Study On The Effect Of Group Caps Of Piles Bearing Vertical Load

Pile-foundation has been used since ancient years. In the last half century, accompanied with the rapidly increasing of high-rise buildings, pile- foundation was used more and more extensive. The study of pile-foundation has been prompted greatly in many directions to catch up the needs of the city architecture.A great deal of information and references have been read in the research, so to familiar to the development of any aspects of The study of pile-foundation and to understand the using condition of different methods. The prominent study project of the subject is mastered.Because the subsurface soils are different and there're a great deal of architecture types, the study of pile-foundation is done on many directions, such as piles setting into rock, fraction piles, etc.. And there're many study methods, such as mould pile test, pile field test, theory research, etc.. Today, it is a hot point to study the joint-action of piles-soils-structure. Up to now, many researchers focus on the study of joint-action of piles-soils-structure in the cases such as full-piles under a block foundation, or full-piles under a raft foundation. There're mere study on the joint-action of piles-soils-structure in the cases of group caps of piles. In the case of using group caps of piles, man usually calculates the pile caps one by one. The joint-action of soils, piles and caps was not considered, so to the joint-action of soils, piles and structure. As a result, there are some problems in settlement calculating of foundation and the influence of settlement on the stress of up-structure.The work focuses on a large-span building, which use group-caps of piles as foundation. The settlement of the foundation and its influence on the stress of structure is studied. The elastic theory suggested be polous is used in the work. The formula is improved to make it more reasonable and more accuracy. The improved formula is used to study the joint-action of piles-soils-caps- structure. A program is made using FORTRAN computer language. The load-settlement behavior of the small group of piles with low-cap is study firstly. Then a method is found to replace each low-cap piles group by a equivalent single pier with a low-cap. This method is creative. It makes the equivalentsingle pier with a low-cap having similar load-settlement behavior even the joint-action of caps is considered.A computer program using finite element is made to calculate the inner stress and point displacement of the large-span building. The constructing step and the progress of rigidity increasing can be considered. The program can also work together with the program calculating joint-action of piles-soils-caps, so to realize the joint-action of piles-soils-caps-structure. The foundation settlement and the structure stress are determined by the programs and contrasted with the result of regardless the joint-action. From the conclude, it can be found that the foundation settlement has a shape similar a pan. The shape and the value of the settlement agree with the measure in the engineering. It proves the rationalization and the practice of the method. The result of structure stress contrasting shows that the pillar stress increase at the location of corners and fringes, but the pillar stress decrease at the inner place while considering the joint-action. For the structure beams, the joint-action let the biggest stress increasing. The result illustrates that the main reason causing cracks in some beams is the subordinate stress caused by the settlement. The other reason may be in the design which did not consider the safety enough or the quality of the construction is not very good.