三角锥平板网架的几何不变性进行了理论分析,并通过三十个不同荷载、不同约束方案的实际计算指出: 1.周边支承的蜂窝形三角锥平板网架,其几何不变性与支座约束情况有关; 2.这种网架空间几何不变性的机动分析可简化为上弦平面内的平面机动分析; 3.在各支座处除有一个铅垂约束外,只要在全部支座(个数为J)范围内按着机动分析的充分条件适当布置J个或多于J个的水平约束,使网架上弦所形成的平面系统呈几何不变体系,这时可不必增加任何其他杆件,即可保证网架整体的几何不变性; 4.当荷载不变时,支座水平约束的变化只影响上弦杆件内力,对下弦杆件内力及腹杆内力无影响; 5.在实际工程中,支座多呈三向弹性约束,结构形成超静定的几何不变体系; 6.当采用铅垂固定约束及平行边梁轴线方向的固定约束,且只有铅垂荷载时,虽然能算出结果,但从理论分析是几何可变的,属于不稳定平衡情形,仍潜伏着结构瞬时可变的危险性,在结构设计中应有相应措施以保证结构的稳定平衡。
In this paper, the geometrical invariance of the honeycomb-supported triangular-pyramidal flat-plate grid is theoretically analyzed. Through the actual calculation of thirty different loads and different constraining schemes, it is pointed out that: The geometric invariability is related to the constraints of the support. 2. The maneuver analysis of the geometric invariance of the space of the grid can be simplified to the plane maneuver analysis in the upper chord plane; 3. In addition to a vertical constraint at each bearing, As long as J or more than J horizontal constraints are properly arranged in the full range of the support (number of J) according to the sufficient conditions for the maneuvering analysis, the planar system formed by the grid chord is geometrically invariant. It is not necessary to add any other rods to ensure the geometric invariability of the entire grid; 4. When the load is constant, the change of the horizontal constraint of the support only affects the internal force of the upper chord member, and there is no internal force of the lower chord member and the internal force of the abdominal member. Impact; 5. In practical projects, bearings are mostly three-way elastic constraints, the structure forms a statically indeterminate geometric invariant system; 6. When the use of vertical fixed constraints and fixed constraints in the direction of the parallel beam side axis, and only lead In the case of vertical loads, The result, but the theory is a variable geometry, are unstable equilibrium situation, still lurking variable structure instantaneous risk, there should be corresponding measures in the structural design to ensure a stable equilibrium structure.