疲劳荷载下双开洞钢筋混凝土梁性能演变和变形预测

Performance Evolution and Deformation Prediction of RC Beams with Double Openings Under Fatigue Loading

在复杂的交通枢纽结构设计中因管道线路的铺设需要在钢筋混凝土(RC)梁腹板进行开洞,为研究双开洞RC梁的疲劳性能,以荷载水平比、荷载作用洞口位置、疲劳次数为变化参数设计了6根双开洞RC梁,并对其进行反复荷载作用下的疲劳试验。研究了疲劳加载过程中双开洞RC梁内的受力状态和破坏模式,讨论了各变化参数对双开洞RC梁疲劳性能的影响规律,提出了变形协调模型,并基于该模型揭示了双开洞RC梁在疲劳荷载作用下的损伤演化规律和破坏机理。研究表明:循环荷载作用下,双开洞RC梁疲劳破坏形态为洞口的上下梁斜向裂缝和洞口角部裂缝;荷载上限为0.7 P u和荷载位置作用在洞口中部的试件发生疲劳破坏,双开洞RC梁在0.5 P u荷载水平下具有至少41万次的疲劳寿命;疲劳试验后剩余极限承载力、抗弯刚度和延性随着荷载水平的增大发生退化;当荷载位于洞口中部时试件疲劳后的剩余性能更差;疲劳周期增大至41万次对剩余极限弯矩影响在7%左右,剩余抗弯刚度和延性退化25%左右。基于CEB-FIP 2010提出了适用于双开洞RC梁的疲劳变形预测方法,误差在7%以内。

In the design of complex transportation hub structures,due to the laying of pipeline routes,openings are required in the web of reinforced concrete(RC)beams.In order to study the fatigue performance of RC beams with double openings,six RC beams with double openings were designed using load level ratio,load acting hole location,and fatigue times as variable parameters,and fatigue tests were conducted on them under repeated loads.The stress states and failure modes in a RC beam with double openings during fatigue loading were studied,and the effects of various parameters on the fatigue performance of the beam were discussed.A deformation compatibility model was proposed.Based on the model,the damage evolution and failure mechanism of the RC beam with double openings under fatigue loading were revealed.The research showed that under cyclic loading,the fatigue failure modes of RC beams with double openings were diagonal cracks in the upper and lower beams of the openings and cracks in the corners of the openings.The specimen with an upper load limit of 0.7 P u and a load position acting on the middle of the opening underwent fatigue failure.The RC beam with double openings had a fatigue life of at least 410000 times under a load level of 0.5 P u.After the fatigue test,the residual ultimate bearing capacity,flexural stiffness,and ductility deteriorated with the increase of the load level.When the load was located in the middle of the opening,the residual performance of the specimen after fatigue became worse.Increasing the fatigue cycle to 410000 times had an impact on the residual ultimate bending moment of about 7%,and the residual bending stiffness and ductility degraded by about 25%.Based on the specifications,a fatigue deformation prediction method for RC beams with double openings was proposed,with an error of less than 7%.