Shaking table test and numerical analysis of a 1:12 scale model of a special concentrically braced steel frame with pinned connections

This paper describes shaking table tests of a 1：12 scale model of a special concentrically braced steel frame with pinned connections, which was fabricated according to a one-bay braced frame selected from a typical main factory building of a large thermal power plant. In order to investigate the seismic performance of this type of structure, several ground motion accelerations with different levels for seismic intensity Ⅷ, based on the Chinese Code for Seismic Design of Buildings, were selected to excite the model. The results show that the design methods of the members and the connections are adequate and that the structural system will perform well in regions of high seismicity. In addition to the tests, numerical simulations were also conducted and the results showed good agreement with the test results. Thus, the numerical model is shown to be accurate and the beam element can be used to model this structural system.

Nonlinear Seismic Response of Steel Concentrically Braced Frames Using Endurance Time Analysis Method

In present paper application of Endurance Time Analysis （ETA） method in nonlinear seismic assessment of steel concentrically braced frames is studied. In this method structure is subjected to a set of predesigned increasing acceleration functions and various responses of the structure are recorded during synthetic seismic excitation. The averages of maximum values for various responses in Nonlinear Time-History Analyses （NTHA） extracted from real ground motions are expected to be close to those obtained from ETA up to equivalent target time. For this purpose a set of 9, 11, 13 and 15 stories steel frames were designed and plastic hinge method was selected as source of nonlinearity in all cases. Responses were compared based on interstory drift ratio and story shear in two methods and results show satisfactory consistency between two methods. Finally, it was concluded that the ETA method can be used as alternative method in nonlinear seismic analysis of concentrically braced steel frames.

Effectiveness of two conventional methods for seismic retrofit of steel and RC moment resisting frames based on damage control criteria

This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation methods, concentric chevron bracing（CCB） and cylindrical friction damper（CFD） were selected. The performance assessment procedure of the frames is divided into two distinct phases. First, the limit state probabilities of the structures before and after rehabilitation are investigated. In the second phase, the seismic risk of structures in terms of life safety and financial losses（decision variables） using the recently published FEMA P58 methodology is evaluated. The results show that the proposed retrofitting methods improve the serviceability and life safety performance levels of steel and RC structures at different rates when subjected to earthquake loads. Moreover, these procedures reveal that financial losses are greatly decreased, and were more tangible by the application of CFD rather than using CCB. Although using both retrofitting methods reduced damage state probabilities, incorporation of a site-specific seismic hazard curve to evaluate mean annual occurrence frequency at the collapse prevention limit state caused unexpected results to be obtained. Contrary to CFD, the collapse probability of the structures retrofitted with CCB increased when compared with the primary structures.

Cyclic responses of three 2-story seismic concentrically braced frames

Three full scale two-story steel concentrically braced frames(CBFs)were tested at the National Center for Research on Earthquake Engineering(NCREE)in Taipei.The specimen is a single bay with the braces arranged in a two-story X-brace configuration.The main differences among the three tests are the brace types(hollow structural or wide-flange section)and the design criteria adopted for the gusset plate connections.Results of these three tests confirm that the two-story X-shape steel CBFs all have rather good energy dissipation characteristics up to a story drift of about 0.03 radians under the cyclically increasing lateral displacements.Severe brace local buckling and out-of-plane displacements were observed during each test.Tests confirm that both the 2tlinear and 8t-elliptical designs of the gusset plate connection provide satisfactory ductility for the steel CBF.Hollow structural section(HSS)braces fractured at a story drift smaller than that found using wide flange sections.The nonlinear fine element method(FEM)program ABAQUS was used to simulate the responses of the specimen.The base shear versus the story drift relationships obtained from the tests and the FEM analytical results are quite agreeable in various levels of lateral frame displacement.The analytical results confirm that the severe out-of-plane buckling of the braces can be accurately simulated.FEM analyses also illustrate that the steel moment resisting frame takes about 40%story shear when the inter-story drift is greater than 0.02 radians.