Approximate Analytical Method for Skin Friction of Tunnel-Type Anchorage Used in Suspension Bridge Engineering

Based on the theory of elasticity, the calculation formulas for the skin friction stress of tunnel-type anchorages used in suspension bridge engineering is provided, taking into account the boundary conditions on the two ends of the anchorage. Firstly, an analysis model is established in light of the practical loading conditions on the anchorage. Then, considering the conditions that the shear stresses on the two ends of the anchorage are individually equal to zero and that the entire anchorage is in a static equilibrium state, a calibrated computation formula for the skin friction stress of the anchorage is proposed based on the shear stress expression of Mindlin solution. Finally, a test model is cited to verify the acceptability of the proposed method, and the distribution characteristics of the skin friction stress are further revealed by using a practical example of tunnel-type anchorage. The analysis results show that the distribution of the skin friction stress along the axial direction of the anchorage is unimodal. The skin friction stress computed using the proposed method agrees well with that obtained using three-dimensional numerical simulation method. The average error between the maximum skin friction stresses of the two methods is about 8.5%. The calculation results also show that the skin friction stress is very small owing to the effect of self-weight load of the anchorage if the actual tension force on the main cable is close to the design value; however, the effect decreases with increase in tension force （e.g. 3.5 times the design value）. In particular, the local interface between the anchorage and the surrounding rock is likely to be in a failure state with increase in the tension force. This causes a corresponding adjustment of the skin friction stress to keep the entire anchorage in balance.