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This study reports a deformation limit for the initiation of ductile fracture failure in fatigue-cracked circular hollow section (CHS) X-joints subjected to brace in-plane bending. The proposed approach sets the deformation limit as the calculated crack driving force in a fatigue crack at the hot-spot location in the tubular joint reaches the material fracture toughness measured from standard fracture specimens. The calibration of the proposed approach and the numerical procedure utilizes two large-scale X-joint specimens with fatigue generated surface cracks. The subsequent numerical investigation covers X-joints with two different brace-to-chord intersection angles, a wide range of geometric parameters and a practical range of material parameters. The development of the deformation limit includes a non-dimensional material toughness, which covers both the geometric parameters and material properties. The lower-bound deformation limit thus developed exhibits a linear relationship with respect to the crack depth ratio and indicates consistent values among X-joints with different brace-to-chord intersection angles. 相似文献
954.
This paper presents a novel numerical method through which less mesh-sensitive local stress calculations can be achieved based on the 3D solid finite element, adhering strictly to the original definition of hot spot stress. The traction stress, which is defined at 0.5t and 1.5t away from the weld toe, was calculated using either a force equivalent or work equivalent approach, both of which are based on the internal nodal forces on the imaginary cut planes. To confirm the validity of the proposed method, 5 typical welded joints widely used in ships and offshore structures were analyzed using 5 different solid element types and 4 different mesh sizes. Finally, the methodology was applied to the more complicated pontoon-column connection part of a semi-submersible RIG under a realistic wave load, and the performance of the proposed method was compared with the traditionally used surface stress extrapolation method. 相似文献
955.
The impacts of the built environment characteristics in residential neighborhoods on commuting behavior are explored in the literature. Scant evidence, however, is provided to scrutinize the role of the built environment characteristics at job locations. Studies also overlooked the potential error correlations between commuting mode and commuting distance due to the unobserved factors that influence both variables. We examined the impacts of the built environment characteristics at both residential and job locations on commuting mode and distance, by applying a discrete-continuous copula-based model on 857 workers in Shanghai. In contrast with studies of Western countries, we showed residential built environment characteristics are more influential on commute behavior than the built environment characteristics at job locations. This suggests the importance of local specificity in policymaking process. We also found the proportion of four-way intersections, road density, and population density in residential areas are negatively associated with driving probability, with elasticity amounts of −1.00, −0.23, and −0.08, respectively. Hence, dense and pedestrian- and cyclist-oriented development help to reduce travel distance and encourage walking, biking, and transit modes of travel. 相似文献
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通过对某大桥箱梁湿接缝的承载能力、抗弯刚度和抗裂性能的计算与分析,综合评估了25 m预应力混凝土小箱梁采用较宽的湿接缝后结构的安全性和可靠性。 相似文献
958.
在面向订单的烟草生产企业中,客户需求的动态性导致了企业的运输满载率不高。针对这一种情况,以车辆满载率最大化作为优化目标,建立了整数线性规划模型,利用启发式算法求解模型,使得配送中心能够较快的求出装载货物的满意方案, 达到提高车辆装载率的目的。且根据车辆满载率的大小设计了三种匹配原则,并提出共同配送半径的概念,有效提高了烟草配送的客户满意度、降低了总成本 相似文献
959.
岩体中的节理一般是满足一定统计规律的随机网络.利用UDEC实现了蒙特卡罗随机节理网络,在此基础上考虑了隧道的开挖和初喷加固.设计了未采取初喷加固方案,采取初喷加固时初喷混凝土黏聚力为0.1、0.2、0.4、0.6、0.8 MPa计算方案和初喷混凝土厚度为10、15、20、25、30 cm计算方案,计算对比不同工况的塑性区、应力和监测点位移值,发现:不采取初期衬砌,隧道的破坏形式主要是洞顶掉块;初喷厚度一定时,初喷接触面材料黏聚力越低块体越易脱落,超过0.4 MPa时则围岩稳定;初喷接触面材料强度一定时,初喷厚度对围岩稳定性有影响,存在临界厚度,过大过小均不利于隧道围岩稳定.这些特征值可以作为同类围岩条件下隧道设计的极限值. 相似文献
960.
装配式纤维混凝土组合桥面体系试验 总被引:1,自引:0,他引:1
针对正交异性钢桥面疲劳开裂,传统沥青混凝土铺装层破损以及纤维混凝土铺装层采用整体现浇施工时需要大面积现场养护等技术难题,提出了一种新型装配式组合桥面体系,即:装配式活性粉末混凝土(RPC)层本体为现浇RPC层,其中嵌合有周围布设企口接头的预制RPC桥面板,并通过剪力钉与正交异性钢桥面板联合成整体,形成组合桥面。为验证该企口接缝的强度,进行了装配式纤维混凝土组合桥面结构模型试验及理论分析。研究结果表明:采用新型钢-RPC组合桥面结构后,钢桥面结构中的拉应力降幅可达49%;当企口接缝处出现肉眼可见的细微裂缝时,与接缝位置对应的同断面现浇RPC强度为12.5 MPa,表明此种接头形式将接缝承受的拉应力部分转化为剪应力,从而有效降低了装配式纤维混凝土组合桥面开裂的风险。 相似文献