输电钢管塔空间KK型管板连接节点极限承载力

空间KK型管板连接节点作为输电钢管塔中最主要的节点型式,其安全性是整个塔架结构安全的重要保证。相比较于平面K型节点,在考虑实际结构中节点空间效应后的KK型节点的受力性能更为复杂。在平面K型管板节点的试验研究基础上,对两类空间KK型管板节点展开参数化分析,重点讨论了节点几何尺寸参数和主管轴压应力比等因素对节点极限承载力的影响变化规律。结合大量有限元参数分析所得计算结果,并综合考虑各种因素对节点极限承载力的影响,提出了空间KK型管板连接节点在主管管壁局部屈曲破坏模式下的极限承载力建议计算方法。     

Selection of four hoisting points for large span steel trusses based on strain energy method

The strain energy method is applied to hoisting point selection in structural hoisting, and the feasibility of this method is investigated. Based on the number of hoisting points, a structural analysis is carried out for each possible combination of hoisting points in the whole variable space of nodes. The strain energy corresponding to the each combination is obtained based on the member forces from the structural analysis. The combinations are sorted based on their magnitudes of strain energy, and the combination with the smallest strain energy is picked out. The structure needed to be hoisted is in a rational state when it has low strain energy. The combination with the smallest strain energy is treated as the best selection of hoisting points. Hoisting construction of a workshop in Chongqing was taken as an example and three construction conditions were considered. The commercial package ANSYS was used to conduct the structural analysis and obtain the strain energy. The best selections were verified by another software MADIS.     

Effect of different temperatures and strain rates on the critical damage factor of 7075 aluminum alloy

The computation principle of Cockroft-Lathem ductile cumulative damage is analyzed. A method to solve the critical damage factor based on the evolution rules of damage sensitive rate is brought forward. Several series of billet samples are compressed on heat physical simulation machine under different deformation temperatures and strain rates, and then the collected true stress-strain data are used to calculate the performance of computations. As the outer edge of upsetting drum where the maximum damage value appears is concerned, a typical damage softening rule is obtained and described as the damage sensitive rate decreases rapidly at the initial deformation, then gradually tends to 0. In further, damage softening is more sensitive to strain rate than temperature. A principle that critical damage factor arises when damage sensitive rate decreases to 0 is assumed, then the distribution of critical damage factor under temperature 573～723 K and strain rate 0.01～10 s-1 is obtained. The results show that the critical damage factor of 7075 aluminum alloy is not a constant but a change within a range of 0.255 ~ 0.453, and it is more sensitive to strain rate in high temperature and more sensitive to temperature in high strain rate.