Calibration Of Seismic Provision For RC Frame-wall Structure Based On Nonlinear Dynamical Analysis

Although our national design codes specify serial design methods and seismic measures for frame-wall structures, according to test results, earthquake disasters, engineering experience and the mature foreign codes, the methods and measures still have not been verified by valid means. In recent years, analyses of series typical structures with several ground motion inputs have been carried out through nonlinear dynamic response analysis program in order to verify some seismic design methods and measures in foreign codes. To supply this gap in our national codes, nonlinear dynamic response analyses of seven typical frame-wall structures whose heights are not more than 60 meters subjected to several ground motions are carried out in this thesis, based on the nonlinear dynamic response analysis quasi-tridimensional program TS-EPA, which is verified earnestly and applicable to RC frame, frame-wall and frame-tube structures. These seven frame-wall structures are designed strictly according to our revised national codes: Code for design of concrete structures (GB50010-2002), Code for Seismic Design of Buildings (GB50011-2001) and Technical Specification for Concrete Structures of Tall Building (JGJ3-2002). These frame-walls are as following: (1) two 16-storey and two 18-storey frame-wall structures with slender coupling beams in regions of Intensity 8(0.2 g), designed respectively according to considering and not considering the reduction of the stiffness of coupling beams; (2) two 16-storey frame-wall structures with slender coupling beams in regions of Intensity 8(0.3 g), designed respectively according to considering and not considering the reduction of the stiffness of coupling beams; (3) one 18-storey frame-wall structure with the small span-to-depth coupling beams in regions of Intensity 8(0.3 g), considering the reduction of the stiffness of coupling beams. According to the analyses at three design levels defined in our national codes stated above, the conclusions are as following: ①Under rare earthquake actions, all the members of the frames in the seven frame-wall structures work elastically. Hence, for the frame-wall structures adopted in this thesis, it is feasible in our national codes that seismic class of the frame in the frame-wall structure within 60m in regions of Intensity 8 can be reduced one level. ②Under rare earthquake actions, the coupling beams in frame-wall structures yield firstly, and quite a few yield at both ends, the maximal equivalent rotation ductility of which is up to 2.5 after yield. This shows that the coupling beam is the first member to resist earthquake in the frame-wall structure. Therefore, in order to make it possible for the coupling beam to develop its important anti-earthquake function, it is necessary to give more concerns to its shear capacity and the measures to satisfy the ductility demanded. ③According to comparison of the analytic results of three couples, considering and not considering the reduction of stiffness of the coupling beam, it can be found that the reduction of stiffness will bring a little of unfavorable influence on the dynamic response of the frame-wall structure, in terms of the dynamic response and the demand of ductility under rare earthquake motion. ④From the analytic results of the frame-wall structure with small span-to-depth (2.25) coupling beams in regions of Intensity 8(0.3g), it can be found that the maximal equivalent rotation ductility of the coupling beams exceed 4.0 under rare earthquake actions because of the reduction of stiffness (the reduction coefficient is 0.5 and the shears of a few of coupling beams exceed the limit of shear V ≤0.2fcbhc by 10%). This demand of ductility has exceeded the ductility capacity of the small span-to-depth ratio coupling beam reinforced according to normal method. ⑤According to the analytic results of all seven frame-walls, the design base shear of the structure is between the maximal shear under frequent earthquake action and that under design earthquake action, and near to the latter. ⑥According to the analytic results of all seven frame-walls, nonlinear dynamic response of these structures is small. Therefore, the seismic design methods and measures adopted in our national codes for this kind of structure are reasonable in terms of these seven frame-wall structures. In addition, two plane frames in region of Intensity 8 (0.2g) and 9 (0.4g) respectively, are designed in this thesis. And nonlinear dynamic response analyses of them under the rare motion input, EI Centro, are carried out according to various combinations of the values of the first and second stiffness in the adopted three line hysteresis model. From the responses of frames under these combinations, the values of the first and second stiffness have very important influence on the results of the nonlinear dynamic response analyses. Whether the values of the first and second stiffness match or not the actual dynamic characteristic of members determines whether the nonlinear dynamic response analysis can reflect the dynamic behavior of the structure accurately or not. Therefore, emphases should be placed on the problem of the two values for all the researchers engaged in the nonlinear dynamic respond analyses of RC structures. From the analytic results in this thesis, it is suggestedthat the value of the first stiffness should be 0.9-time elastic stiffness, and the value of the second stiffness can be defined according to 0.7-time yield rotation and the yield moment. Here, the yield rotation is determined by the statistic formula, which were proposed by Panagiotakos and Fardis based on 1136 tests.