Effect of Slab-Truss Combination Pattern on Fatigue Damage of Integral Joint in Steel Truss Bridge
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摘要: 钢桁梁桥桥面系与主桁的共同作用效应将显著影响纵横梁内力和主桥刚度,对整体节点与相应受力构件连接细节的应力水平产生影响,进而影响相关构造细节的疲劳损伤效应。半结合和全结合的板桁结合形式是当前钢-混凝土组合桥面系最常用的两种形式,不同结合方式对桥面系与主桁共同作用效应有显著影响。为探究板桁结合方式对典型下承式钢桁梁桥整体节点疲劳损伤特征的影响效应,以一座宽幅大跨径下承式钢桁梁桥为例,通过分析控制横梁与节点连接细节和主桁下弦与节点对接细节疲劳损伤特征的内力分布规律,确定了两类构造细节对应的最不利整体节点位置,并基于等效结构应力法和线性损伤累积理论对其开展了多尺度疲劳损伤分析,确定了在板桁半结合和全结合方式下两类构造细节的主要开裂模式在标准疲劳荷载下的应力历程,从而剖析了两类构造细节的疲劳损伤特征,并基于串联失效模型确定了整体节点控制疲劳开裂模式,从而量化了板桁结合方式对整体节点疲劳损伤的影响效应。
研究结果表明:钢桁梁桥板桁全结合方式相较于半结合方式而言,能显著提高主桥刚度,从而减小横梁面外弯矩和主桁弦杆内力,但对横梁面内弯矩影响不明显;横梁与节点连接细节的疲劳损伤最不利整体节点位置为支座附近节点,主桁下弦与节点对接细节的疲劳损伤最不利位置为跨中附近节点,两类板桁结合方式下最不利节点位置没有差异;相较于板桁半结合方式,全结合方式使横梁与节点连接细节的等效结构应力幅降低了60%以上,主桁下弦与节点对接细节的等效结构应力幅降低了80%;整体节点控制疲劳开裂模式为裂纹起裂于横梁上翼缘与节点板连接焊缝的节点板焊趾,全结合方式下整体节点疲劳损伤度相较于半结合方式降低了64%。板桁结合方式对下承式钢桁梁桥的桥面共同作用效应产生显著影响,从而改变桥面系纵横梁和主桁杆件的受力状态,进而对整体节点疲劳损伤产生显著影响,因此在进行整体节点疲劳性能评估时应充分考虑桥面板与主桁的共同作用效应的影响。Abstract: The interaction effect between the deck system and the main truss of the steel truss bridge will significantly affect the internal force of the longitudinal and transverse beams and the stiffness of the main bridge, thus affecting the stress level of the connection details between the overall joints and the corresponding stressed members, and then affecting the fatigue damage effect of the relevant structural details. Semi-combined and fully combined slab-truss combination are the two most commonly used forms of steel-concrete composite bridge deck system. Different combination methods have a significant impact on the interaction effect between bridge deck system and main truss. In order to explore the effect of slab-truss combination on the fatigue damage characteristics of the integral joints of a typical steel truss bridge, taking a wide and long-span steel truss bridge as an example, the most unfavorable integral joint positions corresponding to the two types of structural details are determined by analyzing the internal force distribution law which controlling the fatigue damage characteristics of the connection details between the beam and the joint as well as the butt joint details between the lower chord of the main truss and the joint. Based on the equivalent structural stress method and the linear damage accumulation theory, the multi-scale fatigue damage analysis is carried out, and the stress history of the main cracking modes of the two types of structural details under the standard fatigue load is determined, so as to analyze the fatigue damage characteristics of the two types of structural details. Based on the series failure model, the controlled fatigue cracking mode of the integral joint is determined, so as to quantify the effect of the slab-truss combination on the fatigue damage of the integral joint.
The results show that:compared with the semi-combined method, the full combined method of steel truss bridge will significantly improve the stiffness of the main bridge, so as to reduce the out of plane bending moment of the beam and the internal force of the main truss chord, but it has no obvious effect on the in-plane bending moment of the beam; the most disadvantageous position of the integral joint is the joint near the support, and the most disadvantageous position of the butt joint detail between the lower chord of the main truss and the joint is the joint near the mid span. There is no difference in the most disadvantageous joint position between the two types of slab-truss combination; compared with the semi-combination method, the full combination method reduces the equivalent structural stress amplitude of the connection details between the beam and the joint by more than 60%, and the equivalent structural stress amplitude of the butt joint details between the lower chord of the main truss and the joint by 80%; the controlled fatigue cracking mode of the integral joint is that the crack starts at the weld toe of the joint plate connecting the upper flange of the transverse beam and the joint plate. The fatigue damage degree of the integral joint under the full combination mode is 64% lower than that under the semi-combination mode. The slab-truss combination mode will have a significant impact on the deck interaction effect of steel truss bridge, so as to change the stress state of longitudinal and transverse beams and main truss members of the deck system, and then have a significant impact on the fatigue damage of the integral joint. Therefore, the impact of the interaction effect of bridge deck and main truss should be fully considered when evaluating the fatigue performance of the integral joint. -
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