Study On Tendon System And Substructure Hybrid Test

To improve the recoverability and anti-collapse properties of building structures,a tendon system was proposed,which consists of a set of swaying columns and tendons.The swaying columns stand along the existing frame.They are linked to the frame at each floor level and pinned to the ground,so that the plastic deformation of existing frame is able to be redistributed uniformly along the height.The tendons are used to connect the swaying columns to the ground to provide extra stiffness in the entire range of deformation,which renders the entire frame a re-centering capability.In this study,parametric analyses and hybrid tests are conducted for the tendon system using a developed internet online hybrid test system capable of implementing internal dynamic DOFs of the test substructure.The main content of the paper are as follows:1.In order to effectively change the deformation modes of a structure with weak floor and reduce the residual deformation,a tendon system is proposed.Three steel moment-resisting frames,each having three,four and six stories,respectively,are designed and analyzed by time history analyses using three sets of ground motions.The stiffness of the swaying column,the stiffness and position of the tendons,the number of stories and the base shear coefficient of the existing structure are taken as the major parameters,whose influence on the tendon system is studied by the maximum residual story drift and the maximum story deformation.2.A prototype of a four-story steel frame is designed and intentionally weakened at the first story.It is then scaled to a 1/15 specimen.Online hybrid tests are carried out on the scaled specimen,respectively adopting four ground motions,artificial ground motion and Kumamoto ground motion,each with two peaking ground acceleration levels,i.e.,0.4g and 0.8g.The responses are compared between the structure with tendon system and that without tendon system.The results show that the tendon system can effectively relieve the story drift concentration of the weak story,and significantly reduce residual deformation of the structure.3.The traditional peer-to-peer internet online hybrid test system can only implement the static substructures,which is not the common case.A method that can deal with tested substructures with the internal dynamic DOFs is developed in this study.Substructure boundaries are coordinated by the static condensation technique and the BFGS method.For the test substructure,the initial stiffness matrix and the test substructure dynamic equation are used to update the displacement of the internal-DOF.Numerical simulation demonstrates that the proposed method has good accuracy and applicable for structures with highly nonlinearities.4.To fully demonstrate the proposed online hybrid test method,a four-story steel frame is used as the target for the hybrid test.Two substructures are employed,the top two stories as the numerical substructure,while the rest treated experimentally.Two actuators are used to load the test substructure,and the responses of the four-story structure are examined.Both linear elastic and nonlinear cases are studied,and ground motions are scaled to different levels.OpenSees is used for the overall simulation of the structure.The comparison shows that the proposed online hybrid test system has a good accuracy and stability.