| Tower crane,also known as tower machine,is a kind of fixed jib mounted on the upper part of the tower of the rotating lifting machinery.The tower crane foundation is an important part to ensure the safety and normal use of the tower crane.Traditional tower foundations are often made at the construction site to complete,to spend a considerable part of the time cost,and can not be reused,resulting in waste,so gradually replaced by prefabricated assembled tower foundations.But the prefabricated assembled tower foundation are required to set in the pit or rigid foundation,is strictly prohibited to set in the water-soaked foundation.At present,for the high water table and difficult to precipitation of the pit environment and quicksand and other soft geological environment under the normal excavation of the pit engineering environment,the mainstream of the market can not be applied to the tower base.In view of the problems of high water table in the foundation pit and difficult to carry out precipitation and difficult to excavate the foundation pit normally in the soft geological environment such as quicksand,this thesis proposes a new type of sinkhole type prefabricated stacked tower foundation(referred to as sinkhole type tower foundation).The tower foundation is redesigned for the engineering application environment,and a structural scheme of the tower foundation combining the sinkhole structure and the stacked structure is proposed.As a new type of tower foundation,it faces many technical problems,mainly focusing on the safety of the sinkhole structure,the cooperative working performance of the stacked structure,and the overall safety of the sinkhole tower foundation.In this thesis,the structural safety and mechanical properties of sinkhole tower base in engineering environment are studied through a combination of experiments and numerical simulations,and the main research contents and conclusions are as follows:(1)The structural scheme of the tower base with the combination of prefabricated assembly sinkhole and prefabricated laminated structure was proposed,and the construction drawing design of the sinkhole tower base was completed.The finite element software is used to complete the safety verification of the prefabricated components’ transient working condition and the construction stage of the sinkhole structure to ensure the safety of the sinkhole tower base in the production and installation stage.The structural scheme is as follows: the plane shape of the tower base is octagonal,and the structure is divided into two parts: the sinkhole structure and the stacked structure.The sinkhole structure is assembled by four side plates,and the side plates are fixed with bolts.The reinforcement is placed in the prefabricated slab in advance,and after the prefabricated slab is lifted to the established position during construction,the inserted reinforcement is inserted and the concrete is poured.The results of the study are as follows: after finite element software calculation,the deformation and stress values of the precast members under the working conditions of demoulding and lifting meet the structural safety requirements of the short working conditions of the members,and the deformation and stress values of the sinkhole structure meet the structural safety requirements of the construction stage under the most unfavorable working conditions of the construction sinking stage.(2)The differences between the performance of precast elements of sunken tower foundations and cast-in-place concrete working together with cast-in-place specimens were studied.Considering that tower foundations are mainly used in two types of engineering environments,one is the construction method of underwater casting because of the high water table and the difficulty of precipitation,and the other is the weak geological environment where it is difficult to excavate the foundation pit normally,such as quicksand,the dry and wet stacked state was selected as one of the test variables,and the precast construction measures were selected as another variable.The two-point loading flexural tests of cast-in-place specimen XJ,dry stacked specimens YK and DK,and wet stacked specimen JK were conducted in turn.The mechanical performance indexes are compared to study the changes of the performance of the precast tower base and cast-in-place concrete under two types of stacking conditions and different structural measures,namely dry stacking and wet stacking.The results show that:(a)The dry laminated specimens and cast-in-place specimens are bending damaged and the laminated surfaces are well bonded,while the wet laminated specimens are shear damaged and the laminated surfaces are detached;(b)The ratio of yield load of specimens XJ,YK,DK and JK is1:0.98:0.94:0.82,the ratio of ultimate load is 1:0.99:1:0.75,and the ratio of ductility is1.0.95:0.89:0.83;the dry laminated specimens were better than the wet laminated specimens in terms of stiffness,bearing capacity,and damage of the laminated surface;(c)Before loading to cracking,the stiffness of the laminated specimens were all comparable to that of the cast-in-place beams,and the overall synergistic working performance was good.However,at the later stage of loading,the damage of the laminated surface of the wet laminated specimens is rapid and the ultimate load is greatly reduced;(d)For the laminated specimens in this thesis,the cracking load is calculated according to the formula of the concrete structural design code,and the results are on the safe side.(3)A simulation calculation method is developed for the sinkhole tower base stacked members,and the key data are selected and compared with the test results to verify its reliability.The modeling method is as follows:(a)The reinforced concrete adopts the separated model,which does not consider the influence of concrete and the bond slip between concrete and reinforcement;(b)The superimposed surface selects the "face-to-face" contact in the general contact,defining the concrete post-cast layer as the master surface and the precast slab contact surface as the slave surface;(c)The contact properties are divided into normal and tangential.Normal is defined as "hard contact",which is equivalent to the contact between two rigid bodies,and tangential is defined as Coulomb friction,and the size of tangential force is controlled by the friction coefficient,which is 0.8 for dry stacking environment and 0.4 for underwater stacking environment.(4)The overall safety and overturning resistance of the sinkhole tower base were verified.Using ABAQUS simulation software,taking XGT6015A-8S tower as an example,the overall structural safety and overturning resistance of the tower base is verified for two types of stacking states,namely dry stacking environment and underwater stacking environment,and 0° and 45° overturning directions in the engineering application stage.The results show that:(a)Under the most unfavorable load on the tower,the deformation and stress values of the sinkhole tower base steel stress,the plain concrete area of the tower,and the connection between the pre-buried bolts and the tower base are all within the safe range;(b)The weak concrete area is the connection between the pre-buried bolts and the tower base,and the weak steel area is the top of the side slab,the bottom beam and the structural bend;(c)After considering the influence of the foundation soil deformation on the tower base overturning,the overturning resistance of the tower base still meets the engineering application conditions and will not produce overturning.(5)Combined with the results of experimental and numerical simulation studies,improvement methods and engineering application suggestions are proposed from the perspectives of design and fabrication of prefabricated components of tower foundation scheme and construction of sinkhole-type prefabricated stacked tower foundation respectively.There are 84 figures,24 tables and 87 references in this thesis. |
PDF Full Text Request