【作者】 王新；

【导师】 魏纲； 崔允亮；

【作者基本信息】 浙江大学 ， 工程硕士（专业学位）， 2020， 硕士

【摘要】 随着国家基础建设的大力发展,跨海大桥等大型工程也得到迅速发展,大跨径的桥梁对基础结构的要求也更高,各类大直径桩基础在一座座大桥的建设工程中发挥了重要作用。海洋环境下施工条件较为恶劣,地质条件较为复杂以及桩基施工较为困难,桥梁建设向大跨度发展的同时桩型也在优化。钢管复合桩就是从工程建设中慢慢发展而来的,众多工程的广泛应用证明了其工程价值,然而相关研究却滞后于工程,故本文以超长大直径变截面钢管复合桩为研究对象,通过现场试验、数值模拟及理论研究等手段进行承载性能研究,具体内容如下:(1)依托鱼山大桥工程开展了现场试验。对大直径变截面钢管复合桩(45#桩)利用墩身及箱梁自重为荷载,并布置分布式光纤进行监测,成功开发了光纤安装工艺和监测方法,得到了其桩身轴力分布规律;对大直径变截面钢管复合桩(37#桩)开展了自平衡试验,得到了其荷载与桩身位移的关系曲线,并根据规范得到其转换为传统静载荷试验的单桩竖向极限承载力值。(2)利用数值软件ABAQUS建立三维模型,与自平衡试验结果对比验证其正确性,并研究了竖向荷载下桩基的承载性能,结果表明:变截面以上桩身轴力减小较缓,变截面处桩身轴力先增大后减小,变截面以下桩身轴力减小较快,到桩端轴力仍没减小到零,桩端阻力对桩整体承载力有贡献;钢管竖向应力曲线呈“鱼肚型”,Mises应力在钢管底最大。(3)利用数值软件ABAQUS建立三维模型,与光纤监测试验结果对比验证其正确性,并研究了桩基在压弯剪扭荷载下的承载性能,结果表明:桩身位移和应力满足设计要求和材料强度指标,钢管、钢环和混凝土能够发挥协同作用,使桩身受力更加合理;桩身变截面位置1:1时在相同荷载作用下其桩身位移最小;钢管壁厚越大位移越小;剪力环间距越小,在相同荷载下桩基的水平位移越小。(4)使用现行规范对依托工程桩基进行竖向承载力计算,与实测结果对比发现计算值偏差过大,分析了桩基荷载传递机理,选取桩基极限受力状态,利用桩土位移协调关系推导了超长大直径变截面钢管复合桩竖向极限承载力公式,公式计算结果与实测值相差较小,验证了其较为合理。更多还原

【Abstract】 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.更多还原