| With the rapid development of national infrastructure,large projects such as cross-sea bridges have been developed rapidly.And the requirements of long-span bridges on the foundation structure are also higher,all kinds of large-diameter pile foundations play an important role in carrying a bridge construction project.In marine environment,the construction conditions are relatively harsh,the geological conditions are relatively complex and the pile foundation construction is relatively difficult,so the bridge construction is developing towards large span and the pile type is also optimized.The steel composite pile is developed slowly from the engineering construction,and its engineering value has been proved by the extensive application of many projects,but the related research lags behind the project,so this paper takes the super-long and large diameter variable cross-section steel composite pile as the research object,and carries on the bearing performance research through the field test,the numerical simulation and the theoretical research and so on.:(1)Relying on the Yushan Bridge Project,the field test was carried out.The large diameter variable cross-section steel composite pile(45#pile)is loaded by the weight of the pier and box beam,and the distributed optical fiber is arranged for monitoring,the optical fiber installation technology and monitoring method are successfully developed,and the axial force distribution law of the pile body is obtained;The self-balanced test of large diameter variable cross-section steel composite pile(37#pile)was carried out,and the load-displacement relationship curve was obtained,and the vertical ultimate bearing capacity of single pile was obtained according to the code.(2)The three-dimensional model is established by the numerical software ABAQUS,and its correctness is verified by comparing with the results of the self-balanced test,and the bearing performance of the pile foundation under vertical load is studied.The results show that the axial force of the pile body above the variable section decreases slowly,the axial force of the pile body at the variable section increases at first and then decreases,the axial force at the lower pile body with the variable section decreases rapidly,and the axial force at the pile end still does not decrease to zero.The pile tip resistance contributes to the overall bearing capacity of the pile;The vertical stress curve of the steel tube is fish-belly,and the maximum Mises stress is at the bottom of the steel tube.(3)The three-dimensional model is established by the numerical software ABAQUS,and its correctness is verified by comparing with the results of the optical fiber monitoring test,and the bearing performance of the pile foundation under compression-bending-shear-torsion load is studied.The results show that the displacement and stress of the pile body fully meet the requirements of design and the index of material strength,and the steel tube,steel ring and concrete can play a synergistic role to make the force of the pile body more reasonable;The displacement of the pile is the smallest when the variable section position is 1:1 and the load is the same;The larger the wall thickness of the steel tube,the smaller the displacement;The smaller the distance between shear rings,the smaller the horizontal displacement of pile foundation under the same load.(4)Using the current code to calculate the vertical bearing capacity of the pile foundation,and comparing with the measured value,it is found that the deviation is too large.The load transfer process of the pile foundation is analyzed.The ultimate stress state of the pile is selected,and the vertical ultimate bearing capacity formula of the super-long large-diameter variable cross-section steel composite pile is derived by using the coordinated relationship of pile-soil displacement.The difference between the calculated results and the measured values is small,which verifies that the formula is more reasonable. |
PDF Full Text Request