Stress Characteristics and Design Optimization of Shield Initial Reaction Frame in Confined Space

Objective The size of the reaction frame is strictly constrained in shield tunnel initial operation under limited space environment. In view of this, to ensure the frame can withstand the huge reaction force generated during the start-up of the large-diameter shield machine and effectively control the stress deformation, it is proposed to study and design a reaction frame with sufficient strength and stiffness, compact structure, and adaptability to space-limited environments. Method Taking the JCXSG-8 section of Shanghai Airport Link project as the background, the stress and deformation characteristics of the reaction frame under different back-support modes are studied in depth in terms of the actual situation of limited reaction frame size. Through optimizing the local structure of the reaction frame and the layout of the force transmission support, an improvement scheme is proposed and verified in combination with the actual construction conditions on site to ensure the rationality and effectiveness of the design. Result & Conclusion In the setting of the reaction frame back-support, the use of shear walls is superior than the diagonal braces, and can effectively improve the structural stability. In addition, adding middle supports to the lower inclined beam significantly reduces the bending moment of the lower inclined beam end support, thereby effectively reducing the torque of the bottom beam and mullion beam, and improving the load-bearing capacity of the overall structure. At the same time, the number and arrangement of force transmitting struts on the upper inclined beam have a significant influence on the maximum bending moment and deformation of the reaction frame. In the actual construction of this project, a 1-m-thick reaction frame is used with a 900-mm-thick shear wall setting up in its back-support position. At the same time, a support is added on the lower inclined beam of the reaction frame, and the number of force transmitting struts on the upper inclined beam is appropriately reduced.