Research On The Seismic Design Of Braced Frame And Slits Shear Wall

Braced frame and steel frame- slits shear wall are commonly used as the resisting lateral force in the earthquake zone. The recommended methods of GB50011 and JGJ 99-98 for design of steel brace are to amplify design force of braces. It is different from the method of European, American and Japanese. And in the design of slits wall, there are not the corresponding connection between the beam and wall so that wall will ineluctably carry vertical loads. It has violated the design principle of slits wall. The computation model proposed by JGJ 99-98 can not predict the shear force carried by the end of girder when frame bear horizontal load. Based on different braces design methods, the paper analyses the seismic behavior of braced frames and proposed the reasonable design suggestions; In order to obtain the reasonable computation model and mode of construction, the effect of shear force in end of girder and the connection between girder and slits wall were analyses.Braced frames are designed in two different philosophies, one is to amplify design force of braces to achieve a strong-shear frame, and the other does not. This paper analyzed the nonlinear elastic-plastic time-history responses of these two types of frames under many earthquake records. The kinds of braced frame include "one-story and one-bay", "one-story and multi-bay" and "multi-story and multi-bay". It was found that (1) Columns in strong-shear braced frames will buckle in a non-sway mode before yielding of the braces, and then horizontal and vertical displacement of frame rapidly increases. But the deformation of a weak-shear braced frame is in a sway mode. (2) Curves of inter-story shear force-lateral displacement and the stress-strain response of the brace and the column do not form a hysteretic loop in the strong-shear frame; Energy dissipating capacity is unable to be developed to reduce the earthquake response. Energy dissipating capacity depends on the column's buckling in a non-sway mode, and structure become a single lateral resistant system which is harmfulto resist earthquake. (3) In the weak shear frame, the brace yields first, then the brace and the frame may hysteretically deform laterally and continually to develop their ductility and the energy-dissipating capacity to reduce the earthquake response, the frame comprising part of the bracing frame functions as a secondary structural system against earthquake. Based on these findings, it is suggested that check be carried out to make sure that the brace in the weakest story yields before the connecting columns buckle in a non-sway mode, i.e. to ensure a strong-column weak-brace system.This paper provided a review of the design method for slit reinforced concrete wall system, supplementary design rules and detailing requirements are proposed to implement the design philosophy of the slit wall. These include: (1)shear strength check for the beam-column connection and beam web with specially calculated shear force; (2)when the shear strength is not satisfied, an additional shear connection is recommended between the column and the slit wall; this shear connection is also necessary for convenient installation; (3)in order to implement the slit wall's design philosophy of carrying horizontal load only, slit holes are recommended in the HSFB connection between slit wall and the top beam to allow slip to occur and its vertical load carrying capacity should be limited to the expansion force of the concrete; (4)check for buckling of web under concrete expansion force; (5)design of pre-embedded steel plate and shear connectors to transfer the shear force and the expansion force and their related eccentricity; (6) the shear strength check for the reinforced slit wall based on the design procedure for beam-columns in Chinese code for reinforced concrete structures GB50010 is recommended instead of the currently specified method in JGJ99-98.Analytic models of frame-slit-wall system (FSWS) suggested by JGJ99-98 were discussed and the necessity of considering shear deformation of web of steel beams was pointed out when determining the section of equivalent cross bracing or shear plate. The models suggested by JGJ99-98 cannot predict the actual shear forces in steel beams, its bending deformation has not be included either. This paper suggested a wall-column model, the rigidities of various parts in this model are proposed. A very low axial rigidity is assigned to the wall-columns modeling the slit walls to implement the design philosophy of carrying no vertical loads by slit wall. Comparison between three models is carried out and it is found that, when the number of stories is small, the wall-column models predict lowest lateral stiffness. As the height of the structures increases, three models predict nearly the same lateral stiffness. But the wall-column model can correctly predict the internal forces and deformations of each memberin the model, thus implies an improvement over the cross bracing or shear plate models. When shear keys were added between columns and slits wall, the behavior of FSWS is analyses. Through comparing the results of FSWS and model, it has been gotten that adding shear keys can improve behavior of girders and shear walls, and design principle was realized.Considered concrete nonlinear, the FSWS is researched. The results indicate that shear wall appears serial small cracks during the entire process of loading. The deform mode of shear wall with flexure deformation mainly is similar with wall column. Lateral stiffness of shear wall reduces slowly so as to work with frame easily. So FSWS is fit to used in the earthquake zone.