Load-Carrying Mechanisms And Stability Of Gravity Anchorages With Stepped Bottom For Long-Span Suspension Bridges

Suspension bridge has become an important type of long-span bridge because of its strong spanning capacity,high bearing efficiency and beautiful alignment.As the key bearing structure of suspension bridge,the anti-sliding stability of anchorage is very important to the safety of the whole suspension bridge.The gravity anchorage with stepped bottom is widely used in practice because of its good anti-sliding stability and smaller anchorage volume.However,there is a lack of in-depth study on its bearing mechanism and anti-sliding stability,and a lack of reasonable design and calculation theory.In this thesis,the stability and bearing behavior of the gravity anchorage with stepped bottom for a long-span suspension bridge are analyzed by means of theoretical method and numerical simulation method.The main research contents and conclusions are as follows:(1)The design theory and calculation method for gravity anchorages are reviewed summarized.According to the in-situ test data and the design data of the gravity anchorage,the stability of the gravity anchorage with stepped bottom for a long-span suspension bridge is calculated according to the method provided by design codes.The anti-overturning stability meets the requirements,but the anti-sliding stability is slightly insufficient.(2)Linear elastic finite element analysis is carried out for the stresses in the gravity anchorage of the suspension bridge.The tensile force in the cable and the stresses in the anchorage saddle support,the stresses in the critical section,and the stressed in the back anchor face are analyzed.The results show that the main tensile stress of the anchorage concrete is larger near the anchor zone of the back anchor face,and the stress of the rest parts of the concrete meets the design requirements under the designed load.(3)Considering the nonlinearity of geotechnical material and the contact nonlinearity between gravity anchorage and rock base,elastoplastic finite element analysis is carried out on the anchorage-rock base interaction and the load bearing mechanisms of the gravity anchorage.The anti-sliding effect of vertical face of stepped bottom is analyzed,the development of plastic zone,anchorage displacement change and stress change of contact surface of stepped bottom in the process of load change are studied.The failure modes of stepped bottom anchorage are summarized.The safety and stability coefficient is determined,and the influence of rock parameters on the bearing capacity is investigated.The study shows that the anti-sliding contribution of the vertical surface of the stepped bottom is obvious,and the anti-sliding stability coefficient obtained by considering the stepped foundation effect is 37% higher than that obtained by the code-based method.With the increase of load,the effect of the front stepped bottom becomes more and more obvious,while the effect of the middle and rear stepped bottom decreases.The final failure mode of the stepped bottom anchorage is that the front bedrock inclines forward and upward under the action of the cable tension,and finally loses stability.The increase of cohesion and internal friction angle will increase the ultimate bearing capacity of the anchorage.