Study On Mechanical Behavior Of Precast Concrete Foundation Joint Of Wind Turbine Tower

Absorbing and improving the foundation of the supporting wind turbine tower,combined with the node connection technology of the prefabricated structure,the assembled foundation of the wind power tower is proposed.It is a new type of assembled monolithic wind turbine foundation that is fully prefabricated and only needs to be assembled on site.Compared with the traditional spread foundation of wind turbine towers,it has the advantages of less material consumption and shorter construction period.At present,scholars at home and abroad have done a lot of research on the connection technology of prefabricated structures.However,the connection of post-pouring belt joint and bolted joint,which are different from the traditional connection technology in the wind turbine tower assembly foundation structure,is still rarely studied.In response to this problem,firstly,the load-displacement curve,strain,bearing capacity,failure mode,etc.of the specimen were analyzed by field test and the force mechanism of the joint was explored.(1)Through the flexural test of 4 specimens and the shearing test of 5 specimens,the influence of different lap lengths and the diameters of bolt bars on the mechanical properties of post-cast belt joints was studied respectively;(2)Through the shearing test of 5 specimens and the tensile test of 4specimens,the effects of different bolt diameters,pre-tightening force,and shear key area on the mechanical properties of bolt joints are studied respectively.Finally,the ABAQUS finite element software was used to simulate the specimen and compared with the test results,and the following conclusions were obtained:(1)Put forward the post-cast belt joint of loop lapped reinforcements and the preembedded connection box-type bolt joint suitable for the wind turbine tower assembly type foundation structure.(2)The flexural test of the post-cast belt joints shows that increasing the diameter of bolt reinforcement is helpful for force transferring,the formula in the code for design concrete structures can be used to calculate its bending capacity.The maximum crack width of the specimen occurred at the joint surface and was significantly larger than the cast-in-place specimen.Based on the force mechanism,a practical calculation method for the maximum crack width is proposed.The shearing test of the post-cast belt joints shows that the failure modes of out-of-plane shear and in-plane shear are the same,and both are direct shear failure.The lap length and the diameter of bolt reinforcement have little influence on the shear capacity.According to its force mechanism,The calculation formulas of interface shear bearing capacity proposed by various codes and documents are sorted out,and the calculated values of the formulas are compared with the experimental values.a recommended calculation formula for shear capacity is given.The finite element simulation results are similar to those of the experiment.Among them,the tensile damage and compression damage in the model can indicate the degree of concrete damage,it can better reflect the cracking failure and damage area of the post-cast belt joint specimen.(3)The shear test of bolted joints shows that the failure mode of each specimen is the direct shear failure caused by the shear damage at the bottom of shear key.The increase of bolt pretension,bolt diameter,and shear key area can effectively improve the bearing capacity of the test piece.Combining the working mechanism of the specimen,a formula for calculating the shear capacity based on the contribution of shear key and the contribution of shear friction is proposed.The tensile test of the bolt joints shows that the failure mode of the specimen is similar to that of the high-strength bolt with pretension.When the tensile bearing capacity is 0.8 times the bolt pre-tension,the joint will not open and meet the requirements of use.The finite element simulation showed that the bolt joint failure mode and bearing capacity were similar to the test results,the compression damage and compression damage in the model show the failure location and failure mode of the bolt joint specimen.(4)When the lap length in the design is 0.35 times the "Lap Length of the code for design concrete structures ",The bearing performance of the post-casting belt joint with loop lapped reinforcements can be basically equivalent to that of the cast-in-place.It is suggested that the flexural bearing capacity should be calculated according to the " code for design concrete structures ",and the maximum crack width should be calculated according to the formula proposed in this article considering the joints of the post-cast belt,When the shear bearing capacity is calculated according to the MC(2010)model code or the AASHTO LRFD specification.(5)The pre-embedded connection box-type bolt joint design method adopted is safe and applicable.The calculation formula of its shear capacity can only consider the effect of the shear key,And the tensile bearing capacity is 0.8 times of bolt preload.